CN112271533B - Chirped pulse amplification system and implementation method thereof - Google Patents

Chirped pulse amplification system and implementation method thereof Download PDF

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Publication number
CN112271533B
CN112271533B CN202011294672.XA CN202011294672A CN112271533B CN 112271533 B CN112271533 B CN 112271533B CN 202011294672 A CN202011294672 A CN 202011294672A CN 112271533 B CN112271533 B CN 112271533B
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beam expanding
stage
isolator
expanding system
energy
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CN112271533A (en
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赵研英
耿易星
颜学庆
吴旻剑
肖超凡
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Peking University
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Peking University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0064—Anti-reflection devices, e.g. optical isolaters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0057—Temporal shaping, e.g. pulse compression, frequency chirping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0071—Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1301—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

The invention discloses a device for isolated targeting return light of chirped pulse amplified laser and an implementation method thereof. The invention places an isolator in front of the second stage amplifier; for a first stage beam expanding system comprising a sub-beam expanding system, an isolator is placed between the first stage beam expanding system and the second stage amplifier; or the first-stage beam expanding system comprises a plurality of sub-beam expanding systems, and the isolator is arranged among the sub-beam expanding systems of the first-stage beam expanding system; the sub beam expanding system consists of a positive lens and a negative lens; before the isolator is placed in the second-stage amplifier, the energy flow density is low, and the isolator is not damaged; meanwhile, the light spot size is relatively smaller, so that the size of the isolator can be reduced, the purchase cost of the isolator is reduced, the manufacturing cost is further reduced, and 100% return light isolation can be ensured.

Description

Chirped pulse amplification system and implementation method thereof
Technical Field
The invention relates to a laser technology, in particular to a chirped pulse amplification system and an implementation method thereof.
Background
After the chirped laser pulse amplification (CPA) is proposed, the peak power of the laser device is developed in a leap way, the peak power of the laser pulse can reach a plurality of PW (10 15 W), and the laser light intensity can reach 10 22 W/cm < 2 >. Such intense field lasers are widely used in laser plasma interactions.
As shown in fig. 1, a common CPA system uses an oscillator to generate ultra-short pulses (the pulse width is usually in the order of picoseconds or femtoseconds) as a seed source, and uses a stretcher to stretch the pulses in time to obtain long pulses (the pulse width length is in the order of tens of picoseconds to nanoseconds, the pulse width length after stretching depends on the energy which needs to be amplified finally), uses an amplifier group to amplify the stretched long pulses to obtain high-energy pulses, and finally uses a compressor to compress the time scale of the pulses to the minimum (the pulse width order of returning to the seed source) to obtain high-peak-power high-field laser pulses. High peak power intense field lasers are delivered to the target to interact with the target.
Laser plasma interactions are achieved by laser interactions with the target. At this time, when the laser is targeted, the target reflects the incident laser, and part of the laser returns to the laser system along the original path, and this part of the light is called return light. For a CPA system, the beam is directed from the seed to the compression cavity with a larger spot size to match the beam fluence within the optical element safety range. But the propagation direction of the return light is opposite, the return light is transmitted from the compression cavity to the seed direction, the light spot size is smaller and smaller in the transmission process, and the return light is further amplified by the amplifiers at all stages, so that the energy flow density of the light beam is higher and higher, the light beam is unsafe for the amplifiers, and the safety of a laser system is seriously threatened. In order to prevent the return light from causing fatal damage to the laser system, an isolator needs to be placed in the laser system to isolate the return light.
The choice of the position of the isolator is very important to the degree of protection of the laser system and the cost of the isolator itself. In the prior art, the isolator is placed behind the compressor, so that return light can be completely isolated outside the laser system, and the whole laser system is effectively protected, but the laser pulse width is ultra-short pulse width, usually picosecond or femtosecond pulse, and when the laser pulse is transmitted through the isolator, the laser pulse with extremely high peak power is in the isolator, and the quality of a laser beam is reduced and the isolator is damaged due to the nonlinear effect of the laser in an optical element in the isolator.
Disclosure of Invention
Aiming at the fact that the isolator is not suitable for being placed after the compressor in the prior art, the invention provides the chirped pulse amplification CPA system and the implementation method thereof before the isolator is placed in the compressor, and the proper selection of the position of the isolator can effectively isolate the return light protection laser system and effectively reduce the caliber of the isolator and the laser manufacturing cost in consideration of the high price of a large-caliber optical element.
It is an object of the present invention to provide a chirped pulse amplification CPA system.
The CPA system sequentially comprises a seed source, a stretcher, an amplifier group and a compressor; the amplifier group comprises a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier, a second-stage amplifier, a first-stage beam expanding system and a second-stage beam expanding system, wherein the front-stage amplifier group comprises m amplifiers, and m is a natural number more than or equal to 0; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then the laser beam enters an amplifier group, the laser beam sequentially passes through a pre-stage amplifier and a pre-stage beam expanding system, the energy is amplified by the first-stage amplifier, the amplified energy is A, the diameter of a light spot is enlarged from a to B by the first-stage beam expanding system, the laser beam enters a second-stage amplifier to amplify the energy, the amplified energy is B, and the energy B is more than 2A, so that high-energy laser pulses are obtained; expanding the diameter of the light spot from B to c through a second-stage beam expanding system, then entering a compressor to compress the pulse width, wherein the compression efficiency of the compressor is X, the energy output after compression is XB, and X 2 B is more than A, and transmitting the compressed laser to a target area for targeting; the target is returned by return light along the original path of the transmission path to the laser, the unit of energy is joule, and the unit of diameter is centimeter.
Placing an isolator for isolating the target shooting return light in front of the second-stage amplifier; wherein the first stage beam expanding system comprises one sub-beam expanding system, or the first stage beam expanding system comprises a plurality of sub-beam expanding systems;
For a first stage beam expanding system comprising a sub-beam expanding system, an isolator is placed between the first stage beam expanding system and the second stage amplifier; when the incident main light passes through the second amplifier, the energy is amplified to B, and the energy flow density is at the moment The energy of the return light reaching the isolator is X 2 B, which is the energy density of the currentSo that all optical elements in the optical path are not damaged; the damage threshold of the optical element in the isolator is the same as that of the optical element in the amplifier group, the energy flow density is lower than that of the second-stage amplifier before the isolator is placed in the second-stage amplifier, the isolator is not damaged, and the isolator ensures 100% return light isolation;
For the first-stage beam expanding system comprising N sub-beam expanding systems, wherein N is a natural number which is more than or equal to 2, an isolator is arranged between an ith sub-beam expanding system and an (i+1) th sub-beam expanding system of the first-stage beam expanding system, and i is more than or equal to 1 and less than or equal to N-1; the ith sub-beam expanding system of the first-stage beam expanding system expands the light spot of the incident main light to b 1, and expands the light spot to b through the (i+1) th sub-system of the first-stage beam expanding system, wherein b 1＜b;b1 meets the condition: Wherein T is the damage threshold of the isolator, the unit is J/cm 2, and when the return light reaches the isolator, the energy X 2 B of the highest return light is condensed to the energy density of Less than the damage threshold T of the isolator; the isolator is arranged between two sub-beam expanding systems of the first-stage beam expanding system, light spots are larger than those before an ith sub-beam expanding system of the first beam expanding system, the energy density is low, and the isolator cannot be damaged; meanwhile, compared with the spot size b, the spot size is relatively smaller, so that the size of the isolator can be reduced, and the manufacturing cost is further reduced; thus, the two-stage amplification ensures the safety of the isolator, reduces the purchase cost of the isolator, and ensures 100% return light isolation when the isolator is placed.
The size of the isolator is larger than that of the passing light spot, and the invention makes the size of the light spot passing through the isolator smaller before the second-stage amplifier, thereby reducing the size of the isolator and realizing the reduction of the manufacturing cost of the optical element.
The isolator sequentially comprises a first gram prism, a Faraday rotator, a wave plate and a second gram prism along the laser transmission direction; in the transmission direction of the incident main light, the polarization of the input laser and the output laser is vertical due to the actions of the Faraday rotator and the wave plate, and the incident main light can continue to be transmitted forwards without changing the transmission direction; in the return light transmission direction, the polarization of the input laser light and the output laser light are the same, and the glaring prism reflects the return light out of the main light path. Since the isolator system can separate the return light from the incident main light in the optical path, the energy of the return light can be measured by placing an energy meter at the return light outlet.
Each sub-beam expanding system consists of a positive lens and a negative lens.
The compression efficiency X of the compressor is less than 0.7.
Another object of the present invention is to provide a method for implementing a chirped pulse amplification CPA system.
The implementation method of the chirped pulse amplification CPA system comprises the following two conditions:
1. The first stage beam expanding system comprises a sub-beam expanding system
1) Constructing a light path:
The CPA system sequentially comprises a seed source, a stretcher, an amplifier group and a compressor; the amplifier group comprises a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier, a second-stage amplifier, a first-stage beam expanding system and a second-stage beam expanding system, wherein the front-stage amplifier group comprises m amplifiers, and m is a natural number more than or equal to 0; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then the laser beam enters an amplifier group, the laser beam sequentially passes through a pre-stage amplifier and a pre-stage beam expanding system, the energy is amplified by the first-stage amplifier, the amplified energy is A, the diameter of a light spot is enlarged from a to B by the first-stage beam expanding system, the laser beam enters a second-stage amplifier to amplify the energy, the amplified energy is B, and the energy B is more than 2A, so that high-energy laser pulses are obtained; expanding the diameter of the light spot from B to c through a second-stage beam expanding system, then entering a compressor to compress the pulse width, wherein the compression efficiency of the compressor is X, the energy output after compression is XB, and X 2 B is more than A, and transmitting the compressed laser to a target area for targeting; returning returned light to the laser along the original path of the transmission path at the target shooting position, wherein the unit of energy is joule, and the unit of diameter is centimeter;
Placing an isolator between the first stage beam expanding system and the second stage amplifier;
2) When the incident main light passes through the second amplifier, the energy is amplified to B, and the energy flow density is at the moment The energy of the return light reaching the isolator is X 2 B, which is the energy density of the current without damaging the optical elementSo that the optical element is not damaged; the damage threshold of the optical element in the isolator is the same as that of the optical element in the amplifier group, the energy density is low before the isolator is placed in the second-stage amplifier, the isolator is not damaged, and the isolator ensures 100% return light isolation;
2. The first-stage beam expanding system comprises N sub beam expanding systems, wherein N is a natural number more than or equal to 2
1) Constructing a light path:
The CPA system sequentially comprises a seed source, a stretcher, an amplifier group and a compressor; the amplifier group comprises a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier, a second-stage amplifier, a first-stage beam expanding system and a second-stage beam expanding system, wherein the front-stage amplifier group comprises m amplifiers, and m is a natural number more than or equal to 0; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then the laser beam enters an amplifier group, the laser beam sequentially passes through a pre-stage amplifier and a pre-stage beam expanding system, the energy is amplified by the first-stage amplifier, the amplified energy is A, the diameter of a light spot is enlarged from a to B by the first-stage beam expanding system, the laser beam enters a second-stage amplifier to amplify the energy, the amplified energy is B, and the energy B is more than 2A, so that high-energy laser pulses are obtained; expanding the light spot from the diameter B to c through a second-stage beam expanding system, then entering a compressor to compress the pulse width, wherein the compression efficiency of the compressor is X, the energy output after compression is XB, and X 2 B is more than A, and transmitting the compressed laser to a target area for targeting; returning returned light to the laser along the original path of the transmission path at the target shooting position, wherein the unit of energy is joule, and the unit of diameter is centimeter;
placing an isolator between an ith sub-beam expanding system and an (i+1) th sub-beam expanding system of the first-stage beam expanding system, wherein i is more than or equal to 1 and less than or equal to N-1;
2) The ith sub-beam expanding system of the first-stage beam expanding system expands the light spot of the incident main light to b 1, and expands the light spot to b through the (i+1) th sub-system of the first-stage beam expanding system, wherein b 1＜b;b1 meets the condition: Wherein T is the damage threshold of the isolator, the unit is J/cm 2, and when the return light reaches the isolator, the energy X 2 B of the highest return light is condensed to the energy density of Less than the damage threshold T of the isolator; the isolator is arranged between two sub-beam expanding systems of the first-stage beam expanding system, wherein light spots are larger than those before an ith sub-beam expanding system of the first beam expanding system, the energy density is low, and the isolator cannot be damaged; meanwhile, compared with the spot size b, the spot size is relatively smaller, so that the size of the isolator can be reduced, and the manufacturing cost is further reduced; thus, the two-stage amplification ensures the safety of the isolator, reduces the purchase cost of the isolator, and ensures 100% return light isolation when the isolator is placed.
The invention has the advantages that:
The invention places an isolator in front of the second stage amplifier; for a first stage beam expanding system comprising a sub-beam expanding system, an isolator is placed between the first stage beam expanding system and the second stage amplifier; or the first-stage beam expanding system comprises a plurality of sub-beam expanding systems, and the isolator is arranged among the sub-beam expanding systems of the first-stage beam expanding system; the sub beam expanding system consists of a positive lens and a negative lens; before the isolator is placed in the second-stage amplifier, the energy flow density is low, and the isolator is not damaged; meanwhile, the light spot size is relatively smaller, so that the size of the isolator can be reduced, the purchase cost of the isolator is reduced, the manufacturing cost is further reduced, and 100% return light isolation can be ensured.
Drawings
FIG. 1 is a block diagram of a CPA system;
FIG. 2 is a block diagram of the amplifier bank to target configuration;
FIG. 3 is a block diagram of an isolator for isolating the return light of a target practice of the present invention;
FIG. 4 is a schematic diagram of a first beam expanding system of a first embodiment of an isolator for isolating target return light according to the present invention;
FIG. 5 is a block diagram of the placement position of an isolator according to a first embodiment of the present invention;
FIG. 6 is a schematic diagram of a first beam expanding system of a second embodiment of an isolator for isolating target return light according to the present invention;
FIG. 7 is a block diagram of the placement position of an isolator according to a second embodiment of the present invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in conjunction with the accompanying drawings.
As shown in fig. 1, the CPA system sequentially comprises a seed source, a stretcher, an amplifier group, and a compressor; as shown in fig. 2, the amplifier group includes a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier and a second-stage amplifier, and the first-stage beam expanding system and the second-stage beam expanding system, where the front-stage amplifier group includes m amplifiers, where m is a natural number greater than or equal to 0, and the front-stage amplifier group is determined as needed, i.e., when m=0, the front-stage amplifier group is not required to be set; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then the laser beam enters an amplifier group, the laser beam sequentially passes through a pre-stage amplifier and a pre-stage beam expanding system, the energy is amplified by the first-stage amplifier, the amplified energy is A, the diameter of a light spot is enlarged from a to B by the first-stage beam expanding system, the laser beam enters a second-stage amplifier to amplify the energy, the amplified energy is B, and the energy B is more than 2A, so that high-energy laser pulses are obtained; expanding the light spot from the diameter B to c through a second-stage beam expanding system, then entering a compressor to compress the pulse width, wherein the compression efficiency of the compressor is X, X is less than 0.7, the energy output after compression is XB, X 2 B is more than A, and transmitting the compressed laser to a target area for targeting; the target is returned by the return light to the laser along the original path of the transmission path, the unit of energy is joule, and the unit of diameter is centimeter. The energy and the spot size obtained by amplifying the laser amplifier meet the fluence density: energy/spot area < damage threshold of the amplifier optics.
In an extreme case, the laser is returned to the laser system entirely by a mirror at the target area, which is the highest energy that can be reflected back to the laser system during the entire targeting process. Here, neglecting transmission losses from the compressor to the target range, the maximum energy of the laser light returned through the compressor to the second stage amplifier is X 2 B < B. Since the amplification of the return light by the second-stage amplifier is not considered, the energy X 2 B of the return light is smaller than the output energy of the second-stage amplifier and does not damage the second-stage amplifier element, and therefore the isolator does not have to be placed after the second-stage amplifier.
As shown in fig. 3, the isolator includes a first grazing prism, a faraday rotator, a wave plate, and a second grazing prism in this order along the laser transmission direction; in the transmission direction of the incident main light, the polarization of the input laser and the output laser is vertical due to the actions of the Faraday rotator and the wave plate, and the incident main light can continue to be transmitted forwards without changing the transmission direction; in the return light transmission direction, the polarization of the input laser and the output laser are the same, and the glaring prism reflects the laser return light out of the main light path. Since the isolator system is capable of separating the return light from the incident main light in the optical path, the energy of the return light can be measured by placing an energy meter at the return light outlet.
Example 1
In this embodiment, the first-stage beam expanding system is composed of a positive lens and a negative lens, as shown in fig. 4, and the isolator is placed between the first-stage beam expanding system and the second-stage amplifier, as shown in fig. 5, where the light spot is large enough and the laser energy density is low, so that the isolator can be well protected from being damaged; meanwhile, the isolator is prevented from being placed in front of a compressor with larger light spots, so that the manufacturing cost of the isolator can be well reduced; the light spot of the laser is directly expanded to b through a first-stage beam expanding system; when the energy of the laser is amplified to B after passing through the second amplifier, the energy flow density at the momentNot damage all optical elements in the light path, when the energy of the returned light is X 2 B, the energy flow density isSo that all optical elements in the optical path are not damaged; the damage threshold of the optical element in the isolator is the same as that of the optical element in the amplifier group, the energy density is low before the isolator is placed in the second-stage amplifier, the isolator cannot be damaged, and the isolator ensures 100% return light isolation.
The isolator can separate the return light from the incident main light in the light path, so that the energy of the return light can be measured by placing an energy meter at the return light outlet.
Example two
In this embodiment, the first stage beam expanding system includes two sub-beam expanding systems, as shown in fig. 6, each of which is composed of a positive lens and a negative lens, and then an isolator is placed between the first sub-beam expanding system and the second sub-beam expanding system of the first stage beam expanding system, as shown in fig. 7; the first sub-beam expanding system of the first-stage beam expanding system expands the light spot to b 1, and then expands the light spot to b through the second sub-system of the first-stage beam expanding system, wherein b 1＜b;b1 meets the condition: Wherein T is the damage threshold of the isolator in J/cm 2, so that the energy X 2 B of the highest return light is condensed to the energy density of Less than the damage threshold T of the isolator; the isolator is arranged between two sub beam expanding systems of the first-stage beam expanding system, the light spots are relatively large, the laser energy flow density is low, and the isolator is not damaged; meanwhile, compared with the spot size b of the laser, the size of the isolator is relatively small, and the manufacturing cost is further reduced; thus, the two-stage amplification ensures the safety of the isolator, reduces the purchase cost of the isolator, and ensures 100% return light isolation when the isolator is placed.
Finally, it should be noted that the examples are disclosed for the purpose of aiding in the further understanding of the present invention, but those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.

Claims (6)

1. A chirped pulse amplification CPA system, comprising in order a seed source, a stretcher, an amplifier bank and a compressor; the amplifier group comprises a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier, a second-stage amplifier, a first-stage beam expanding system and a second-stage beam expanding system, wherein the front-stage amplifier group comprises m amplifiers, and m is a natural number more than or equal to 0; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then enters an amplifier group, and after passing through a pre-stage amplifier and a pre-stage beam expanding system in turn, the energy is amplified by a first-stage amplifier, and the amplified energy isThe diameter of the light spot is changed by the first-stage beam expanding systemTo be enlarged toThen enters a second-stage amplifier to amplify the energy, and the amplified energy isAnd (2) and>2Obtaining high-energy laser pulses; then the diameter of the light spot is changed fromTo be enlarged toThen, the pulse width is compressed by a compressor, the compression efficiency of the compressor is thatThe energy output after compression isA kind of electronic deviceA, transmitting compressed laser to a target area for targeting; the method is characterized in that an isolator for isolating the return light of the target shooting is arranged in front of a second-stage amplifier; wherein the first-stage beam expanding system comprises a sub-beam expanding system or the first-stage beam expanding system comprises a plurality of sub-beam expanding systems, and each sub-beam expanding system consists of a positive lens and a negative lens;
When the first stage beam expanding system comprises a sub beam expanding system, an isolator is arranged between the first stage beam expanding system and the second stage amplifier; when the incident main light passes through the second amplifier, the energy is amplified to Energy flow density at this timeNot damage all optical elements in the light path, when the return light reaches the isolator, the energy isEnergy flow density at this time＜So that all optical elements in the optical path are not damaged; the damage threshold of the optical element in the isolator is the same as that of the optical element in the amplifier group, the energy flow density is lower than that of the second-stage amplifier before the isolator is placed in the second-stage amplifier, the isolator is not damaged, and the isolator ensures 100% return light isolation;
When the first stage beam expanding system comprises In the case of a sub-beam expanding system,Is a natural number more than or equal to 2, the isolator is arranged at the first stage of the beam expanding systemSub-beam expanding system and the firstBetween the sub beam expanding systems, the number of the sub beam expanding systems is less than or equal to 1N-1 is not more than; the second sub-beam expanding system of the first-stage beam expanding system expands the light spot of the incident main light toThen the beam is expanded to the first stage of the sub-system of the beam expanding systemWherein＜；The conditions are satisfied: Wherein Is the damage threshold of the isolator, the unit is J/cm 2, when the return light reaches the isolator, the return light passes throughThe sub-beam expanding system expands the energy of the highest return lightBeam shrinking to energy density ofLess than the damage threshold of the isolator; Placing an isolator between two sub-beam expanding systems of the first stage beam expanding system, where the spot is relative to the first stage beam expanding systemThe light spots in front of the sub beam expanding system are larger, the energy flow density is low, and the isolator is not damaged; while the spot size is relativeIn terms of the relatively small size, the size of the separator can be reduced, and the manufacturing cost is further reduced; thus, the two-stage amplification ensures the safety of the isolator, reduces the purchase cost of the isolator, and ensures 100% return light isolation when the isolator is placed in the isolator;
the isolator includes along laser transmission direction in proper order: a first gram prism, a Faraday rotator, a wave plate and a second gram prism; in the transmission direction of the incident main light, the polarization of the input laser and the output laser is vertical due to the actions of the Faraday rotator and the wave plate, and the incident main light can continue to be transmitted forwards without changing the transmission direction; in the return light transmission direction, the polarization of the input laser light and the output laser light are the same, and the glaring prism reflects the return light out of the main light path.
2. The chirped pulse amplification CPA system of claim 1 further comprising an energy meter positioned at the exit of the return light to measure the energy of the return light.
3. The chirped pulse amplification CPA system of claim 1 wherein the compressor has a compression efficiency＜0.7。
4. A method of implementing a chirped pulse amplification CPA system of claim 1, the method comprising the steps of:
1. When the first stage beam expanding system comprises a sub-beam expanding system
1) Constructing a light path:
The CPA system sequentially comprises a seed source, a stretcher, an amplifier group and a compressor; the amplifier group comprises a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier, a second-stage amplifier, a first-stage beam expanding system and a second-stage beam expanding system, wherein the front-stage amplifier group comprises m amplifiers, and m is a natural number more than or equal to 0; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then enters an amplifier group, and after passing through a pre-stage amplifier and a pre-stage beam expanding system in turn, the energy is amplified by a first-stage amplifier, and the amplified energy is The diameter of the light spot is changed by the first-stage beam expanding systemTo be enlarged toThen enters a second-stage amplifier to amplify the energy, and the amplified energy isAnd (2) and>2Obtaining high-energy laser pulses; then the diameter of the light spot is changed fromTo be enlarged toThen, the pulse width is compressed by a compressor, the compression efficiency of the compressor is thatThe energy output after compression isA kind of electronic deviceA, transmitting compressed laser to a target area for targeting; returning returned light to the laser along the original path of the transmission path at the target shooting position, wherein the unit of energy is joule, and the unit of diameter is centimeter;
Placing an isolator between the first stage beam expanding system and the second stage amplifier;
2) When the incident main light passes through the second amplifier, the energy is amplified to Energy flow density at this timeThe optical element is not damaged, and when the return light reaches the isolator, the energy isEnergy flow density at this time＜So the optical element is not damaged; the damage threshold of the optical element in the isolator is the same as that of the optical element in the amplifier group, the energy density is low before the isolator is placed in the second-stage amplifier, the isolator is not damaged, and the isolator ensures 100% return light isolation;
2. when the first stage beam expanding system comprises In the case of a sub-beam expanding system,Natural number of not less than 2
1) Constructing a light path:
The CPA system sequentially comprises a seed source, a stretcher, an amplifier group and a compressor; the amplifier group comprises a front-stage amplifier group, a front-stage beam expanding system, a first-stage amplifier, a second-stage amplifier, a first-stage beam expanding system and a second-stage beam expanding system, wherein the front-stage amplifier group comprises m amplifiers, and m is a natural number more than or equal to 0; the seed source carries out time stretching on the pulse through a stretcher to obtain long laser pulse; then enters an amplifier group, and after passing through a pre-stage amplifier and a pre-stage beam expanding system in turn, the energy is amplified by a first-stage amplifier, and the amplified energy is The diameter of the light spot is changed by the first-stage beam expanding systemTo be enlarged toThen enters a second-stage amplifier to amplify the energy, and the amplified energy isAnd (2) and>2Obtaining high-energy laser pulses; then the diameter of the light spot is changed fromTo be enlarged toThen, the pulse width is compressed by a compressor, the compression efficiency of the compressor is thatThe energy output after compression isA kind of electronic deviceA, transmitting compressed laser to a target area for targeting; returning returned light to the laser along the original path of the transmission path at the target shooting position, wherein the unit of energy is joule, and the unit of diameter is centimeter;
placing an isolator in the first stage beam expanding system Sub-beam expanding system and the firstBetween the sub beam expanding systems, the number of the sub beam expanding systems is less than or equal to 1≤N-1；
2) First stage beam expanding SystemThe sub-beam expanding system expands the light spot of the incident main light toThen pass through the first stage beam expanding systemSubsystem beam expansion toWherein＜；The conditions are satisfied: Wherein Is the damage threshold of the isolator, the unit is J/cm 2, when the return light reaches the isolator, the return light passes throughThe +1 sub-beam expander system expands the energy of the highest return lightBeam shrinking to energy density ofLess than the damage threshold of the isolator; Placing an isolator between two sub-beam expanding systems of the first stage beam expanding system, where the spot is opposite to the first stage beam expanding systemThe light spots in front of the sub beam expanding system are larger, the energy flow density is low, and the isolator is not damaged; while the spot size is relativeIn terms of being relatively small, the size of the separator can be reduced, and the manufacturing cost is further reduced; thus, the two-stage amplification ensures the safety of the isolator, reduces the purchase cost of the isolator, and ensures 100% return light isolation when the isolator is placed.
5. The method of claim 4, wherein each sub-beam expanding system consists of a positive lens and a negative lens.
6. The implementation method of claim 4, wherein the compression efficiency of the compressor＜0.7。
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