CN117968865A - Method and device for improving uniformity of single cross-correlation incident light beam - Google Patents
Method and device for improving uniformity of single cross-correlation incident light beam Download PDFInfo
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- CN117968865A CN117968865A CN202410067799.XA CN202410067799A CN117968865A CN 117968865 A CN117968865 A CN 117968865A CN 202410067799 A CN202410067799 A CN 202410067799A CN 117968865 A CN117968865 A CN 117968865A
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- 238000000034 method Methods 0.000 title claims abstract description 21
- 239000013078 crystal Substances 0.000 claims abstract description 14
- 238000005259 measurement Methods 0.000 claims abstract description 12
- 239000002131 composite material Substances 0.000 claims abstract description 7
- 230000001105 regulatory effect Effects 0.000 claims abstract description 5
- 239000010409 thin film Substances 0.000 claims description 2
- 230000002596 correlated effect Effects 0.000 claims 1
- 230000001276 controlling effect Effects 0.000 abstract description 2
- 238000005070 sampling Methods 0.000 description 12
- 239000013307 optical fiber Substances 0.000 description 9
- 238000010586 diagram Methods 0.000 description 6
- 230000010287 polarization Effects 0.000 description 5
- 230000003287 optical effect Effects 0.000 description 4
- 230000001934 delay Effects 0.000 description 3
- 238000006073 displacement reaction Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 238000007493 shaping process Methods 0.000 description 2
- 229910004261 CaF 2 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000002123 temporal effect Effects 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J11/00—Measuring the characteristics of individual optical pulses or of optical pulse trains
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Abstract
The invention discloses a method and a device for improving uniformity of single cross-correlation incident light beams. Dividing an incident light beam into two sub-beams, carrying out space transverse translation dislocation, and then, overlapping again to form a section of composite light beam in an overlapping area of the two light beams; regulating and controlling the time delay of the two sub-beams to enable the two sub-beams to reach the surface of the measuring crystal at the same time; the relative intensity of the two sub-beams is regulated and controlled, so that the one-dimensional intensity distribution of the synthesized beam is uniform; the width of the uniform region of the synthesized beam is regulated and controlled by using a telescope system, so that the width is not smaller than the effective width of the crystal. The method can be used for a space-time coding single cross correlator, greatly reduces the influence of the space non-uniformity of the incident light beam on the measurement result, and improves the measurement fidelity.
Description
Technical Field
The invention belongs to the technical field of lasers, and particularly relates to a method and a device for improving uniformity of single cross-correlation incident light beams.
Background
The single cross correlator is mainly used for measuring the time domain characteristics of the low-repetition-frequency laser, including pulse width and pulse contrast. In order to realize the single-shot measurement function, the single cross-correlation often adopts a space-time coding principle, namely, the time intensity distribution of the light beam to be measured is converted into the one-dimensional space intensity distribution of the cross-correlation signal, and the one-dimensional space intensity distribution is received by the array detector. For example, in the single cross correlator for measuring the pulse contrast, through the non-collinear cross correlation effect of the light beam to be measured and the sampling light beam with higher contrast in the width direction of the crystal, the relative time delays of the arrival of the light beam to be measured and the sampling light beam at different spatial positions on the width of the crystal are different, so that the sampling detection of the sampling pulse to be measured for different time interval intensity information of the pulse to be measured under single exposure is realized.
In principle, this space-time coded single cross-correlation process requires that the spatial intensity of the incident beam (including the beam to be measured and the sample beam) be uniform in the coded spatial direction, otherwise the spatial intensity distribution of the cross-correlated signal is affected, resulting in distortion of the measurement of the time characteristics. However, the spatial intensity of the laser beam tends to be a non-uniform gaussian distribution, making it difficult to directly enter the single cross-correlation. The common method is to use a part with relatively uniform center as an incident beam of single cross correlation after expanding the Gaussian beam in a large proportion, but the method can cause great energy waste.
In addition, beam shapers based on Diffractive Optical Elements (DOEs) can also convert gaussian beams into flat top beams, but the strong dispersive effects of DOE elements can interfere with the temporal properties of the beam. How to homogenize the one-dimensional spatial intensity of Gaussian beams without disturbing the time information of the pulses is the key to achieve high fidelity single cross-correlation measurement.
Disclosure of Invention
The invention provides a method for improving the uniformity of single cross-correlation incident light beams based on the principle of 'light beam space dislocation superposition', which is universal and flexible and is easy to implement.
The technical scheme of the invention is as follows:
in one aspect, the present invention provides a method for improving uniformity of a single cross-correlated incident beam, the method comprising:
The incident light beam is divided into two sub-light beams, the two sub-light beams are overlapped after space transverse translation dislocation, a section of synthesized light beam is formed in the overlapped area of the two sub-light beams, and meanwhile, the two sub-light beams reach the surface of the crystal to be detected at the same time by regulating and controlling the time delay and the relative intensity of the two sub-light beams, and the one-dimensional intensity distribution of the synthesized light beam is uniform.
On the other hand, the invention also provides a device for improving the uniformity of the single cross-correlated incident beam, which is characterized by comprising a beam splitter, at least two adjusting modules and a beam combiner, wherein the beam splitter splits the incident beam into two sub-beams, and the beam combiner re-superimposes the two sub-beams and forms a composite beam with uniform one-dimensional intensity distribution in a superposition area; the adjusting module adjusts the position and the direction of incidence of the sub-beams to the beam combining lens and the relative time delay of the two sub-beams, so that the two sub-beams are horizontally translated in space and respectively transmitted and reflected by the beam combining lens and then simultaneously reach the surface of the crystal to be detected.
Further, a telescope system is included for adjusting the spot size of the combined beam to meet measurement needs. The telescope system may be omitted if the combined beam size has met the measurement needs.
The device for implementing the method comprises an incident light beam, a beam splitter, an attenuator (optional), a half-wave plate (optional), a reflector, a time delay line, a beam combiner and a telescope system (optional);
Optionally, the beam splitter is a thin film beam splitter or a polarization beam splitter.
Optionally, the adjusting module is a time delay line and a mirror group.
Compared with the prior art, the invention has the beneficial effects that:
1) The applicability is strong, and the wavelength and the pulse width are not depended;
2) The shaping efficiency is high, and is close to 50% when a polarization beam splitter and a polarization beam combiner are adopted;
3) The beam time characteristics are not significantly disturbed while spatially shaping.
Drawings
The above, as well as additional purposes, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description when read in conjunction with the accompanying drawings. Several embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which:
FIG. 1 is a schematic diagram of the principle of beam homogenization by "beam spatial misalignment superposition";
FIG. 2 is a schematic diagram of an apparatus for improving the uniformity of a single cross-correlated incident beam based on the principle of "beam spatial misalignment superposition";
FIG. 3 is a schematic diagram of the optical path of a single cross-correlation in one embodiment of the present invention;
FIG. 4 is a diagram of a spatially homogenized single cross-correlation test beam generated by using the principle of "beam spatial misalignment superposition" according to one embodiment of the present invention;
FIG. 5 is a graph showing a cross-correlation signal generated by homogenizing a light beam to be measured according to one embodiment of the present invention;
Wherein, 1-incident Gaussian beam, 2-beam splitter, 3-sub-beam I, 4-sub-beam II, 5-displacement table, 6-high-reflection mirror I, 7-high-reflection mirror II, 8-high-reflection mirror III, 9-high-reflection mirror IV, 10-high-reflection mirror V;11—high reflection mirror VI;12—beam combining lens; 13—a composite beam; 14—a telescope set; 15-shaped homogenized beam;
Detailed Description
The invention is further illustrated in the following figures and examples, which should not be taken as limiting the scope of the invention.
A method of improving the uniformity of a single cross-correlated incident beam, comprising the steps of:
step one, dividing an incident light beam into two sub-light beams:
dividing an incident light beam into two sub-light beams by using a beam splitter, wherein the intensity of the two sub-light beams can be adjusted through the beam splitting proportion of the beam splitter, and can also be adjusted through an external attenuator after beam splitting;
one or two of the two sub-beams pass through a time delay line, and the relative time delay of the two sub-beams is adjusted;
the two sub-beams pass through a plurality of reflectors and the spatial orientation of the two sub-beams is adjusted;
Step two, spatial dislocation beam combination of two sub-beams:
the two sub-beams are recombined by using a beam combiner;
the two sub-beams are adjusted, so that the centers of the two sub-beams translate a certain distance in a certain space direction;
The two sub-beams are adjusted to be emitted out of the beam splitter in parallel;
the two sub-beams are adjusted to be emitted out of the beam splitter at the same time;
The two sub-beams are adjusted to form a composite beam with uniform one-dimensional spatial intensity distribution in an overlapping area;
Step three, size adjustment of the combined light beam:
the spot size of the synthesized beam is adjusted by utilizing a telescope system, so that the subsequent measurement requirement is met;
the telescope system can be a one-dimensional telescope formed by cylindrical lenses or a two-dimensional telescope formed by round lenses.
The telescope system can be a beam shrinking system, a beam expanding system and a one-dimensional shrinking Shu Lingyi-dimensional beam expanding system; the telescope system may be omitted if the combined beam size has met the measurement needs.
Example 1
As shown in fig. 1, a gaussian beam, having a beam width d (full width at half maximum), is split into two identical sub-beams; translating the transmission shafts of the two sub-beams along the direction of the space x by a certain distance delta x and then superposing the two sub-beams together; in the overlapping area of the two sub-beams, a section of area with the width deltax and the intensity of which is uniformly distributed in one dimension is formed.
A schematic diagram of an apparatus for improving uniformity of a single cross-correlated incident beam, as shown in fig. 2, comprising: the incident Gaussian beam 1 is equally divided into two sub-beams, namely a sub-beam I3 and a sub-beam II 4 by a beam splitter 2; the sub-beam I3 is reflected by the high-reflection mirror I6 and the high-reflection mirror II 7 and then reaches the beam combining mirror 12; the sub-beam II 4 passes through a high-reflection mirror III 8, a high-reflection mirror IV 9, a high-reflection mirror V10 and a high-reflection mirror VI 11 and then reaches a beam combining mirror 12; the high reflection mirror III 8 and the high reflection mirror IV 9 are placed on the displacement stage 5 to constitute a time delay line. Adjusting the time delays of the sub-beam I3 and the sub-beam II 4; the sub-beam I3 is transmitted through the beam combiner 12, and the sub-beam II 4 is reflected through the beam combiner 12; the position and the direction of the incident beam combining lens 12 of the sub beam I are controlled through the high reflecting mirror I6 and the high reflecting mirror II 7; the position and the direction of the incident beam combining lens 12 of the sub-beam II are controlled through the high reflecting mirror V10 and the high reflecting mirror VI 11; the sub-beams I and II are overlapped again with a certain lateral dislocation after passing through the beam combiner 12 to form a composite beam 13, and after passing through the telescope set 14, the shaped homogenized beam 15 is output.
An application embodiment is described below:
The optical path diagram of the single cross correlator using the invention is shown in figure 3: the light source is a titanium sapphire laser with the wavelength of 800nm, the light spot is a Gaussian beam, and the full width at half maximum is 8mm; dividing the light beam into two beams by a beam splitting sheet, wherein one beam is used as light to be detected, and the other beam is used for pumping an optical parametric amplifier OPA to generate clean sampling light with the wavelength of 2042 nm; the light to be measured firstly passes through a half-wave plate to change the polarization direction from horizontal to vertical, and then passes through a telescope system consisting of a concave mirror and a convex mirror to expand to 15mm, and still is Gaussian light. The method of the invention is adopted to homogenize the light beam to be measured: dividing the light to be measured into two sub-beams by using a semi-transparent semi-reflective beam splitter; the sub-beam I is guided to the beam combining lens through the two-sided reflecting mirrors and penetrates through the beam combining lens; the sub-beam II is guided to a beam combining lens through a two-sided reflecting mirror after passing through a time delay line and is reflected on the surface of the beam combining lens; adjusting the time delay line to ensure that the two sub-beams simultaneously exit the beam combining lens; the posture of the reflecting mirror is adjusted, the spatial orientation and the transverse displacement of the two sub-beams passing through the beam combining mirror can be adjusted, and a uniform area is created in the overlapping area of the two beams. The homogenized light beam to be measured is focused into a one-dimensional light spot through a focusing cylindrical lens with the focal length of 200 mm; the CCD is used for measuring the intensity distribution of one-dimensional light spots, and the light intensity distribution of the other path can be obtained independently by shielding one path of light overlapped in a staggered manner. As shown in fig. 4, the light intensity of the individual sub-beam I or sub-beam II is continuously attenuated according to the position change in the x direction; the light intensity of the light beam to be measured homogenized by the method is contributed by the sub-beam I and the sub-beam II, and the relatively uniform light intensity distribution is maintained at a transverse distance of 8 mm.
The nonlinear crystal used in the single cross-correlator shown in FIG. 3 was PPLN, 15mm in size (width). Times.5 mm in length). Times.0.5 mm in thickness, and the polarization period was 5. Mu.m. In order to match the PPLN crystal width, a one-dimensional telescope system is used to perform one-dimensional 1 on the homogenized light beam to be measured: 2, and obtaining a transverse intensity distribution area of 16 mm. The beam to be detected after beam expansion is incident from one side of the width of the crystal through a focusing cylindrical lens with the focal length of 200mm, the sampling beam is incident from one side of the length of the crystal through a CaF 2 spherical lens with the focal length of 150mm, the beam to be detected and the sampling beam perform orthogonal cross-correlation in the crystal, and the generated 575nm related signal has the transverse width of 15mm; the optical fiber array is coupled into the optical fiber array (the transverse width is about 12.5 mm) after passing through an imaging cylindrical lens with the focal length of 75mm and a focusing cylindrical lens with the focal length of 38.1 mm; the optical fiber array comprises 100 optical fibers with different lengths, the lengths of the optical fibers are sequentially increased by 1m from 1 st to 100 th, and signals output by the optical fiber bundles are 100 time serial signals with adjacent time intervals of 5 ns; the detector adopts a photomultiplier, a 580nm narrow-band filter is arranged between the optical fiber bundle and the photomultiplier, and the narrow-band filter is used for eliminating the interference of the space stray light of 800nm light to be detected and 2042nm sampling light on measurement; the output signal of the photomultiplier is input into an oscilloscope for analysis.
The inspection process of the beam space misalignment superposition method using the single cross-correlator shown in fig. 3: the single cross correlator shown in fig. 3 is utilized to carry out cross correlation and frequency summation with sampling light at different transverse positions of the light beam to be detected, the intensity of a generated cross correlation main peak signal is measured, and whether the uniformity of the incident light beam is realized by 'light beam space dislocation superposition' is verified; moving a translation stage of one path of the sampling light to find a cross-correlation main peak signal; increasing or decreasing the time delay between the sampling light and the light beam to be detected, namely changing the transverse space position of the main peak of the sampling light and the light beam to be detected to generate a cross-correlation signal; reading the intensity of the main cross-correlation peak generated under different time delays on the oscilloscope, recording the corresponding optical fiber serial number, and scanning the main cross-correlation peak at the position of the full window; the cross-correlation main peak signal intensity generated by the light of the other path can be obtained by shielding the light of the staggered and overlapped path respectively; the measurement result is shown in fig. 5, and the cross-correlation signal is imaged to 90 optical fibers (from 7 to 96) in a full window; the intensity of the cross correlation main peak after the 'light beam space dislocation superposition' method is kept relatively stable in the whole transverse space of the crystal; the intensity distribution of the main peak of the cross correlation generated by the independent sub-beams I and II is consistent with the intensity distribution of the light beam to be measured in FIG. 4, and the light beam to be measured respectively attenuates along the opposite directions along with the change of the transverse distance; the beam space dislocation superposition realizes the uniformity of the incident beam, can be used for a high-fidelity single cross-correlation measuring device, and proves the effectiveness and the accuracy of the method.
Claims (5)
1. A method for improving uniformity of a single cross-correlated incident beam, the method comprising:
The incident light beam is divided into two sub-light beams, the two sub-light beams are overlapped after space transverse translation dislocation, a section of synthesized light beam is formed in the overlapped area of the two sub-light beams, and meanwhile, the two sub-light beams reach the surface of the crystal to be detected at the same time by regulating the time delay and the relative intensity of the two sub-light beams, and the light beams with uniform one-dimensional intensity distribution are synthesized.
2. The device for improving the uniformity of the single cross-correlation incident light beam is characterized by comprising a beam splitter, at least two adjusting modules and a beam combiner, wherein the beam splitter divides the incident light beam into two sub-light beams, and the beam combiner re-superimposes the two sub-light beams and forms a composite light beam with uniform one-dimensional intensity distribution in a superposition area; the adjusting module adjusts the position and the direction of incidence of the sub-beams to the beam combining lens and the relative time delay of the two sub-beams, so that the two sub-beams are horizontally translated in space and respectively transmitted and reflected by the beam combining lens and then simultaneously reach the surface of the crystal to be detected.
3. The apparatus for improving the uniformity of a single correlated incident beam of claim 2, further comprising a telescopic system for adjusting the spot size of the composite beam to meet measurement requirements.
4. The apparatus for improving the uniformity of a single cross-correlated incident beam of claim 2, wherein the beam splitter is a thin film beam splitter or a polarizing beam splitter.
5. The apparatus for improving the uniformity of a single cross-correlated incident beam of claim 2, wherein the adjustment module is a time delay line and mirror set.
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| CN202410067799.XA CN117968865A (en) | 2024-01-17 | 2024-01-17 | Method and device for improving uniformity of single cross-correlation incident light beam |
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| CN202410067799.XA CN117968865A (en) | 2024-01-17 | 2024-01-17 | Method and device for improving uniformity of single cross-correlation incident light beam |
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