U.S. patent application number 10/224385 was filed with the patent office on 2004-01-22 for laser beam focusing apparatus and method for focusing a laser beam.
This patent application is currently assigned to OSAKA UNIVERSITY. Invention is credited to Kitagawa, Yoneyoshi, Kodama, Ryosuke, Mima, Kunioki, Sentoku, Yasuhiko, Tanaka, Kazuo, Yamanaka, Tatsuhiko.
Application Number | 20040012864 10/224385 |
Document ID | / |
Family ID | 29774675 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040012864 |
Kind Code |
A1 |
Mima, Kunioki ; et
al. |
January 22, 2004 |
Laser Beam Focusing Apparatus and Method for Focusing a Laser
Beam
Abstract
A hollow tube having a pair of openings which have their
respective different diameters and arm opposed each other is
prepared. Then, a pulsed laser beam is introduced into the hollow
tube from the larger opening thereof and then, reflected multiply
on the inner wall surface of the hollow tube. The introduced pulsed
laser beam is focused during the traveling for the smaller opening
of the hollow tube to generate a focused laser beam. The thus
obtained focused laser beam is output from the smaller opening of
the hollow tube.
Inventors: |
Mima, Kunioki; (Takatsuki
City, JP) ; Kodama, Ryosuke; (Minoo City, JP)
; Yamanaka, Tatsuhiko; (Toyonaka City, JP) ;
Kitagawa, Yoneyoshi; (Minoo City, JP) ; Tanaka,
Kazuo; (Minoo City, JP) ; Sentoku, Yasuhiko;
(San Diego, CA) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
OSAKA UNIVERSITY
Suita City
JP
|
Family ID: |
29774675 |
Appl. No.: |
10/224385 |
Filed: |
August 21, 2002 |
Current U.S.
Class: |
359/853 ;
359/852 |
Current CPC
Class: |
G02B 19/0019 20130101;
G02B 19/0023 20130101; G02B 19/0033 20130101; G02B 27/0994
20130101; G02B 6/10 20130101 |
Class at
Publication: |
359/853 ;
359/852 |
International
Class: |
G02B 005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2002 |
JP |
2002-211,116 |
Claims
What is claimed is:
1. A laser beam focusing apparatus comprising a hollow tube having
a pair of openings which are opposed each other, one opening
serving as a laser beam inlet, the other opening serving as a laser
beam outlet, the diameter of said laser beam inlet being set larger
than the diameter of said laser beam outlet.
2. A laser beam focusing apparatus as defined in claim 1, wherein
the diameter of the laser beam inlet is set within 100-1000 .mu.m
and the diameter of the laser beam outlet is set within 1-100
.mu.m.
3. A laser beam focusing apparatus as defined in claim 1, wherein
the average surface roughness Ra of the inner wall of said hollow
tube is set to 0.1 .mu.m or below.
4. A laser beam focusing apparatus as defined in claim 1, wherein
said hollow tube is made of at least one material selected from the
group consisting of Pb, W, Au, Cu, Ag, Pt, Al and Fe.
5. A laser beam focusing apparatus as defined in claim 1, wherein
said hollow tube has a revolution-paraboloid shape.
6. A laser beam focusing apparatus as defined in claim 1, wherein
said hollow tube has a cone shape.
7. A laser beam focusing apparatus comprising a filmy member having
plural pits, each pit having a pair of openings which are opposed
each other, one opening of each pit serving as a laser beam inlet,
the other opening of each pit serving as a laser beam outlet, the
diameter of said laser beam inlet being set larger than the
diameter of said laser beam outlet.
8. A laser beam focusing apparatus as defined in claim 7, wherein
the diameter of the laser beam inlet is set within 100-1000 .mu.m
and the diameter of the laser beam outlet is set within 1-100
.mu.m.
9. A laser beam focusing apparatus as defined in claim 7, wherein
the average surface roughness Ra of the inner wall of each pit is
set to 0.1 .mu.m or below.
10. A laser beam focusing apparatus as defined in claim 7, wherein
said filmy member is made of at least one material selected from
the group consisting of Pb, W, Au, Cu, Ag, Pt, Al and Fe.
11. A laser beam focusing apparatus as defined in claim 7, wherein
each pit has a revolution-paraboloid shape.
12. A laser beam focusing apparatus as defined in claim 7, wherein
said hollow tube has a cone shape.
13. A method for focusing a laser beam, comprising the steps of:
preparing a hollow tube having a pair of openings which have their
respective different diameters and are opposed each other,
introducing a pulsed laser beam into said hollow tube from the
larger opening of said hollow tube reflecting multiply said pulsed
laser beam on the inner wall surface of said hollow tube and
traveling said pulsed laser beam toward the smaller opening of said
hollow tube with focusing, to generate a focused laser beam, and
outputting said focused laser beam from the smaller opening of said
hollow tube.
14. A focusing method as defined in claim 13, further comprising
the step of forming, on the inner wall surface of said hollow tube,
a plasma layer having a smaller thickness than the wavelength of
said pulsed laser beam.
15. A focusing method as defined in claim 13, wherein the spot size
of said focused laser beam is 10 .mu.m or below.
16. A method for focusing a laser beam, comprising the steps of:
preparing a filmy member having plural pits, each pit having a pair
of opening which have their respective different diameters and are
opposed each other, introducing a pulsed laser beam into each pit
from the larger opening thereof, reflecting multiply said pulsed
laser beam on the inner wall surface of each pit and traveling said
pulsed laser beam toward the smaller opening thereof with
condensation, to generate a focused laser beam, and outputting said
focused laser beam from the smaller opening of each pit.
17. A focusing method as defined in claim 16, further comprising
the step of forming, on the inner wall surface of each pit, a
plasma layer having a smaller thickness than the wavelength of said
pulsed laser beam.
18. A focusing method as defined in claim 16, wherein the spot size
of said focused laser beam is 10 .mu.m or below.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a laser beam focusing apparatus
and a method for focusing a laser beam, particularly usable for
laser nuclear fusion and laser particle acceleration and induced
nuclear reactions.
[0003] 2. Description of the Prior Art
[0004] Recently, much attention is paid to such research and
development as to generate nuclear fusion by heating
instantaneously a ultra high density plasma (solid plasma or more
dense plasma) using a short pulse high intensity laser and is also
paid to various structural analyses using laser produced high
energy particles.
[0005] Conventionally, such a high intensity laser beam is
generated by focusing a laser beam by a focus lens system or
mirror. In such a conventional means, however, it is difficult to
focus the laser beam in high intensity because of the wavefront
distortion of the laser beam, so a focused laser beam having a spot
size of 10 .mu.m or below is not easy to be realized. In this point
of view, such an attempt is made as to focus a laser beam by means
of a complicated optical system with an optical waveguide, but the
operationallity is deteriorated and the cost is increased because
of the complicated optical system.
SUMMERY OF THE INVENTION
[0006] It is an object of the present invention, in this point of
view, to provide a new apparatus and a new method whereby a laser
beam of high intensity can be obtained through focusing a pulsed
laser without a complicated optical system.
[0007] In order to achieve the above object, this invention relates
to a laser beam focusing apparatus comprising a hollow tube having
a pair of openings which are opposed each other,
[0008] one opening serving as a laser beam inlet,
[0009] the other opening serving as a laser beam outlet,
[0010] the diameter of the laser beam inlet being set larger than
the diameter of the laser beam outlet.
[0011] Also, this invention relates to a method for focusing a
laser beam, comprising the steps of:
[0012] preparing a hollow tube having a pair of openings which have
their respective different diameters and are opposed each
other,
[0013] introducing a pulsed laser beam into said hollow tube from
the larger opening of said hollow tube
[0014] reflecting multiply said pulsed laser beam on the inner wall
surface of said hollow tube and traveling said pulsed laser beam
toward the smaller opening of said hollow tube with condensation,
to generate a focused laser beam, and
[0015] outputting said focused laser beam from the smaller opening
of said hollow tube.
[0016] The inventor had intensely studied to achieve the above
object. As a result, the inventor found out the following fact.
First of all, a hollow tube having a pair of openings which are
opposed each other is prepared. Then, a given pulsed laser beam is
introduced into the hollow tube from the larger opening. In this
case, a plasma layer having a thickness much smaller than the
wavelength of the laser beam is created on the inner wall of the
hollow tube, and the introduced laser beam is reflected multiply on
the inner wall of the hollow tube toward the smaller opening from
the larger opening, to generate a highly focused laser beam.
Therefore, when the size of the smaller opening is set to a desired
size, the pulsed laser beam can be focused to a diffraction-limited
spot size of about 10 .mu.m and emitted outside.
[0017] According to the present invention, only if such a hollow
tube having a pair of openings which have different sizes and are
opposed each other, a laser beam of high intensity can be easily
obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] For better understanding of the present invention, reference
is made to the attached drawings, wherein
[0019] FIG. 1 is a perspective view showing a laser beam focusing
apparatus according to the present invention,
[0020] FIG. 2 is a perspective view showing another laser beam
focusing apparatus according to the present invention,
[0021] FIG. 3 is a plan view showing a modified laser beam focusing
apparatus according to the present invention,
[0022] FIG. 4 is a cross sectional view showing the modified laser
beam focusing apparatus illustrated in FIG. 3, taken on line X-X,
and
[0023] FIG. 5 is a cross sectional view showing the modified laser
beam focusing apparatus illustrated in FIG. 3, taken on line
X-X.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] This invention will be described in detail with reference to
the accompanying drawings. FIG. 1 is a perspective view showing a
laser beam focusing apparatus according to the present invention.
The laser beam apparatus focusing illustrated in FIG. 1 includes a
revolution-paraboloid hollow tube 1 having a pair of openings 2 and
3 which are opposed each other.
[0025] The larger opening 2 serves as a laser beam inlet, and the
smaller opening 3 serves as a laser beam outlet. The diameter D of
the opening 2 is set larger than the diameter d of the opening 3.
Concretely, the diameter D is preferably set within 100-1000 .mu.m,
particularly within 200-500 .mu.m. The diameter d is preferably set
within 1-100 .mu.m, particularly within 5-50 .mu.m. In this case, a
pulsed laser beam introduced can be focused effectively to generate
a ultra intense laser beam having a diffraction-limited spot size
easily. For example, a laser beam having a wavelength of 1 .mu.m
can be focused to a spot size of 10 .mu.m or less.
[0026] Herein, if the diameters D and d of the openings 2 and 3 are
set within the above ranges, it is desired that the length L of the
hollow tube 1 is set within 0.2-3 mm.
[0027] The hollow tube 1 may be made of a laser beam reflection
material, and concretely, made of at least one material selected
from the group consisting of Pb, W, Au, Cu, Ag, Pt, Al and Fe. In
this case, in addition to the high laser beam reflectionity, the
mechanical strength of the hollow tube 1 can be enhanced and it is
easy to handle the hollow tube 1 when attached in an apparatus
[0028] Similarly, the thickness t of the side wall 1B of the hollow
tube 1 is preferably set within 5-50 .mu.m if the tube 1 is made of
such a heavy metal as mentioned above.
[0029] in order to perform the multiple reflection of the
introduced pulsed laser beam effectively without energy loss, the
inner wall surface 1A of the hollow tube 1 is made smooth.
Concretely, the average surface roughness Ra of the inner wall
surface 1A is set to 1.0 .mu.m or below, preferably 0.05 .mu.m or
below.
[0030] Next, the focusing principle of laser beam for the laser
beam focusing apparatus illustrated in FIG. 1 will be described. A
pulsed laser beam from a laser source not shown is spread spatially
to some extent and then introduced into the hollow tube 1 through
the opening 2. At that time, a plasma layer having a thickness much
smaller than the wavelength of the pulsed laser beam is created on
the inner wall surface 1A of the hollow tube 1.
[0031] The upper component A of the introduced pulsed laser beam is
collided with and then, reflected multiply on the inner wall
surface 1A to be traveled toward the opening 3 along the direction
defined by the arrows. Similarly, the lower component C of the
introduced pulsed laser beam is also collided with and then,
reflected multiply on the inner wall surface 1A to be traveled
toward the opening 3 along the direction defined by the arrows. The
center component B of the introduced pulsed laser beam is traveled
toward the opening 3 without the multiple reflection for the inner
wall surface 1A.
[0032] As mentioned above, since the diameter D of the opening 2 is
set larger than the diameter d of the opening 3, that is, the
diameter d of the opening 3 is set smaller than the diameter D of
the opening 2, the upper component A and the lower component C are
converged to the center portion of the hollow tube 1 during the
traveling for the opening 3. As a result, the introduced pulsed
laser beam is focused in the hollow tube 1 to generate and then
output a given focused laser beam from the opening 3.
[0033] If a pulsed laser beam having a wavelength of 1 .mu.m is
employed, it can be focused to a spot size of about 10 .mu.m. If
the configuration and size of the hollow tube 1 is controlled
appropriately, the pulsed laser beam can be focused to a spot size
of about 1 .mu.m.
[0034] FIG. 2 is a perspective view showing another laser beam
focusing according to the present invention. The laser beam
focusing illustrated in FIG. 2 includes a cone-shaped hollow tube
11 having a pair of openings 12 and 13 which are opposed each
other. When such a cone-shaped hollow tube 11 is employed, a pulsed
laser beam can be also focused effectively as well as the
revolution-paraboloid hollow tube 1 as shown in FIG. 1. Like
properties are required for the hollow tube 11 as the
above-mentioned hollow tube 1.
[0035] The diameter D of the opening 12 is preferably set within
100-1000 .mu.m, particularly within 200-500 .mu.m. The diameter d
of the opening 13 is preferably set within 1-100 .mu.m,
particularly within 5-50 .mu.m. The hollow tube 11 is preferably
made of a heavy metal or the like as mentioned above. The average
surface roughness Ra of the inner wall surface 11A is set to 1.0
.mu.m or below, preferably 0.05 .mu.m or below. The length L of the
hollow tube 11 is set within 0.2-3 mm, and the thickness t of the
side wall 11B of the hollow tube 11 is preferably set within 5-50
.mu.m.
[0036] A pulsed laser beam from a laser source not shown is spread
spatially to some extent and then introduced into the hollow tube
11 through the opening 12, as mentioned above. At that time, a
plasma layer having a smaller thickness than the wavelength of the
introduced pulsed laser beam is created on the inner wall surface
11A of the hollow tube 11. The upper component A of the introduced
pulsed laser beam is collided with and then, reflected multiply on
the inner wall surface 11A located vertically to be traveled toward
the opening 3 along the direction defined by the arrows. Similarly,
the lower component C of the introduced pulsed laser beam is also
collided with and then, reflected multiply on the inner wall
surface 11A located vertically to be traveled toward the opening 3
along the direction defined by the arrows. The center component B
of the introduced pulsed laser beam is traveled toward the opening
3 without the multiple reflection for the inner wall surface
11A.
[0037] As a result, the introduced pulsed laser beam is focused in
the vicinity of the opening 13 to generate and then output a
focused laser beam from the opening 13. If a pulsed laser beam
having a wavelength of 1 .mu.m is employed, it can be focused to a
spot size of about 10 .mu.m or less. If the configuration and size
of the hollow tube 11 is controlled appropriately, the pulsed laser
beam can be focused to a spot size of about 1 .mu.m.
[0038] FIGS. 3-5 are structural views showing a modified laser beam
focusing according to the present invention. FIGS. 4 and 5 are
cross sectional views of the laser beam focusing apparatus
illustrated in FIG. 3, taken on line X-X. The laser beam focusing
apparatus illustrated in FIGS. 3-5 is composed of a filmy member 21
having plural pits 25, each pit having a pair of openings 22 and 23
which are opposed each other. Each pit may have a
revolution-paraboloid shape or a cone shape as the hollow tube 1 or
11 illustrated in FIG. 1 or 2.
[0039] The diameter D of the opening 22 and the diameter d of the
opening 23 of each pit and the thickness L of the filmy member 21
may be set in similar fashion to the hollow tube 1 or 11 as shown
in FIG. 1 or 2. Also, the average surface roughness Ra may be set
in similar fashion to the hollow tube 1 or 11 to be made
smooth.
[0040] A pulsed laser beam from a laser source not shown is spread
spatially to some extent and then introduced into each pit 25 of
the filmy member 21 from the opening 22. At that time, a plasma
layer having a smaller thickness than the wavelength of the pulsed
laser beam is created on the inner wall surface 25A of each pit 25,
as explained in FIG. 1 or 2. Therefore, the upper and lower
components of the pulsed laser beam are reflected multiply on the
inner wall surface 25A of each pit 25 to be traveled toward the
opening 23 with converged in the center portion of each pit 25. As
a result, the introduced pulsed laser beam is focused in the
vicinity of the opening 23 to generate and output a focused laser
beam from the opening 23.
[0041] In other words, in the laser beam focusing illustrated in
FIGS. 3-5, each pit 25 serves as the hollow tube 1 or 11 shown in
FIG. 1 or 2. Therefore, the laser beam focusing apparatus
illustrated in FIGS. 3-5 is so constructed as having plural laser
beam focusing apparatus shown in FIG. 1 or 2. As a result, plural
pulsed laser beams can be focused to generate plural high density
laser beams simultaneously.
[0042] The filmy member 21 may be made of at least one material
selected from the group consisting of Pb, W, Au, Cu, Ag, Pt, Al and
Fe, as the hollow tube 1 or 11.
[0043] Although the present invention was described in detail with
reference to the above examples, this invention is not limited to
the above disclosure and every kind of variation and modification
may be made without departing from the scope of the present
invention. For example, although in the above examples, the hollow
tube and the pit have revolution-paraboloid shape or cone shape,
they may have any shape.
[0044] As mentioned above, according to the present invention, a
new apparatus and a new method whereby a laser beam of high
intensity can be obtained through the focusing of a pulsed laser
without a complicated optical system can be provided.
* * * * *