CN108594461B - Internal light distribution type grating compressor - Google Patents

Abstract

An internal beam-splitting grating compressor characterized in that it comprises: the grating array comprises a first grating pair consisting of a first grating and a second grating which are parallel to each other, a second grating pair consisting of a third grating and a fourth grating which are parallel to each other, a third grating pair consisting of a fifth grating and a sixth grating which are parallel to each other, …, an Nth grating pair consisting of a 2N-1 th grating and a 2N grating which are parallel to each other, an N +1 th grating pair consisting of a 2N +1 th grating and a 2N +2 th grating which are parallel to each other, a first beam splitting sheet, a second beam splitting sheet, …, an N-1 th beam splitting sheet and a reflector. The invention divides the incident chirped laser pulse into at most N compressed femtosecond laser pulses inside the compressor for output, thereby avoiding the limitation of the last compressed grating on the compressed pulse energy and improving the laser pulse energy compressed and output by the compressor in multiples.

Description

Internal split type grating compressor

technical field

The invention relates to the science, technology and application fields of super-intense and ultra-short lasers, in particular to the field of research and application of chirped pulse compression for compression terminals in high-power chirped pulse amplification of petawatts or optical parametric chirped pulse amplification systems, and is suitable for compressed output High peak power chirped pulse compression with laser energy density higher than the damage threshold of the last compressed grating.

Background technique

Ultra-strong and ultra-short laser pulses provide unprecedented new experimental means and extreme physical conditions for human beings, and are used in major frontier scientific researches such as strong laser laboratory astrophysics, strong laser electron and proton accelerators, nuclear fusion fast ignition, and laser plasma physics. field has important applications. Because of these important application prospects, ultra-intense and ultra-short laser outputs in the order of petawatts have been achieved at home and abroad.

At present, high-power ultra-intense ultra-short pulse laser technology mainly includes chirped pulse amplification (CPA) and optical parameter chirped pulse amplification (OPCPA). Both of these methods are relatively mature and widely used. The basic idea of the two methods is to first use a grating stretcher to introduce positive dispersion to the incident femtosecond ( ^10-15 s) seed pulse, thereby extending the seed laser pulse width from femtoseconds to nanoseconds ( ^10-9 s). ) magnitude. The laser after pulse broadening can be amplified in laser medium (such as Ti:sapphire crystal) or nonlinear crystal (such as BBO, KDP crystal, OPCPA amplification). The corresponding is the OPCPA technology. Finally, the amplified laser pulse passes through a compressor composed of gratings to compress the laser pulse width from nanoseconds back to femtoseconds, thereby realizing the output of ultra-strong and ultra-short laser pulses. In the compressor, according to the grating equation d(sinα+sinβ)=mλ (here, d is the grating line density, α is the incident angle, β diffraction angle, λ is the laser wavelength, m is the diffraction order, here is usually 1 ), after the laser passes through the grating, lasers of different wavelengths will be diffracted to different directions, resulting in different optical paths of different wavelengths, thereby introducing dispersion-compressed laser pulses.

In a high-power ultra-intense ultra-short laser device, the terminal compressors are all reflective grating compressors, and the device structure is relatively simple, because the grating can obtain a large amount of dispersion, and the reflective grating can avoid damage to the components. At present, the typical optical path of this type of large-diameter grating compressor is shown in Figure 1, which is mainly composed of two groups of parallel reflection grating pairs, grating 1 and grating 2, and grating 3 and grating 4. The basic working principle is that the amplified output chirped laser pulse is first diffracted by grating 1, and then diffracted again by grating 2 of parallel grating 1 to become a parallel laser, and then diffracted and compressed by grating 3 and grating 4 to obtain femtosecond laser output. . Wherein grating 3 and grating 4 are usually placed as mirror images of grating 1 and grating 2 .

However, as the amplified output laser pulse energy becomes larger and larger, the laser spot becomes larger and larger, and the laser energy density hitting the grating also becomes higher and higher. Due to the limitation of the compressed grating processing technology, the processing of large-sized gratings is extremely difficult, expensive, and has certain size limitations, which greatly limits the pulse compression of higher-energy lasers, thereby limiting the acquisition of higher peak values. Powerful ultra-intense ultra-short laser pulses. In order to solve this problem, some people propose to directly split the laser beam after amplification, then enter into different grating compressors for compression, and finally combine the laser beams to obtain ultra-intense ultra-short laser beams. However, this method requires multiple independent vacuum grating compressors, which is costly, and it is also very difficult to group laser beams after passing through multiple independent vacuum compressors.

Since the grating is coated with a metal or dielectric reflective film, the damage threshold of these highly reflective films decreases with the narrowing of the laser pulse. The pulse width of the last output grating is only in the order of femtoseconds or picoseconds, and the peak power is very high, which is very easy to be damaged. Depending on the coating material and method, the damage threshold of the first grating (withstanding nanosecond laser damage) may be more than 3 times higher than the damage threshold of the last grating (withstanding femtosecond or picosecond laser damage), or even higher.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and to propose an internal light splitting type grating compressor, which divides laser light into N beams of laser light inside the compressor for compression respectively. The grating compressor breaks through the limitation of the last grating damage threshold on the output energy, and significantly increases the upper limit of the output laser energy of the grating compressor.

The technical solution of the present invention is as follows:

An internal partial light type grating compressor is characterized in that its composition comprises: a first grating pair consisting of a first grating and a second grating parallel to each other, and a second grating pair consisting of a third grating and a fourth grating parallel to each other , the third grating pair composed of the fifth and sixth gratings parallel to each other, ..., the Nth grating pair composed of the mutually parallel 2N-1 gratings and the 2N gratings, the Nth grating pair composed of the mutually parallel 2N+1 gratings The N+1th grating pair composed of the block grating and the 2N+2th grating, the first beam splitter, the second beam splitter, ..., the N-1th beam splitter and a mirror; where, N is a natural number, and N and The damage threshold A of the laser pulse on the first grating, the damage threshold B of the laser pulse on the fourth grating are related to the diffraction efficiency C of the grating, and the value of N is an integer of (A/B*C);

The first beam splitter is arranged in the output light direction of the first grating pair, the first beam splitter divides the input light into transmitted light and reflected light, and the transmitted light direction of the first beam splitter is The second grating pair, in the reflected light direction of the first beam splitter, is the second beam splitter (10), . The reflected light directions of the second beam splitter, ..., the N-1th beam splitter and the reflector are the third grating pair, ..., the Nth grating pair and the N+1th grating pair, respectively;

The incident high-energy chirped laser pulse is first introduced into the first grating pair, and after the first compression, it becomes parallel light, and the parallel beam is divided into transmitted light and reflected light by the first beam splitter after the second grating, so The transmitted light is compressed again by the second grating pair, and the reflected light of the second beam splitter, ..., the N-1th beam splitter and the mirror is injected into the third grating pair, ..., the Nth grating The pair and the Nth grating pair are compressed again, and finally N beams of compressed femtosecond lasers are output.

The first beam splitter, the second beam splitter, . Beam splitting horizontally.

All the gratings described are metal film gratings, dielectric film gratings or metal-media mixed film gratings.

The reflecting mirror can provide a suitable time delay to precisely synchronize the time delay of the laser beams after different beam splitting and compression.

The present invention has the following remarkable features:

1. The present invention divides the laser into at most N beams inside the compressor, which avoids the damage of the last compressed grating. Among them, N depends on the damage threshold A of the first grating and the damage threshold B of the fourth grating, and the compression diffraction efficiency C of the laser passing through the first to fourth gratings, and the value of N is an integer of (A/B*C) , usually greater than or equal to 2, with the ability to double the output laser energy.

2. The present invention shares the first grating and the second grating. Compared with splitting the laser beam before the compressor, the number of gratings used is saved, thereby greatly reducing the cost.

3. The present invention shares the first grating and the second grating. Compared with the recompression of laser beam splitting before the compressor, the optical path is simpler and more compact, the size of the device and the vacuum compression cavity will be reduced, the cost is lower, and the device is more compact. Stable and more convenient to adjust.

4. The present invention shares the first grating and the second grating, the optical path is simpler and more compact, the N-beam laser can be compressed in the same vacuum compression cavity, the device is also more stable, and the compressed N-beam laser group is easier to realize.

Description of drawings

Figure 1 is a schematic diagram of the optical path structure of a typical existing chirped laser pulse grating compressor

FIG. 2 is a schematic diagram of the optical path structure of the grating compressor with 1-divided N beams in the first embodiment of the present invention

FIG. 3 is a schematic diagram of an optimized optical path structure of a grating compressor with one light divided into two beams in Embodiment 2 of the present invention

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited by this.

Please refer to FIG. 2 first. FIG. 2 is a schematic diagram of the optical path structure of the grating compressor that divides the light into N beams. It can be seen from the figure that the internal light-division grating compressor of the present invention includes: a first grating 5 that is parallel to each other. The first grating pair composed of the second grating 6 and the third grating 8 and the fourth grating 9 are parallel to each other, and the third grating is composed of the fifth grating 11 and the sixth grating 12 which are parallel to each other. Right,...,Nth grating pair consisting of the 2N-1th grating and 2Nth grating parallel to each other,N+1th grating pair consisting of the 2N+1th grating and 2N+2th grating parallel to each other, the first beam splitter 7, second beam splitter 10, . . ., N-1th beam splitter, and mirror 13;

N is a natural number, N is related to the damage threshold A of the laser pulse on the first grating 5, the damage threshold B of the laser pulse on the fourth grating 9, and the diffraction efficiency C of the grating, and the value of N is an integer of (A/B*C) ;

The first beam splitter 7 is arranged in the output light direction of the first grating pair, and the first beam splitter 7 divides the input light into transmitted light and reflected light. The light direction is the second grating pair, and the reflected light direction of the first beam splitter 7 is the second beam splitter 10, . . . , the N-1th beam splitter and the mirror 13, in the The reflected light directions of the second beam splitter 10, .

The incident high-energy chirped laser pulse is first introduced into the first grating pair, and after being compressed for the first time, it becomes a parallel beam, and the parallel beam is divided into transmitted light and reflected light by the first beam splitter 7 behind the second grating 6 , the transmitted light is compressed again by the second grating pair, and the reflected light of the second beam splitter 10, . The Nth grating pair and the Nth grating pair are compressed again, and finally N beams of compressed femtosecond laser light are output.

The first beam splitter 7, the second beam splitter 10, . . . , the N-1th beam splitter behind the second grating 6 can split the laser beam on the horizontal plane of the grating propagation, or the vertical beam according to needs. The beam splitting is performed on the horizontal plane of the grating propagation.

All the gratings described are metal film gratings, dielectric film gratings or metal-media mixed film gratings.

FIG. 3 is a schematic diagram of an optimized optical path structure of a grating compressor in which one light is divided into two beams according to Embodiment 2 of the present invention. The compressor of this embodiment mainly includes: a first grating pair composed of a first grating 5 and a second grating 6 , a 50% beam splitter 7 , a second grating pair composed of a third grating 8 and a fourth grating 9 , and a reflecting mirror 10 , and a third grating pair composed of the fifth grating 11 and the sixth grating 12 .

The pulse width of the incident laser light is 4 ns, the output is about 3 ns after being compressed by the first grating 5, and then compressed to about 2 ns by the second grating 6, and the laser light also becomes a parallel beam. The beam splitter 7 divides the parallel beam into two parts with equal energy. The laser beam that transmits half of the energy continues to be incident on the third grating 8 and is compressed to about 1 ns, and finally incident to the fourth grating 9, and the laser pulse is compressed to about 30 femtoseconds. Output as beam 1. The laser light reflected from the beam splitter 7 passes through the mirror 10 and is injected into the fifth grating 11 to be compressed to about 1 ns, and finally passes through the sixth grating 12 to compress and output the laser output of about 30 femtoseconds as the beam 2 .

Since the laser energy received by the fourth grating 9 and the sixth grating 12 is halved during the implementation process, the damage of the high-energy laser to the final compressed grating: the fourth grating 9 and the sixth grating 12 is avoided, and the super energy doubling is realized. Strong ultra-short laser output.

Claims (3)

1. An internal partial light type grating compressor, characterized in that its composition comprises: a first grating pair consisting of a first grating (5) and a second grating (6) that are parallel to each other, and a third grating (8) that is parallel to each other. ) and the fourth grating (9), the third grating pair consisting of the fifth grating (11) and the sixth grating (12) parallel to each other, ..., consisting of the 2N-1 grating parallel to each other and the Nth grating pair composed of the 2Nth grating, the N+1th grating pair composed of the 2N+1th grating and the 2N+2th grating that are parallel to each other, the first beam splitter (7), the second beam splitter ( 10), ..., the N-1th beam splitter and the mirror (13); wherein, N is a natural number, N and the damage threshold A of the laser pulse on the first grating (5), and the laser pulse on the fourth grating (9) The damage threshold B is related to the diffraction efficiency C of the grating, and the N value is an integer of A/B*C; The first beam splitting sheet (7) is arranged in the output light direction of the first grating pair, and the first beam splitting sheet (7) divides the input light into transmitted light and reflected light. The transmitted light direction of the sheet (7) is the second grating pair, and the reflected light direction of the first beam splitter sheet (7) is the second beam splitter sheet (10), ..., the N-1th A beam splitter and a reflector (13), the reflected light directions of the second beam splitter (10), ..., the N-1th beam splitter and the reflector (13) are respectively the third grating pair, ..., the Nth grating pair and the N+1th grating pair; The incident high-energy chirped laser pulse is first introduced into the first grating pair, and after being compressed for the first time, it becomes a parallel beam, and the parallel beam is divided into transmission by the first beam splitter (7) behind the second grating (6). light and reflected light, the transmitted light is compressed again by the second grating, the reflected light of the second beam splitter (10), ..., the N-1th beam splitter and the mirror (13), The third grating pair, ..., the Nth grating pair and the Nth grating pair are respectively injected to compress again, and finally N beams of compressed femtosecond laser light are output. 2. The internal beam splitting type grating compressor according to claim 1, characterized in that the first beam splitter (7), the second beam splitter (10), ..., behind the second grating (6) The N-1th beam splitter, as required, splits the laser beam on the horizontal plane of grating propagation, or splits the beam on the horizontal plane of vertical grating propagation. 3 . The internal split-light grating compressor according to claim 1 , wherein all the gratings are metal film gratings, dielectric film gratings or metal-dielectric hybrid film gratings. 4 .

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