CN117526066A - High-energy ultrafast laser device and working method - Google Patents
High-energy ultrafast laser device and working method Download PDFInfo
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
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Abstract
The invention provides a high-energy ultrafast laser device and a working method thereof, comprising the following steps: the device comprises a seed laser, a regenerative amplifier, a traveling wave amplifier, a side pumped main amplifier and a synchronous signal controller; the invention utilizes Nd-YVO 4 The stimulated Raman scattering effect in the crystal amplification process amplifies and shapes laser into hollow distribution, and the regeneration amplification technology, the circular polarization amplification technology, the divergent beam amplification technology and the thermally induced birefringence compensation technology are used in a matched mode, so that damage to an optical element and a small-scale self-focusing effect during high-peak power amplification are avoided, and finally ultrafast laser output with high energy and good beam quality and stability is realized. The invention provides an alternative scheme of the traditional technology, and makes up the defects of the prior art; meanwhile, the invention makes the high-energy ultrafast laser system simplerThe device has lower manufacturing cost, higher reliability and efficiency, and is more beneficial to engineering design.
Description
Technical Field
The invention relates to the technical field of high-energy ultrafast lasers, in particular to a high-energy ultrafast laser device and a working method thereof.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
In recent years, the development of ultra-short pulse laser technology has a great pushing effect on the development of precision material processing, scientific research, medical equipment and military national defense. The ultra-fast laser with high repetition frequency and high peak power is an excellent light source in the fields of material cold working, optical parameter chirped pulse amplification, ultra-remote laser ranging, ultraviolet light generation, terahertz generation and the like.
Laser radiation of high beam quality, high repetition frequency, high peak power and short pulse duration can be obtained with a main oscillation-power amplification system. However, optical element damage and small-scale self-focusing effects caused by high peak power densities are major obstacles to further increasing the ultrashort pulse energy and repetition frequency of the main oscillation-power amplification scheme. The small-scale self-focusing effect can lead to the degradation of the quality of the light beam, the change of the light beam distribution and the damage of the laser rod, and limits the application of the high-energy ultrashort pulse laser.
In order to avoid damage to optical elements and small-scale self-focusing effects at high peak power densities, chirped pulse amplification is widely used because of its strength-reducing effect during amplification. However, yb-YAG laser systems employing chirped pulse amplification techniques are more complex and expensive due to their large footprint, optical losses of grating-based stretcher and compressor, and the need for cryocooling to shift the medium from a quasi-three energy level to a more advantageous four-energy level system. Bulk material laser systems generally have higher efficiency and simpler construction, making them attractive in many applications.
Currently, in bulk material high energy laser amplifiers, the possibility of small scale self-focusing is typically reduced by means of soft side aperture in combination with relay imaging and spatial filters. Firstly, a soft-side aperture is utilized to select a uniform part of a beam to realize flat-top distribution of laser; and then adopting a relay imaging system to transfer and image the flat-top beam, and setting a pinhole at the focus of the relay imaging device to realize spatial filtering. However, structures with soft-sided apertures may result in frequent replacement of devices during long-term operation, and the device may cause significant energy loss, reducing system efficiency. At the same time, multiple relay imaging systems and vacuum tubes for preventing air breakdown at their focal points would increase the size, complexity and cost of the laser system. The space filter has more limiting conditions on the small holes, has high requirements on the directivity of the light beams and is not beneficial to engineering design.
Disclosure of Invention
Aiming at the defects existing in the current high-energy ultrafast laser amplification technology, the invention provides a high-energy ultrafast laser device based on stimulated Raman scattering to inhibit the small-scale self-focusing effect and a working method thereof, and YVO is adopted through Nd 4 The stimulated Raman scattering effect in the crystal amplification process is used for amplifying and shaping laser into hollow distribution, and the regenerative amplification technology, the circular polarization amplification technology, the divergent beam amplification technology and the thermally induced birefringence compensation technology are used in combination, so that the damage of an optical element and the small-scale self-focusing effect during high-peak power amplification are avoided, and finally, the ultrafast laser output with high energy and good beam quality and stability is realized; meanwhile, the invention simplifies and miniaturizes the high-energy ultrafast laser system, has higher reliability and efficiency, and is more beneficial to engineering design.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
in a first aspect, the present invention provides a high energy ultrafast laser device.
A high energy ultrafast laser device, comprising: the synchronous signal controller is respectively connected with the seed laser, the regenerative amplifier, the traveling wave amplifier and the side pumping main amplifier;
a synchronization signal controller configured to at least: the method comprises the steps of taking a mode locking synchronous signal output by an optical fiber mode locking seed source in a synchronous seed laser as a clock reference signal, taking a frequency division synchronous signal output by an acousto-optic menu module in the synchronous seed laser as an external trigger signal and generating a plurality of paths of trigger signals, wherein the plurality of paths of trigger signals are used for providing pulse synchronous signals for the regenerative amplifier, the traveling wave amplifier and the side pumping main amplifier.
As a further limitation of the first aspect of the present invention, the seed laser includes an optical fiber mode-locking seed source and an acousto-optic menu module, the optical fiber mode-locking seed source is used for generating high-reliability ultrafast laser seed light, a part of light splitting of the seed source is sampled and amplified by a photoelectric detector and then outputs a mode-locking synchronization signal, and the acousto-optic menu module is used for dividing frequency of the mode-locking seed laser and outputting a frequency division synchronization signal.
As a further definition of the first aspect of the invention, a regenerative amplifier is used to pre-amplify the seed laser of several nJ levels of energy to several mJ levels of energy.
As a further limitation of the first aspect of the present invention, the traveling wave amplifier comprises a gain crystal, a first beam shaping system, a pumping system and a second dichroic mirror, wherein the gain crystal is Nd: YVO 4 And the crystal is used for expanding and collimating the pulse laser output by the regenerative amplifier by the first beam shaping system.
As a further limitation of the first aspect of the present invention, the pump system includes a pump source, a pump shaping system and a first dichroic mirror, wherein the pump source is used for providing pump energy for the gain crystal, the synchronization signal controller is used for providing a pulse synchronization signal, the pump shaping system is used for shaping pump light into a required size, and the pump light enters the gain crystal through the first dichroic mirror after being shaped by the pump shaping system, so as to provide pump energy for the gain crystal.
As a further limitation of the first aspect of the present invention, the second dichroic mirror is used for separating the fundamental light, the raman light and the pump light, and the second dichroic mirror is coated with a high reflection film of the fundamental light, the raman light and the pump light.
As a further limitation of the first aspect of the present invention, the side pumped main amplifier comprises a second beam shaping system, a first optical isolation system, a first thin film polarizer, a first quarter wave plate, a first side pump module, a first thermal compensation mirror, a first faraday rotator, a first 0 ° total reflection mirror, a second beam shaping system, a second optical isolation system, a second thin film polarizer, a second quarter wave plate, a second side pump module, a second thermal compensation mirror, a third side pump module, a second faraday rotator, and a second 0 ° total reflection mirror, which are sequentially arranged along the optical path.
As a further limitation of the first aspect of the present invention, the first optical isolation system and the second optical isolation system are used for preventing the amplified return light from damaging the front optical element, the second beam shaping system is used for collimating the output laser beam of the traveling wave amplifier to match the size of the aperture of the first side pump module, and the first film polarizer and the second film polarizer are used for outputting the amplified return light;
the first quarter wave plate and the second quarter wave plate are used for reducing nonlinear interaction of laser in the gain medium and other optical elements so as to avoid damage to the optical elements and small-scale self-focusing effect.
As a further limitation of the first aspect of the present invention, the first side pump module, the second side pump module and the third side pump module all use a large-caliber Nd: YAG crystal as a laser gain medium, the pumping wavelength is 808nm, and the pulse synchronization signal is provided by the synchronization signal generator;
the first thermal compensation mirror and the second thermal compensation mirror are used for compensating a thermal lens effect of the side pump module under high-power operation so as to avoid damage to optical elements caused by undersize light spots;
the first Faraday rotator and the second Faraday rotator are used for compensating thermal depolarization of the Nd-YAG crystal, and the first 0-degree total reflection mirror and the second 0-degree total reflection mirror are used for reflecting fundamental frequency light after single-pass amplification so as to realize double-pass amplification.
In a second aspect, the present invention provides a method of operating a high energy ultrafast laser device.
A method of operating a high energy ultrafast laser device, comprising the steps of:
mode locking pulse laser output from an optical fiber mode locking seed source firstly passes through an acousto-optic menu module to perform menu frequency reduction to obtain pulse laser with required heavy frequency, the selected pulse laser with heavy frequency then enters a regenerative amplifier to be preamplified, the seed light with nJ level energy is amplified to mJ level, and higher beam quality is realized based on the characteristic of independent cavity formation of regenerative amplification;
the laser output from the regenerative amplifier enters the traveling wave amplifier and sequentially passes through a first beam shaping system, a first dichroic mirror, a gain crystal and a second dichroic mirror; the first beam shaping system expands and collimates the pulse laser output by the regenerative amplifier, and the first beam shaping system changes the size of the collimated beam so as to control the laser intensity;
the shaped light beam is reflected by a first dichroic mirror, enters a gain crystal for amplification, and a part with higher intensity of the center of the light beam is subjected to higher stimulated Raman scattering conversion in a Raman crystal to realize the intensity distribution of a flat-top or hollow fundamental frequency light beam, and the light beam is split by a second dichroic mirror after passing through the gain crystal, wherein the fundamental frequency light beam is highly reflected, and the Raman light beam and the pump light are highly transmitted;
the amplified light subjected to the shaping of the laser Raman scattering effect enters a main amplifier of a side pump, passes through a first optical isolation system and a second optical beam shaping system, wherein the second optical beam shaping system expands and collimates a beam into a size matched with the caliber of a first side pump module, and the expanded and collimated beam passes through a first film polarizer in a horizontal polarization state, is converted into a circular polarization state through a first quarter wave plate and enters the first side pump module;
the thermal lens and the thermally induced depolarization effect generated under the high-power operation of the first side pump module are respectively compensated by a first thermal compensation mirror and a first Faraday rotator of a double-pass structure, the single-pass amplified fundamental frequency light is reflected by a first 0-degree total reflection mirror to realize double-pass amplification, the amplified light in a circular polarization state is changed into a vertical polarization state after passing through a first quarter wave plate for the second time, and the amplified light is reflected and output by a first film polaroid and enters the next amplification stage;
the amplifying stage formed by the second side pump module and the third side pump module is similar to that of the first side pump module, but the caliber of the side pump module and the size of the incident beam are gradually increased, and the high-energy ultrafast laser based on the stimulated Raman scattering restraining small-scale self-focusing effect is output from the second film polaroid.
Compared with the prior art, the invention has the beneficial effects that:
at present, a method of combining soft-edge aperture with relay imaging and a spatial filter is generally adopted in a high-energy ultrafast laser amplification technology to inhibit a small-scale self-focusing effect, so that damage to an optical element and degradation of beam quality are avoided, however, the method has a plurality of inherent defects, and mainly comprises the following steps: (1) The structure with the soft-edge aperture has large energy loss and low system efficiency, and can cause frequent replacement of devices when working for a long time; (2) Multiple relay imaging systems and vacuum tubes to prevent air breakdown at their focal points would increase the size, complexity and cost of the laser system; (3) The small hole of the spatial filter has more limiting conditions and higher requirements on the directivity of the light beam, which is not beneficial to engineering design;
the invention aims to solve the problems existing in the current high-energy ultrafast laser amplification technology and utilizes Nd: YVO 4 The stimulated Raman scattering effect in the crystal amplification process is used for amplifying and shaping laser into hollow distribution, and the regenerative amplification technology, the circular polarization amplification technology, the divergent beam amplification technology and the thermally induced birefringence compensation technology are used in combination, so that the damage of an optical element and the small-scale self-focusing effect during high-peak power amplification are avoided, and finally, the ultrafast laser output with high energy and good beam quality and stability is realized; the invention provides an alternative scheme of the traditional technology, and makes up the defects of the prior art; meanwhile, the invention simplifies and miniaturizes the high-energy ultrafast laser system, and has lower cost, higher reliability and efficiency, and better performanceIs beneficial to engineering design.
Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a graph showing the intensity distribution of a light beam after a small-scale self-focusing effect is generated in the strong laser amplification process according to embodiment 1 of the present invention;
fig. 2 is a schematic structural diagram of a high-energy ultrafast laser device according to embodiment 1 of the present invention;
FIG. 3 is a graph showing the intensity distribution of the light beam after being amplified and shaped into a hollow space by using the stimulated Raman scattering effect according to the embodiment 1 of the present invention;
FIG. 4 is a graph showing the far field intensity distribution of an infrared ultrafast laser at energy output of hundred mJ according to example 1 of the present invention;
1, a seed laser; 2. a regenerative amplifier; 301. a first beam shaping system; 302. a first 45 ° total reflection mirror; 303. a first dichroic mirror; 304. a pump light shaping system; 305. a pump source; 306. a gain crystal; 307. a second dichroic mirror; 401. a second beam shaping system; 402. a second 45 ° total reflection mirror; 403. a first optical isolation system; 404. a first thin film polarizer; 405. a first quarter wave plate; 406. a first side pump module; 407. a first thermal compensation mirror; 408. a first Faraday rotator; 409. a first 0 ° total reflection mirror; 501. a third 45 ° total reflection mirror; 502. a third beam shaping system; 503. a second optical isolation system; 504. a fourth 45 ° total reflection mirror; 505. a fifth 45 ° total reflection mirror; 601. a second thin film polarizer; 602. a second quarter wave plate; 603. a second side pump module; 604. a second thermal compensation mirror; 605. a third side pump module; 606. a second Faraday rotator; 607. a second 0 total reflection mirror.
Detailed Description
The invention will be further described with reference to the drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Embodiments of the invention and features of the embodiments may be combined with each other without conflict.
Example 1:
as shown in fig. 1, to avoid the small-scale self-focusing effect generated during the strong laser amplification and solve the defects existing in the current large-energy ultrafast amplification technology, the present invention proposes a large-energy ultrafast laser for suppressing the small-scale self-focusing effect by using the stimulated raman scattering effect during the amplification, as shown in fig. 2, including: seed laser 1, regenerative amplifier 2, traveling wave amplifier, side pumped main amplifier and synchronous signal controller.
The seed laser 1 comprises an optical fiber mode locking seed source and an acousto-optic menu module; the optical fiber mode locking seed source is used for providing high-reliability ultrafast laser seed light, and part of light of the seed source is sampled and amplified by the photoelectric detector and then outputs a mode locking synchronous signal; the acousto-optic menu module is used for dividing the frequency of the mode locking seed laser and outputting a frequency division synchronous signal.
In this embodiment, preferably, the repetition frequency of the optical fiber mode locking seed source is 30MHz, the pulse energy is 1nJ, the pulse width is 100ps, the center wavelength is 1064.3nm, and the mode locking synchronization signal of 30MHz is output.
In this embodiment, preferably, the acousto-optic menu module divides the frequency of the mode-locked seed laser to 1kHz or less, and outputs a corresponding frequency division synchronization signal.
The regenerative amplifier 2 is used for realizing high-gain pre-amplification of seed laser, and the pumping sources in the regenerative amplifier are synchronously pumped by pulse and are identicalThe step signal controller provides a pulse synchronization signal. The pulse synchronous pumping mode can greatly reduce the thermal effect of the gain crystal, and the characteristics of the independent cavity formation of the regenerative amplification can output good beam quality. By controlling the electro-optical switch in the regenerative amplifier, the selected seed light is continuously regenerated, oscillated and amplified in the regenerative amplifying cavity, the high voltage is removed when the highest gain is realized, the pulse laser output is regenerated and amplified, and the energy gain can reach 5 multiplied by 10 6 The seed laser of 1nJ was amplified to several mJ orders of magnitude.
The traveling wave amplifier is used for further amplifying Gaussian beams output by the regenerative amplifier, and amplifying and shaping the beams into hollow distribution by utilizing the stimulated Raman scattering effect of the gain crystal. The traveling wave amplifier includes a first beam shaping system 301, a first 45 ° total reflection mirror 302, a first dichroic mirror 303, a pump light shaping system 304, a pump source 305, a gain crystal 306, and a second dichroic mirror 307, which are disposed in this order according to the propagation path of light.
In this embodiment, the gain crystal 306 is preferably Nd/YVO 4 Crystal, nd: YVO 4 Is a stimulated raman scattering crystal. The stimulated Raman scattering is a third-order nonlinear optical effect and passes YVO 4 The stimulated raman scattering process of the crystal, 1064nm fundamental light will be converted into raman light consisting of different stokes waves, the first stokes wave λ=1176 nm, having a power gain G, where the power gain G satisfies the relationship g=gril, where gR is the raman gain, I is the amplified fundamental light intensity, and L is the length of the nonlinear raman medium. The first Stokes wavelength beam will appear at a G of 25-30, and the Raman medium Nd: YVO used in the invention 4 The Raman gain gR of (2) is 16.13cm/GW, so that when IL is more than or equal to 1.55GW/cm, nd: YVO 4 The raman power gain of the crystal will be above the stimulated raman scattering threshold and a first stokes wave will be generated.
In this embodiment, preferably, the first beam shaping system 301 is configured to expand and collimate the pulse laser output by the regenerative amplifier, and is composed of a plano-concave lens and a plano-convex lens, and since the stokes wave power gain G of the raman light is proportional to the laser intensity, the laser intensity is changed by changing the size of the collimated beam by the first beam shaping system, so that the portion with higher beam center intensity is higher than the stimulated raman scattering threshold, thereby realizing stronger stimulated raman scattering conversion, and finally realizing flat-top or hollow fundamental frequency beam intensity distribution.
In this embodiment, preferably, the fundamental frequency light beam collimated by the first beam shaping system 301 is reflected by the first 45 ° total reflection mirror 302 and the first dichroic mirror 303 and enters the gain crystal 306.
In this embodiment, the pump source 305 is preferably configured to provide pump energy to the gain crystal 306, and the synchronization signal controller provides a pulse synchronization signal, so that the pump source 305 in one embodiment of the present invention outputs pump light with a center wavelength of 808nm, a peak power of 200W, and a pulse width of 100 μs. The pump light is shaped to a desired size by a pump light shaping system 304, and enters a gain crystal 306 through the first dichroic mirror 303, providing pump energy to the gain crystal 306.
The fundamental frequency light amplified by the gain crystal 306 is separated from the generated raman light at the second dichroic mirror 307, and the second dichroic mirror 307 is coated with a fundamental frequency light highly reflective film, a raman light, and a pump light highly transmissive film.
As shown in fig. 3, the stimulated raman scattering effect is utilized to amplify and reshape the light beam into a hollow intensity distribution map, and the hollow light beam intensity distribution is filled in the amplifying process of the subsequent stage due to stronger amplifying capability of the center of the subsequent main amplifier module, so that the small-scale self-focusing effect of overhigh light beam center intensity as shown in fig. 1 is avoided. In one embodiment of the present invention, the fundamental light energy amplified by the gain crystal 306 is amplified from a few mJ to a dozen mJ while maintaining a hollow beam intensity distribution.
The side pumped main amplifier of the present invention is used for further amplifying the hollow beam output by the traveling wave amplifier, and comprises a second beam shaping system 401, a second 45 ° total reflection mirror 402, a first optical isolation system 403, a first thin film polarizer 404, a first quarter wave plate 405, a first side pump module 406, a first thermal compensation mirror 407, a first faraday rotator 408, a first 0 ° total reflection mirror 409, a third 45 ° total reflection mirror 501, a third beam shaping system 502, a second optical isolation system 503, a fourth 45 ° total reflection mirror 504, a fifth 45 ° total reflection mirror 505, a second thin film polarizer 601, a second quarter wave plate 602, a second side pump module 603, a second thermal compensation mirror 604, a third side pump module 605, a second faraday rotator 606, and a second 0 ° total reflection mirror 607, which are sequentially arranged according to the propagation path of light.
The second beam shaping system 401 is used for expanding and collimating the output laser beam of the traveling wave amplifier into a size matched with the caliber of the first side pump module, so that the damage of the side pump module crystal caused by too small beam is avoided, and the extraction efficiency of the amplified light on the energy storage of the side pump module is improved. The laser beam collimated by the second beam shaping system 401 is reflected by the second 45 ° total reflection mirror 402 and enters the first optical isolation system 403. The first optical isolation system 403 is composed of two half-wave plates and an isolator, and is used for preventing the return light amplified by the main amplifier from damaging the optical elements in the traveling wave amplifier.
The light beam passes through a second half-wave plate in the first light isolation system 403 and then becomes horizontally polarized and passes through the first thin film polarizer 404. The first thin film polarizer 404 is placed at brewster's angle, transmits laser light in a horizontal polarization state, and reflects laser light in a vertical polarization state. After passing through the first quarter waveplate 405, the light beam becomes circularly polarized. The quarter wave plate 405 serves to reduce the nonlinear interaction of the laser light in the gain medium and other optical elements because the nonlinear interaction of circularly polarized light is 1.5 times weaker than linearly polarized light, thereby avoiding optical element damage and small scale self-focusing effects.
The circularly polarized light beam after passing through the first quarter wave plate 405 enters the first side pump module 406 for single pass amplification. The first side pump module 406 used in one embodiment of the present invention pumps 808nm in wavelength, 4000W in peak power, and 230 mus in pulse width, and the pulse synchronization signal is provided by a synchronization signal generator. The gain crystal used in the first side pump module 406 was a 7mm diameter Nd: YAG rod, cooled with circulating water at 20 ℃.
The first thermal compensation mirror 407 of the present invention is used to compensate for thermal lens effects of the first side pump module 406 under high power operation, and avoid damage to the optical elements caused by undersize light spots. The first thermally compensating mirror 407 employed in one embodiment of the invention is a plano-concave lens with a focal length f of-500 mm.
The first faraday rotator 408 of the present invention is used to compensate for thermally induced depolarization of the Nd: YAG crystal in the first side pump module 406. The thermally induced depolarization is due to the high power pumping of the first side pump module 406 to heat the laser crystal, coupled with the cooling of the crystal rod surface, resulting in an uneven internal temperature distribution of the crystal rod, resulting in thermal stress induced birefringence with radial and tangential principal axes. As linearly polarized light passes through the crystal rod, the radial and tangential components experience different phase delays, resulting in significant thermally induced depolarization. When the beam is rotated twice through the same laser crystal path with the first faraday rotator 408 at a polarization of 90 °, both radial and tangential polarizations will travel the same path length, which compensates for the thermally induced birefringence effect. The first faraday rotator 408 employed in one embodiment of the present invention is 45 ° rotated in polarization and the beam is reflected by the first 0 ° total reflection mirror 409, twice rotated by 90 ° in polarization by the first faraday rotator 408, and enters the first side pump module 406 for two-pass amplification. This compensation reduces the thermally induced depolarization component from 25% to 3% and greatly suppresses the loss of thermally induced depolarization of the first side pump module 406.
The circularly polarized light amplified by the first side pump module 406 is changed into a vertical polarization state by the first quarter wave plate 405 for the second time, and is reflected and output by the first thin film polarizer 404. In one embodiment of the present invention, the fundamental light energy amplified by the first side pump module 406 in a double pass is amplified from tens of mJ to tens of mJ.
The amplified light output by the reflection of the first thin film polarizer 404 is reflected by the third 45 ° total reflection mirror 501, and sequentially passes through the third beam shaping system 502 and the second optical isolation system 503. The third beam shaping system 502 is configured to collimate the laser beam amplified by the first side pump module 406 to match the sizes of the apertures of the second side pump module 603 and the third side pump module 605; the second optical isolation system 503 is used to prevent the amplified return light from the second side pump module 603 and the third side pump module 605 from damaging the optical elements of the first side pump module 406. The light beam passes through the second thin film polarizer 601 in a horizontally polarized posture after being reflected by the fourth 45 ° total reflection mirror 504 and the fifth 45 ° total reflection mirror 505 in this order, and becomes a circular polarized state after passing through the second quarter wave plate 602. The second quarter wave plate 602 also serves to reduce nonlinear interactions of the laser light in the gain medium and other optical elements, thereby avoiding optical element damage and small scale self-focusing effects.
The circularly polarized light beam passing through the second quarter wave plate 602 enters the second side pump module 603 and the third side pump module 605 for single pass amplification. The second side pump module 603 and the third side pump module 605 employed in one embodiment of the present invention pump 808nm in wavelength, 5600W peak power, and 230 mus pulse width, and the pulse synchronization signal is provided by a synchronization signal generator. The gain crystals used in the second side pump module 603 and the third side pump module 605 are Nd-YAG rods with diameters of 15mm, and circulating water at 20 ℃ is used for cooling.
Similar to the first side pump module 406 amplification stage, the second side pump module 603 and the third side pump module 605 amplification stage also employ a second thermal compensation mirror 604 and a second faraday rotator 606 for compensating thermal lenses and thermally induced birefringence effects, respectively. The final amplified light is reflected out of the second thin film polarizer 601 in a vertically polarized attitude. In one embodiment of the present invention, the fundamental frequency light energy amplified by the second side pump module 603 and the third side pump module 605 in a double pass manner is amplified from tens of mJ to hundreds of mJ, and fig. 4 is a diagram showing a far field intensity distribution of the light beam of the infrared ultrafast laser according to one embodiment of the present invention when the infrared ultrafast laser outputs energy in hundreds of millijoules.
Example 2:
embodiment 2 of the present invention provides a working method of the high-energy ultrafast laser device of embodiment 1, comprising the following steps: :
mode locking pulse laser output from an optical fiber mode locking seed source firstly passes through an acousto-optic menu module to perform menu frequency reduction to obtain pulse laser with required repetition frequency;
the selected seed light then enters a regenerative amplifier 2 for pre-amplification, the seed light with nJ level energy is amplified to mJ level, and the energy gain is as high as 10 6 The method is double, and based on the characteristic of independent cavity formation of regeneration amplification, good beam quality can be realized;
the laser light output from the regenerative amplifier 2 enters the traveling wave amplifier, and sequentially passes through a first beam shaping system 301, a first 45 ° total reflection mirror 302, a first dichroic mirror 303, a gain crystal 306 and a second dichroic mirror 307; wherein the first beam shaping system 301 expands and collimates the pulse laser output by the regenerative amplifier 2, and the first beam shaping system 301 changes the size of the collimated beam so as to control the laser intensity; the shaped beam is reflected by the first dichroic mirror 303, enters the gain crystal 306 for amplification, and the part with higher intensity of the beam center obtains higher stimulated Raman scattering conversion in the Raman crystal, so that the intensity distribution of the flat-top or hollow fundamental frequency beam is finally realized; the light beam after passing through the gain crystal 306 is split by a second dichroic mirror 307, and the second dichroic mirror 307 has high reflection to the fundamental frequency light, and high transmission to the raman light and the pump light;
the amplified light shaped by the laser raman scattering effect enters the main amplifier of the side pump, and firstly passes through a second beam shaping system 401 and a first optical isolation system 403, wherein the second beam shaping system 401 expands and collimates the light beam to be matched with the size of the caliber of the first side pump module 406; the beam after beam expansion collimation passes through the first film polaroid 404 in a horizontal polarization state, is converted into a circular polarization state by the first quarter wave plate 405 and enters the first side pump module 406; the thermal lens and the thermally depolarization effect generated by the first side pump module 406 under high power operation are respectively compensated by the first thermal compensation mirror 407 and the first faraday rotator 408 with double-pass structures, the first 0 ° total reflection mirror 409 reflects the fundamental frequency light after single-pass amplification to realize double-pass amplification, the amplified light with the circular polarization state after passing through the first quarter wave plate 405 for the second time is changed into a vertical polarization state, and the vertical polarization state is reflected and output by the first film polarizer 404 and enters the next amplification stage; the amplification stage of the second side pump module 603 and the third side pump module 605 is similar to that of the first side pump module 406, except that the caliber of the side pump module and the size of the incident beam are gradually increased;
finally, a large-energy ultrafast laser suppressing the small-scale self-focusing effect based on stimulated raman scattering is output from the second thin film polarizer 601.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A high-energy ultrafast laser device is characterized in that,
comprising the following steps: the synchronous signal controller is respectively connected with the seed laser, the regenerative amplifier, the traveling wave amplifier and the side pumping main amplifier;
a synchronization signal controller configured to at least: the method comprises the steps of taking a mode locking synchronous signal output by an optical fiber mode locking seed source in a synchronous seed laser as a clock reference signal, taking a frequency division synchronous signal output by an acousto-optic menu module in the synchronous seed laser as an external trigger signal and generating a plurality of paths of trigger signals, wherein the plurality of paths of trigger signals are used for providing pulse synchronous signals for the regenerative amplifier, the traveling wave amplifier and the side pumping main amplifier.
2. A high energy ultrafast laser device, as recited in claim 1, wherein,
the seed laser comprises an optical fiber mode locking seed source and an acousto-optic menu module, wherein the optical fiber mode locking seed source is used for generating high-reliability ultrafast laser seed light, a part of light of the seed source is sampled and amplified by the photoelectric detector and then outputs a mode locking synchronous signal, and the acousto-optic menu module is used for dividing the frequency of the mode locking seed laser and outputting a frequency dividing synchronous signal.
3. A high energy ultrafast laser device, as recited in claim 1, wherein,
the regenerative amplifier is used to pre-amplify seed lasers of several nJ levels of energy to several mJ levels of energy.
4. A high energy ultrafast laser device, as recited in claim 1, wherein,
the traveling wave amplifier comprises a gain crystal, a first beam shaping system, a pumping system and a second dichroic mirror, wherein the gain crystal is Nd:YVO 4 And the crystal is used for expanding and collimating the pulse laser output by the regenerative amplifier by the first beam shaping system.
5. A high energy ultrafast laser device, as recited in claim 4, wherein,
the pumping system comprises a pumping source, a pumping light shaping system and a first dichroic mirror, wherein the pumping source is used for providing pumping energy for the gain crystal, the synchronous signal controller is used for providing a pulse synchronous signal, the pumping light shaping system is used for shaping the pumping light into a required size, and the pumping light enters the gain crystal through the first dichroic mirror after being shaped by the pumping light shaping system, so as to provide pumping energy for the gain crystal.
6. A high energy ultrafast laser device, as recited in claim 4, wherein,
the second dichroic mirror is used for separating fundamental frequency light, raman light and pump light, and is plated with a high-reflection film of the fundamental frequency light, a high-transmission film of the Raman light and the pump light.
7. A high-energy ultrafast laser device, as recited in any one of claims 1-6, wherein,
the side-pumped main amplifier comprises a second beam shaping system, a first optical isolation system, a first thin film polarizer, a first quarter wave plate, a first side pump module, a first thermal compensation mirror, a first Faraday rotator, a first 0-degree total reflection mirror, a second beam shaping system, a second optical isolation system, a second thin film polarizer, a second quarter wave plate, a second side pump module, a second thermal compensation mirror, a third side pump module, a second Faraday rotator and a second 0-degree total reflection mirror which are sequentially arranged along an optical path.
8. A high energy ultrafast laser device, as recited in claim 7, wherein,
the first optical isolation system and the second optical isolation system are used for preventing the amplified return light from damaging the front optical element, the second beam shaping system is used for collimating the output laser beam of the traveling wave amplifier into a size matched with the caliber of the first side pump module, and the first thin film polaroid and the second thin film polaroid are used for outputting the amplified return light;
the first quarter wave plate and the second quarter wave plate are used for reducing nonlinear interaction of laser in the gain medium and other optical elements so as to avoid damage to the optical elements and small-scale self-focusing effect.
9. A high energy ultrafast laser device, as recited in claim 7, wherein,
YAG crystals with large caliber are used as laser gain media, pumping wavelength is 808nm, and pulse synchronous signals are provided by a synchronous signal generator;
the first thermal compensation mirror and the second thermal compensation mirror are used for compensating a thermal lens effect of the side pump module under high-power operation so as to avoid damage to optical elements caused by undersize light spots;
the first Faraday rotator and the second Faraday rotator are used for compensating thermal depolarization of the Nd-YAG crystal, and the first 0-degree total reflection mirror and the second 0-degree total reflection mirror are used for reflecting fundamental frequency light after single-pass amplification so as to realize double-pass amplification.
10. A method of operating a high energy ultrafast laser device, characterized by using a high energy ultrafast laser device as recited in any one of claims 1-9, comprising the following process:
mode locking pulse laser output from an optical fiber mode locking seed source firstly passes through an acousto-optic menu module to perform menu frequency reduction to obtain pulse laser with required heavy frequency, the selected pulse laser with heavy frequency then enters a regenerative amplifier to be preamplified, the seed light with nJ level energy is amplified to mJ level, and higher beam quality is realized based on the characteristic of independent cavity formation of regenerative amplification;
the laser output from the regenerative amplifier enters the traveling wave amplifier and sequentially passes through a first beam shaping system, a first dichroic mirror, a gain crystal and a second dichroic mirror; the first beam shaping system expands and collimates the pulse laser output by the regenerative amplifier, and the first beam shaping system changes the size of the collimated beam so as to control the laser intensity;
the shaped light beam is reflected by a first dichroic mirror, enters a gain crystal for amplification, and a part with higher intensity of the center of the light beam is subjected to higher stimulated Raman scattering conversion in a Raman crystal to realize the intensity distribution of a flat-top or hollow fundamental frequency light beam, and the light beam is split by a second dichroic mirror after passing through the gain crystal, wherein the fundamental frequency light beam is highly reflected, and the Raman light beam and the pump light are highly transmitted;
the amplified light subjected to the shaping of the laser Raman scattering effect enters a main amplifier of a side pump, passes through a first optical isolation system and a second optical beam shaping system, wherein the second optical beam shaping system expands and collimates a beam into a size matched with the caliber of a first side pump module, and the expanded and collimated beam passes through a first film polarizer in a horizontal polarization state, is converted into a circular polarization state through a first quarter wave plate and enters the first side pump module;
the thermal lens and the thermally induced depolarization effect generated under the high-power operation of the first side pump module are respectively compensated by a first thermal compensation mirror and a first Faraday rotator of a double-pass structure, the single-pass amplified fundamental frequency light is reflected by a first 0-degree total reflection mirror to realize double-pass amplification, the amplified light in a circular polarization state is changed into a vertical polarization state after passing through a first quarter wave plate for the second time, and the amplified light is reflected and output by a first film polaroid and enters the next amplification stage;
the amplifying stage formed by the second side pump module and the third side pump module is similar to that of the first side pump module, but the caliber of the side pump module and the size of the incident beam are gradually increased, and the high-energy ultrafast laser based on the stimulated Raman scattering restraining small-scale self-focusing effect is output from the second film polaroid.
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