U.S. patent application number 11/649223 was filed with the patent office on 2008-07-10 for rectangular flat-top beam shaper.
Invention is credited to Francis Cayer.
Application Number | 20080165425 11/649223 |
Document ID | / |
Family ID | 39594011 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080165425 |
Kind Code |
A1 |
Cayer; Francis |
July 10, 2008 |
Rectangular flat-top beam shaper
Abstract
The invention relates to a beam shaping system for providing a
square or rectangular laser beam having a controlled intensity
profile (uniform, super gaussian or cosine corrected for example)
from an incident non-uniform beam intensity profile laser beam
source (a Gaussian profile, a profile with astigmatism or any
non-rotationally symmetric and non-uniform profile for example).
The beam shaping system uses a first acylindrical lens for shaping
the incident laser beam along a first axis and a second
acylindrical lens orthogonally disposed relative to the first
acylindrical lens and for shaping the incident beam along a second
axis. The thereby provided light beam is a rectangular beam having
a controlled intensity distribution in the far field.
Inventors: |
Cayer; Francis;
(Saint-Eustache, CA) |
Correspondence
Address: |
OGILVY RENAULT LLP
1981 MCGILL COLLEGE AVENUE, SUITE 1600
MONTREAL
QC
H3A2Y3
omitted
|
Family ID: |
39594011 |
Appl. No.: |
11/649223 |
Filed: |
January 4, 2007 |
Current U.S.
Class: |
359/641 ;
359/719 |
Current CPC
Class: |
G02B 3/02 20130101; G02B
27/0927 20130101; G02B 27/095 20130101 |
Class at
Publication: |
359/641 ;
359/719 |
International
Class: |
G02B 27/09 20060101
G02B027/09; G02B 27/30 20060101 G02B027/30 |
Claims
1. A beam shaping system for providing a shaped beam substantially
rectangular and having a controlled intensity profile in a far
field region, from an incident beam having a predetermined
intensity profile along a first and a second axis, said beam
shaping system comprising: a first and a second acylindrical lens
each having a primary acylindrical surface with a base curve, said
first and said second acylindrical lenses being disposed
substantially orthogonally to one another, said first acylindrical
lens for shaping said incident beam along said first axis and said
second acylindrical lens for shaping said incident beam along said
second axis, thereby providing said substantially rectangular
shaped beam; wherein said base curve of said first lens fits a
first equation in a Cartesian coordinate system (x,y), said first
equation being y = c 1 x 2 1 + ( 1 - ( 1 + Q 1 ) c 1 2 x 2 ) 1 / 2
+ f 1 ( x ) , ##EQU00008## c.sub.1 being a first curvature
constant, Q.sub.1 being a first conic constant and f.sub.1(x) being
a first correction function, said first correction function being
continuous; and wherein said base curve of said second lens fits a
second equation in another Cartesian coordinate system (x,y), said
second equation being y = c 2 x 2 1 + ( 1 - ( 1 + Q 2 ) c 2 2 x 2 )
1 / 2 + f 2 ( x ) , ##EQU00009## c.sub.2 being a second curvature
constant and Q.sub.2 being a second conic constant and f.sub.2(x)
being a second correction function, said second correction function
being continuous.
2. The beam shaping system as claimed in claim 1, wherein a
magnitude of the absolute value of the product Q.sub.1c.sub.1 and a
magnitude of the absolute value of the product Q.sub.2c.sub.2 lie
between 0.25 and 1000 mm.sup.-1 and wherein Q.sub.1 and Q.sub.2 are
less than -1.
3. The beam shaping system as claimed in claim 1, wherein said
first acylindrical lens and said second acylindrical lens each
comprise a secondary surface, each of said secondary surface being
one of a planar surface and a cylindrical surface.
4. The beam shaping system as claimed in claim 1, wherein said
first and said second acylindrical lenses are positive lenses.
5. The beam shaping system as claimed in claim 1, wherein an input
surface of said first and said second acylindrical lenses is said
primary surface.
6. The beam shaping system as claimed in claim 1, further
comprising collimating lens means for collimating said shaped
beam.
7. The beam shaping system as claimed in claim 6, wherein said
collimating lens means comprise a first cylindrical collimating
lens for collimating said shaped beam along said first axis and a
second cylindrical collimating lens for collimating said shaped
beam along said second axis in order to eliminate an astigmatism
caused by a distance between said first and said second
acylindrical lenses.
8. The beam shaping system as claimed in claim 6, wherein said
first acylindrical lens has a first point source and said second
acylindrical lens has a second point source and wherein said
collimating lens means comprise a first cylindrical collimating
lens for collimating said shaped beam along said first axis and a
second cylindrical collimating lens for collimating said shaped
beam along said second axis, said a first cylindrical collimating
lens having a first focal length and being located at one first
focal length distance from said first point source and said second
cylindrical collimating lens having a second focal length and being
located at one second focal length distance from said second point
source.
9. The beam shaping system as claimed in claim 1, further
comprising focusing lens means for focusing said shaped beam, said
focusing lens means comprising a positive lens device.
10. The beam shaping system as claimed in claim 9, wherein said
focusing lens means further comprise a negative lens device
positioned between said second acylindrical lens, said negative
lens device for providing a retro-focus focusing lens system.
11. The beam shaping system as claimed in claim 9, wherein said
focusing lens means comprise a first cylindrical focusing lens for
focusing said shaped beam along said first axis and a second
cylindrical focusing lens for focusing said shaped beam along said
second axis in order to eliminate an astigmatism of said shaped
beam.
12. The beam shaping system as claimed in claim 1, wherein said
incident beam has astigmatism.
13. The beam shaping system as claimed in claim 1, wherein said
incident beam is a substantially collimated and rotationally
symmetrical Gaussian beam.
14. The beam shaping system as claimed in claim 1, wherein said
incident beam is non-rotationally symmetrical.
15. The beam shaping system as claimed in claim 1, wherein said
shaped beam has at least one of a cosine corrected, a
super-gaussian and a uniform intensity profile along each one of
said first and said second axes, in a far field region.
16. The beam shaping system as claimed in claim 1, further
comprising beam splitting means for producing a pattern of a
plurality of substantially rectangular beams.
17. The beam shaping system as claimed in claim 16, wherein said
beam splitting means comprises a diffractive beam splitter.
18. A rectangular beam light source for providing a substantially
rectangular shaped beam having a controlled intensity profile, said
rectangular beam light source comprising: an incident light source
for providing an incident beam having a predetermined
cross-sectional intensity profile along a first axis and a second
axis; and a first and a second acylindrical lens each having a
primary acylindrical surface with a base curve, said first and said
second acylindrical lenses being disposed substantially
orthogonally to one another, said first acylindrical lens for
shaping said incident beam along said first axis and said second
acylindrical lens for shaping said incident beam along said second
axis, thereby providing said substantially rectangular shaped beam;
wherein said base curve of said first lens fits a first equation in
a Cartesian coordinate system (x,y), said first equation being y =
c 1 x 2 1 + ( 1 - ( 1 + Q 1 ) c 1 2 x 2 ) 1 / 2 + f 1 ( x ) ,
##EQU00010## c.sub.1 being a first curvature constant, Q.sub.1
being a first conic constant and f.sub.1(x) being a first
correction function, said first correction function being
continuous; and wherein said base curve of said second lens fits a
second equation in another Cartesian coordinate system (x,y), said
second equation being y = c 2 x 2 1 + ( 1 - ( 1 + Q 2 ) c 2 2 x 2 )
1 / 2 + f 2 ( x ) , ##EQU00011## c.sub.2 being a second curvature
constant and Q.sub.2 being a second conic constant and f.sub.2(x)
being a second correction function, said second correction function
being continuous.
19. The rectangular beam light source as claimed in claim 18,
wherein a magnitude of the absolute value of the product
Q.sub.1c.sub.1 and a magnitude of the absolute value of the product
Q.sub.2c.sub.2 lie between 0.25 and 1000 mm.sup.-1 and wherein
Q.sub.1 and Q.sub.2 are less than -1.
20. The rectangular beam light source as claimed in claim 18,
wherein said first acylindrical lens and said second acylindrical
lens each comprise a secondary surface, each of said secondary
surface being one of a planar surface and a cylindrical
surface.
21. The rectangular beam light source as claimed in claim 18,
further comprising collimating lens means for collimating said
shaped beam.
22. The rectangular beam light source as claimed in claim 18,
further comprising focusing lens means for focusing said shaped
beam, said focusing lens means comprising a positive lens
device.
23. The rectangular beam light source as claimed in claim 22,
wherein said focusing lens means further comprise a negative lens
device positioned between said second acylindrical lens, said
negative lens device for providing a retro-focus focusing lens
system.
24. The rectangular beam light source as claimed in claim 18,
wherein said shaped beam has at least one of a cosine corrected, a
super-gaussian and a uniform intensity profile along each one of
said first and said second axes, in a far field region.
25. A beam shaping system for providing a substantially rectangular
beam having a controlled intensity profile from an incident beam
having a predetermined intensity profile along a first axis and a
second axis, said beam shaping system comprising: a first and a
second acylindrical lens each having a primary acylindrical surface
having a base curve substantially in the shape of an angle with a
rounded apex, said first lens for shaping said incident beam along
said first axis and said second lens for shaping said incident beam
along said second axis; wherein said first and said second
acylindrical lenses are disposed substantially orthogonally to one
another, thereby providing said substantially rectangular shaped
beam in a far field region.
26. The beam shaping system as claimed in claim 25, wherein said
first acylindrical lens and said second acylindrical lens each
comprise a secondary surface, each of said secondary surface being
one of a planar surface and a cylindrical surface.
27. The beam shaping system as claimed in claim 25, further
comprising collimating lens means for collimating said shaped
beam.
28. The beam shaping system as claimed in claim 25, further
comprising focusing lens means for focusing said shaped beam, said
focusing lens means comprising a positive lens device.
29. The beam shaping system as claimed in claim 28, wherein said
focusing lens means further comprise a negative lens device
positioned between said second acylindrical lens, said negative
lens device for providing a retro-focus focusing lens system.
30. The beam shaping system as claimed in claim 25, wherein said
shaped beam has at least one of a cosine corrected, a
super-gaussian and a uniform intensity profile along each one of
said first and said second axes, in a far field region.
31. A beam shaping system for providing a substantially rectangular
beam having a controlled intensity profile from an incident beam
having a predetermined intensity profile along a first axis and a
second axis, said beam shaping system comprising: a first and a
second lens each having a primary acylindrical surface having a
base curve with a radius of curvature that varies along said base
curve, said radius of curvature being smaller in a center of said
base curve and increasing smoothly towards both of extremities of
said base curve; wherein said first lens and said second lens are
disposed orthogonally to one another, said first lens for shaping
said incident beam along said first axis and said second lens for
shaping said incident beam along said second axis, thereby
providing said substantially rectangular beam in a far field
region.
32. The beam shaping system as claimed in claim 31, wherein said
first acylindrical lens and said second acylindrical lens each
comprise a secondary surface, each of said secondary surface being
one of a planar surface and a cylindrical surface.
33. The beam shaping system as claimed in claim 31, further
comprising collimating lens means for collimating said shaped
beam.
34. The beam shaping system as claimed in claim 31, further
comprising focusing lens means for focusing said shaped beam, said
focusing lens means comprising a positive lens device.
35. The beam shaping system as claimed in claim 34, wherein said
focusing lens means further comprise a negative lens device
positioned between said second acylindrical lens, said negative
lens device for providing a retro-focus focusing lens system.
36. The beam shaping system as claimed in claim 31, wherein said
shaped beam has at least one of a cosine corrected, a
super-gaussian and a uniform intensity profile along each one of
said first and said second axes, in a far field region.
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The invention relates to laser beam shaping. More
particularly, the invention relates to a beam shaping system for
providing a square or rectangular laser beam with controlled
intensity distribution.
[0003] 2) Description of the Prior Art
[0004] While most laser sources and more precisely laser diodes
sources produce an astigmatic beam of light having a substantially
non-uniform intensity profile, numerous laser applications require
a uniform illumination of a rectangular target. Such applications
include biomedical applications, such as bio-detection, wherein,
for example, a uniform illumination of a blood sample is required.
Other applications include micromachining, microscopy, night vision
and range finding of distant object.
[0005] Shaping a Gaussian-like laser beam using diffractive optics
can provide a flat-top laser beam. One drawback of diffractive beam
shapers is the wavelength dependency of their optical response.
Another drawback is the low efficiency. Diffractive beam shapers
are thus not suitable for wide spectrum or multiple wavelength
illumination.
[0006] Refractive beam shaping techniques are efficient and provide
low wavelength dependency. Conventional refractive techniques using
aspherical lenses are suitable for generating a rotationally
symmetrical flat-top beam from a rotationally symmetrical Gaussian
input beam, but they are not adapted to shape an incident beam that
is not rotationally symmetrical, like laser diode beams. Laser
diodes have an elliptical intensity profile and suffer from
astigmatism.
[0007] U.S. Pat. No. 4,826,299 to Powell, provides a lens for
expanding a laser beam along one axis in order to provide a laser
line of uniform intensity and width. Such a diverging lens has an
acylindrical surface defined by a base curve in the shape of an
angle with a rounded apex. The radius of curvature of the
acylindrical surface is thus smaller in the center and increases
smoothly towards both ends. As described in Powell, the
acylindrical surface fits to a base curve defined in a Cartesian
coordinate system (x,y,z) by the following equation:
y = cx 2 1 + ( 1 - ( 1 + Q ) c 2 x 2 ) 1 / 2 ##EQU00001##
wherein c is a curvature constant and Q is a conic constant, and
wherein the product Qc lies between 0.25 and 50 mm.sup.-1 and Q is
less than -1. The second surface of the acylindrical lens may
either be flat or cylindrical.
[0008] Acylindrical lenses have been created and used in the prior
art for providing a laser line of uniform intensity. Laser lines
are used, for example, for alignment purposes. The provided laser
line should then be long and thin. Acylindrical lenses described in
Powell provides a high divergence to provide the required line
length.
SUMMARY OF THE INVENTION
[0009] The invention relates to a beam shaping system for providing
a square or rectangular laser beam having a controlled intensity
profile (uniform, super gaussian or cosine corrected for example)
from an incident non-uniform beam intensity profile laser beam
source (a Gaussian profile, a profile with astigmatism or any
non-rotationally symmetric and non-uniform profile). The beam
shaping system uses a first acylindrical lens for shaping the
incident laser beam along a first axis and a second acylindrical
lens orthogonally disposed relative to the first acylindrical lens
and for shaping the incident beam along a second axis. The thereby
provided light beam is a rectangular beam having a controlled
intensity distribution in the far field.
[0010] This light beam may be collimated using a collimating lens
system for maintaining its intensity profile and size over a
significant distance and maintain the controlled intensity profile
(i.e. flat-top, cosine corrected, etc.).
[0011] Alternatively, the light beam may be focused for an
efficient illumination of a typically submillimeter dimensioned
target with a controlled intensity distribution at the Fourier
plane of the focusing lens.
[0012] Furthermore, a diffractive or refractive beam splitter, a
micro lenses array for example, may be used to generate a multiple
rectangular flat-top pattern arranged in a row or in a
two-dimensional array.
[0013] The present invention provides a way to independently shape
the intensity profile of a light beam along two mutually
independent and perpendicular axis. Suppose a normal Cartesian
coordinates system X, Y and Z, Z being the propagation axis of the
light beam. The present invention can be used to provide, for
example, a laser beam with a flat top intensity distribution along
the X axis and a cosine fourth corrected intensity distribution
along the Y axis.
[0014] One aspect of the invention provides a beam shaping system
for providing a shaped beam substantially rectangular and having a
controlled intensity profile in a far field region, from an
incident beam having a predetermined intensity profile along a
first and a second axis. The beam shaping system comprising a first
and a second acylindrical lens each having a primary acylindrical
surface with a base curve. The first and the second acylindrical
lenses are disposed substantially orthogonally to one another. The
first acylindrical lens is for shaping the incident beam along the
first axis and the second acylindrical lens is for shaping the
incident beam along the second axis, thereby providing the
substantially rectangular shaped beam. The base curve of the first
lens fits a first equation in a Cartesian coordinate system (x,y),
the first equation being
y = c 1 x 2 1 + ( 1 - ( 1 + Q 1 ) c 1 2 x 2 ) 1 / 2 + f 1 ( x ) ,
##EQU00002##
c1 being a first curvature constant, Q1 being a first conic
constant and f.sub.1(x) being a first correction function, the
first correction function being continuous. The base curve of the
second lens fits a second equation in another Cartesian coordinate
system (x,y), the second equation being
y = c 2 x 2 1 + ( 1 - ( 1 + Q 2 ) c 2 2 x 2 ) 1 / 2 + f 2 ( x ) ,
##EQU00003##
[0015] c2 being a second curvature constant and Q2 being a second
conic constant and f.sub.2(x) being a second correction function,
the second correction function being continuous.
[0016] Another aspect of the invention provides a rectangular beam
light source for providing a substantially rectangular shaped beam
having a controlled intensity profile. The rectangular beam light
source comprises an incident light source for providing an incident
beam having a predetermined cross-sectional intensity profile along
a first axis and a second axis, and a first and a second
acylindrical lens each having a primary acylindrical surface with a
base curve. The first and the second acylindrical lenses being
disposed substantially orthogonally to one another. The first
acylindrical lens is for shaping the incident beam along the first
axis and the second acylindrical lens is for shaping the incident
beam along the second axis, thereby providing the substantially
rectangular shaped beam. The base curve of the first lens fits a
first equation in a Cartesian coordinate system (x,y). The first
equation being
y = c 1 x 2 1 + ( 1 - ( 1 + Q 1 ) c 1 2 x 2 ) 1 / 2 + f 1 ( x ) ,
##EQU00004##
c.sub.1 being a first curvature constant, Q.sub.1 being a first
conic constant and f.sub.1(x) being a first correction function,
the first correction function being continuous. The base curve of
the second lens fits a second equation in another Cartesian
coordinate system (x,y). The second equation being
y = c 2 x 2 1 + ( 1 - ( 1 + Q 2 ) c 2 2 x 2 ) 1 / 2 + f 2 ( x ) ,
##EQU00005##
c.sub.2 being a second curvature constant and Q.sub.2 being a
second conic constant and f.sub.2(x) being a second correction
function, the second correction function being continuous.
[0017] Yet another aspect of the invention provides a beam shaping
system for providing a substantially rectangular beam having a
controlled intensity profile from an incident beam having a
predetermined intensity profile along a first axis and a second
axis. The beam shaping system comprises a first and a second
acylindrical lens each having a primary acylindrical surface having
a base curve substantially in the shape of an angle with a rounded
apex. The first lens is for shaping the incident beam along the
first axis and the second lens is for shaping the incident beam
along the second axis. The first and the second acylindrical lenses
are disposed substantially orthogonally to one another, thereby
providing the substantially rectangular shaped beam in a far field
region.
[0018] Still another aspect of the invention provides a beam
shaping system for providing a substantially rectangular beam
having a controlled intensity profile from an incident beam having
a predetermined intensity profile along a first axis and a second
axis. The beam shaping system comprises a first and a second lens
each having a primary acylindrical surface having a base curve with
a radius of curvature that varies along the base curve. The radius
of curvature is smaller in a center of the base curve and increases
smoothly towards both of extremities of the base curve. The first
lens and the second lens are disposed orthogonally to one another.
The first lens is for shaping the incident beam along the first
axis and the second lens is for shaping the incident beam along the
second axis, thereby providing the substantially rectangular beam
in a far field region.
[0019] In this specification, the term "acylindrical surface" is
intended to mean a surface generated by a straight line which moves
so that it always intersects a given plane curve called the base
curve, and remains normal to the plane of the base curve, the base
curve not consisting of a segment of a circle. A "cylindrical
surface" is intended to mean a surface as defined above but the
base curve consisting of a segment of a circle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further features and advantages of the present invention
will become apparent from the following detailed description, taken
in combination with the appended drawings, in which:
[0021] FIG. 1 is a schematic representation of a rectangular beam
shaping system comprising two orthogonally disposed positive
acylindrical lenses;
[0022] FIGS. 2A and 2B are graphs showing an incident laser beam
intensity profile along the X-axis and the Y-axis respectively;
[0023] FIGS. 3A and 3B are graphs showing a rectangular beam
intensity profile in the far field and obtained using the beam
shaping system of FIG. 1 and along the X-axis and the Y-axis
respectively;
[0024] FIGS. 4A, 4B and 4C are graphs showing the rectangular beam
intensity profile obtained using the beam shaping system of FIG. 1,
in the near field and along the X-axis, wherein FIGS. 4A, 4B and 4C
respectively correspond to the intensity profile at a distance of
30, 500 and 700 mm in front of the beam shaping system;
[0025] FIG. 5 is a schematic representation of a rectangular beam
shaping system using two orthogonally disposed acylindrical lenses
along with a retro-focus rotationally symmetrical focusing lens
system;
[0026] FIGS. 6A and 6B are graphs showing a rectangular beam
intensity profile obtained using the beam shaping system of FIG. 5
and along the X-axis and the Y-axis respectively;
[0027] FIGS. 7A and 7B are graphs showing a rectangular beam
intensity profile obtained using the beam shaping system of FIG. 5
for two different input wavelengths (superimposed on the graphs)
and along the X-axis and the Y-axis respectively;
[0028] FIG. 8 is a schematic representation of a rectangular beam
shaping system using two orthogonally disposed acylindrical lenses
along with a single rotationally symmetrical collimating lens;
[0029] FIG. 9 is a schematic representation of a rectangular beam
shaping system using two orthogonally disposed acylindrical lenses
along with a collimating lens system comprising two orthogonally
disposed cylindrical collimating lenses;
[0030] FIG. 10 is a schematic representation of a rectangular beam
shaping system using the system of FIG. 5 along with a diffractive
beam splitter;
[0031] FIG. 11 is a graph illustrating a rectangular beam array
obtained using the beam shaping system of FIG. 10; and
[0032] FIG. 12 is a schematic representation of a rectangular beam
shaping system comprising two orthogonally disposed negative
acylindrical lenses.
[0033] It will be noted that throughout the appended drawings, like
features are identified by like reference numerals.
DETAILED DESCRIPTION
[0034] Now referring to the drawings, FIG. 1 illustrates a beam
shaping system 100 for providing a square or rectangular laser beam
B having a controlled intensity profile from an incident laser beam
A having a predetermined non-uniform intensity profile. The beam
shaping system uses two orthogonally disposed acylindrical lenses
112,114, the first acylindrical lens 112 for shaping the incident
beam A along the X-axis and the second acylindrical lens 114 for
shaping the incident beam A along the Y-axis. It is noted that the
curvature of the acylindrical surfaces 130 and 134 are exaggerated
in FIG. 1 for the purpose of illustration.
[0035] Since the beam shaping system 100 includes a different
acylindrical shaping lens 112,114 for each orthogonal axis, the two
orthogonal axes of the intensity profile are shaped
independently.
[0036] In this embodiment, the incident laser beam A is an
elliptical beam (see FIGS. 2A and 2B), but in alternative
embodiments, the incident laser beam A has a rotationally symmetric
Gaussian profile, a profile with astigmatism or any
non-rotationally symmetric and non-uniform profile. Also in this
embodiment, the two crossed acylindrical lenses 112,114 are adapted
to provide a resulting rectangular laser beam B having a flat-top
profile along the X-axis and a cosine corrected profile along the
Y-axis in the far field. In alternative embodiments, the two
orthogonally disposed acylindrical lenses 112,114 have different
shapes for providing a uniform, a super Gaussian, a cosine
corrected or any other controlled intensity profile on each of the
X- and Y-axes.
[0037] The first and the second acylindrical lenses 112,114 are a
positive lenses. The input surface 130 of the first acylindrical
lens 112 is a convex acylindrical surface having a variable radius
of curvature along the X-axis. The radius of curvature is smaller
in the center of the surface and increases smoothly toward both
X-extremities of the lens. It results in a greater divergence in
the center of the lens which spreads out the beam in the center
while containing it on the edges. The optical intensity is thus
spatially redistributed and, when the curvature and the conic
constants are suitably adapted to the incident beam intensity
profile, it provides a controlled intensity distribution along the
X-axis. The first acylindrical lens 112 expends the incident beam A
along the X-axis to provide a diverging beam intensity profile
along the X-axis. At the output of the first acylindrical lens 112,
the beam intensity profile remains substantially unchanged along
the Y-axis. The output surface 132 of the first acylindrical lens
112 is a planar surface. Alternatively, the output surface 132
could by a cylindrical surface diverging (or converging) along the
X-axis for reducing or increasing the optical power of the
lens.
[0038] The second acylindrical lens 114 is orthogonally disposed
relative to the first acylindrical lens 112 in order to shape the
incident beam intensity profile along the Y-axis. The second
acylindrical lens 114 is similar to the first acylindrical lens 112
but the exact shape of the input 130,134 and output 132,136
surfaces of the first 112 and the second lens 114 are independently
selected as a function of the X and Y-profiles of the incident beam
A and of the required intensity profile of the resulting
rectangular beam B.
[0039] The two acylindrical lenses 112,114 substantially fits to a
base curve defined in a Cartesian coordinate system (x,y,z) by the
following equation:
y = cx 2 1 + ( 1 - ( 1 + Q ) c 2 x 2 ) 1 / 2 , ##EQU00006##
wherein c is a curvature constant and Q is a conic constant.
[0040] A continuous correction function f(x) can be added, the
correction function being defined by
f ( x ) = i a i x i , ##EQU00007##
wherein a.sub.i are small value constants for small added
corrections.
[0041] Typically, the acylindrical lenses 112,114 are made of glass
with an index of refraction lying between 1.4 and 2, but other
transparent materials such as polycarbonate and silicones can
alternatively be used. In this embodiment, the first acylindrical
lens 112 is made of Bk7 glass by Schott.TM. and has a divergence of
5 mrad, a curvature constant c.sub.1 of 0.0118 and a conic constant
Q.sub.1 of -25000, and the second acylindrical lens 114 is also
made of Bk7 glass but has a divergence of 17 mrad, a curvature
constant c.sub.2 of 0.0250 and a conic constant Q.sub.2 of
-2500.
[0042] It is noted that, alternatively, the acylindrical surface of
one or both acylindrical lenses could be a concave surface, thereby
providing a negative lens instead of a positive lens. Furthermore,
in the embodiment of FIG. 1, the acylindrical surface is the input
surface of the acylindrical lenses but the acylindrical surface
could alternatively be provided as the output surface of the
acylindrical lenses.
[0043] It is noted that, according to simulations, an appropriate
absolute value of the product Qc lies between about 0.25 and 1000
mm.sup.-1 and that Q should be less than -1.
[0044] FIGS. 2A and 2B illustrate the intensity profile, along the
X-axis and the Y-axis respectively, of the incident laser beam A of
FIG. 1. The laser source is a laser diode source providing a laser
beam of 100 mW of power with a wavelength of 660 nm, used in pair
with an aspheric collimator with a focal length of 4.5 mm. The
aspherical collimator collimates the incoming beam from the laser
diode source. The collimated beam, i.e. the incident beam A, has a
substantially elliptical shape in the plane normal to the
propagation (the X-Y plane). The size of the short (X) and the long
(Y) axes of the ellipse at 13.5% (1/e.sup.2) of the relative
intensity profile is of 1.4.times.2.6 mm. The intensity profile
substantially fits a gauss-lorentzian shape along the X-axis and a
gaussian shape along the Y-axis.
[0045] It is noted that the incident laser beam source could
alternatively be any mono-mode or multi-mode laser source with a
wavelength from about 275 to 1600 .mu.m, such as an argon laser, an
excimer laser or a tunable laser source. In some specific
applications, it is required that the target be quite uniformly
illuminated with a laser light comprising two or more wavelength
components. The two or more wavelength components can be provided
by combining two or more laser source beams and providing the
combined incident laser beam to the beam shaping system 100. The
beam shaping system 100 having low wavelength dependency, it is
adapted to similarly shape the various wavelength components.
[0046] FIGS. 3A and 3B show the intensity profile in the far field
of the rectangular beam B obtained by numerical simulations, using
the beam shaping system 100 of FIG. 1 and the incident laser beam A
illustrated in FIGS. 2A and 2B. FIGS. 3A and 3B shows the intensity
profile along the X- and Y-axis respectively.
[0047] The far field is defined as the distance where the intensity
profile is completely formed, i.e. where z>>.phi./FA, wherein
.phi. is the input beam diameter and FA the fan angle. This
condition needs to be respected in order to have a completely
formed pattern. In this case, FA=5 mrad and .phi.=1.4 mm for the
first acylindrical lens 112 and FA=17 mrad and .phi.=2.6 mm.
Accordingly, the far field is defined by a distance z>>300
mm.
[0048] FIG. 3A and FIG. 3B show the intensity profile at a distance
of 2000 mm in front of the beam shaping system 100. The resulting
intensity profile fits a super Gaussian profile along the X-axis
(FIG. 3A) and a cosine fourth corrected profile along the Y-axis
(FIG. 3B). The cosine fourth corrected profile is of particular
interest for compensating the fall off of the intensity profile
when observed with a camera, according the known cosine fourth
law.
[0049] FIGS. 4A, 4B and 4C show the rectangular beam B intensity
profile obtained using the beam shaping system of FIG. 1, in the
near field and along the X-axis. FIGS. 4A, 4B and 4C respectively
correspond to the intensity profile at a distance of 30, 500 and
700 mm in front of the beam shaping system 100.
[0050] FIG. 5 illustrates a beam shaping system 500 using the pair
of crossed acylindrical lenses 512,514 along with retro-focus
rotationally symmetrical focusing lens system 516. Thanks to the
focusing lens system 516, the rectangular laser beam B can be used
to illuminate a target in the near field. A typical target being of
submillimeter dimensions, the beam needs to be focused into a
submillimeter rectangle for an efficient uniform illumination of
the target. The beam shaping system 500 thus comprise two
orthogonally disposed acylindrical lenses 512,514 similar to the
acylindrical lenses 112,114 of the system 100 of FIG. 1 and further
comprise retro-focus focusing lens system 516.
[0051] A principle of optics provides that the beam intensity
profile in the far field of a system is imaged at the Fourier plane
(focal plane) using the focusing lens system. Using a focusing lens
system with a short focal length, it is possible to produce a small
rectangularly shaped beam profile in the near field with a
controlled intensity profile. The size of the focused pattern is
given by bs=2*f*tan(FA/2), wherein f is the focal length of the
focusing lens system and FA is the divergence of the acylindrical
lenses 512,514.
[0052] The retro-focus focusing lens system 516 comprise a negative
(diverging) lens device 518, e.g. a double concave lens with a
focal length of -18 mm, and a positive (converging) lens device
520, e.g. a positive achromatic doublet with a focal length of 20
mm. The negative lens device 518 is located between the
acylindrical lenses 512,514 and the positive lens device 520. The
retro-focus focusing system 516 has a total focal length of 10 mm
and a working distance of 30 mm. Used in pair with the pair of
crossed acylindrical lenses 512,514 respectively having a
divergence of 17 mrad and 34 mrad, a 200.times.500 .mu.m
rectangular flat-top profile is generated. The resulting flat-top
profile is illustrated in FIGS. 6A and 6B.
[0053] In order to provide low aspherical aberration, the positive
lens device 520 is an achromatic doublet but any other positive
lens device, such as a simple biconvex lens, could alternatively be
used. Furthermore, it is contemplated that the negative lens device
518 and the positive lens device 520 may use aspheric lenses to
eliminate spherical aberrations.
[0054] It is noted that, alternatively, a simple positive lens
arrangement could be used as focusing lens means.
[0055] FIGS. 6A and 6B show the focused beam intensity profile
obtained using the beam shaping system 500 of FIG. 5, along the X-
and Y-axis respectively. The resulting profile is a substantially
flat-top profile along both X- and Y-axes.
[0056] FIGS. 7A and 7B show a rectangular beam intensity profile
obtained using the beam shaping system of FIG. 5 for two different
input wavelengths (superimposed on the graphs) and along the X- and
Y-axis respectively. Since the system based on refractive optics,
it is possible to have a multiple wavelength input beam. A first
laser source has a wavelength of 532 nm and second source, a
wavelength of 780 nm. FIG. 7A shows the superimposition of the
intensity profiles obtained along the X-axis for both wavelengths.
Similarly, FIG. 7B shows the intensity profiles obtained along the
Y-axis.
[0057] It is noted that, the equations defining the acylindrical
surfaces are adapted to the incident beam intensity profile. In a
case where two or more laser sources are combined up-front for
providing more than one wavelength components, the intensity
distribution should ideally be alike for each wavelength components
on the incident beam. If it is not the case, the output intensity
distribution corresponding to each wavelength component will differ
and may deviate from the target profile. If the application does
not tolerate relaxed uniformity requirements on one of the
wavelength components, the beam intensity profiles of the sources
may be matched up-front.
[0058] FIG. 8 illustrates a collimation-type beam shaping system
800 using two crossed acylindrical lenses 812,814 similar to the
acylindrical lenses 112,144 of FIG. 1, along with collimating lens
means 816. The collimating lens means 816 comprises a single
rotationally symmetrical positive lens 818. The collimating lens
means 816 provides a rectangular beam intensity profile and a beam
size that is maintained over a significant distance. The
collimating lens 818 is a rotationally symmetrical piano-convex
single having a focal length of 30 mm and positioned at one focal
length distance in front of the diverging point source D of the
beam shaping system 100.
[0059] The point source D is longitudinally stretched because of
the spherical aberration of the pair of crossed acylindrical lenses
812,814. However it is still possible to quasi collimate the
rectangular beam provided at the output of the system 100.
[0060] Since the point sources of the two crossed acylindrical
lenses 812,814 are located at different positions along the
propagation distance, the system has astigmatism aberration. Thus,
to eliminate the astigmatism and to further improve the
collimation, two orthogonally independent collimating systems could
alternatively be used. FIG. 9 illustrates such beam shaping system
900. The beam shaping system 900 uses two orthogonally disposed
acylindrical lenses 912,914 similar to the acylindrical lenses
112,144 of FIG. 1, along with collimating lens means 916. The
collimating lens means 916 comprises two orthogonally disposed
cylindrical collimating lenses 918,920. The first cylindrical
collimating lens 918 is located at one focal length from the point
source D' of the first acylindrical lens 912 and the second
cylindrical collimating lens 920 is located at one focal length
from the point source D'' of the second acylindrical lens 914.
Using this configuration, it is possible to achieve a collimated
beam with an almost diffraction limited wavefront.
[0061] Similarly, the focusing system of FIG. 5 could also use
pairs of orthogonally disposed cylindrical lenses instead of
rotationally symmetrical lenses 518,520 for eliminating
astigmatism.
[0062] FIG. 10 illustrates a rectangular beam shaping system 1000
using the beam shaping system 500 of FIG. 5 along with a
diffractive beam splitter 1022 for generating an array of
rectangular patterns of uniform intensity. The diffractive beam
splitter 1022 is a transmission grating optimized for a wavelength
of 660 nm and producing a 7.times.7 pattern array. Alternatively, a
micro lenses array could be used to produce an array of rectangular
flat-top patterns at the Fourier plan of the micro lenses
array.
[0063] FIG. 11 illustrates a rectangular beam array obtained using
the beam shaping system 1000 of FIG. 10.
[0064] FIG. 12 illustrates an alternative embodiment of the
embodiment of FIG. 1. The beam shaping system 1200 uses two
orthogonally disposed acylindrical lenses 1212,1214. The first and
the second acylindrical lens 1212,1412 are negative lenses. The
input surface 1230 of the first acylindrical lens 1212 is a convex
cylindrical surface which provides divergence along the X-axis and
the output surface 1232 is a concave acylindrical surface having a
variable radius of curvature along the X-axis for shaping the
incident beam along the X-axis. At the output of the first
acylindrical lens 1212, the beam intensity profile remains
substantially unchanged along the Y-axis. The second acylindrical
lens 1214 is similar to the first acylindrical lens 1212 and is
orthogonally disposed relative to the first acylindrical lens 1212
in order to shape the incident beam intensity profile along the
Y-axis.
[0065] The embodiments of the invention described above are
intended to be exemplary only. The scope of the invention is
therefore intended to be limited solely by the scope of the
appended claims.
* * * * *