U.S. patent application number 17/144858 was filed with the patent office on 2021-04-29 for apparatuses and methods for synchronous multi-laser processing of transparent workpieces.
The applicant listed for this patent is Corning Incorporated. Invention is credited to Marina Irmgard Heiss, Uwe Stute, Ralf Joachim Terbrueggen.
Application Number | 20210122663 17/144858 |
Document ID | / |
Family ID | 1000005329572 |
Filed Date | 2021-04-29 |
![](/patent/app/20210122663/US20210122663A1-20210429\US20210122663A1-2021042)
United States Patent
Application |
20210122663 |
Kind Code |
A1 |
Heiss; Marina Irmgard ; et
al. |
April 29, 2021 |
APPARATUSES AND METHODS FOR SYNCHRONOUS MULTI-LASER PROCESSING OF
TRANSPARENT WORKPIECES
Abstract
A method for laser processing a transparent workpiece includes
focusing a pulsed laser beam output by a pulsed laser beam source
into a pulsed laser beam focal line directed into the transparent
workpiece, thereby forming a pulsed laser beam spot on the
transparent workpiece and producing a defect within the transparent
workpiece, directing an infrared laser beam output onto the
transparent workpiece to form an annular infrared beam spot that
circumscribes the pulsed laser beam spot at the imaging surface and
heats the transparent workpiece. Further, the method includes
translating the transparent workpiece and the pulsed laser beam
focal line relative to each other along a separation path and
translating the transparent workpiece and the annular infrared beam
spot relative to each other along the separation path synchronous
with the translation of the transparent workpiece and the pulsed
laser beam focal line relative to each other.
Inventors: |
Heiss; Marina Irmgard;
(Penzing, DE) ; Stute; Uwe; (Neustadt am
Rubenberge, DE) ; Terbrueggen; Ralf Joachim;
(Neuried, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
1000005329572 |
Appl. No.: |
17/144858 |
Filed: |
January 8, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16057284 |
Aug 7, 2018 |
10906832 |
|
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17144858 |
|
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62544208 |
Aug 11, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 26/53 20151001;
B23K 2103/56 20180801; B23K 2103/52 20180801; B23K 26/0734
20130101; B23K 26/364 20151001; B23K 26/067 20130101; B23K 2103/54
20180801; B23K 26/0738 20130101; B23K 26/0608 20130101; C03B 33/091
20130101; B23K 26/082 20151001; C03B 33/0222 20130101 |
International
Class: |
C03B 33/02 20060101
C03B033/02; B23K 26/06 20060101 B23K026/06; B23K 26/073 20060101
B23K026/073; B23K 26/082 20060101 B23K026/082; B23K 26/067 20060101
B23K026/067; B23K 26/53 20060101 B23K026/53; B23K 26/364 20060101
B23K026/364; C03B 33/09 20060101 C03B033/09 |
Claims
1. A method for laser processing a transparent workpiece, the
method comprising: focusing a pulsed laser beam output by a pulsed
laser beam source into a pulsed laser beam focal line oriented
along a beam propagation direction and directed into the
transparent workpiece, thereby forming a pulsed laser beam spot on
an imaging surface of the transparent workpiece, wherein: the
pulsed laser beam focal line generates an induced absorption within
the transparent workpiece; and the induced absorption produces a
defect along the pulsed laser beam focal line within the
transparent workpiece; directing an infrared laser beam output by
an infrared beam source onto the transparent workpiece such that
the infrared laser beam forms an infrared beam spot on the imaging
surface, wherein: the infrared beam spot is spaced a spacing
distance from the pulsed laser beam spot at the imaging surface;
and the infrared laser beam heats the transparent workpiece;
translating the transparent workpiece and the pulsed laser beam
focal line relative to each other along a separation path, thereby
laser forming a plurality of defects that define a contour line
within the transparent workpiece along the separation path; and
translating the transparent workpiece and the infrared beam spot
relative to each other along the separation path synchronous with
the translation of the transparent workpiece relative to the pulsed
laser beam focal line such that the pulsed laser beam spot remains
spaced the spacing distance from the infrared beam spot during
relative motion of the transparent workpiece and the pulsed laser
beam focal line and irradiates the transparent workpiece along or
near the contour line to separate the transparent workpiece along
the contour line.
2. The method of claim 1, wherein the spacing distance comprises
from about 1 .mu.m to about 100 mm.
3. The method of claim 1, wherein the infrared laser beam is
redirected by a beam directing element onto the transparent
workpiece at an approach angle that is non-parallel to the beam
propagation direction of the pulsed laser beam.
4. The method of claim 3, wherein the infrared laser beam is
directed through a beam conditioning element thereby altering a
cross-sectional beam profile of the infrared laser beam.
5. The method of claim 1, wherein: the infrared beam spot and the
transparent workpiece are translated relative to one another at a
speed from about 1 mm/s to about 10 m/s; the pulsed laser beam
focal line and the transparent workpiece are translated relative to
each other at a speed that is equal to the speed of relative motion
between the infrared beam spot and the transparent workpiece.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of and claims the benefit
of priority under 35 U.S.C. .sctn. 120 of U.S. application Ser. No.
16/057,284, filed on Aug. 7, 2018, which claims the benefit of
priority under 35 U.S.C. .sctn. 119 of U.S. Provisional Application
Ser. No. 62/544,208 filed on Aug. 11, 2017, the contents of which
are relied upon and incorporated herein by reference in their
entirety.
FIELD
[0002] The present specification generally relates to apparatuses
and methods for laser processing transparent workpieces, and more
particularly, to separating transparent workpieces.
TECHNICAL BACKGROUND
[0003] The area of laser processing of materials encompasses a wide
variety of applications that involve cutting, drilling, milling,
welding, melting, etc. of different types of materials. Among these
processes, one that is of particular interest is cutting or
separating different types of transparent substrates in a process
that may be utilized in the production of materials such as glass,
sapphire, or fused silica for thin film transistors (TFT) or
display materials for electronic devices.
[0004] From process development and cost perspectives there are
many opportunities for improvement in cutting and separating glass
substrates. It is of great interest to have a faster, cleaner,
cheaper, more repeatable and more reliable method of separating
glass substrates than what is currently practiced in the market.
Accordingly, a need exists for alternative improved methods for
separating glass substrates.
SUMMARY
[0005] According to one embodiment, a method for laser processing a
transparent workpiece includes focusing a pulsed laser beam output
by a pulsed laser beam source into a pulsed laser beam focal line
oriented along a beam propagation direction and directed into the
transparent workpiece, thereby forming a pulsed laser beam spot on
an imaging surface of the transparent workpiece. The pulsed laser
beam focal line generates an induced absorption within the
transparent workpiece and the induced absorption produces a defect
along the pulsed laser beam focal line within the transparent
workpiece. The method also includes directing an infrared laser
beam output by an infrared beam source onto the transparent
workpiece such that the infrared laser beam forms an annular
infrared beam spot on the imaging surface. The annular infrared
beam spot circumscribes the pulsed laser beam spot at the imaging
surface and the infrared laser beam heats the transparent
workpiece. Further, the method includes translating the transparent
workpiece and the pulsed laser beam focal line relative to each
other along a separation path, thereby laser forming a plurality of
defects that define a contour line within the transparent workpiece
along the separation path and translating the transparent workpiece
and the annular infrared beam spot relative to each other along the
separation path synchronous with the translation of the transparent
workpiece and the pulsed laser beam focal line relative to each
other, such that the annular infrared beam spot circumscribes the
pulsed laser beam spot during relative motion of the transparent
workpiece and the pulsed laser beam focal line and irradiates the
transparent workpiece along or near the contour line to separate
the transparent workpiece along the contour line.
[0006] In another embodiment, a method for laser processing a
transparent workpiece, the method includes focusing a pulsed laser
beam output by a pulsed laser beam source into a pulsed laser beam
focal line oriented along a beam propagation direction and directed
into the transparent workpiece, thereby forming a pulsed laser beam
spot on an imaging surface of the transparent workpiece. The pulsed
laser beam focal line generates an induced absorption within the
transparent workpiece and the induced absorption produces a defect
along the pulsed laser beam focal line within the transparent
workpiece. The method also includes directing an infrared laser
beam output by an infrared beam source onto the transparent
workpiece such that the infrared laser beam forms an infrared beam
spot on the imaging surface. The infrared beam spot is spaced a
spacing distance from the pulsed laser beam spot at the imaging
surface and the infrared laser beam heats the transparent
workpiece. Further, the method includes translating the transparent
workpiece and the pulsed laser beam focal line relative to each
other along a separation path, thereby laser forming a plurality of
defects that define a contour line within the transparent workpiece
along the separation path and translating the transparent workpiece
and the infrared beam spot relative to each other along the
separation path synchronous with the translation of the transparent
workpiece relative to the pulsed laser beam focal line such that
the pulsed laser beam spot remains spaced the spacing distance from
the infrared beam spot during relative motion of the transparent
workpiece and the pulsed laser beam focal line and irradiates the
transparent workpiece along or near the contour line to separate
the transparent workpiece along the contour line.
[0007] Additional features and advantages of the processes and
systems described herein will be set forth in the detailed
description which follows, and in part will be readily apparent to
those skilled in the art from that description or recognized by
practicing the embodiments described herein, including the detailed
description which follows, the claims, as well as the appended
drawings.
[0008] It is to be understood that both the foregoing general
description and the following detailed description describe various
embodiments and are intended to provide an overview or framework
for understanding the nature and character of the claimed subject
matter. The accompanying drawings are included to provide a further
understanding of the various embodiments, and are incorporated into
and constitute a part of this specification. The drawings
illustrate the various embodiments described herein, and together
with the description serve to explain the principles and operations
of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1A schematically depicts a pulsed laser beam spot
circumscribed by an infrared beam spot, where each are traversing a
separation path of a transparent workpiece, according to one or
more embodiments described herein;
[0010] FIG. 1B schematically depicts a pulsed laser beam spot
offset from an infrared beam spot, where each are traversing a
separation path of a transparent workpiece, according to one or
more embodiments described herein;
[0011] FIG. 2A schematically depicts an optical system comprising a
pulsed beam optical assembly and an infrared optical assembly for
laser processing a transparent workpiece, according to one or more
embodiments described herein;
[0012] FIG. 2B schematically depicted an optical system comprising
the pulsed beam optical assembly of FIG. 2A and another infrared
optical assembly for laser processing a transparent workpiece,
according to one or more embodiments described herein;
[0013] FIG. 3 schematically depicts the formation and separation of
a contour line of defects in the transparent workpiece of FIGS. 2A
and 2B, according to one or more embodiments described herein;
[0014] FIG. 4 schematically depicts an example positioning of a
pulsed laser beam focal line during processing of a transparent
workpiece, according to one or more embodiments described
herein;
[0015] FIG. 5A schematically depicts an optical assembly for pulsed
beam laser processing, according to one or more embodiments
described herein;
[0016] FIG. 5B-1 schematically depicts a first embodiment of a
pulsed beam laser focal line in relationship to a transparent
workpiece, according to one or more embodiments described
herein;
[0017] FIG. 5B-2 schematically depicts a second embodiment of a
pulsed beam laser focal line in relationship to a transparent
workpiece, according to one or more embodiments described
herein;
[0018] FIG. 5B-3 schematically depicts a third embodiment of a
pulsed beam laser focal line in relationship to a transparent
workpiece, according to one or more embodiments described
herein;
[0019] FIG. 5B-4 schematically depicts a fourth embodiment of a
pulsed laser beam focal line in relationship to a transparent
workpiece, according to one or more embodiments described
herein;
[0020] FIG. 6A graphically depicts the relative intensity of laser
pulses within an exemplary pulse burst vs. time, with each
exemplary pulse burst having 7 pulses, according to one or more
embodiments described herein; and
[0021] FIG. 6B graphically depicts relative intensity of laser
pulses vs. time within an exemplary pulse burst, with each
exemplary pulse burst containing 9 pulses, according to one or more
embodiments described herein.
DETAILED DESCRIPTION
[0022] Reference will now be made in detail to embodiments of
processes for laser processing transparent workpieces, such as
glass workpieces, examples of which are illustrated in the
accompanying drawings. Whenever possible, the same reference
numerals will be used throughout the drawings to refer to the same
or like parts. According to one or more embodiments described
herein, a transparent workpiece may be laser processed to separate
the transparent workpiece into two or more portions. Generally, the
process involves at least a forming a contour line comprising
defects in the transparent workpiece, and separating the
transparent workpiece along the contour line by subjecting the
transparent workpiece to an infrared laser beam at or near the
contour line. For example, a pulsed laser beam may be utilized to
create a series of defects in the transparent workpiece thereby
defining the contour line. These defects may be referred to herein
as perforations or nano-perforations in the transparent
workpiece.
[0023] The infrared laser may then be utilized to heat the area of
the transparent workpiece adjacent and/or along the contour line to
separate the transparent workpiece at the contour line. Separation
along the contour line may be caused by mechanical stresses in the
transparent workpiece caused by differences in the temperature of
the transparent workpiece at its different portions caused by the
heating from the infrared laser beam. Further, in the embodiments
described herein, laser forming the plurality of defects and
heating these defects with the infrared laser beam may occur in a
single, synchronized step. In some embodiments, the infrared laser
beam may form an infrared beam spot on the transparent workpiece
(which in some embodiments may be an annular infrared beam spot)
and the pulsed laser beam may be directed into the transparent
workpiece such that the infrared beam spot (e.g., an annular
infrared beam spot) surrounds (e.g., circumscribes) a pulsed laser
beam spot form by the pulsed laser beam on an imaging surface of
the transparent workpiece. In other embodiments, the infrared laser
beam may form the infrared beam spot on the transparent workpiece
and the pulsed laser beam may be directed into the transparent
workpiece such that the pulsed laser beam spot formed by the pulsed
laser beam is spaced apart from the infrared laser beam by a
spacing distance. In each of these embodiments, the defect line is
formed by the pulsed laser beam and separated by the infrared laser
beam and the transparent workpiece is separated along the defect
line by synchronous relative motion between the transparent
workpiece and both the pulsed laser beam and the infrared laser
beam. Various embodiments of methods and apparatuses for separating
a transparent workpiece will be described herein with specific
reference to the appended drawings.
[0024] According to one or more embodiments, the present disclosure
provides methods for processing transparent workpieces. As used
herein, "laser processing" may include forming contour lines in
transparent workpieces, separating transparent workpieces, or
combinations thereof. The phrase "transparent workpiece," as used
herein, means a workpiece formed from glass, glass-ceramic, or a
semiconductor material, which are transparent, where the term
"transparent," as used herein, means that the material has an
optical absorption of less than about 10% per mm of material depth,
such as less than about 1% per mm of material depth for the
specified pulsed laser wavelength. According to some embodiments,
at least a portion of the transparent workpiece, such as the
portion which is separated, has a coefficient of thermal expansion
of less than about 5.times.10.sup.-6/K, such as less than about
4.times.10.sup.-6/K, or less than about 3.5.times.10.sup.-6/K. For
example, the transparent workpiece may have a coefficient of
thermal expansion of about 3.2.times.10.sup.-6/K. The transparent
workpiece may have a thickness of from about 50 microns to about 10
mm (such as from about 100 microns to about 5 mm, or from about 0.5
mm to about 3 mm.
[0025] Transparent workpieces may comprise glass workpieces formed
from glass compositions, such as borosilicate glass, soda-lime
glass, aluminosilicate glass, alkali aluminosilicate, alkaline
earth aluminosilicate glass, alkaline earth boro-aluminosilicate
glass, fused silica, or crystalline materials such as sapphire,
silicon, gallium arsenide, or combinations thereof. In some
embodiments, the glass may be ion-exchangeable, such that the glass
composition can undergo ion-exchange for mechanical strengthening
before or after laser processing the transparent workpiece. For
example, the transparent workpiece may comprise ion exchanged and
ion exchangeable glass, such as Corning Gorilla.RTM. Glass
available from Corning Incorporated of Corning, N.Y. (e.g., code
2318, code 2319, and code 2320). Further, these ion exchangeable
glasses may have coefficients of thermal expansion (CTE) of from
about 6 ppm/.degree. C. to about 10 ppm/.degree. C. In some
embodiments, the glass composition of the transparent workpiece may
include greater than about 1.0 mol. % boron and/or compounds
containing boron, including, without limitation, B.sub.2O.sub.3. In
another embodiment, the glass compositions from which the
transparent workpieces are formed include less than or equal to
about 1.0 mol. % of oxides of boron and/or compounds containing
boron. Moreover, the transparent workpiece may comprise other
components which are transparent to the wavelength of the laser,
for example, crystals such as sapphire or zinc selenide.
[0026] Some transparent workpieces may be utilized as display
and/or TFT (thin film transistor) substrates. Some examples of such
glasses or glass compositions suitable for display or TFT use are
EAGLE XG.RTM., CONTEGO, and CORNING LOTUS.TM. available from
Corning Incorporated of Corning, N.Y. The alkaline earth
boro-aluminosilicate glass compositions may be formulated to be
suitable for use as substrates for electronic applications
including, without limitation, substrates for TFTs. The glass
compositions used in conjunction with TFTs typically have CTEs
similar to that of silicon (such as less than 5.times.10.sup.-6/K,
or even less than 4.times.10.sup.-6/K, for example, approximately
3.times.10.sup.-6/K, or about 2.5.times.10.sup.-6/K to about
3.5.times.10.sup.-6/K), and have low levels of alkali within the
glass. Low levels of alkali (e.g., trace amounts of about 0 wt. %
to 2 wt. %, such as less than 1 wt. %, for example, less than 0.5
wt. %) may be used in TFT applications because alkali dopants,
under some conditions, leach out of glass and contaminate or
"poison" the TFTs, possibly rendering the TFTs inoperable.
According to embodiments, the laser cutting processes described
herein may be used to separate transparent workpieces in a
controlled fashion with negligible debris, minimum defects, and low
subsurface damage to the edges, preserving workpiece integrity and
strength.
[0027] The phrase "contour line," as used herein, denotes a line
(e.g., a line, a curve, etc.) of intended separation on the surface
of a transparent workpiece along which the transparent workpiece
will be separated into multiple portions upon exposure to the
appropriate processing conditions. The contour line generally
consists of one or more defects introduced into the transparent
workpiece using various techniques. As used herein, a "defect" may
include an area of modified material (relative to the bulk
material), void space, scratch, flaw, hole, or other deformalities
in the transparent workpiece, which may be formed by irradiating
the transparent workpiece with a pulsed laser beam. The defects of
the contour line enable separation of the transparent workpiece
along the contour line by an additional heat treatment, such as by
infrared laser processing (as described herein), mechanical stress,
or a spontaneous break occurring without further heating or
mechanical separation steps, due to stress present in the
transparent workpiece 160, depending on the type, thickness, and
structure of the transparent workpiece 160 (for example, a
transparent workpiece 160 having a high CTE may undergo spontaneous
break after formation of the contour line). Further, as also used
herein the "imaging surface" of the transparent workpiece is the
surface of the transparent workpiece at which the pulsed laser beam
initially contacts the transparent workpiece.
[0028] A transparent workpiece, such as a glass substrate or the
like, may be separated into multiple portions by forming a contour
line on the surface of the transparent workpiece and, thereafter
heating the surface of the transparent workpiece along the contour
line to create thermal stresses in the transparent workpiece. The
stresses ultimately lead to the separation (e.g., spontaneous
separation) of the transparent workpiece along the contour line.
Heating the surface of the transparent workpiece may be carried
out, for example, using an infrared laser. Moreover, formation of
the contour line comprising defects and heating the surface of the
transparent workpiece along the contour line may be by synchronous
relative motion between the transparent workpiece and both the
pulsed laser beam and the infrared laser beam. By synchronizing the
formation of the contour line with the subsequent heating of the
contour line, the laser processing time for separating the
transparent workpiece (e.g., the tact time) may be reduced, for
example, halved.
[0029] Referring now to FIGS. 1A and 1B, by way of example, a
transparent workpiece 160, such as a glass workpiece or a
glass-ceramic workpiece, is schematically depicted undergoing
synchronized defect formation and separation according to the
methods described herein. As depicted, a contour line 170 is formed
in the transparent workpiece 160 along a separation path 165, which
is a line of intended separation about which the transparent
workpiece 160 will be separated into two or more portions. The
contour line 170 comprises a series of defects 172 in the
transparent workpiece 160 and each defect 172 may be formed by
directing a pulsed laser beam focal line 113 (FIGS. 2 and 3) into
the transparent workpiece 160. The pulsed laser beam focal line 113
comprises a portion of a pulsed laser beam 112 (FIGS. 2 and 3),
which forms a pulsed laser beam spot 114 on an imaging surface 162
of the transparent workpiece 160. Some example methods and
apparatuses for forming a "perforated" contour line (e.g., forming
the contour line 170 in the transparent workpiece 160) are
disclosed in U.S. Patent Application Publication No. 2015/0360991,
published Dec. 17, 2015, incorporated herein by reference in its
entirety. While the contour line 170 is depicted in FIGS. 1A and 1B
as being substantially linear, it should be understood that other
configurations are contemplated and possible including, without
limitation, curves, patterns, regular geometric shapes, irregular
shapes, and the like. As noted herein, the defects 172 of the
contour line 170 which may be heated by an infrared laser beam 212
(FIGS. 2A, 2B, and 3) to induce separation of the transparent
workpiece 160 along the contour line 170. As depicted in FIGS. 1A
and 1B, the infrared laser beam 212 forms an infrared beam spot 214
on the imaging surface 162 of the transparent workpiece 160.
[0030] The contour line 170 may comprise line shaped defects,
(e.g., defects 172) that extend within the transparent workpiece
160, for example, extend from the imaging surface 162 into the
transparent workpiece 160, and delineate the desired shape of the
separated workpiece and establish a path for crack propagation and,
hence, separation of the transparent workpiece 160 into separate
portions along the contour line 170. To form the contour line 170,
the transparent workpiece 160 may be irradiated with the pulsed
laser beam 112 (FIGS. 2A, 2B, and 3), which may comprise an
ultra-short pulsed (i.e., having a pulse width less than 100 psec)
laser beam at wavelengths at or below 1064 nm that is condensed
into a high aspect ratio line focus (i.e. the pulsed laser beam
focal line 113 of FIGS. 2A, 2B, and 3) that penetrates through at
least a portion of the thickness of the transparent workpiece 160.
Within this volume of high energy density, the material of the
transparent workpiece 160 along the contour line 170 is modified
via nonlinear effects (e.g., by two photon absorption),
specifically creating defects 172 in the material of the
transparent workpiece 160. By scanning the pulsed laser beam 112
over a desired line or path (i.e. the separation path 165), narrow
line defects (e.g., a few microns wide) defining the contour line
170 may be formed. This contour line 170 may define the perimeter
or shape to be separated from the transparent workpiece 160 in a
subsequent heating step.
[0031] Referring now to FIGS. 1A-3, synchronized with the formation
of the contour line 170 in the transparent workpiece 160, a thermal
source, such as the infrared laser beam 212, may be utilized to
separate the transparent workpiece 160 along the contour line 170.
According to embodiments, the thermal source may be used to create
thermal stress and thereby separate the transparent workpiece 160
at the contour line 170. As described in more detail below,
relative movement of the infrared laser beam 212 along the contour
line 170 may be synchronized with relative movement of the pulsed
laser beam 112 along the separation path 165 such that formation
and separation of the contour line 170 may occur in a single pass
(i.e. a single, synchronized traversal of the pulsed laser beam 112
and the infrared laser beam 212 along the separation path 165).
[0032] The infrared laser beam 212 comprises a laser beam produced
by an infrared laser beam source 210, such as a carbon dioxide
laser (a "CO.sub.2 laser"), a carbon monoxide laser (a "CO laser"),
a solid state laser, a laser diode, or combinations thereof, is a
controlled heat source that rapidly increases the temperature of
the transparent workpiece 160 at or near the contour line 170. This
rapid heating may build compressive stress in the transparent
workpiece 160 on or adjacent to the contour line 170. Since the
area of the heated glass surface is relatively small compared to
the overall surface area of the transparent workpiece 160, the
heated area cools relatively rapidly. The resultant temperature
gradient induces tensile stress in the transparent workpiece 160
sufficient to propagate a crack along the contour line 170 and
through the thickness of the transparent workpiece 160, resulting
in full separation of the transparent workpiece 160 along the
contour line 170. Without being bound by theory, it is believed
that the tensile stress may be caused by expansion of the glass
(i.e., changed density) in portions of the transparent workpiece
160 with higher local temperature.
[0033] Referring still to FIGS. 1A-3, in the embodiments described
herein, the infrared laser beam 212 may be directed onto the
transparent workpiece 160 (thereby projecting the infrared beam
spot 214 onto the transparent workpiece 160) and translated
relative to the transparent workpiece 160 along the contour line
170 in a processing direction 10. In operation, a separated portion
164 of the contour line 170 is formed by heating the contour line
170 with the infrared laser beam 212 (e.g., by traversing the
infrared beam spot 214), thereby causing a crack to propagate along
the contour line 170 and through its thickness causing separation
to occur. The separated portion 164 of the contour line 170 trails
the infrared beam spot 214 as it moves in the processing direction
10. According to one or more embodiments, the infrared laser beam
212 may be translated across the transparent workpiece 160 by
motion of the transparent workpiece 160, motion of the infrared
laser beam 212 (i.e., motion of the infrared beam spot 214), or
motion of both the transparent workpiece 160 and the infrared laser
beam 212. By translating the infrared beam spot 214 relative to the
transparent workpiece 160, the transparent workpiece 160 may be
separated along the contour line 170.
[0034] While not intending to be limited by theory, heating the
transparent workpiece 160 on both sides of the contour line 170
creates the thermal stress to facilitate separation of the
transparent workpiece 160 along the contour line 170. However,
while the total amount of energy imparted to the transparent
workpiece 160 to facilitate separation along the contour line 170
may be the same as if the infrared laser beam 212 was focused with
maximum intensity directly on the contour line 170 (e.g., a
Gaussian beam profile), heating the transparent workpiece on both
sides of the contour line 170 rather than with maximum intensity
directly on the contour line 170 spreads the total amount of
thermal energy over a larger area, thereby mitigating the formation
of cracks lateral to the contour line 170 due to overheating and
also reducing or even mitigating melting of the material of the
transparent workpiece 160 adjacent to or at the contour line 170.
Indeed, heating the transparent workpiece 160 with maximum
intensity on both sides of the contour line 170 rather than with
maximum intensity directly on the contour line 170 may actually
allow for a greater amount of total thermal energy to be introduced
into the transparent workpiece 160 without the formation of
undesired lateral cracks and/or melting, thereby enabling laser
separation of transparent workpieces 160 formed from materials
having relatively low CTEs.
[0035] In some embodiments, the infrared beam spot 214 of infrared
laser beam 212 used to facilitate separation may comprise an
annular beam profile (e.g., an annular infrared beam spot), such as
the circular symmetric beam profile depicted in FIGS. 1A and 1B, in
order to transfer a greater amount of energy onto the areas
adjacent the contour line 170 than directly onto the contour line
170 and also allow the infrared beam spot 214 to circumscribe the
pulsed laser beam 112 at the imaging surface 162 of the transparent
workpiece 160 (i.e. circumscribe the pulsed laser beam spot 114 in
the embodiment depicted in FIG. 1A). Thus, the infrared beam spot
214 facilitates synchronous formation and separation of the
transparent workpiece 160 along the contour line 170. As depicted
in FIGS. 1A and 1B, in embodiments in which the infrared beam spot
214 comprises an annular infrared beam spot, the infrared beam spot
214 comprises an inner diameter 216 and an outer diameter 218.
Further, as used herein, an annular beam profile (e.g., of the
annular infrared beam spot) refers to any laser beam profile which
generally has a maximum intensity away from the center of the beam
and has an intensity trough at its center relative to the maximum
intensity. The trough may include complete lack of energy at the
center of the beam, (i.e. the intensity of the beam is 0 at its
center). Moreover, while the infrared beam spot 214 is depicted in
FIGS. 1A and 1B as comprising a circular annulus (e.g., circularly
symmetric relative to the contour line 170), it should be
understood that other annular beam profiles are contemplated, such
as an oval shape, an elliptical shape, a Lissajous pattern, a
plurality of discrete spots, a plurality of rings, or the like.
Further, it should be understood that in some embodiments, the
infrared beam spot 214 may comprise non-annular shapes such as a
Gaussian beam spot comprising that does not include the inner
diameter 216 and projects laser energy at substantially all
locations within the outer diameter 218.
[0036] Referring again to FIGS. 1A and 1B, synchronous formation of
the defects 172 of the contour line 170 may comprise synchronous
relative motion between the transparent workpiece 160 and both the
pulsed laser beam spot 114 and the infrared beam spot 214 in
arrangements in which the pulsed laser beam spot 114 and the
infrared beam spot 214 are positioned near one another along the
separation path 165. To facilitate synchronous relative motion, the
pulsed laser beam spot 114 (and thereby the pulsed laser beam focal
line 113) may be translated at a speed that is equal the speed of
relative motion between the infrared beam spot 214 and the
transparent workpiece 160. For example, relative translation
between the transparent workpiece 160 and each of the infrared beam
spot 214 and the pulsed laser beam spot 114 may be from about 1
mm/s to about 10 m/s, such as about 2 mm/s, 5 mm/s, 10 mm/s, 25
mm/s, 50 mm/s, 75 mm/s, 100 mm/s, 250 mm/s, 500 mm/s, 750 mm/s, 1
m/s, 2.5 m/s, 5 m/s, 7.5 m/s, or the like.
[0037] As depicted in FIG. 1A, in some embodiments, the infrared
beam spot 214 may comprise an annular infrared beam spot and may
circumscribe the pulsed laser beam spot 114 on the imaging surface
162 of the transparent workpiece 160, as depicted in FIG. 1A. When
the infrared beam spot 214 circumscribes the pulsed laser beam spot
114, synchronous formation and separation of the transparent
workpiece 160 along the contour line 170 comprises translating the
transparent workpiece 160 and the infrared beam spot 214 relative
to each other along the separation path 165 (e.g., in the
processing direction 10) synchronous with the translation of the
transparent workpiece 160 and the pulsed laser beam spot 114 (and
thereby the pulsed laser beam focal line 113) relative to each
other, such that the infrared beam spot 214 circumscribes the
pulsed laser beam spot 114 during relative motion of the
transparent workpiece 160 and the pulsed laser beam spot 114 (and
thereby the pulsed laser beam focal line 113). In the embodiment
depicted in FIG. 1A, the pulsed laser beam spot 114 and the
infrared beam spot 214 are coaxial (i.e. each share a common center
point). However, it should be understood that the pulsed laser beam
spot 114 may be positioned at any location within the inner
diameter 216 of the infrared beam spot 214 while still
circumscribing the pulsed laser beam spot 114. Further, in some
embodiments, the pulsed laser beam spot 114 may be positioned
within the inner diameter 126 of the infrared beam spot 214 such
that the pulsed laser beam spot 114 and the nearest portion of the
infrared beam spot 214 is about 3 mm from the pulsed laser beam
spot 114 or more, for example, 4 mm or more 5 mm or more 6 mm or
more, or the like.
[0038] Referring now to FIG. 1B, in some embodiments, the infrared
beam spot 214 may be spaced a spacing distance 15 from the pulsed
laser beam spot 114, such that the infrared beam spot 214 trails
the pulsed laser beam spot 114 along the processing direction 10.
The spacing distance 15 between the pulsed laser beam spot 114 and
the infrared beam spot 214 may be from about 1 .mu.m and about 100
mm, for example, about 2 .mu.m, 5 .mu.m, 10 .mu.m, 25 .mu.m, 50
.mu.m, 100 .mu.m, 250 .mu.m, 500 .mu.m, 1 mm, 2 mm, 5 mm, 10 mm, 25
mm, 50 mm, 75 mm, or the like. When the infrared beam spot 214 is
spaced apart from the pulsed laser beam spot 114 by the spacing
distance 15, synchronous formation and separation of the
transparent workpiece 160 along the contour line 170 comprises
translating the transparent workpiece 160 and the infrared beam
spot 214 relative to each other along the separation path 165
(e.g., in the processing direction 10) synchronous with the
translation of the transparent workpiece 160 and the pulsed laser
beam spot 114 (and thereby the pulsed laser beam focal line 113)
relative to each other such that the infrared beam spot 214 remains
spaced the spacing distance 15 from the pulsed laser beam spot 114
from during relative motion of the transparent workpiece 160 and
the pulsed laser beam spot 114 (and thereby the pulsed laser beam
focal line 113) and irradiates the transparent workpiece 160 along
or near the contour line 170 to separate the transparent workpiece
160 along the contour line 170. Further, while the infrared beam
spot 214 is depicted as an annular infrared beam spot in FIG. 1B,
in embodiments in which the infrared beam spot 214 is spaced a
spacing distance 15 from the pulsed laser beam spot 114, the
infrared beam spot 214 may comprise a non-annular shape, for
example, a Gaussian beam spot.
[0039] While FIGS. 1A and 1B depict embodiments in which the pulsed
laser beam spot 114 and the infrared beam spot 214 do not overlap
on the imaging surface 162 of the transparent workpiece 160, in
other embodiments, the pulsed laser beam spot 114 and the infrared
beam spot 214 may overlap. For example, in embodiments in which the
transparent workpiece 160 comprises a low CTE, the pulsed laser
beam spot 114 and the infrared beam spot 214 may overlap and
synchronous formation and separation of the transparent workpiece
160 along the contour line 170 may comprise translating the
transparent workpiece 160 and the infrared beam spot 214 relative
to each other along the separation path 165 (e.g., in the
processing direction 10) synchronous with the translation of the
transparent workpiece 160 and the pulsed laser beam spot 114 (and
thereby the pulsed laser beam focal line 113) relative to each
other while the infrared beam spot 214 retains an overlap with the
pulsed laser beam spot 114. While not intending to be limited by
theory, when the transparent workpiece 160 comprises a low CTE,
interference between the pulsed laser beam 112 and the infrared
laser beam 212 at the transparent workpiece 160 is minimized,
minimizing unwanted alterations of the refractive index of local
portions of the transparent workpiece 160 irradiated by the
infrared laser beam 212 and the pulsed laser beam 112.
[0040] Referring again to FIGS. 1A and 1B, the inner diameter 216
is defined as twice the distance (i.e., a radius) where 86% of the
beam energy is outside of that distance from the center of the
beam. Similarly, the outer diameter 218 is defined as twice the
distance (i.e., a radius) where 86% of the beam energy is inside of
that distance from the beam center. According to embodiments, the
outer diameter 218 may be from about 0.5 mm to about 30 mm, such as
from about 1 mm to about 10 mm, from about 2 mm to about 8 mm, or
from about 3 mm to about 6 mm. The inner diameter 216 may be from
about 0.01 mm to about 15 mm, from about 0.1 mm to about 10 mm, or
from about 0.7 mm to about 3 mm. For example, the inner diameter
216 may be from about 5% to about 95% of the outer diameter 218,
such as from about 10% to about 50%, from about 20% to about 45%,
or from about 30% to about 40% of the outer diameter 218. According
to some embodiments, the maximum power from the infrared laser beam
212 (as well as maximum temperature in the transparent workpiece
160) may be at a distance from the contour line 170 about equal to
about the half the inner diameter 216.
[0041] Referring now to FIGS. 2A and 2B, an optical system 100 for
synchronous formation and separation of the contour line 170 is
schematically depicted. The optical system 100 comprises a pulsed
beam optical assembly 101 and an infrared beam optical assembly 201
(FIG. 2A) or 201' (FIG. 2B). The pulsed beam optical assembly 101
comprises a pulsed laser beam source 110 and one or more optical
components for forming the pulsed laser beam 112 into a pulsed
laser beam focal line 113 such that the pulsed laser beam focal
line 113 may form the defects 172 of the contour line 170 in the
transparent workpiece 160. The infrared beam optical assembly 201,
201' comprises the infrared laser beam source 210 (not shown in
FIG. 2B) for generating the infrared laser beam 212 and comprises
one or more optical components for directing the infrared laser
beam 212 onto the imaging surface 162 of the transparent workpiece
160. As depicted in FIGS. 2A and 2B, the pulsed beam optical
assembly 101 may include a housing 102 for housing and physically
coupling the components of the pulsed beam optical assembly 101 and
the infrared beam optical assembly 201, 201' may include a housing
202, 202' for housing and physically coupling the components of the
infrared beam optical assembly 201, 201'.
[0042] The optical system 100 may further comprise a mounting unit
182 and both the housing 102 of the pulsed beam optical assembly
101 and the housing 202, 202' of the infrared beam optical assembly
201 may be coupled to the mounting unit 182, for example, movably
coupled to the mounting unit 182 to facilitate translational motion
of the pulsed laser beam 112 generated by the pulsed laser beam
source 110 of the pulsed beam optical assembly 101 and
translational motion of the infrared laser beam 212 generated by
the infrared laser beam source 210. Further, the optical system 100
comprises a translatable stage 180. As depicted in FIGS. 2A and 2B,
the transparent workpiece 160 may be mounted on the translatable
stage 180, which facilitates translation motion of the transparent
workpiece 160. Thus, relative motion between transparent workpiece
160 and each of the pulsed laser beam 112 and the infrared laser
beam 212 (e.g., synchronous relative motion) may be generated by
movement of the translatable stage 180, movement of the housing 102
of the pulsed beam optical assembly 101 and the housing 202, 202'
of the infrared beam optical assembly 201, 201' along the mounting
unit 182, movement of the mounting unit 182 itself, or combinations
thereof.
[0043] Referring now to FIG. 2A, the infrared beam optical assembly
201 comprises the infrared laser beam source 210, an aspheric
optical element 220, a first plano-convex lens 222, a second
plano-convex lens 224, a beam conditioning element 226, and a beam
directing element 230. While not intending to be limited by theory,
the infrared laser beam 212 may comprise a Gaussian beam having
diameter of from about 8 mm to about 10 mm (according to its
1/e.sup.2 diameter), and the aspheric optical element 220 may
comprise an axicon lens, which may comprise a conical surface
having an angle of about 1.2.degree., such as from about
0.5.degree. to about 5.degree., or from about 1.degree. to about
1.5.degree., or even from about 0.5.degree. to about 5.degree. (the
angle measured relative to the flat surface upon which the infrared
laser beam 212 enters the aspheric optical element 220. The
aspheric optical element 220 (e.g., the axicon lens) shapes the
incoming infrared laser beam 212 (which comprises a Gaussian beam)
into a Bessel beam. In some embodiments, the aspheric optical
element 220 may comprise a refractive axicon, a reflective axicon,
waxicon, negative axicon, a spatial light modulator, a diffractive
optic, a cubically shaped optical element, or any optical element
for shaping a Gaussian beam into a Bessel beam.
[0044] Referring still to FIG. 2A, the first plano-convex lens 222
and the second plano-convex lens 224 are positioned downstream from
the aspheric optical element 220 such that the infrared laser beam
212 output by the infrared laser beam source 210 is directed
through the aspheric optical element 220 and, thereafter, through
the first plano-convex lens 222 and the second plano-convex lens
224. As used herein "upstream" and "downstream" refer to the
relative position of two locations or components of an optical
assembly (e.g., the pulsed beam optical assembly 101 or the
infrared beam optical assembly 201) with respect to a beam source
(e.g., the pulsed laser beam source 110 or the infrared laser beam
source 210). For example, a first component is upstream from a
second component if the beam output by the beam source traverses
the first component before traversing the second component.
Further, a first component is downstream from a second component if
the beam output by the beam source traverses the second component
before traversing the first component.
[0045] In operation, the first plano-convex lens 222 and the second
plano-convex lens 224 collimate the Bessel beam (e.g., the infrared
laser beam 212 after the infrared laser beam traverses the aspheric
optical element 220) and adjust the diameter(s) of the infrared
laser beam 212 (e.g., adjust the inner diameter 216 and the outer
diameter 218 of the infrared beam spot 214 formed on the imaging
surface 162 of the transparent workpiece 160). In some embodiments,
the first plano-convex lens 222 may have a focal length of from
about 50 mm to about 200 mm (such as from about 50 mm to about 150
mm, or from about 75 mm to about 100 mm), and the second
plano-convex lens 224 may have a focal length less than that of the
first plano-convex lens 222, such as from about 25 mm to about 50
mm.
[0046] The beam directing element 230 may comprise a mirror or
other reflective component, a rotatable scanner, such as a
galvanometer scanning mirror, a 2D scanner, or the like, or any
other known or yet-to-be-developed optical component for
redirecting a laser beam. In the embodiment of the infrared beam
optical assembly 201 depicted in FIG. 2A, the beam directing
element 230 is positioned downstream the aspheric optical element
220, the first plano-convex lens 222, and the second plano-convex
lens 224 such that the infrared laser beam 212 is redirected by the
beam directing element 230 while converging from the second
plano-convex lens 224. However, in other embodiments, the beam
directing element 230 may be positioned upstream one or more of the
aspheric optical element 220, the first plano-convex lens 222, and
the second plano-convex lens 224.
[0047] As depicted in FIG. 2A, the beam directing element 230 is
optically coupled to the infrared laser beam source 210 such that
the beam directing element 230 redirects (e.g., reflects) the
incoming infrared laser beam 212. Thus, the portion of the infrared
laser beam 212 downstream the beam directing element 230 propagates
from the beam directing element 230 to the transparent workpiece
160 in a direction 14, such that the infrared laser beam 212
irradiates the transparent workpiece at an approach angle .theta.,
which is the angular difference between the beam propagation
direction of the pulsed laser beam 112 (i.e. direction 12) and the
beam propagation direction of the infrared laser beam 212
downstream the beam directing element 230 (i.e. direction 14). In
some embodiments, the approach angle .theta. may be from about
30.degree. to about 75.degree., from about 40.degree. to about
65.degree., or the like, such as about 30.degree., 35.degree.,
40.degree., 45.degree., 50.degree., 55.degree., 60.degree.,
65.degree., 70.degree., 75.degree., or the like. Further, the
approach angle .theta. is non-parallel to the beam propagation
direction of the pulsed laser beam 112 (i.e. direction 12). Thus,
the components of the infrared beam optical assembly 201 and the
pulsed beam optical assembly 101 may be positioned apart from one
another and the infrared laser beam 212 and the pulsed laser beam
112 do not need to be coaxial for the infrared beam spot 214 formed
on the imaging surface 162 of the transparent workpiece 160 to
circumscribe the pulsed laser beam spot 114 formed on the imaging
surface 162 of the transparent workpiece 160 (FIG. 1A).
[0048] Moreover, in embodiments in which the pulsed laser beam spot
114 is offset from the infrared beam spot 214 at the imaging
surface 162 of the transparent workpiece 160 (FIG. 1B), it may
still be advantageous to redirect the infrared laser beam 212 such
that the portion of the infrared laser beam 212 downstream beam
directing element 230 propagates from the beam directing element
230 to the transparent workpiece 160 in the direction 14 at the
approach angle .theta. as the spacing distance 15 (FIG. 1B) may be
too small to for the infrared beam optical assembly 201 and the
pulsed beam optical assembly 101 form two parallel beams offset by
the spacing distance 15. In other embodiments, the infrared beam
optical assembly 201 may further comprise another beam directing
element positioned downstream the beam directing element 230 to
reorient the infrared laser beam 212 parallel the pulsed laser beam
112 (e.g., direct the pulsed laser beam into the direction 12) such
that the infrared laser beam 212 irradiates the imaging surface 162
of the transparent workpiece 160 parallel and offset from the
pulsed laser beam spot 114 by the spacing distance 15.
[0049] Further, the beam conditioning element 226 is configured to
alter the cross-sectional beam profile of the infrared laser beam
212, for example, to account for the alteration of the shape of the
infrared beam spot 214 caused by irradiating the imaging surface
162 of the transparent workpiece 160 at the approach angle .theta..
In particular, the beam conditioning element 226 is configured to
alter the cross-sectional beam profile of the pulsed laser beam 112
such that the infrared beam spot 214 projected onto the imaging
surface 162 of the transparent workpiece 160 comprises a desired
shape (e.g., circular, elliptical, or the like). For example, if
the portion of the infrared laser beam 212 comprises a circular
cross-sectional beam profile after redirection by the beam
directing element 230 and thereafter irradiates the imaging surface
162 of the transparent workpiece 160 at the approach angle .theta.
(without traversal through the beam conditioning element 226), the
resultant shape of the infrared beam spot 214 will not be circular.
However, the beam conditioning element 226 may alter the
cross-sectional beam profile of the infrared laser beam 212 such
that the resultant shape of the infrared beam spot 214 is circular.
The beam conditioning element 226 may comprise a cylindrical lens,
a prism, a diffractive optical element, a telescope lens, or the
like. As depicted in FIG. 2A, the beam conditioning element 226 is
positioned downstream the beam directing element 230 such that the
beam conditioning element 226 alters the cross-sectional beam
profile of the infrared laser beam 212 after the beam directing
element 230 redirects the infrared laser beam 212 into the
direction 14. In other embodiments, the beam conditioning element
226 may be positioned upstream the beam directing element 230 such
that the beam conditioning element 226 alters the cross-sectional
beam profile of the infrared laser beam 212 before the beam
directing element 230 redirects the infrared laser beam 212 into
the direction 14.
[0050] Referring now to FIG. 2B, the infrared beam optical assembly
201' has a beam directing element 230' that comprises a 2D scanning
system. In some embodiments, the 2D scanning system 230' may house
the optical components of the infrared beam optical assembly 201'
such that the housing of the 2D scanning system 230' is the housing
202' of the infrared beam optical assembly 201'. In operation, the
infrared laser beam 212 may be output by the 2D scanning system
230' and thereby directed onto the transparent workpiece 160. In
some embodiments the 2D scanning system 230' is coupled to the
mounting unit 182. For example, the 2D scanning system 230' may be
rotatably coupled to the mounting unit 182 such that the 2D
scanning system 230' is rotatable about an axis of rotation 205. In
some embodiments, the 2D scanning system 230' is also translatable
relative to the transparent workpiece 160 along the Z direction.
Thus, when the direction of the direction 14 of the infrared laser
beam 212 is altered (thereby altering the approach angle .theta.)
and the position of the 2D scanning system 230' along to Z
direction may also be altered such that the infrared laser beam 212
may irradiate the transparent workpiece 160 at a desired location.
Further, while not depicted, the infrared beam optical assembly
201' further comprises the infrared laser beam source (which may be
a component of the 2D scanning system 230' and thereby housed
within the housing 202'). Further, the 2D scanning system 230' may
be configured to output a Gaussian infrared beam or a Bessel
infrared beam. In embodiments in which the 2D scanning system 230'
outputs a Gaussian beam, the infrared beam optical assembly 201'
may further comprise an aspheric optical element housed within the
2D scanning system 230' or positioned downstream the 2D scanning
system 230' to shape the Gaussian beam into a Bessel beam.
Moreover, in some embodiments, the infrared beam optical assembly
201' may further comprise one or more lens (such as first and
second plano-convex lens) and a beam conditioning element, as
described above with respect to FIG. 2A.
[0051] Referring again to FIGS. 2A and 2B, the pulsed beam optical
assembly 101 for producing the pulsed laser beam 112 and forming
the pulsed laser beam 112 into the pulsed laser beam focal line 113
comprises the pulsed laser beam source 110 and an aspheric optical
element 120. The aspheric optical element 120 may comprise an
axicon, such as refractive axicon, a reflective axicon, or negative
axicon, a waxicon, a spatial light modulator, a diffractive optic,
or a cubically shaped optical element. The pulsed laser beam 112
output by the pulsed laser beam source 110 may comprise a Gaussian
beam, which is converted into a Gauss-Bessel beam by the aspheric
optical element 120. Without intending to be limited by theory, a
Gauss-Bessel beam diffracts much more slowly than a Gaussian beam
(e.g., the Gauss-Bessel beam may maintain single micron diameter
spot sizes for ranges of hundreds of microns or millimeters as
opposed to a few tens of microns or less). In other words, the
aspheric optical element 120 condenses the pulsed laser beam 112 a
high intensity region of cylindrical shape and high aspect ratio
(long length and small diameter). Due to the high intensity created
with the condensed laser beam, while the pulsed laser beam 112 is
directed into the transparent workpiece 160 (e.g., when the pulsed
laser beam focal line 113 is directed into the transparent
workpiece 160) nonlinear interaction of the electromagnetic field
of the laser and the workpiece material may occur and the laser
energy may be transferred to the transparent workpiece to effect
formation of defects that become constituents of the contour line.
However, it is important to realize that in the areas of the
material where the laser energy intensity is not high (e.g., the
glass volume of workpiece surrounding the central convergence
line), the material of the transparent workpiece is largely
unaffected by the laser and there is no mechanism for transferring
energy from the laser to the material. As a result, nothing happens
to the workpiece directly at the focal zone when the laser
intensity is below the nonlinear threshold.
[0052] While the aspheric optical element 120 may convert the
pulsed laser beam into a Gauss-Bessel beam and focus the pulsed
laser beam 112 into a pulsed laser beam focal line 113, in some
embodiments, the pulsed beam optical assembly 101 may further
comprise additional optical components to help form the pulsed
laser beam 112 into the pulsed laser beam focal line 113. For
example, the pulsed beam optical assembly 101 depicted in FIGS. 2A
and 2B comprises a first lens 130 and a second lens 132, each
positioned downstream the aspheric optical element 120 to collimate
and thereafter focus the pulsed laser beam 112 into the pulsed
laser beam focal line 113. Other optical components are described
in embodiments of the pulsed beam optical assembly 101 depicted in
FIGS. 4 and 5A, described below.
[0053] Further, the transparent workpiece 160 is positioned such
that the pulsed laser beam 112 output by the pulsed laser beam
source 110 irradiates the transparent workpiece 160. In operation,
the pulsed beam optical assembly 101 may form the pulsed laser beam
112 into a pulsed laser beam focal line 113, which may be directed
into the transparent workpiece 160 to induce absorption within the
transparent workpiece 160, for example, along the separation path
165, to form an individual defect 172. Moreover, translating the
pulsed laser beam focal line 113 and the transparent workpiece 160
relative to one another may form the contour line 170 comprising
the plurality of defects 172.
[0054] In operation, the pulsed laser beam 112 (e.g., the pulsed
laser beam focal line 113) may create multi-photon absorption (MPA)
in substantially transparent materials such as the transparent
workpiece 160 to form the defects 172 of the contour line 170. MPA
is the simultaneous absorption of two or more photons of identical
or different frequencies that excites a molecule from one state
(usually the ground state) to a higher energy electronic state
(i.e., ionization). The energy difference between the involved
lower and upper states of the molecule is equal to the sum of the
energies of the involved photons. MPA, also called induced
absorption, can be a second-order or third-order process (or higher
order), for example, that is several orders of magnitude weaker
than linear absorption. It differs from linear absorption in that
the strength of second-order induced absorption may be proportional
to the square of the light intensity, for example, and thus it is a
nonlinear optical process.
[0055] Referring now to FIG. 3, the transparent workpiece 160
undergoing laser processing by the pulsed laser beam 112 and the
infrared laser beam 212 to synchronously form the contour line 170
and separate the transparent workpiece 160 along the contour line
170 is depicted in more detail. While not intending to be being
bound by theory, it is believed that the high aspect ratio of the
defects 172 created by the ultra-short pulsed laser (e.g. the
pulsed laser beam focal line 113 of the pulsed laser beam 112)
facilitates extension of the defects 172 from the top to the bottom
surfaces of the transparent workpiece 160 (i.e. from imaging
surface 162 to the second surface 163). In principle, this defect
may be created by a single pulse and if necessary, additional
pulses may be used to increase the extension of the affected area
(depth and width). In embodiments, the pulsed laser beam focal line
113 may have a length in a range of from about 0.1 mm to about 10
mm, or from about 0.5 mm to about 5 mm, for example, about 1 mm,
about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 6 mm, about 7
mm, about 8 mm, or about 9 mm, or a length in a range of from about
0.1 mm to about 2 mm, or from 0.1 mm to about 1 mm. In embodiments,
the pulsed laser beam focal line may have an average spot diameter
in a range of from about 0.1 micron to about 5 microns. The defects
172 each may have a diameter of from about 0.1 microns to 30
microns, for example, from about 0.25 microns to about 5 microns
(e.g., from about 0.25 microns to about 0.75 microns).
[0056] While contour lines may be linear, like the contour line 170
illustrated in FIGS. 1A, 1B, and 3, the contours lines may also be
nonlinear (i.e., having a curvature). Curved contour lines may be
produced, for example, by translating either the transparent
workpiece 160 or pulsed laser beam 112 with respect to the other in
two dimensions instead of one dimension. Further, in embodiments in
which the contour line 170 comprises a curvature and the infrared
laser beam 212 forms an infrared beam spot 214 comprising an
elliptical or oval shape, it may be advantageous for the beam
directing element 230, 230' (FIGS. 2A and 2B) to comprise a
rotatable scanner configured to rotate the infrared laser beam 212
and thereby rotate the infrared beam spot 214. In particular, when
the infrared beam spot 214 comprises an ellipse or an oval, the
infrared beam spot 214 may be oriented such that the major axis
(e.g., the longest diameter of the infrared beam spot 214) extends
along the contour line 170. Thus, when the contour line 170 has a
curvature, the rotatable scanner may rotate the infrared laser beam
212 such that the infrared beam spot 214 rotates when translating
along the imaging surface 162 of the transparent workpiece 160 and
in some embodiments, the major axis of the infrared beam spot 214
remains oriented along the contour line 170 when the infrared laser
beam 212 is translated relative to the transparent workpiece 160
along the curved contour line 170.
[0057] Further, in some embodiments, the distance, or periodicity,
between adjacent defects 172 along the direction of the contour
line 170 may be at least about 0.1 micron or 1 micron and less than
or equal to about 20 microns or even 30 microns. For example, in
some transparent workpieces, the periodicity between adjacent
defects 172 may be from about 0.5 to about 15 microns, or from
about 3 microns to about 10 microns, or from about 0.5 microns to
about 3.0 microns. For example, in some transparent workpieces the
periodicity between adjacent defects 172 may be from about 0.5
micron to about 1.0 micron. However for alkaline earth
boro-aluminosilicate glass compositions, especially those 0.5 mm
thick or of greater thickness, the periodicity between adjacent
defects 172 may be at least about 1 microns, such as at least about
5 microns, or from about 1 microns to about 15 microns.
[0058] Referring now to FIG. 4, formation of the contour line 170
using the pulsed beam optical assembly 101 may include focusing the
pulsed laser beam 112 into the pulsed laser beam focal line 113
comprising a length L. The transparent workpiece 160 is positioned
to at least partially overlap the pulsed laser beam focal line 113
of pulsed laser beam 112. The pulsed laser beam focal line 113 is
thus directed into the transparent workpiece 160 having a depth d.
Further, as depicted in FIG. 4, the impingement location 115 of the
transparent workpiece 160 is aligned orthogonal to the pulsed laser
beam focal line 113. The transparent workpiece 160 may be
positioned relative to the pulsed laser beam focal line 113 such
that the pulsed laser beam focal line 113 starts before or at the
imaging surface 162 of the transparent workpiece 160 and stops
before a second surface 163 of the transparent workpiece 160 (i.e.,
the pulsed laser beam focal line 113 terminates within the
transparent workpiece 160 and does not extend beyond the second
surface 163).
[0059] Moreover, it is desirable to position the pulsed laser beam
focal line 113 relative to the transparent workpiece 160 such that
the pulsed laser beam focal line 113 extends into the transparent
workpiece 160 orthogonal to the imaging surface 162 of the
transparent workpiece 160 at the impingement location 115 of the
transparent workpiece 160. If the pulsed laser beam focal line 113
is not orthogonal the transparent workpiece 160, the pulsed laser
beam focal line 113 shifts and spreads along the depth of the
transparent workpiece 160, causing the pulsed laser beam focal line
113 to distribute energy over a larger volume of the transparent
workpiece 160, lowering the sharpness and focus of the pulsed laser
beam focal line 113 and generating lower quality, less uniform
defects 172 within the transparent workpiece 160.
[0060] Referring still to FIG. 4, in the overlapping area of the
pulsed laser beam focal line 113 with the transparent workpiece 160
(i.e., in the transparent workpiece material covered by the pulsed
laser beam focal line 113), the pulsed laser beam focal line 113
generates (assuming suitable laser intensity along the pulsed laser
beam focal line 113, which intensity is ensured by the focusing of
pulsed laser beam 112 on a section of length L, i.e. a line focus
of length L) a section 113a (aligned along the longitudinal beam
direction) along which an induced absorption is generated in the
material of the transparent workpiece 160. The induced absorption
produces the defect 172 in the transparent workpiece 160 along
section 113a. Formation of the defect 172 is not only local, but
over the entire length of the section 113a of the induced
absorption. The length of section 113a (which corresponds to the
length of the overlapping of the pulsed laser beam focal line 113
with the transparent workpiece 160) is labeled with reference A.
The internal diameter of the defect area (i.e., the defect 172) at
the section 113a of the induced absorption is labeled with
reference D. This internal diameter D corresponds to the average
diameter of the pulsed laser beam focal line 113, that is, an
average spot diameter in a range of between about 0.1 .mu.m and
about 5 .mu.m.
[0061] Referring now to FIG. 5A, an example of the pulsed beam
optical assembly 101 comprises an aspheric optical element (not
pictured), a lens 133 and an aperture 134 (e.g., a circular
aperture). As depicted in FIG. 5A, the pulsed laser beam 112
emitted by the pulsed laser beam source 110 is directed onto the
aperture 134 which is opaque to the wavelength of laser radiation
of the pulsed laser beam 112. Aperture 134 is oriented
perpendicular to the longitudinal beam axis and is centered on the
central portion of the pulsed laser beam 112. The diameter of the
aperture 134 is selected in such a way that the laser radiation
near the center of the pulsed laser beam 112 (i.e., the central
beam portion, here labeled with 112Z) hit the aperture 134 and is
completely absorbed by it. Only the beams in the outer perimeter
range of the pulsed laser beam 112 (i.e., marginal rays, here
labeled with 112R) are not absorbed by the circular aperture 134
due to the reduced aperture size compared to the beam diameter, and
pass aperture 134 laterally and hit the marginal areas of the lens
133 which, in this embodiment, is designed as a spherically cut,
bi-convex lens.
[0062] As illustrated in FIG. 5A, the pulsed laser beam focal line
113 may not only be a single focal point for the pulsed laser beam
112, but rather a series of focal points for different rays in the
pulsed laser beam 112. The series of focal points form an elongated
pulsed laser beam focal line 113 of a defined length, shown in FIG.
5A as the length L of the pulsed laser beam focal line 113. Lens
133 may be centered on the central beam and may be designed as a
non-corrected, bi-convex focusing lens in the form of a common,
spherically cut lens. As an alternative, aspheres or multi-lens
systems deviating from ideally corrected systems, which do not form
an ideal focal point but a distinct, elongated pulsed laser beam
focal line 113 of a defined length, may also be used (i.e., lenses
or systems which do not have a single focal point). The zones of
the lens 133 thus focus along the pulsed laser beam focal line 113,
subject to the distance from the lens center. The diameter of
aperture 134 across the beam direction may be approximately 90% of
the diameter of the pulsed laser beam 112 (defined by the distance
required for the intensity of the beam to decrease to 1/e.sup.2 of
the peak intensity) and approximately 75% of the diameter of the
lens 133. The pulsed laser beam focal line 113 of a
non-aberration-corrected spherical lens 133 generated by blocking
out the beam bundles in the center is thus used. FIG. 5A shows a
section in one plane through the central beam, and the complete
three-dimensional bundle may be seen when the depicted beams are
rotated around the pulsed laser beam focal line 113.
[0063] FIG. 5B-1 through FIG. 5B-4 show that the position of the
pulsed laser beam focal line 113 may be controlled by suitably
positioning and/or aligning components of the pulsed beam optical
assembly 101 relative to the transparent workpiece 160 as well as
by suitably selecting the parameters of the pulsed beam optical
assembly 101. Further, the length L of the pulsed laser beam focal
line 113 is schematically depicted in FIG. 5B-1 through FIG. 5B-4
for illustrative purposed. In operation, the length L of the pulsed
laser beam focal line 113 depends on the position of the pulsed
laser beam focal line 113 within the transparent workpiece 160 and
the index of refraction of the transparent workpiece 160. As FIG.
5B-1 illustrates, the length L of the pulsed laser beam focal line
113 may be adjusted in such a way that it exceeds the depth d of
the transparent workpiece 160 (here by factor 2). If the
transparent workpiece 160 is placed (viewed in longitudinal beam
direction) centrally to the pulsed laser beam focal line 113, the
extensive section of induced absorption (e.g., section 113a of
length A) may be generated over the entire workpiece depth d. The
pulsed laser beam focal line 113 may have a length L in a range of
from about 0.01 mm to about 100 mm or in a range of from about 0.1
mm to about 10 mm. Various embodiments may be configured to have a
pulsed laser beam focal line 113 with a length L in air of about
0.1 mm, about 0.2 mm, about 0.3 mm, about 0.4 mm, about 0.5 mm,
about 0.7 mm, about 1 mm, about 2 mm, about 3 mm, about 4 mm, or
about 5 mm e.g., from about 0.5 mm to about 5 mm. In some
embodiments, the length L of the pulsed laser beam focal line 113
may be tuned, using the pulsed beam optical assembly 101, to
correspond with the depth d of the transparent workpiece 160, for
example, the pulsed laser beam focal line 113 may be tuned, using
the pulsed beam optical assembly 101, such that the length L of the
pulsed laser beam focal line 113 is between about 1.1 to about 1.8
times larger than the depth d of the transparent workpiece 160, for
example 1.25, 1.5, or the like. As one example, in embodiments in
which the transparent workpiece 160 comprises a depth of about 0.7
mm, the pulsed laser beam focal line 113 may comprise a length of
about 0.9 mm. Further, in other embodiments, the pulsed laser beam
focal line 113 may be tuned, using the pulsed beam optical assembly
101, such that the length L of the pulsed laser beam focal line 113
is substantially equal the depth d of the transparent workpiece
160.
[0064] In the case shown in FIG. 5B-2, a pulsed laser beam focal
line 113 of length L is generated which generally corresponds to
the workpiece depth d. Since the transparent workpiece 160 is
positioned relative to the pulsed laser beam focal line 113 in such
a way that the pulsed laser beam focal line 113 starts at a point
outside the transparent workpiece 160, the length A of the
extensive section of induced absorption 113a (which extends from
the imaging surface 162 to a defined workpiece depth, but not to
the second surface 163 is smaller than the length L of the pulsed
laser beam focal line 113. FIG. 5B-3 shows the case in which the
transparent workpiece 160 (viewed along a direction perpendicular
to the beam direction) is positioned above the starting point of
the pulsed laser beam focal line 113 so that, as in FIG. 5B-2, the
length L of pulsed laser beam focal line 113 is greater than the
length A of the section of induced absorption 113a in the
transparent workpiece 160. The pulsed laser beam focal line 113
thus starts within the transparent workpiece 160 and extends beyond
the second surface 163. FIG. 5B-4 shows the case in which the focal
line length L is smaller than the workpiece depth d so that, in the
case of a central positioning of the transparent workpiece 160
relative to the pulsed laser beam focal line 113 viewed in the
direction of incidence, the pulsed laser beam focal line 113 starts
near the imaging surface 162 within the transparent workpiece 160
and ends near the second surface 163 within the transparent
workpiece 160 (e.g., L=0.75 d).
[0065] Referring again to FIGS. 2A-5A, the pulsed laser beam source
110 may comprise any known or yet to be developed pulsed laser beam
source 110 configured to output pulsed laser beams 112. As
described above, the defects 172 of the contour line 170 are
produced by interaction of the transparent workpiece 160 with the
pulsed laser beam 112 output by the pulsed laser beam source 110.
In some embodiments, the pulsed laser beam source 110 may output a
pulsed laser beam 112 comprising a wavelength of for example, 1064
nm, 1030 nm, 532 nm, 530 nm, 355 nm, 343 nm, or 266 nm, or 215 nm.
Further, the pulsed laser beam 112 used to form defects 172 in the
transparent workpiece 160 may be well suited for materials that are
transparent to the selected pulsed laser wavelength.
[0066] Suitable laser wavelengths for forming defects 172 are
wavelengths at which the combined losses of absorption and
scattering by the transparent workpiece 160 are sufficiently low.
In embodiments, the combined losses due to absorption and
scattering by the transparent workpiece 160 at the wavelength are
less than 20%/mm, or less than 15%/mm, or less than 10%/mm, or less
than 5%/mm, or less than 1%/mm, where the dimension "/mm" means per
millimeter of distance within the transparent workpiece 160 in the
direction of propagation of the pulsed laser beam 112 (e.g., the Z
direction). Representative wavelengths for many glass workpieces
include fundamental and harmonic wavelengths of Nd.sup.3+ (e.g.
Nd.sup.3+:YAG or Nd.sup.3+:YVO.sub.4 having fundamental wavelength
near 1064 nm and higher order harmonic wavelengths near 532 nm, 355
nm, and 266 nm). Other wavelengths in the ultraviolet, visible, and
infrared portions of the spectrum that satisfy the combined
absorption and scattering loss requirement for a given substrate
material can also be used.
[0067] Further, the pulsed laser beam source 110 may output the
pulsed laser beam 112 having a pulse energy of from about 25 .mu.J
to about 1500 .mu.J, for example 100 .mu.J, 200 .mu.J, 250 .mu.J,
300 .mu.J, 400 .mu.J, 500 .mu.J, 600 .mu.J, 700 .mu.J, 750 .mu.J,
800 .mu.J, 900 .mu.J, 1000 .mu.J, 1100 .mu.J, 1200 .mu.J, 1250
.mu.J, 1300 .mu.J, 1400 .mu.J or the like. The pulsed laser beam
source 110 may also be adjustable such that the pulsed laser beam
source 110 may output pulsed laser beams 112 comprising various
pulse energies. In operation, when the pulsed laser beam 112 is
focused into the pulsed laser beam focal line 113, the pulsed laser
beam focal line 113 may also comprise a pulse energy of from about
25 uJ to about 1500 uJ. In some embodiments, the pulse duration of
the individual pulses of the pulsed laser beam 112 is in a range of
from about 1 picosecond to about 100 picoseconds, such as from
about 5 picoseconds to about 20 picoseconds, and the repetition
rate of the individual pulses may be in a range from about 1 kHz to
4 MHz, such as in a range from about 10 kHz to about 3 MHz, or from
about 10 kHz to about 650 kHz.
[0068] Now referring to FIGS. 6A and 6B, it should be understood
that the typical operation of such the pulsed laser beam 112
described herein (e.g., a picosecond laser) creates a burst 500 of
pulses 500A. Each burst 500 contains multiple individual pulses
500A (such as at least two pulses, at least 5 pulses, at least 7
pulses, at least 8 pulses, at least 9 pulses, at least 10 pulses,
at least 15 pulses, at least 20 pulses, or even more pulses) of
very short duration. That is, a burst is a group of pulses, and the
bursts are separated from one another by a longer duration than the
separation of individual adjacent pulses within each burst.
According to one or more embodiments, for cutting or perforating
display glass/TFT glass compositions, the number of pulses per
burst may be from about 1 to 30 (such as from 5 to 20). Pulses 500A
have pulse duration T.sub.d of up to 100 psec (for example, 0.1
psec, 5 psec, 10 psec, 15 psec, 18 psec, 20 psec, 22 psec, 25 psec,
30 psec, 50 psec, 75 psec, or any range therebetween). The energy
or intensity of each individual pulse 500A within the burst may not
be equal to that of other pulses within the burst, and the
intensity distribution of the multiple pulses within a burst 500
often follows an exponential decay in time governed by the laser
design. The use of the pulsed laser beam 112 capable of generating
such bursts is advantageous for cutting or modifying transparent
materials, for example glass. In contrast with the use of single
pulses spaced apart in time by the repetition rate of the
single-pulsed laser, the use of a burst sequence that spreads the
laser energy over a rapid sequence of pulses within the burst
allows access to larger timescales of high intensity interaction
with the material than is possible with single-pulse lasers.
[0069] In some embodiments, each pulse 500A within the burst 500 of
the exemplary embodiments described herein is separated in time
from the subsequent pulse in the burst by a duration T.sub.p of
from about 1 nsec to about 50 nsec (e.g., from about 10 nsec to
about 50 nsec, or from about 10 nsec to about 30 nsec, with the
time often governed by the laser cavity design). For a given laser,
the time separation T.sub.p between adjacent pulses within a burst
500 may be relatively uniform (e.g., within about 10% of one
another). For example, in some embodiments, each pulse within a
burst is separated in time from the subsequent pulse by
approximately 20 nsec (50 MHz). For example, for a pulsed laser
beam source 110 that produces pulse separation T.sub.p of about 20
nsec, the pulse to pulse separation T.sub.p within a burst is
maintained within about .+-.10%, or about .+-.2 nsec. The time
between each burst of pulses (i.e., the time separation T.sub.b
between bursts) will be much longer. For example, the time between
each burst of pulses may be from about 0.25 microseconds to about
1000 microseconds, e.g., from about 1 microsecond to about 10
microseconds, or from about 3 microseconds to about 8
microseconds.
[0070] In some of the exemplary embodiments of the pulsed laser
beam source 110 described herein, the time separation T.sub.b is
about 5 microseconds for a laser with a burst repetition rate of
about 200 kHz. The laser burst repetition rate is related to the
time T.sub.b between the first pulse in a burst to the first pulse
in the subsequent burst (laser burst repetition rate=1/T.sub.b). In
some embodiments, the laser burst repetition rate may be in a range
of from about 1 kHz to about 4 MHz. In embodiments, the laser burst
repetition rates may be, for example, in a range of from about 10
kHz to 650 kHz. The time T.sub.b between the first pulse in each
burst to the first pulse in the subsequent burst may be from about
0.25 microsecond (4 MHz burst repetition rate) to about 1000
microseconds (1 kHz burst repetition rate), for example from about
0.5 microseconds (2 MHz burst repetition rate) to about 40
microseconds (25 kHz burst repetition rate), or from about 2
microseconds (500 kHz burst repetition rate) to about 20
microseconds (50 k Hz burst repetition rate). The exact timing,
pulse duration, and burst repetition rate may vary depending on the
laser design, but short pulses (T.sub.d<20 psec and preferably
T.sub.d.ltoreq.15 psec) of high intensity have been shown to work
particularly well.
[0071] The energy required to modify the material of the
transparent workpiece may be described in terms of the burst energy
(i.e., the energy contained within a burst where each burst 500
contains a series of pulses 500A), or in terms of the energy
contained within a single laser pulse (many of which may comprise a
burst). The energy per burst may be from about 25 .mu.J to about
750 .mu.J, e.g., from about 50 .mu.J to about 500 .mu.J, or from
about 50 .mu.J to about 250 .mu.J. For some glass compositions, the
energy per burst may be from about 100 to about 250 .mu.J. However,
for display or TFT glass compositions, the energy per burst may be
higher (e.g., from about 300 .mu.J to about 500 .mu.J, or from
about 400 .mu.J to about 600 .mu.J, depending on the specific
display/TFT glass composition of the workpiece). The energy of an
individual pulse within the burst will be less, and the exact
individual laser pulse energy will depend on the number of pulses
500A within the burst 500 and the rate of decay (e.g., exponential
decay rate) of the laser pulses with time as shown in FIGS. 6A and
6B. For example, for a constant energy/burst, if a pulse burst
contains 10 individual laser pulses 500A, then each individual
laser pulse 500A will contain less energy than if the same burst
500 had only 2 individual laser pulses.
[0072] While not intending to be limited by theory, the use of a
pulsed laser beam source (such as the pulsed laser beam source 110)
capable of generating such bursts is advantageous for cutting or
modifying transparent materials, for example glass. In contrast
with the use of single pulses spaced apart in time by the
repetition rate of the single-pulsed laser, the use of a burst
sequence that spreads the laser energy over a rapid sequence of
pulses within the burst 500 allows access to larger timescales of
high intensity interaction with the material than is possible with
single-pulse lasers. While a single-pulse may be expanded in time,
the intensity within the pulse is reduced as roughly one over the
pulse width. Therefore, if a 10 psec single pulse is expanded to a
10 nsec pulse, the intensity is reduced by roughly three orders of
magnitude.
[0073] Such a reduction may reduce the optical intensity to the
point where non-linear absorption is no longer significant, and
light-material interaction is no longer sufficient for cutting. In
contrast, with a pulse burst laser, the intensity during each pulse
500A within the burst 500 may remain relevantly high (for example,
three 10 psec pulses 500A spaced apart in time by approximately 10
nsec still allows the energy within each pulse burst to be
approximately three times higher than that of a single 10 psec
pulse) and the laser interacts with the material over a timescale
that is three orders of magnitude larger. For example, often 10
psec pulses 500A spaced apart in time by approximately 10 nsec
results in the energy within each pulse burst to be approximately
ten times higher than that of a single 10 psec pulse and the laser
interacts with the material over a timescale that is now orders of
magnitude larger. In one embodiment, the required amount of burst
energy to modify the material will depend on the workpiece material
composition and the length of the line focus used to interact with
the workpiece.
[0074] While not intending to be limited by theory, the longer the
interaction region, the more the energy is spread out, and higher
burst energy will be required. The exact timing, pulse duration,
and burst repetition rates may vary depending on the laser design,
but short pulses times (e.g., less than about 15 psec, or even less
than or equal to about 10 psec) of high intensity pulses may be
exemplary in some embodiments. In operation, the defect 172 is
formed in the material of the transparent workpiece 160 when a
single burst of pulses strikes essentially the same location on the
transparent workpiece 160. That is, multiple laser pulses within a
single burst correspond to a single defect 172 in the transparent
workpiece 160. Since the transparent workpiece 160 is translated
(e.g., by the translatable stage 180 or the beam moved relative to
the transparent workpiece 160), the individual pulses within the
burst cannot be at exactly the same spatial location on the glass.
However, the individual pulses may be within 1 .mu.m of one another
(i.e., they effectively strike the glass at essentially the same
location). For example, the pulses may strike the glass at a
spacing, sp, from one another where 0<sp.ltoreq.500 nm. When,
for example, a glass location is hit with a burst of 20 pulses the
individual pulses within the burst strike the glass within 250 nm
of each other. Thus, in some embodiments 1 nm<sp<250 nm. In
some embodiments 1 nm<sp<100 nm.
[0075] In one or more embodiments, for the purposes of cutting or
separating the workpiece, pulse burst energy may be from about 100
.mu.J to about 600 .mu.J per burst, such as from about 300 .mu.J to
about 600 .mu.J per burst. For some display glass types the pulse
burst energy may be from about 300 .mu.J to about 500 .mu.J, or for
other display type glass from about 400 .mu.J to about 600 .mu.J. A
pulse burst energy of 400 .mu.J to 500 .mu.J may work well for many
display type glass compositions. Energy density within the line
focus may be optimized for specific display or TFT glasses. For
example, for both EAGLE XG and CONTEGO glasses, a suitable range
for the pulse burst energy may be from about 300 to about 500 .mu.J
and the line focus may be from about 1.0 mm to about 1.4 mm (where
the line focus length is determined by the optical
configuration).
[0076] In one or more embodiments, relatively low pulsed laser
energy densities (e.g., below 300 .mu.J) may form perforations
which do not form as desired, causing the fracture between defects
to not readily materialize during infrared laser processing,
leading to increased break resistance (also referred to herein as a
break strength) in display glass. If the energy density of the
pulsed laser beam is too high (e.g., greater than or equal to 600
.mu.J, or even greater than 500 .mu.J) the heat damage may be
greater, causing the crack connecting the perforation to stray and
not form along the desired path and the break resistance (break
strength) of the display (or TFT) glass to dramatically
increase.
[0077] In view of the foregoing description, it should be
understood that the processing time for laser separation of
transparent workpieces by infrared laser beam may be decreased by
laser forming a plurality of defects in a transparent workpiece
using a pulsed laser beam and heating these defects using an
infrared laser beam in a single, synchronized step of relative
motion between the transparent workpiece and both the infrared
laser beam and the pulsed laser beam. The infrared laser beam may
form an infrared beam spot on the transparent workpiece and the
pulsed laser beam may be directed into the transparent workpiece
such that the infrared beam spot surrounds (e.g., circumscribes) a
pulsed laser beam spot form by the pulsed laser beam on an imaging
surface of the transparent workpiece. Alternatively, the pulsed
laser beam may be directed into the transparent workpiece such that
the pulsed laser beam spot formed by the pulsed laser beam is
spaced apart from the infrared beam spot by a spacing distance. In
each of these embodiments, the defect line is formed by the pulsed
laser beam and separated by the infrared laser beam and the
transparent workpiece is separated along the defect line by
synchronous relative motion between the transparent workpiece and
both the pulsed laser beam and the infrared laser beam.
[0078] Ranges can be expressed herein as from "about" one
particular value, and/or to "about" another particular value. When
such a range is expressed, another embodiment includes from the one
particular value and/or to the other particular value. Similarly,
when values are expressed as approximations, by use of the
antecedent "about," it will be understood that the particular value
forms another embodiment. It will be further understood that the
endpoints of each of the ranges are significant both in relation to
the other endpoint, and independently of the other endpoint.
[0079] Directional terms as used herein--for example up, down,
right, left, front, back, top, bottom--are made only with reference
to the figures as drawn and are not intended to imply ab solute
orientation.
[0080] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order, nor that with any apparatus
specific orientations be required. Accordingly, where a method
claim does not actually recite an order to be followed by its
steps, or that any apparatus claim does not actually recite an
order or orientation to individual components, or it is not
otherwise specifically stated in the claims or description that the
steps are to be limited to a specific order, or that a specific
order or orientation to components of an apparatus is not recited,
it is in no way intended that an order or orientation be inferred,
in any respect. This holds for any possible non-express basis for
interpretation, including: matters of logic with respect to
arrangement of steps, operational flow, order of components, or
orientation of components; plain meaning derived from grammatical
organization or punctuation, and; the number or type of embodiments
described in the specification.
[0081] As used herein, the singular forms "a," "an" and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to "a" component includes
aspects having two or more such components, unless the context
clearly indicates otherwise.
[0082] It will be apparent to those skilled in the art that various
modifications and variations can be made to the embodiments
described herein without departing from the spirit and scope of the
claimed subject matter. Thus it is intended that the specification
cover the modifications and variations of the various embodiments
described herein provided such modification and variations come
within the scope of the appended claims and their equivalents.
* * * * *