Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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THREE-DIMENSIONAL OPTICAL RESONANCE DEVICE, POLARIZED LASER
OSCILLATION METHOD, AND POLARIZED LASER OSCILLATION SYSTEM
TECHNICAL FIELD
[0001]
The present invention relates to a resonance device, a
polarized laser oscillation method, and a polarized laser
oscillation system for a small-sized X-ray source to generate
an X-ray using laser inverse Compton scattering and the like.
BACKGROUND ART
[0002]
As a polarized laser oscillation method used for
generating an X-ray using laser inverse Compton scattering
and the like, there has been known a method to generate strong
polarized laser while guiding laser obtained from a laser
generator to an optical resonator and causing the laser to
resonate.
SUMMARY OF THE INVENTION
[0003]
However, with such a polarized laser generation method,
since circular polarization properties of laser cannot be
split by an optical resonator using two mirrors, it is
required to switch circular polarization using a polarizer,
a Faraday rotator, a quarter-wave plate and the like.
Accordingly, there has been a problem of complicated
adjustment caused accordingly.
[0004]
Further, with such a polarized laser generation method,
switching between right circular polarization and left
circular polarization is required to be performed by
adjusting a polarizer, a Faraday rotator, a quarter-wave
plate and the like respectively. Accordingly, in addition to
difficulty to increase speed of the switching, there has been
a problem that pure circular polarized laser cannot be
guaranteed.
[0005]
Further, with a polarized laser generating device using a
polarized laser generation method described above, since the
entire device is upsized, an X-ray source is to be upsized when
the device is used for the X-ray source by utilizing laser inverse
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Compton scattering and the like.
[0006]
Accordingly, there has been a problem that an X-ray
source incorporating a polarized laser generating device is
difficult to be used with an X-ray for magnetism analysis,
biological investigation, drug development and the like.
[0007]
An object of the present invention is to provide a
polarized laser oscillation method using an optical resonance
device capable of causing laser obtained from a laser light
source to resonate with either right polarization or left
polarization as guiding to an optical resonator which is
three-dimensionally arranged and easily performing switching
therebetween.
[0008]
Further, another object of the present invention is to
provide a polarized laser oscillation system which generates
ultrashort pulse polarized radiation at a collision point
arranged in a three-dimensionally-structured optical
resonator owing to collision between a high-energy electron
beam emitted from a high-energy electron beam generating unit
and pulse laser. of right polarization or left polarization
with a beam size of m or smaller and energy strength of 1
mJ/pulse or higher generated at the collision point in the
three-dimensional optical resonator.
[0009]
In view of the above issues, the present invention, as
a first embodiment, provides a three-dimensional optical
resonance device, comprising: an optical resonator which
includes a pair of flat mirrors and a pair of concave mirrors
as being three-dimensionally arranged and which introduces
laser light emitted from a laser light source unit with an
incident optical system and selecting right circular
polarizaLion or left circular polarization in accordance with
a length of an optical path adjusted by a piezoelectric
element while circulating the laser light on the length-
adjusted optical path to cause the laser light to resonate.
[0010]
Here, the laser light source unit includes a CW laser
oscillator or a mode-locking laser pulse oscillator as a laser
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oscillator, and a polarization face and a beam diameter of laser
emitted from the laser light source which generates laser being
a OW laser type or a pulse laser type are adjusted.
[0011]
Here, the three-dimensional optical resonance device
includes a resonance monitoring unit which measures strength
of laser light resonating in the optical resonator. Further,
the three-dimensional optical resonance device includes a
zero-cross feedback signal generator which generates a
zero-cross feedback signal as splitting laser transmitted
through any of the flat mirrors and the concave mirrors among
laser light resonating in the optical resonator into a
P-polarized component and an S-polarized component, measuring
strength of each polarized component, and obtaining a
differential value therebetween.
[0012]
The three-dimensional optical resonance device includes
a polarization change-over switch which outputs an instruction
signal to assign the selected right circular polarization or
left circular polarization, and a resonance controller which
adjusts the length of the optical path by controlling drive
voltage of the piezoelectric element arranged in the optical
resonator based on output of the polarization change-over switch,
output of the resonance monitoring unit and output of the
zero-cross feedback signal generator and which selectively
accumulates laser of right circular polarization or left
circular polarization into the optical resonator.
[0013]
Here, right polarization pulse laser or left polarization
pulse laser with a beam size of 10 m or smaller and energy
strength of 1 mJ/pulse or higher is collided with an electron
beam emitted from the incident optical system at a collision
point arranged in the optical resonator to generate ultrashort
pulse polarized radiation with a radiation amount thereof
measured.
[0014]
Further, an electron beam with normalized emittance of 10
mmmrad or less emitted from the laser light source unit and pulse
laser in the optical resonator are collided at the collision
point with a collision angle in a range from 8 to 20 degrees
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and collision accuracy of 1pm or less and ultrashort pulse
polarized radiation being a X-ray or a y-ray with
characteristics having energy of 0.25 key or higher is
generated and drawn to the outside.
[0015]
The present invention, as a second embodiment, provides
a polarized laser oscillation method, comprising: guiding
laser light emitted from a laser light source unit to an
optical resonator; adjusting an optical path length in the
optical resonator by deforming a piezoelectric element by
applying ramp-like drive voltage while circulating the laser
light in the optical resonator with a pair of flat mirrors
and a pair of concave mirrors; splitting laser light
transmitted through the pair of concave mirrors or the pair
of flat mirrors into a P-polarized component and an S-
polarized component and measuring strength of each polarized
component; generating a zero-cross feedback signal based on
strength difference value of the polarized components; and
right polarized laser light or left polarized laser light is
caused to resonate and is accumulated in the optical resonator
by fixing a voltage value of the drive voltage.
[0016]
Further, the present invention, as a third embodiment,
provides a polarized laser oscillation system, comprising: a
laser light source unit which has at least either one of a
CW laser oscillator and a mode-locking laser pulse oscillator
and which emits laser light of a CW laser type or a pulse
laser type; an incident optical system which arranges a
polarization face and a beam diameter of the laser light
emitted from the laser light source unit; an optical resonator
which is configured to cause laser light to resonate by
introducing the laser light emitted from the laser light
source unit with the incident optical system and selecting
right circular polarization or left circular polarization in
accordance with an adjusted length of an optical path while
circulating the laser light on the optical path with the
length being adjusted by a piezoelectric element, wherein the
optical resonator includes a pair of flat mirrors and a pair
of concave mirrors; a resonance monitoring unit which
measures strength of the laser light resonating in the optical
resonator; a zero-cross feedback signal generator which
generates a zero-cross feedback signal by splitting laser
light transmitted through any of the flat mirrors and the
concave mirrors among the laser light resonating in the
optical resonator into P-polarized light and S-polarized
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light, measuring strength thereof, and obtaining a
differential value therebetween; a polarization change-over
switch which outputs an instruction signal to assign said
right circular polarization or said left circular
polarization selected at the optical resonator; and a
resonance controller which adjusts the length of the optical
path by controlling drive voltage of the piezoelectric
element arranged in the optical resonator based on output of
the polarization change-over switch, output of the resonance
monitoring unit and output of the zero-cross feedback signal
generator and which selectively accumulates laser light of
said right circular polarization or said left circular
polarization into the optical resonator.
[0017]
With the above, the present invention may enable
polarized laser oscillation using the three-dimensional
optical resonance device capable of causing laser obtained
from the laser light source to resonate with either right
polarization or left polarization as guiding to the optical
resonator which is three-dimensionally arranged and easily
performing switching therebetween.
[0018]
Further, the present invention may actualize the
polarized laser oscillation system which generates ultrashort
pulse polarized radiation at the collision point arranged in
the optical resonator owing to collision between a high-
energy electron beam emitted from a high-energy electron beam
generating unit and pulse laser of right polarization or left
polarization with a beam side of 10 m or smaller and energy
strength of 1 mJ/pulse or higher generated at the collision
point in the optical resonator. BRIEF DESCRIPTION OF THE
DRAWINGS
[0019]
Fig. 1 is a schematic structural view illustrating an
embodiment of a polarized laser oscillation method and a
device thereof according to the present invention.
Fig. 2 is a perspective view illustrating a detailed
structural example of a three-dimensional optical resonator
illustrated in Fig. 1.
Fig. 3 is a schematic structural view illustrating an
example of a polarized radiation generation method and a
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polarized radiation generating system according to the present
invention.
Fig. 4 is a structural view of an optical resonator with
four non-planar mirrors of the present invention.
Fig. 5 is a schematic structural view illustrating a layout
of a system used in a preliminary experimental test.
Fig. 6 is a graph indicating an example of a typical signal
to be observed in a case that incident laser has linear
polarization.
Fig. 7 is a graph plotting a function of "F(8)=Er/Ei" under
conditions of "R1=0.99", "T1=0.01" and "R=0.98".
Fig. 8 is a graph plotting calculation results of a
difference signal "Esr-Epr" and a sum signal "Esr+Epr" of
components "Esr" and "Epr" of a reflection wave "Er" indicated
by a column vector in expression 11 under conditions of "R1=0.99",
"T1=0.01", "R=0.98" and "(l)ge,==-0.0575 rad".
Fig. 9 is a graph plotting calculation results of a
difference signal "Esr-Epr" and a sum signal "Esr+Epr" of
components "Esr" and "Epr" of a reflection wave "Er" indicated
by the column vector in expression 11 under conditions of
"R1=0.999", "T1=0.001", "R=0.998" and "(1)geo=¨ 0.0575 rad".
Fig. 10 is a structural view illustrating a general outline
of experimental equipment prepared for verifying calculation.
Fig. 11 is a graph indicating signals observed in the
vicinity of a resonant point of a three-dimensional optical
resonator illustrated in Fig. 10.
EMBODIMENT OF THE INVENTION
[0020]
1. Introduction
Highly-accurate optical resonators are used in a variety
of scientific fields. Beam strength can be increased by several
steps by entering laser beam from a laser oscillator into an
optical resonator. In a field of accelerator physics, this
technology is required for developing a small-sized X-ray light
source based on a laser Compton scattering method.
[0021]
Resonance of an optical resonator requires maintaining at
a sharp peak. There have been developed a variety of types for
obtaining a difference signal from a resonance curve usable for
controlling a movement direction of a servo system.
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[0022]
The Pound-Drever-Hall method to measure a phase shift of
a reaction wave as introducing a frequency side band at an outer
side of a resonance peak is one of methods which are widely used.
In a tilt-locking method as another method, a phase shift of
a reaction wave is detected using interference between a
fundamental mode and a higher lateral mode. In the
Hansch-Couillaud (HC) method, an optical resonator is set to
have a resonance-polarization-dependent structure by placing
birefringent material in an optical resonator and polarization
variation of reaction wave caused by phase shift due to resonance
is measured. In a multi-mirror optical resonator system using
mirrors installed as being inclined, characteristics of a linear
polarization-dependent structure may occur owing to mirror
stress even in a system with two mirrors. Accordingly,
modification of the HC method can be actualized without
additional material.
[0023]
A four-mirror optical resonator having a
three-dimensional (non-planar) structure can generate a fine
spot at one point in the optical resonator. When a laser Compton
X-ray source is used, effective laser-electron crossing can be
provided with a four-mirror optical resonator, so that generated
X-ray performance (or convergence performance) can be improved.
[0024]
Normally, a non-planar optical resonator has
circular-polarization-dependent characteristics due to image
rotation in a three-dimensional optical path. The inventors
propose a new method for obtaining a difference signal from
resonance of a non-planar optical resonator utilizing the
circular-polarization-dependent characteristics. This method
is modification of the HC method having circular polarization
dependency.
[0025]
2. Experimental equipment
(1) Outline of non-planar optical resonator
Fig. 4 illustrates a structure of a non-planar four-mirror
optical resonator of the present invention. An optical path is
formed along sides of a bilaterally-symmetric tetrahedron with
Laces being isosceles triangles, each having sides of "a", "a"
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and "b". Side "a" is 420 mm long and side "b" is 100 mm long.
The mirrors located at respective vertexes "Pi", "P2", "P3" and
"P4" form a confined light resonator in the order thereof. The
mirrors at vertexes "Pi" and "P2" are flat mirrors and the mirrors
at vertexes "P3" and "P4" are concave mirrors. All of the mirrors
(flat mirrors and concave mirrors) used in this experiment have
a reflection rate of 99% and a transmission factor of 1%. Point
"41" is a midpoint between vertex "Pi" and vertex "P3". Point
"Qz" is a midpoint between vertex "P2" and vertex "P4".
[0026]
(2) Influence of geometric phase
A non-planar optical resonator has uniqueness in
degeneracy and separation of resonance of circular polarization.
Influences of a geometric phase are studied in the following
procedure.
[0027]
Regarding influences at vertex "P2", unit vectors "ki" and
"k2" are a light beam (incident light) from vertex "Pi" to vertex
"Pz" and a light beam from vertex "P2" to vertex "P3" respectively.
[Expression 1]
PEP,P P
=
2
P,I
[0028]
Here, normal vectors "n1" and "n2" of reflection light at
vertexes "P2" and "93" can be expressed with the following
expression.
[Expression 2]
P Q PsQ 2
it = 112 -
Q I IP, Q 2 1
[0029]
Then, faces including the incident light and the reflection
light can be expressed with vectors "al", "a2" expressed as the
following expressions using definitions of unit vectors "k11',
"k2" and normal vectors "n1", "r12".
[Expression 3]
= x . . 2 2
k.11 1132 X i21
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[0030]
Here, angle "a12" between vector "al" and vector "a2"
denotes image rotation occurring at one side of the four-mirror
optical resonator and can be calculated with the following
expression.
[Expression 4]
sin cr,l, =
[0031]
With such a non-planar optical resonator, since image
rotation at each reflection point is to be accumulated, an angle
"4a12" (hereinafter, suitably called a geometric phase "4)geo")
is obtained as an entire effect with one round of an optical
path in the non-planar optical resonator. Further, image
rotation corresponds to phase shift in a case with a rotatory
polarization. Further, since a sign of phase shift with right
polarization is opposite to that with left polarization,
resonance degeneration between two circular polarizations is
split.
[0032]
For example, the angle "4a12" is "-0.0575 rad (as neglecting
integer portion of 2n) with the resonator proposed here.
[0033]
(3) Measurement of resonance with optical resonator
The inventors evaluated polarization characteristics of
the optical resonator proposed here with a preliminary
experimental test. Fig. 5 illustrates a layout of the system
prepared for the above.
[0034]
At that time, a single-mode CW laser (manufactured by
Innolight GmbH, Prometheus-model) was used as a light source.
Polarization of incident laser light was discriminated with a
polarized beam splitter ("PBS"). A pair of lenses ("matching")
is arranged so that the incident laser is matched with a mode
being specific for the optical resonator. An entering position
and an angle of the incident laser against the optical resonator
("3D-4 mirror cavity") were adjusted by a pair of flat mirrors.
One ("concave") of the optical resonator mirrors was attached
onto a piezoelectric control stage having a piezoelectric
element ("piezo") to be capable of varying a length (optical
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path length) of the optical resonator. Resonance in the optical
resonator was evaluated by measuring transmitted laser through
the optical resonator by a pin photodiode ("PD") while applying
ramp voltage (voltage gradually increasing like a slope) to the
piezoelectric element.
[0035]
Fig. 6 illustrates a typical signal observed when incident
laser has linear polarization. The graph is obtained by
measuring the transmitted laser through the optical resonator
with the photodiode while making the optical path length of the
optical resonator sweep using the piezoelectric element. The
upper graph indicates the entire period of a free spectrum range.
The highest peak corresponds to a fundamental lateral mode. The
lower graph is obtained by enlarging one of the peaks of the
fundamental mode.
[0036]
Fig. 6 illustrates a double-peak structure in which one
of two resonance peaks corresponds to right polarization and
the other corresponds to left polarization. Since the incident
laser includes two types of circular polarization respectively
by the same amount, the optical resonator provides resonance
with a slightly different phase based on both resonance
conditions.
[0037]
3. Method of locking technology
(1) Calculation
[Description of reflection wave]
Complex resonance "Er" of a reflection wave at each
resonance mirror in the optical resonator can be expressed as
follows.
[Expression 5]
E'= E' ,,,X _______
µIril-Rek'
. _
=E' x- __________ l? car (5 -R +isin 5
*I'
mA"F(5)
01 (1-R) 4- 4R sin ' (5 2)
- _
[0038]
Here, "E" denotes complex resonance of an incident wave
and "Ri"and "Tl" denote a reflection rate and a transmission
factor of a resonance mirror placed at an entering-emitting port
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of the optical resonator respectively. "R" denotes a value
which corresponds to fineness "F" of the optical resonator
defined as "F=n/(1-R)". Here, it is possible to consider "R"
as a reflection rate of a resonance mirror used in a two-mirror
optical resonator which has the same accuracy as that of a
four-mirror optical resonator. Further, "8" denotes a phase
difference derived from resonance conditions.
[0039]
Fig. 7 is a graph plotting a function of "F(8)"=Er/Ei" under
conditions of "R1=0.99", "T1=0.01" and "R=0.98". The upper line
indicates a real number portion and the lower line indicates
an imaginary number portion of the phase difference "8".
[0040]
[Description of polarization]
Wave polarization can be described with the following
expression by applying Jones matrix to the abovementioned
optical resonator.
[Expression 6]
F:=( :)
Here, respective elements "En" and "Es" of a column vector
"E" denote P-polarization and S-polarization respectively. The
electric field is in parallel to and is perpendicular to the
table. When a wave is spectrally separated by a polarized beam
splitter (PBS) which is horizontally placed on the table, two
elements can be measured separately.
[0041]
Circular polarization wave can be expressed as follows.
[Expression 7]
. ___ (1 1 (I
A
VY i)
Here, column vectors "ER" and "EL" denote right
polarization and left polarization of unit resonance,
respectively. Since the eigenstate of a non-planar optical
resonator corresponds to circular polarization, an incident wave
can be conveniently described as superimposition of unit
resonance of right polarization "ER" and unit resonance of left
polarization "EL".
[0042]
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Further, column vector "E45" being unit resonance of line
polarization as being inclined 45 degrees against the table face
can be expressed as follows.
[Expression 8]
f11 . 1 (1 = 1 +/ER 1-1 EL,
I 2 2
[0043]
(2) Method of proposed system
As described at 2-(2), resonance conditions of right
polarization and left polarization are shifted respectively to
have an opposite sign owing to an additional geometric phase.
A right polarization component "Erg" or a left polarization
component "ErL" of a reflection wave can be expressed using the
additional geometric phase "(1)ge." as follows.
[Expression 9]
E; = E;.-Eõ = E;F(5 Oro )t,
[Expression 10]
E; = E;E, =
[0044]
Here, in a case that Fig. 8 is with an incident wave, the
right polarization component "Erg" and the left polarization
component "Eri," of a reflection wave mutually act in the optical
resonator. The superimposed reflection wave "Er" generated
owing to the above is expressed as the following expression.
[Expression 11]
1-1
+ =1+ I F(.5 )Eft + ¨F(5 +0,
2 2
µ
P
t2r..1;11 Ffets )1_ ryi F(5 ) j
[0045]
Fig. 8 is a graph plotting calculation results of a
difference signal "Esr-Epr" and a sum signal "Esr+Epr" of
components "Esr" and "Epr" of a reflection wave "Er" indicated
by a column vector in expression 11 under conditions of "R1=0.99",
"T1=0.01", "R=0.98" and "(I)geo=-0.0575 rad". Here, for easy
understanding of relation with Fig. 10, Fig. 8 indicates
"PD1-PD2" as the difference signal "Esr-Epr" and "PD1+PD2" as the
sum signal "Esr+Epr".
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[0046]
The above corresponds to the structure of the optical
resonator to be the test target here. "Esr-Epr" is the difference
signal for locking the optical resonator proposed here.
[0047]
Further, Fig. 9 indicates calculation with higher accuracy.
This is a calculation example under conditions of "R1=0.999",
"TI=0.001", "R=0.998" and "(1)ge.=-0.0575 rad".
[0048]
As is evident from Figs. 8 and 9, the difference signal
"Esr-Epr" indicated by "PD1-PD2" crosses zero at peaks of
resonance. Owing to selecting signs of the difference signal
"Esr-Epr" which crosses zero (from minus to plus or from plus to
minus), the system can be locked with one circular polarization
resonance of either of right circular polarization and left
circular polarization.
[0049]
(3) Experiment
In order to verify the calculation, the inventors conducted
an experiment using the device illustrated in Fig. 10. A linear
polarization wave was entered into the three-dimensional optical
resonator "3D-cavity". Reflection light from the flat mirror
"reflection" placed at the entering-emitting port (laser beam
in the three-dimensional optical resonator "3D-cavity") was
guided to a detection system "detection system" structured with
the polarization beam splitter "PBS" and the two pin photodiodes
"PD1" and "PD2".
[0050]
The pin photodiode "PD1" monitored the P-polarization
strength "Er" and the pin photodiode "PD2" monitored the
S-polarization strength "Es". Signals from the respective pin
photodiodes "PD1" and "PD2" were supplied to the differential
amplifier "differential amplifier" and difference voltage
"Es-Ep" was output as an output signal "output".
[0051]
A polarization face of incident laser beam and a
polarization face of the detection system "detection system"
were coordinated by adjusting an angle of a half-wave plate "k/2"
placed at the input side of the detection system "detection
system" so as to valance outputs of the two pin photodiodes "PD1"
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and "PD2" even when the half-wave plate "X/2" and the
three-dimensional optical resonator "3D-cavity" are mutually
distanced.
[0052]
The above situation corresponds to that the laser beam
entering to the input side of the polarization beam splitter
"PBS" is expressed as expression 8. The resonance state of the
three-dimensional optical resonator "3D-cavity" was monitored
by measuring strength of transmitted light from the
three-dimensional optical resonator "3D-cavity" (laser beam in
the three-dimensional optical resonator "3D-cavity") using a
pin photodiode "PDO".
[0053]
The inventors measured the output signal "output" of the
differential amplifier "differential amplifier" while scanning
the optical path length of the three-dimensional optical
resonator "3D-cavity" using a piezoelectric control mirror
having the position thereof adjusted by the piezoelectric
element "piezo". Fig. 11 illustrates signals observed at the
vicinity of resonance points of the three-dimensional optical
resonator "3D-cavity". The lowermost line is a signal of the
pin photodiode "PDO" measuring the transmitted light as
indicating the resonance points of the three-dimensional optical
resonator "3D-cavity". The center line is the output signal
"output" of the differential amplifier "differential amplifier"
and the output signal is matched with the calculation result
of Fig. 8. The output signal "output" of the differential
amplifier "differential amplifier" crosses zero respectively
at the two resonance points and have mutually different signs
at the vicinity of the respective circular polarization peaks.
Accordingly, owing to that the optical path length of the
three-dimensional optical resonator "3D-cavity" is adjusted so
that the output signal "output" of the differential
amplifier "differential amplifier" is matched with either of
the respective zero-crossing points, locking can be performed
at either of the two resonance peaks of the three-dimensional
optical resonator "3D-cavity".
[0054]
According to the present invention, the three-dimensional
optical resonator "3D-cavity" can be caused to resonate with
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either right polarization or left polarization owing to locking
at one of the two resonance peaks of the three-dimensional
optical resonator "3D-cavity" using the abovementioned locking
method.
[0055]
<First embodiment>
Fig. 1 is a schematic structural view illustrating an
embodiment of a polarized laser oscillation method and a
polarized laser oscillation system of the present invention
utilizing the abovementioned principle.
[0056]
A polarized laser oscillation system 1 illustrated in this
drawing is provided with a laser light source 2 which includes
a CW laser oscillator and a mode-locking laser pulse oscillator
and which generates laser such as CW laser and pulse laser, an
incident optical system 3 which adjusts a polarization face and
a beam diameter of laser emitted from the laser light source
2, a three-dimensional optical resonator 4 which receives laser
emitted from the incident optical system 3 and accumulates the
laser as selecting right circular polarization or left circular
polarization in accordance with an adjusted optical path length,
a resonance monitoring unit 5 which monitors strength of laser
resonating in the three-dimensional optical resonator 4, a
zero-cross feedback signal generator 6 which generates a
zero-cross feedback signal as separating laser transmitted
through a flat mirror 21 among laser resonating in the
three-dimensional optical resonator 4 into P-polarized light
and S-polarized light, measuring strength thereof and obtaining
a differential value therebetween, a polarization change-over
switch 7 which outputs an instruction signal to assign right
circular polarization or left circular polarization which is
selected at the three-dimensional optical resonator 4, and a
resonance controller 8 which controls the optical path length
of the three-dimensional optical resonator 4 based on output
of the polarization change-over switch 7, output of the resonance
monitoring unit 5 and output of the zero-cross feedback signal
generator 6 and selectively accumulates laser of right circular
polarization or left circular polarization into the
three-dimensional optical resonator 4. The polarized laser
oscillation system 1 generates high-strength pulse laser with
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right or left circular polarization in the three-dimensional
optical resonator 4 having a time width of 30 psec or shorter,
abeam size of 10 gm or smaller, and energy strength of 1 mJ/pulse
or higher while the laser light source 2 and the
three-dimensional optical resonator 4 are controlled by the
resonance controller 8 based on the instruction signal output
from the polarization change-over switch 7, a monitored result
of the resonance monitoring unit 5, a zero-cross detection signal
output from the zero-cross feedback signal generator 6 and the
like.
[0057]
The laser light source 2 includes the CW laser oscillator
which generates CW laser, the mode-locking laser pulse
oscillator which generates pulse laser, and the like. The laser
light source 2 generates laser such as CW laser and pulse laser
as activating either the CW laser oscillator or the mode-locking
laser pulse oscillator based on an instruction from the resonance
controller 8 and enters the laser into the incident optical
system 3.
[0058]
The incident optical system 3 includes a plurality of flat
mirrors 9 which guide the laser emitted from the laser light
source 2 to the three-dimensional optical resonator 4, a
plurality of collimated lenses 10 which adjust a polarization
face and a beam diameter of the laser emitted from the laser
light source 2 as being placed on an optical path which is defined
by the respective flat mirrors 9, and a polarization beam
splitter 11 which makes laser be linearly polarized as being
placed on the optical path which is defined by the respective
flat mirrors 9. The incident optical system 3 enters the laser
into the three-dimensional optical resonator 4 while adjusting
a polarization face and a beam diameter of the laser emitted
from the laser light source 2.
[0059]
As illustrated in Fig. 2, the three-dimensional optical
resonator 4 includes two ring members 12, 13 which are made of
material being resistant to electron beams and radiation with
a small coefficient of thermal expansion and which is sized to
be capable of being accommodated in a collision chamber arranged
at an emission path of a high-energy electron beam generating
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device, four rod members 14 which are made of material being
resistant to electron beams and radiation with a small
coefficient of thermal expansion and which keep the respective
ring members 12 distanced in parallel by a predetermined distance,
a flat plate 15 which is made of material being resistant to
electron beams and radiation with a small coefficient of thermal
expansion and which is attached to the one ring member 12 as
being inclined 45 degrees clockwise against the horizontal
direction, two reflection mirror holding frames (stages) 16,
17 which are made of material being resistant to electron beams
and radiation with a small coefficient of thermal expansion and
which are attached to round holes formed at the flat plate 15,
a flat plate 18 which is made of material being resistant to
electron beams and radiation with a small coefficient of thermal
expansion and which is attached to the other ring member 13 as
being inclined 45 degrees counterclockwise against the
horizontal direction, and two reflection mirror holding frames
(stages) 19, 20 which are made of material being resistant to
electron beams and radiation with a small coefficient of thermal
expansion and which are attached to round holes formed at the
flat plate 18.
[0060]
Further, the three-dimensional optical resonator 4
includes the flat mirror 21 which has a reflection rate of 0.999
and a transmission factor of 0.001 and which reflects laser from
the other ring member 13 side while causing laser emitted from
the incident optical system 3 to transmit therethrough as being
attached to the reflection mirror holding frame 16 placed at
an entering port for laser emitted from the incident optical
system 3 among the respective reflection mirror holding frames
16, 17, 19, 20; a flat mirror 22 which has a reflection rate
of 0.999 and a transmission factor of 0.001 and which reflects
laser transmitted through the flat mirror 21 and laser reflected
by the flat mirror 21 as being arranged at the reflection mirror
holding frame 19 at the ring member 13 faced to the ring member
12 with the flat mirror 21 arranged among the respective
reflection mirror holding frames 16, 17, 19, 20; a concave mirror
23 which has a reflection rate of 0.999 and a transmission factor
of 0.001 and which reflects laser reflected by the flat mirror
22 and condenses the laser to be 10 gm or smaller in beam size
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at a collision point set on an electron beam path 37 as being
arranged at the reflection mirror holding frame 17 at the ring
member 12 with the flat mirror 21 arranged among the respective
reflection mirror holding frames 16, 17, 19, 20; a concave mirror
24 which has a reflection rate of 0.999 and a transmission factor
of 0.001 and which restores laser collimated by the concave
mirror 23 to parallel laser and returns the laser to the flat
mirror 21 as being arranged at the reflection mirror holding
frame 20 at the ring member 13 faced to the ring member 12 with
the concave mirror 23 among the respective reflection mirror
holding frames 16, 17, 19, 20; and a piezoelectric element 25
which is arranged between the concave mirror 24 and the
reflection mirror holding frame 20 and which adjusts the position
of the concave mirror 24 as being deformed in accordance with
drive voltage supplied from the resonance controller 8.
[0061]
Then, the laser emitted from the incident optical system
3 is introduced and accumulated as being confined in a route
in the order of the flat mirror 21, the flat mirror 22, the concave
mirror 23, the concave mirror 24 and the flat mirror 21 with
selection of right circular polarization or left circular
polarization corresponding to the optical path length adjusted
by the piezoelectric element 25.
[0062]
The resonance monitoring unit 5 includes a flat mirror 26
which reflects laser transmitted through the flat mirror 22 of
the three-dimensional optical resonator 4 and a pin photodiode
27 which receives laser reflected by the flat mirror 26 and which
generates a monitor signal having a voltage value corresponding
to laser strength (a signal indicating strength of laser
resonating in the three-dimensional optical resonator 4). The
resonance monitoring unit 5 generates the monitor signal as
measuring strength of laser transmitted through the flat mirror
22 of the three-dimensional optical resonator 4 and supplies
the signal to the resonance controller 8.
[0063]
The zero-cross feedback signal generator 6 includes a
plurality of flat mirrors 28 which reflect laser transmitted
through the flat mirror 21 out of resonating laser in the
three-dimensional optical resonator 4 and guides the laser to
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a position being apart from the three-dimensional optical
resonator 4 by a predetermined distance, a half-wave plate 29
which adjusts a polarization face of the laser reflected by the
flat mirror 28 of the final stage as being adjusted to form an
attaching angle corresponding to a distance from the
three-dimensional optical resonator 4, a polarization beam
splitter 30 which splits the laser with the polarization face
adjusted by the half-wave plate 29 into P-polarized light and
S-polarized light, a flat mirror 31 which reflects laser of the
S-polarized light side split by the polarization beam splitter
30, a pin photodiode 32 which receives the laser of the
S-polarized light side reflected by the flat mirror 31 and
generates an S-polarized light strength signal indicating laser
strength of the S-polarized light side, a flat mirror 33 which
reflects laser of the P-polarized light side split by the
polarization beam splitter 30, a pin photodiode 34 which receives
the laser of the P-polarized light side reflected by the flat
mirror 33 and generates a P-polarized light strength signal
indicating laser strength of the P-polarized light side, a.
differential amplifier 35 which calculates difference between
the S-polarized light strength signal output from the pin
photodiode 32 and the P-polarized light strength signal output
from the pin photodiode 34 and generates a difference signal,
and a zero-cross determination circuit 36 which generates a
zero-cross feedback signal indicating a result of determination
whether or not zero-crossing occurs at the difference signal
output from the differential amplifier 35, whether zero-crossing
occurs from the plus side to the minus side or from the minus
side to the plus side when zero-crossing occurs, and the like.
The zero-cross feedback signal generator 6 performs introducing
of the laser transmitted through the flat mirror 21 out of the
resonating laser in the three-dimensional optical resonator 4,
splitting of the laser into P-polarized light and S-polarized
light, measuring of strength thereof, obtaining of the
difference value therebetween, generating the zero-cross
feedback signal indicating whether or not zero-crossing occurs
at the difference signal output from the differential amplifier
35, whether zero-crossing occurs from the plus side to the minus
side or from the minus side to the plus side when zero-crossing
occurs, and the like, and supplying the signal to the resonance
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controller 8.
[0064]
The polarization change-over switch 7 generates, based on
settings, an instruction signal to alternately assign right
circular polarization or left circular polarization in
accordance with an instruction signal assigning right circular
polarization (or left circular polarization) or a high frequency
signal output from the high frequency signal generating unit
and supplies the signal to the resonance controller 8.
[0065]
The resonance controller 8 includes a calculation
substrate on which a microprocessor to perform a variety of
calculations, a LSI with a calculating function assembled or
the like is mounted. The resonance controller 8 generates drive
voltage having a ramp-shaped voltage value or a voltage value
required for selecting laser of right circular polarization or
left circular polarization in the three-dimensional optical
resonator 4 based on the instruction signal output from the
polarization change-over switch 7, a monitor signal output from
the resonance monitoring unit 5 and a zero-cross feedback signal
output from the zero-cross feedback signal generator 6, and
supplies the drive voltage to the piezoelectric element 25 of
the three-dimensional optical resonator 4. Thus, the resonance
controller 8 controls the optical path length of the
three-dimensional optical resonator 4 and selectively
accumulates laser of right circular polarization or left
circular polarization into the three-dimensional optical
resonator 4.
[0066]
Next, operation of the polarized laser oscillation system
1 will be described with reference to the schematic structural
view of Fig. 1 and the perspective view of Fig. 2.
[0061]
When an activation switch of the polarized laser
oscillation system 1 is turned on and laser such as CW laser
starts to be emitted from the laser light source 2, the laser
enters to the flat mirror 21 of the three-dimensional optical
resonator 4 with a polarization face and a beam diameter of the
laser adjusted by the incident optical system 3 and the laser
transmitted through the flat mirror 21 is confined in the route
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in the order of the flat mirror 21, the flat mirror 22, the concave
mirror 23, the concave mirror 24 and the flat mirror 21.
[0068]
Further, in parallel to the above operation, the resonance
motoring device 5 generates a monitor signal as measuring
strength of laser transmitted through the flat mirror 22 of the
three-dimensional optical resonator 4 and supplies the signal
to the resonance controller 8.
[0069]
Further, in parallel to the above operation, according to
the zero-cross feedback signal generator 6, the laser
transmitted through the flat mirror 21 is introduced out of the
resonating laser in the three-dimensional optical resonator 4
and is split into P-polarized light and S-polarized light, and
then, strength thereof is measured and a difference value
therebetween is obtained. Subsequently, a zero-cross feedback
signal is generated as determining whether or not zero-crossing
occurs and is supplied to the resonance controller 8.
[0070]
Furthermore, in parallel to the above operation, drive
voltage with a voltage value increased like a ramp-shape is
generated by the resonance controller 8 and is supplied to the
piezoelectric element 25 in the three-dimensional optical
resonator 4, so that the optical path length of the
three-dimensional optical resonator 4 is adjusted.
[0071]
Here, either right circular polarization or left circular
polarization (e.g., right circular polarization) is assigned
with an instruction signal output from the polarization
change-over switch 7. Under the above conditions, when a
zero-cross feedback signal indicating detection of right
circular polarization is generated by the zero-cross feedback
signal generator 6 and a monitor signal indicating that laser
is resonating in the three-dimensional optical resonator 4 is
output from the resonance monitoring unit 5, the resonance
controller 8 fixes the voltage value of the drive voltage as
detecting the above.
[0072]
Accordingly, the optical path length in the
three-dimensional optical resonator 4 is fixed at that time and
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resonance against the laser of right circular polarization is
maintained in the three-dimensional optical resonator 4 for a
specified period.
[0073]
Similar control is performed as well in a case that
high-strength pulse laser generated with mode-locking
oscillation is emitted from the laser light source 2, so that
pulse laser of right circular polarization (high-strength pulse
laser) or pulse laser of left circular polarization
(high-strength pulse laser) resonates and is accumulated in the
three-dimensional optical resonator 4 and the above is
maintained at least for 0.001 sec.
[0074]
Here, a line width of the pulse laser is determined by a
mode-locking oscillation frequency and a time width of the pulse
laser. Further, a beam size of the pulse laser at the collision
point is 10 m or smaller in the three-dimensional optical
resonator 4. Accordingly, as long as the time width of the pulse
laser is-30 psec or shorter, it is possible to set energy strength
at the collision point in the three-dimensional optical
resonator 4 to be 1 mJ/pulse or higher.
[0075]
Similar control is performed as well in a case that an
instruction signal assigning right circular polarization and
left circular polarization alternately is output from the
polarization change-over switch 7, so that pulse laser of right
circular polarization (high-strength pulse laser) and pulse
laser of left circular polarization (high-strength pulse laser)
alternatively resonate and are accumulated in the
three-dimensional optical resonator 4.
[0076]
In this case as well, a line width of the pulse laser is
determined by a mode-locking oscillation frequency and a time
width of the pulse laser. Further, a beam size of the pulse laser
at the collision point is 10 m or smaller in the
three-dimensional optical resonator 4. Accordingly, as long as
the time width of the pulse laser is 30 psec or shorter, it is
possible to set energy strength at the collision point in the
three-dimensional optical resonator 4 to be 1 mJ/pul se or higher.
[0077]
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As described above, in the embodiment, it is possible to
cause laser obtained from the laser light source 2 to resonate
either with right polarization or left polarization as guiding
the laser to the three-dimensional optical resonator 4 and to
easily perform switching only with operation of the polarization
change-over switch 7.
[0078]
Further, in the embodiment, it is possible to cause
high-strength pulse laser obtained from the laser light source
2 to resonate either with right polarization or left polarization
as guiding the laser to the three-dimensional light source 4
and to generate pulse laser having a beam size of 10 gm or smaller
and energy strength of 1 mJ/pulse or higher at the collision
point arranged in the three-dimensional optical resonator 4.
[0079]
Further, in the embodiment, it is possible to cause
high-strength pulse laser having a time width of 30 psec or
shorter obtained from the laser light source 2 to resonate either
with right polarization or left polarization as guiding the laser
to the three-dimensional optical resonator 4 and to generate
pulse laser having a beam size of 10 gm or smaller and energy
strength of 1 mJ/pulse or higher at the collision point arranged
in the three-dimensional optical resonator 4.
[0080]
Furthermore, according to the embodiment, it is possible
to alternatively generate right polarization pulse laser and
left polarization pulse laser having a beam size of 10 gm or
smaller and energy strength of 1 mJ/pulse or higher at the
collision point arranged in the three-dimensional optical
resonator 4 as guiding high-strength pulse laser obtained from
the laser light source 2 to the three-dimensional optical
resonator 4.
[0081]
<Second embodiment>
Fig. 3 is a schematic structural view illustrating an
example of a polarized radiation generation method and a
polarized radiation generating system using the polarized laser
oscillation system 1 illustrated in Fig. 1. In this drawing,
the same numeral is given to a portion corresponding to Fig.
1 or Fig. 2.
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[0082]
A polarized radiation generating system 51 illustrated in
the drawing includes a high frequency signal generating unit
52 which generates a high frequency signal required for
synchronizing the system, a high-energy electron beam generating
unit 53 which includes an accelerator and which emits an electron
beam as accelerating electrons by using high frequency voltage
synchronized with the high frequency signal output from the high
frequency signal generating unit 32, the polarized laser
oscillation system 1 which includes the laser light source, the
mode-locking laser oscillator and the like and which generates
laser obtained with OW oscillation or pulse laser synchronized
with the high frequency signal output from the high frequency
signal generating unit 52, a collision chamber 54 which
accommodates the three-dimensional optical resonator 4
structuring the polarized laser oscillation system 1 so that
collision occurs with collision accuracy of 1 gm or less while
a collision angle between the electron beam emitted from the
high-energy electron beam generating unit 53 and laser in the
three-dimensional optical resonator 4 is in a range from 8 to
20 degrees and which generates radiation with inverse Compton
scattering occurs when collision occurs with the laser in the
three-dimensional optical resonator 4, and a radiation detecting
unit 55 which draws radiation generated at the collision chamber
54 and which measures a radiation amount.
[0083]
Then, high-strength polarization pulse laser which has
left circular polarization characteristics (or left circular
polarization characteristics) having ultrahigh cycling
characteristics of 100 MHz or higher with a pulse time width
of 30 psec or shorter and a beam size of 10 gm or smaller is
generated at the three-dimensional optical resonator 4 of the
polarized laser oscillation system 1 while the high-energy
electron beam generating unit 53 and the polarized laser
oscillation system I are perfectly synchronized owing to the
high frequency signal output from the high frequency signal
generating unit 52. A high-energy electron beam having high
quality characteristics with normalized emittance of 10 mmmrad
or less is emitted from the high-energy electron beam generating
unit 53. Then, the high-energy electron beam and the
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high-strength polarization pulse laser are collided in the
collision chamber 54.
[0084]
With the above, it is possible that ultrashort pulse
polarized radiation having energy of 0.25 keV or higher is
generated with inverse Compton scattering and is guided to the
outside as being drawn by the radiation detecting unit 55 and
that a radiation amount of the radiation guided to the outside
is measured and displayed with an indicator (not illustrated)
or the like.
[0085]
As described above, in the embodiment, ultrashort pulse
polarized radiation can be generated at the collision point
arranged in the three-dimensional optical resonator 4 owing to
collision between the high-energy electron beam emitted from
the high-energy electron beam generating unit 53 and the pulse
laser of right polarization or left polarization with a beam
size of 10 m or smaller and energy strength of 1 mJ/pulse or
higher generated at the collision point in the three-dimensional
optical resonator 4.
[0086]
Further, in the embodiment, ultrashort pulse polarized
radiation having energy of 0.25 keV or higher can be generated
at the collision point arranged in the three-dimensional optical
resonator 4 owing to collision between the high-energy electron
beam having high quality characteristics with normalized
emittance of 10 mmmrad or less emitted from the high-energy
electron beam generating unit 53 and the pulse laser of right
polarization or left polarization with a beam size of 10 m or
smaller and energy strength of 1 mJ/pulse or higher generated
at the collision point in the three-dimensional optical
resonator 4 with a collision angle in a range from 8 to 20 degrees
being close to frontal collision and collision accuracy of 1
m or less.
[0087]
Further, in the embodiment, ultrashort pulse polarized
radiation with characteristics having energy of 0.25 keV or
higher can be generated at the collision point arranged in the
three-dimensional optical resonator 4 owing to coins ion between
the high-energy electron beam having high quality
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characteristics with normalized emittance of 10 mmmrad or less
emitted from the high-energy electron beam generating unit 53
and the high-strength polarization pulse laser having right or
left circular polarization which has ultrahigh cycling
characteristics of 100 MHz or higher with a beam size of 10 m
or smaller and energy strength of 1 mJ/pulse or higher generated
at the collision point in the three-dimensional optical
resonator 4 with a collision angle in a range from 8 to 20 degrees
being close to frontal collision and collision accuracy of 1
m or less.
[0088]
Furthermore, in the embodiment, an X-ray or a 7-ray with
ultrashort pulse polarization having energy of 0.25 keV or higher
can be generated at the collision point arranged in the
three-dimensional optical resonator 4 owing to collision between
the high-energy electron beam having high quality
characteristics with normalized emittance of 10 mmmrad or less
emitted from the high-energy electron beam generating unit 53
and the pulse laser of right polarization or left polarization
with a beam size of 10 m or smaller and energy strength of 1
mJ/pulse or higher generated at the collision point in the
three-dimensional optical resonator 4 with a collision angle
in a range from 8 to 20 degrees being close to frontal collision
and collision accuracy of 1 m or less.
INDUSTRIAL APPLICABILITY
[0089]
The present invention has industrial applicability as
relating to a polarized laser oscillation method, a polarized
radiation generation method, and a device and a system thereof
for a small-sized X-ray source to generate an X-ray using laser
inverse Compton scattering and the like, and in particular,
relating to a polarized laser oscillation method, a polarized
radiation generation method, and a device and a system thereof
being capable of freely selecting right or left circular
polarization.
EXPLANATION OF REFERENCES
[0090]
1: Polarized laser oscillation system
2: Laser light source
3: Incident optical system
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4: Three-dimensional optical resonator
5: Resonance monitoring unit
6: Zero-cross feedback signal generator
7: Polarization change-over switch
8: Resonance controller
9: Flat mirror
10: Collimated lens
11: Polarization beam splitter
12: Ring member
13: Ring member
14: Rod member
15: Flat plate
16: Reflection mirror holding frame
17: Reflection mirror holding frame
18: Flat plate
19: Reflection mirror holding frame
20: Reflection mirror holding frame
21: Flat mirror
22: Flat mirror
23: Concave mirror
24: Concave mirror
25: Piezo element (Piezoelectric element)
26: Flat mirror
27: Pin photodiode
28: Flat mirror
29: Half-wave plate
30: Polarization beam splitter
31: Flat mirror
32: Pin photodiode
33: Flat mirror
34: Pin photodiode
35: Differential amplifier
36: Zero-cross determination circuit
37: Electron beam path
51: Polarized radiation generating system
52: High frequency signal generating unit
53: High-energy electron beam generating unit
54: Collision chamber
55: Radiation detecting unit
27
