Laser multi-pass regenerative amplification device and method

Abstract

The invention discloses a laser multi-pass regenerative amplification device and method. The device at least comprises an oscillator, a pulse selector and a multi-pass regenerative amplifier, a single laser pulse output by an oscillator is selected by a pulse selector at a set repetition frequency and enters a multi-pass regeneration cavity of a multi-pass regeneration amplifier, and the selected laser pulse goes back and forth for one circle of the multi-pass regeneration cavity for four times or six times through polarization control and is amplified by a laser gain medium; the selected laser pulse can be output from the multi-pass regeneration cavity after obtaining 4N or 6N times of gain amplification by adjusting the high-voltage duration time of the pulse selector; n is the high-pressure duration divided by the time that the pulse goes back and forth the regeneration cavity. According to the invention, through the design of the multi-pass regeneration cavity, the number of amplification times of single reciprocating of a laser pulse to the regeneration cavity is increased, and the number of gain turns required by saturation amplification can be reduced, so that the repetition frequency of the regenerative amplifier is improved; and the gain extraction in the laser pulse regeneration amplification process can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser pulse amplification, and in particular to a laser multi-pass regeneration amplification device and method. Background Art

[0002] High average power all-solid-state lasers are widely used in research fields such as physics, chemistry, biomedicine, and ultra-fine processing. Currently, low-power all-solid-state lasers cannot meet actual needs, and short pulse amplification technology is needed to amplify low average power laser pulses to target high power laser pulses to meet application needs in various fields.

[0003] At present, the main amplification methods are mainly

[0004] (1) Regenerative amplification: The Pockels cell can be used to conveniently control the number of times the seed light is amplified in the regenerative cavity to achieve saturated gain. It has high energy stability, is relatively simple to build and adjust, and requires no maintenance.

[0005] (2) Multi-pass amplification: It passes through the Pockels cell only once. In the construction of high peak power lasers, the relative regenerative amplification reduces the dispersion and transmission losses caused by the wave plate and the Pockels cell.

[0006] In order to meet the needs of researchers in the fields of laser processing, high-energy physics, precision measurement and attosecond lasers, the high average power femtosecond lasers used need to have the characteristics of high power, large energy and short pulses. The higher the laser power and the greater the single pulse energy, the faster the processing rate, the wider the range of materials that can be ablated, and the more obvious the high-order nonlinear optical effects produced; the shorter the pulse, the wider the spectrum, which is more conducive to the generation of supercontinuum spectrum, and can produce cleaner processing boundaries in laser processing.

[0007] The problems and defects of the above technologies are as follows: For the current solution, as the number of gain turns increases, the regenerative amplifier can fully extract the crystal gain, but after repeatedly passing through the Pockels cell and the wave plate, a large material dispersion will be accumulated, and the upper limit of the repetition frequency of the output pulse will be reduced. The amplified spectrum width will also be affected by the gain narrowing effect, resulting in a narrowing of the spectrum. The multi-pass amplifier has a smaller accumulated dispersion but a weaker gain extraction capability, and has extremely high requirements for optical control. The stability of the beam pointing through the laser crystal each time must not only be traced back to the oscillator, but the more times the light path passes, the more difficult it is to adjust, and the higher the requirements for beam quality. The aperture required for its non-collinear amplification reduces the efficiency to 10% to 20%.

[0008] In order to combine the advantages of the two amplification methods, some researchers connected the regenerative amplifier and the multi-pass amplifier in series, first using a more efficient regenerative amplifier to pre-amplify the seed pulse to the millijoule level, and then using a single-stage or multi-stage multi-pass amplifier with smaller dispersion to amplify the pulse to tens of millijoules or even higher. This method greatly increases the system complexity and technical difficulty while greatly increasing the energy of a single pulse. The built laser amplification device is too large and complex. The laser amplifier that combines the above two amplification schemes can amplify to high peak power while ensuring gain and energy stability.

[0009] However, how to balance the accumulated dispersion of the regenerative amplifier and the difficulty of adjusting the multi-pass amplification optical path, fully extract the gain reduction and gain narrowing in the regenerative amplification process, and solve the insufficient gain of high pulse energy and high repetition rate laser regenerative amplifiers are still problems that technical personnel in this field need to solve urgently. Summary of the invention

[0010] In view of this, the present invention provides a laser multi-pass regenerative amplifier device and method, which not only ensures the advantages of energy stability and low beam pointing requirements in regenerative amplification, but also reduces cumulative dispersion while ensuring the same number of amplifications, effectively solving the problem of insufficient gain of high pulse energy and high repetition frequency laser regenerative amplifiers. The method and device are not only simple to operate, scientific and effective, but also highly practical.

[0011] In order to achieve the above object, the present invention adopts the following technical solution:

[0012] In a first aspect, an embodiment of the present invention provides a laser multi-pass regeneration amplifier device, comprising:

[0013] an oscillator, which generates the initial laser pulse;

[0014] A pulse picker selects a single pulse from the laser pulses output by the oscillator so as to enter a four-way regenerative amplifier for amplification;

[0015] A four-way regenerative amplifier, comprising a plurality of optical elements and a first pump source, for amplifying the selected laser pulses multiple times; the first pump source provides energy to the first laser crystal so that it can amplify the laser pulses;

[0016] The plurality of optical elements include: a first polarization beam splitter, a Pockels cell, a first quarter wave plate, a plane reflector, a first focusing lens, a second polarization beam splitter, a first laser crystal, a second quarter wave plate, a first concave mirror, and a second concave mirror;

[0017] The first polarization beam splitter splits the selected laser pulse into two beams, which enter different paths;

[0018] Pockels cell, which controls the polarization state of the laser pulse;

[0019] The first quarter-wave plate rotates the polarization state of the laser pulse by 90 degrees;

[0020] A plane mirror reflects the laser pulse back to the four-way regeneration cavity;

[0021] In the four-way regeneration cavity, along the light propagation direction, the following are in order: a first quarter wave plate, a Pockels cell, a first polarization beam splitter, a first focusing lens, a second polarization beam splitter, a first laser crystal, a second quarter wave plate, a first concave mirror, a second quarter wave plate, a first laser crystal, a second polarization beam splitter, a second concave mirror, a second polarization beam splitter, a first laser crystal, a second quarter wave plate, a first concave mirror, a second quarter wave plate, and a first laser crystal; the four-way regeneration cavity is obtained to pass through the gain medium four times in one circle; the high-voltage duration of the pulse selector is adjusted so that the selected laser pulse is output from the four-way regeneration cavity after obtaining 4N times of gain amplification; N is the high-voltage duration divided by the time it takes for the pulse to travel back and forth to the regeneration cavity.

[0022] Furthermore, the first quarter wave plate and the Pockels cell are placed adjacent to each other.

[0023] Furthermore, the second quarter wave plate and the first laser crystal are placed adjacent to each other.

[0024] Furthermore, the four-pass regenerative cavity laser passes through the gain medium four times in a round trip, twice with horizontal polarization and twice with vertical polarization; the polarizations of the first and fourth passes are the same, and the polarizations of the second and third passes are the same.

[0025] Furthermore, the first quarter wave plate and the second quarter wave plate both have a rotation adjustment mechanism.

[0026] Furthermore, the first focusing lens is used to shape the seed pulse so that it achieves mode matching with the pump light emitted by the first pump source in the first laser crystal.

[0027] In a second aspect, an embodiment of the present invention further provides a laser multi-pass regeneration amplification method, using the laser multi-pass regeneration amplification device as described in any one of the first aspects, the method specifically comprising:

[0028] In the first step, a single laser pulse passes through the first polarization beam splitter in the first direction and enters the four-way regeneration cavity. The Pockels cell is not powered. The seed light passes through the first quarter wave plate, is reflected by the plane reflector, and then passes through the first quarter wave plate and the unpowered Pockels cell again. At this time, the polarization state of the seed light is rotated 90° and reflected downward by the first polarization beam splitter, and the Pockels cell starts to be powered on.

[0029] In the second step, the seed light propagating downward is shaped by the first focusing lens, reflected by the second polarization beam splitter toward the first direction and enters the four-way amplification part;

[0030] In the third step, after the seed light passes through the first laser crystal in the first direction for the first time, it passes through the second quarter wave plate, is reflected by the first concave mirror, and passes through the first laser crystal in the second direction for the second time. At the same time, the polarization state changes. The seed light passes through the second polarization beam splitter, is reflected by the second concave mirror, passes through the first laser crystal for the third time through the second polarization beam splitter, passes through the second quarter wave plate in the first direction, is reflected by the first concave mirror, and passes through the first laser crystal in the second direction for the fourth time. The polarization is restored, and the seed light will be reflected and propagated upward when passing through the second polarization beam splitter.

[0031] The fourth step is to pass through the first focusing lens upwards, and be reflected by the first polarization beam splitter to propagate in the first direction. At this time, the Pockels cell is powered on, and the seed light is transmitted through the half-wave plate formed by the Pockels cell and the first quarter-wave plate, and then reflected by the plane reflector to pass through the half-wave plate for the second time. The polarization state remains unchanged, and the seed light continues to be amplified in the cavity.

[0032] In the fifth step, when the gain reaches the target requirement, the Pockels cell is restored to a low level before the seed light passes through the Pockels cell for the first time in the fourth step. The seed passes through the first quarter-wave plate, is reflected by the plane mirror, and passes through the first quarter-wave plate and the unpowered Pockels cell again. At this time, the polarization state of the seed will cause it to be output outward through the first polarization beam splitter.

[0033] In a third aspect, an embodiment of the present invention further provides a laser multi-pass regeneration amplifier device, comprising:

[0034] an oscillator, which generates the initial laser pulse;

[0035] A pulse picker, which selects a single pulse from the laser pulses output by the oscillator so as to enter the six-pass regenerative amplifier for amplification;

[0036] A six-way regenerative amplifier, composed of a plurality of optical elements and a first pump source and a second pump source, is used to amplify the selected laser pulse multiple times; the first pump source provides energy to the first laser crystal so that it can amplify the laser pulse; the second pump source provides energy to the second laser crystal so that it can amplify the laser pulse;

[0037] The plurality of optical elements include: a first polarization beam splitter, a Pockels cell, a first quarter wave plate, a plane reflector, a first focusing lens, a second polarization beam splitter, a second laser crystal, a second quarter wave plate, a first concave mirror, a second concave mirror, a second focusing lens, and a second laser crystal;

[0038] The first polarization beam splitter splits the selected laser pulse into two beams, which enter different paths;

[0039] Pockels cell, which controls the polarization state of the laser pulse;

[0040] The first quarter-wave plate rotates the polarization state of the laser pulse by 90 degrees;

[0041] A plane mirror reflects the laser pulse back to the six-pass regeneration cavity;

[0042] In the six-pass regeneration cavity, along the light propagation direction, the following are in order: a first quarter wave plate, a Pockels cell, a first polarization beam splitter, a first focusing lens, a second polarization beam splitter, a first laser crystal, a second quarter wave plate, a first concave mirror, a second quarter wave plate, a first laser crystal, a second polarization beam splitter, a second focusing lens, a second laser crystal, a second concave mirror, a second laser crystal, a second focusing lens, a second polarization beam splitter, a first laser crystal, a second quarter wave plate, a first concave mirror, a second quarter wave plate, and a first laser crystal;

[0043] A six-pass regeneration cavity is obtained to pass through the gain medium six times in one circle; the high voltage duration of the pulse selector is adjusted so that the selected laser pulse is output from the six-pass regeneration cavity after obtaining 6N times of gain amplification; N is the high voltage duration divided by the time it takes for the pulse to go back and forth in the regeneration cavity.

[0044] Furthermore, the first quarter wave plate and the Pockels cell are placed adjacent to each other.

[0045] Furthermore, the second quarter wave plate and the first laser crystal are placed adjacent to each other.

[0046] Furthermore, the six-pass regeneration cavity passes through the gain medium six times in one circle, wherein the polarization of the first and fourth times passing through the first laser crystal is the same, and the polarization of the second and third times passing through the first laser crystal is the same as the first and second times passing through the second laser crystal.

[0047] Furthermore, the first quarter wave plate and the second quarter wave plate both have a rotation adjustment mechanism.

[0048] Furthermore, the first focusing lens is used to shape the seed pulse so that it can achieve mode matching with the pump light emitted by the first pump source in the first laser crystal. The second focusing lens is used to shape the seed pulse so that it can achieve mode matching with the pump light emitted by the second pump source in the second laser crystal.

[0049] Furthermore, the first laser crystal and the second laser crystal are both Yb:CaYAlO4.

[0050] In a fourth aspect, an embodiment of the present invention further provides a laser multi-pass regeneration amplification method, using the laser multi-pass regeneration amplification device as described in the third aspect, the method specifically comprising:

[0051] In the first step, a single laser pulse passes through the first polarization beam splitter in the first direction and enters the six-pass regeneration cavity. The Pockels cell is not powered. The seed light passes through the first quarter-wave plate, is reflected by the plane reflector, and then passes through the first quarter-wave plate and the unpowered Pockels cell again. At this time, the polarization state of the seed light is rotated 90° and reflected downward by the first polarization beam splitter, and the Pockels cell starts to be powered on.

[0052] In the second step, the seed light propagating downward is shaped by the first focusing lens, reflected by the second polarization beam splitter toward the first direction and enters the six-channel amplification part;

[0053] In the third step, after the seed light passes through the first laser crystal in the first direction for the first time, it is reflected by the second quarter wave plate and the first concave mirror, and the second quarter wave plate passes through the first laser crystal in the second direction for the second time. At the same time, the polarization state changes. The seed light passes through the second polarization beam splitter and the second focusing lens, passes through the second laser crystal for the first time, and then reflects by the second concave mirror, passes through the second laser crystal for the second time. The seed light passes through the first laser crystal for the third time through the second focusing lens and the second polarization beam splitter, passes through the second quarter wave plate and the first concave mirror in the first direction, and passes through the first laser crystal in the second direction for the fourth time. The polarization is restored, and the seed light will be reflected and propagated upward when passing through the second polarization beam splitter.

[0054] The fourth step is to pass through the first focusing lens upwards, and be reflected by the first polarization beam splitter to propagate in the first direction. At this time, the Pockels cell is powered on, and the seed light is transmitted through the half-wave plate formed by the Pockels cell and the first quarter-wave plate, and then reflected by the plane reflector to pass through the half-wave plate for the second time. The polarization state remains unchanged, and the seed light continues to be amplified in the cavity.

[0055] In the fifth step, when the gain reaches the target requirement, the Pockels cell is restored to a low level before the seed light passes through the Pockels cell for the first time in the fourth step. The seed passes through the first quarter-wave plate, is reflected by the plane mirror, and passes through the first quarter-wave plate and the unpowered Pockels cell again. At this time, the polarization state of the seed will cause it to be output outward through the first polarization beam splitter.

[0056] It can be seen from the above technical solution that compared with the prior art, the present invention has the following advantages:

[0057] The present invention combines the advantages of a multi-pass amplifier and a regenerative amplifier. Through the multi-pass regenerative cavity design, the seed light can be amplified multiple times in the process of a round trip to the regenerative cavity to achieve energy stability. By changing the polarization of the seed light, the multi-pass structure is simplified, the beam pointing stability requirements are reduced, and collinear amplification is achieved to improve efficiency. The emission cross-section spectrum under different polarization states of the crystal is used to optimize gain extraction, thereby ensuring the gain in a high pulse energy and high repetition frequency laser regenerative amplifier.

[0058] In the four-pass regenerative amplifier device, the present invention optimizes the structure of the amplifier, from a simple regenerative amplifier-multi-pass amplifier cascade to a regenerative amplifier-multi-pass amplifier embedded structure. The regenerative amplifier cavity is used to achieve energy stability and simple adjustability, and the embedded colinear multi-pass amplifier achieves high-efficiency amplification. When extracting the same number of gain times, the accumulated dispersion is less, and the beam pointing stability requirements are reduced. Gain narrowing is suppressed by extracting the gain of different emission interfaces of the crystal and reducing the number of gain rounds.

[0059] In the six-pass regenerative amplifier device, the amplifier's amplification capability for seed light is further improved. The number of gain extractions per round is increased by 50% compared to a four-pass regenerative amplifier, and increased by 200% compared to a traditional general regenerative amplifier. This allows for more efficient pulse amplification, faster achievement of target power or pulse energy requirements, and higher repetition frequency output. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0061] Figure 1 This is a structural diagram of the laser multi-pass regenerative amplifier device of the present invention, including a four-pass regenerative amplifier.

[0062] Figure 2 The pulse establishment process and output pulse condition of the regenerative four-way amplifier of the present invention.

[0063] Figure 3 This is a structural diagram of the laser multi-pass regenerative amplifier device of the present invention, including a six-pass regenerative amplifier.

[0064] Figure 4 The pulse establishment process and output pulse condition of the regenerative six-pass amplifier of the present invention.

[0065] Figure 5Emission cross sections of Yb:CaYAlO4 crystal in different polarization directions used as an example.

[0066] Among them, in the figure:

[0067] 1 single seed pulse, 2 first polarization beam splitter, 3 Pockels cell, 4 first quarter wave plate, 5 plane mirror, 6 first focusing lens, 7 second polarization beam splitter, 8 first laser crystal, 9 second quarter wave plate, 10 first concave mirror, 11 second concave mirror, 12 first pump source, 13 second focusing lens, 14 second laser crystal, 15 second pump source. DETAILED DESCRIPTION

[0068] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] Embodiment 1:

[0070] See also Figure 1 The embodiment of the present invention provides a laser multi-pass regeneration amplifier device, comprising: an oscillator, a pulse selector and a four-pass regeneration amplifier, wherein the oscillator generates an initial laser pulse, and the pulse selector selects a single pulse from the laser pulse output by the oscillator so as to enter the four-pass regeneration amplifier for amplification;

[0071] The four-way regenerative amplifier, which is composed of a plurality of optical elements and a first pump source 12, is used to amplify the selected laser pulses multiple times; the first pump source 12 provides energy to the first laser crystal 8 so that it can amplify the laser pulses;

[0072] Among them, multiple optical elements include a first polarization beam splitter 2, a Pockels cell 3, a first quarter wave plate 4, a plane reflector 5, a first focusing lens 6, a second polarization beam splitter 7, a first laser crystal 8, a second quarter wave plate 9, a first concave mirror 10, and a second concave mirror 11.

[0073] The first polarization beam splitter 2 splits the laser pulse into two beams, which enter different paths respectively.

[0074] Pockels cell 3 controls the polarization state of the laser pulse.

[0075] The first quarter wave plate 4 has a rotation adjustment mechanism, which can rotate the polarization state of the laser pulse by 90 degrees.

[0076] The plane mirror 5 reflects the laser pulse back to the four-way regeneration cavity.

[0077] The first focusing lens 6 shapes the laser pulse so that it matches the pump light mode in the laser crystal, thereby improving the gain extraction efficiency.

[0078] The second polarization beam splitter 7 reflects the laser pulse back to the four-way regeneration cavity or outputs the laser pulse.

[0079] The first laser crystal 8 amplifies the laser pulse.

[0080] The second quarter wave plate 9 has a rotation adjustment mechanism to rotate the polarization state of the laser pulse by 90 degrees again.

[0081] The first concave mirror 10 and the second concave mirror 11 are both used to reflect the laser pulse back to the four-way regeneration cavity so that the laser pulse passes through the laser crystal for multiple times for amplification.

[0082] The first pump source 12 provides energy to the first laser crystal 8 .

[0083] The Pockels cell 3 and the first quarter wave plate 4 are placed adjacent to each other. The Pockels cell is a controller of the number of amplification turns in a multi-pass regenerative amplifier and together with the first quarter wave plate serves as the "regeneration" structure of the amplifier to ensure gain and energy stability.

[0084] The second quarter wave plate 9 and the first laser crystal 8 are placed adjacent to each other. The second quarter wave plate changes the polarization state of the seed light. Combining the polarization beam splitter and the first laser crystal can form a "multi-pass" structure, so that the seed passes through the laser crystal multiple times for multi-pass amplification, and simplifies and reduces the difficulty of adjusting the optical path.

[0085] Working principle: A single laser pulse output by the oscillator is selected by a pulse selector with a set repetition frequency to enter the multi-pass regeneration cavity. After polarization control, the selected laser pulse can go back and forth in the multi-pass regeneration cavity for one circle and pass through the laser gain medium for multiple times to be amplified. By adjusting the high-voltage duration of the pulse selector, the selected laser pulse can be output from the multi-pass regeneration cavity after obtaining 4N (N is the high-voltage duration divided by the time it takes for the pulse to go back and forth in the regeneration cavity) times of gain amplification.

[0086] The optical path of the four-pass regeneration amplifier device is specifically as follows: a single laser pulse 1 output by an oscillator is selected by a pulse selector at a set repetition frequency to enter a four-pass regeneration cavity, and in the four-pass regeneration cavity, along the light propagation direction, there are the first quarter wave plate 4, the Pockels cell 3, the first polarization beam splitter 2, the first focusing lens 6, the second polarization beam splitter 7, the first laser crystal 8, the second quarter wave plate 9, the first concave mirror 10, the second quarter wave plate 9, the first laser crystal 8, the second polarization beam splitter 7, the second concave mirror 11, the second polarization beam splitter 7, the first laser crystal 8, the second quarter wave plate 9, the first concave mirror 10, the second quarter wave plate 9, and the first laser crystal 8. The multi-pass regeneration cavity is obtained to pass through the gain medium four times in one circle; the high-voltage duration of the pulse selector is adjusted so that the selected laser pulse can be output from the multi-pass regeneration cavity after obtaining 4N (N is the high-voltage duration divided by the time the pulse goes back and forth in the regeneration cavity) times of gain amplification.

[0087] That is, the four-pass regenerative cavity laser makes a round trip through the gain medium four times, twice with horizontal polarization and twice with vertical polarization. The polarizations of the first and fourth passes are the same, and the polarizations of the second and third passes are the same. Considering that the emission cross-sections of the crystal are inconsistent under different polarization states, different polarizations can be used to extract the gain of different emission cross-sections of the crystal, thereby realizing laser center wavelength amplification (tuning) and spectral bandwidth control.

[0088] The laser multi-pass regeneration amplifier device provided in the embodiment of the present invention realizes multiple amplification of laser pulses through the design of the multi-pass regeneration cavity, effectively improving the energy and power of the laser pulses. At the same time, by controlling the polarization state and the number of round trips of the laser pulses, the central wavelength and spectral bandwidth of the laser can be regulated, the gain narrowing effect can be suppressed, and the output pulse spectrum width can be guaranteed.

[0089] Embodiment 2:

[0090] The laser multi-pass regeneration amplification method provided in the embodiment of the present invention uses the laser multi-pass regeneration amplification device of embodiment 1, and the specific implementation process of amplification is:

[0091] The first step is to refer to Figure 1 As shown, a single laser pulse 1 passes through the first polarization beam splitter 2 to the left and enters the multi-pass regeneration cavity. The Pockels cell 3 is not powered. The seed light passes through the first quarter wave plate 4, is reflected by the plane reflector 5, and passes through the first quarter wave plate 4 and the unpowered Pockels cell 3 again. At this time, the polarization state of the seed light rotates 90° and is reflected downward by the first polarization beam splitter 2, and the Pockels cell 3 starts to power on.

[0092] In the second step, the seed light propagating downward is shaped by the first focusing lens 6, reflected by the second polarization beam splitter 7 to the left and enters the four-way amplification part.

[0093] In the third step, after the seed light passes through the first laser crystal 8 to the left for the first time, it is reflected by the second quarter wave plate 9 and the first concave mirror 10, and the second quarter wave plate 9 passes through the first laser crystal 8 to the right for the second time. At the same time, the polarization state changes, and it passes through the second polarization beam splitter 7, and then reflected by the second concave mirror 11, and passes through the first laser crystal 8 for the third time through the second polarization beam splitter 7, passes through the second quarter wave plate 9 to the left, the first concave mirror 10, and the second quarter wave plate 9 passes through the first laser crystal 8 to the right for the fourth time. The polarization is restored, and it will be reflected and propagated upward when passing through the second polarization beam splitter 7.

[0094] In the fourth step, the seed light passes through the first focusing lens 6 upwards and is reflected by the first polarization beam splitter 2 to propagate to the left. At this time, the Pockels cell 3 is powered on, and the seed light passes through the "half-wave plate" formed by the Pockels cell 3 and the first quarter-wave plate 4, and is then reflected by the plane mirror 6 and passes through the "half-wave plate" for the second time. The polarization state remains unchanged and continues to be amplified in the cavity.

[0095] In the fifth step, when the gain reaches the target requirement, before the seed light passes through the Pockels cell 3 for the first time in the fourth step, the Pockels cell 3 is restored to a low level, the seed passes through the first quarter wave plate 4, is reflected by the plane reflector 5, and passes through the first quarter wave plate 4 and the unpowered Pockels cell 3 again. At this time, the polarization state of the seed will cause it to be output outward through the first polarization beam splitter 2.

[0096] This method can achieve gain narrowing suppression by controlling the crystal placement and the polarization direction of the seed light, combined with the emission spectrum characteristics of the gain medium in different axes. In the amplification experiment of the regenerative four-pass amplifier with a repetition frequency of 100kHz, the amplified pulse establishment process is detected at the plane reflector 5 and the output laser pulse monitored at the output end is as follows Figure 2 As shown, the horizontal axis is time and the vertical axis is signal amplitude. The average output power of the four-way regenerative cavity can reach 41.9W. At a repetition frequency of 10kHz, the pulse energy reaches 2.87mJ.

[0097] Embodiment 3:

[0098] See also Figure 3 , an embodiment of the present invention further provides a laser multi-pass regeneration amplifier device, comprising: an oscillator, a pulse selector and a six-pass regeneration amplifier, the oscillator generates an initial laser pulse, the pulse selector selects a single pulse from the laser pulses output by the oscillator, so as to enter the six-pass regeneration amplifier for amplification;

[0099] The six-pass regenerative amplifier is composed of a plurality of optical elements, a first pump source 12 and a second pump source 15, and is used to amplify the selected laser pulses multiple times; the first pump source 12 provides energy to the first laser crystal 8 so that it can amplify the laser pulses; the second pump source 15 provides energy to the second laser crystal 14 so that it can amplify the laser pulses;

[0100] Among them, multiple optical elements include a first polarization beam splitter 2, a Pockels cell 3, a first quarter wave plate 4, a plane mirror 5, a first focusing lens 6, a second polarization beam splitter 7, a first laser crystal 8, a second quarter wave plate 9, a first concave mirror 10, a second concave mirror 11, a second focusing lens 13, and a second laser crystal 14.

[0101] The first polarization beam splitter 2 splits the selected laser pulse into two beams, which enter different paths respectively.

[0102] Pockels cell 3 controls the polarization state of the laser pulse.

[0103] The first quarter wave plate 4 has a rotation adjustment mechanism, which can rotate the polarization state of the laser pulse by 90 degrees.

[0104] The plane mirror 5 reflects the laser pulse back to the six-pass regeneration cavity.

[0105] The first focusing lens 6 and the second focusing lens 13 are both used to shape the laser pulse so that it matches the pump light mode of the pump source in the laser crystal, thereby improving the gain extraction efficiency.

[0106] The second polarization beam splitter 7 reflects the laser pulse back to the four-way regeneration cavity or outputs the laser pulse.

[0107] The first laser crystal 8 and the second laser crystal 14 are both used to amplify laser pulses.

[0108] The second quarter wave plate 9 has a rotation adjustment mechanism to rotate the polarization state of the laser pulse by 90 degrees again.

[0109] The first concave mirror 10 and the second concave mirror 11 are both used to reflect the laser pulse back to the four-way regeneration cavity so that the laser pulse passes through the laser crystal for multiple times for amplification.

[0110] The first pump source 12 provides energy to the first laser crystal 8 .

[0111] The second pump source 15 provides energy to the second laser crystal 14 .

[0112] The Pockels cell 3 and the first quarter wave plate 4 are placed adjacent to each other. The Pockels cell is a controller of the number of amplification turns in a multi-pass regenerative amplifier and together with the first quarter wave plate serves as the "regeneration" structure of the amplifier to ensure gain and energy stability.

[0113] The second quarter wave plate 9 and the first laser crystal 8 are placed adjacent to each other, and the first laser crystal 8 and the second laser crystal 12 are placed on both sides of the second polarization beam splitter 7. The second quarter wave plate changes the polarization state of the seed light, and can form a "multi-pass" structure in combination with the polarization beam splitter and the first laser crystal and the second laser crystal, so that the seed passes through the laser crystal multiple times for multi-pass amplification, and the difficulty of adjusting the optical path is simplified and reduced.

[0114] Working principle: A single laser pulse output by the oscillator is selected by a pulse selector at a set repetition frequency to enter the multi-pass regeneration cavity. After polarization control, the selected laser pulse can go back and forth in the multi-pass regeneration cavity for one circle and pass through the laser gain medium for multiple times to be amplified. By adjusting the high-voltage duration of the pulse selector, the selected laser pulse can be output from the multi-pass regeneration cavity after obtaining 6N (N is the high-voltage duration divided by the time it takes for the pulse to go back and forth in the regeneration cavity) times of gain amplification.

[0115] The optical path of the six-pass regeneration amplifier device is specifically as follows: a single laser pulse 1 output by an oscillator is selected by a pulse selector at a set repetition frequency to enter the six-pass regeneration cavity, and in the six-pass regeneration cavity, along the light propagation direction, there are the first quarter wave plate 4, the Pockels cell 3, the first polarization beam splitter 2, the first focusing lens 6, the second polarization beam splitter 7, the first laser crystal 8, the second quarter wave plate 9, the first concave mirror 10, the second quarter wave plate 9, the first laser crystal 8, the second polarization beam splitter 7, the second focusing lens 13, the second laser crystal 14, the second concave mirror 11, the second laser crystal 14, the second focusing lens 13, the second polarization beam splitter 7, the first laser crystal 8, the second quarter wave plate 9, the first concave mirror 10, the second quarter wave plate 9, and the first laser crystal 8. The multi-pass regeneration cavity is obtained to pass through the gain medium six times in one circle; and the high-voltage duration of the pulse selector is adjusted so that the selected laser pulse can be output from the multi-pass regeneration cavity after obtaining 6N times of gain amplification.

[0116] That is, the six-pass regenerative cavity laser passes through the gain medium six times in one round, and the six-pass regenerative cavity passes through the gain medium six times in one round, wherein the first and fourth times through the first laser crystal 8 have the same polarization, and the second and third times through the first laser crystal 8 have the same polarization as the first and second times through the second laser crystal 14. The six-pass regenerative cavity can not only use different polarized light to improve the gain of different emission cross sections of the crystal, but also can further realize the central wavelength and spectral bandwidth control on the basis of the above four-pass regenerative amplification by combining different placement methods of two gain media, and suppress the gain narrowing effect by reducing the number of gain turns to ensure the output pulse spectrum width.

[0117] The laser multi-pass regeneration amplifier device provided in the embodiment of the present invention has two pump sources, which are used to pump the first laser crystal and the second laser crystal respectively. The design of the two pump sources can further improve the output power and pulse energy of the laser.

[0118] Embodiment 4:

[0119] The embodiment of the present invention provides a laser multi-pass regeneration amplification method, using the laser multi-pass regeneration amplification device of embodiment 3, and the specific implementation process of amplification is:

[0120] In the first step, a single laser pulse 1 passes through the first polarization beam splitter 2 to the left and enters the multi-pass regeneration cavity. The Pockels cell 3 is not powered. The seed light passes through the first quarter-wave plate 4, is reflected by the plane mirror 5, and passes through the first quarter-wave plate 4 and the unpowered Pockels cell 3 again. At this time, the polarization state of the seed light rotates 90° and is reflected downward by the first polarization beam splitter 2, and the Pockels cell 3 starts to power on.

[0121] In the second step, the seed light propagating downward is shaped by the first focusing lens 6, reflected by the second polarization beam splitter 7 to the left and enters the six-channel amplification part.

[0122] In the third step, after the seed light passes through the first laser crystal 8 to the left for the first time, it is reflected by the second quarter wave plate 9 and the first concave mirror 10, and the second quarter wave plate 9 passes through the first laser crystal 8 to the right for the second time. At the same time, the polarization state changes, and it passes through the second polarization beam splitter 7 and the second focusing lens 13, passes through the second laser crystal 14 for the first time, and then is reflected by the second concave mirror 11, passes through the second laser crystal 14 for the second time, passes through the second focusing lens 13 and the second polarization beam splitter 7 for the third time, passes through the second quarter wave plate 9 and the first concave mirror 10 to the left, and the second quarter wave plate 9 passes through the first laser crystal 8 to the right for the fourth time, and the polarization is restored. When passing through the second polarization beam splitter 7, it will be reflected and propagated upward.

[0123] In the fourth step, the seed light passes through the first focusing lens 6 upwards and is reflected by the first polarization beam splitter 2 to propagate to the left. At this time, the Pockels cell 3 is powered on, and the seed light passes through the "half-wave plate" formed by the Pockels cell 3 and the first quarter-wave plate 4, and is then reflected by the plane mirror 5 and passes through the "half-wave plate" for the second time. The polarization state remains unchanged and continues to be amplified in the cavity.

[0124] In the fifth step, when the gain reaches the target requirement, before the seed light passes through the Pockels cell 3 for the first time in the fourth step, the Pockels cell 3 is restored to a low level, the seed passes through the first quarter wave plate 4, is reflected by the plane reflector 5, and passes through the first quarter wave plate 4 and the unpowered Pockels cell 3 again. At this time, the polarization state of the seed will cause it to be output outward through the first polarization beam splitter 2.

[0125] This method can achieve gain narrowing suppression by controlling the placement of the crystal and the polarization direction of the seed light, combined with the emission spectrum characteristics of the gain medium in different axes. In the amplification experiment of the regenerative six-pass amplifier with a repetition frequency of 50kHz, the average output power of the six-pass regenerative cavity can reach 65.24W. When the repetition frequency reaches 5kHz, the amplified pulse establishment process is detected at the plane reflector 5 and the output laser pulse monitored at the output end is as follows Figure 4 The horizontal axis is time and the vertical axis is signal amplitude; the pulse energy reaches 6.5mJ.

[0126] Among them, the relationship between crystal placement and seed light polarization is as follows: Figure 5 As shown, the horizontal axis Wavelength is the wavelength, in nm; the vertical axis Emission cross section is the cross-sectional area, in 10 -20 cm 2 It can be seen that the half-width of the emission spectrum of the crystal Yb:CaYAlO4 under σ polarization reaches 77nm, and there is a very flat emission interface. Although the gain cross section under π polarization is not as flat as that under σ polarization, there is a depression at 1025nm, which can suppress the strong gain in the central part of the seed light spectrum and achieve gain balance within the spectral range during re-amplification. It can be used to solve the gain narrowing problem in the regenerative amplification process.

[0127] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0128] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser multi-pass regeneration amplifier device, characterized in that: include: an oscillator, which generates the initial laser pulse; A pulse picker selects a single pulse from the laser pulses output by the oscillator so as to enter a four-way regenerative amplifier for amplification; A four-way regenerative amplifier, comprising a plurality of optical elements and a first pump source (12), for amplifying selected laser pulses multiple times; the first pump source (12) provides energy to a first laser crystal (8) so that it can amplify the laser pulses; The plurality of optical elements include: a first polarization beam splitter (2), a Pockels cell (3), a first quarter wave plate (4), a plane reflector (5), a first focusing lens (6), a second polarization beam splitter (7), a first laser crystal (8), a second quarter wave plate (9), a first concave mirror (10) and a second concave mirror (11); A first polarization beam splitter (2) is used to split the selected laser pulse into two beams, which enter different paths respectively; Pockels cell (3), controlling the polarization state of the laser pulse; A first quarter wave plate (4) rotates the polarization state of the laser pulse by 90 degrees; A plane reflector (5) reflects the laser pulse back to the four-way regeneration cavity; In the four-way regeneration cavity, the light propagation direction is sequentially: a first quarter wave plate (4), a Pockels cell (3), a first polarization beam splitter (2), a first focusing lens (6), a second polarization beam splitter (7), a first laser crystal (8), a second quarter wave plate (9), a first concave mirror (10), a second quarter wave plate (9), a first laser crystal (8), a second polarization beam splitter (7), a second concave mirror (11), a second polarization beam splitter (7), a first laser crystal (8), a second quarter wave plate (9), a first concave mirror (10), a second quarter wave plate (9), and a first laser crystal (8); the four-way regeneration cavity is obtained to pass through the gain medium four times in one circle; the high-voltage duration of the pulse selector is adjusted so that the selected laser pulse is output from the four-way regeneration cavity after obtaining 4N times of gain amplification; N is the high-voltage duration divided by the time it takes for the pulse to travel back and forth in the regeneration cavity.

2. A laser multi-pass regeneration amplifier device according to claim 1, characterized in that: The first quarter wave plate (4) and the Pockels cell (3) are placed adjacent to each other.

3. A laser multi-pass regeneration amplifier device according to claim 1, characterized in that: The second quarter wave plate (9) and the first laser crystal (8) are placed adjacent to each other.

4. A laser multi-pass regeneration amplifier device according to claim 1, characterized in that: The four-pass regenerative cavity laser passes through the gain medium four times in one round trip, twice with horizontal polarization and twice with vertical polarization; the polarizations of the first and fourth passes are the same, and the polarizations of the second and third passes are the same.

5. The laser multi-pass regeneration amplifier device according to claim 1, characterized in that: The first quarter wave plate (4) and the second quarter wave plate (9) both have a rotation adjustment mechanism.

6. A laser multi-pass regeneration amplification method and device according to claim 1, characterized in that: The first focusing lens (6) is used to shape the seed pulse so that it achieves mode matching with the pump light emitted by the first pump source (12) in the first laser crystal (8).

7. A laser multi-pass regeneration amplification method and device according to claim 1, characterized in that: The first laser crystal (8) is Yb:CaYAlO4.

8. A laser multi-pass regeneration amplification method, characterized in that: Using the laser multi-pass regeneration amplifier device according to any one of claims 1 to 7, the method specifically comprises: In the first step, a single laser pulse (1) passes through a first polarization beam splitter (2) in a first direction and enters a four-way regeneration cavity. The Pockels cell (3) is not powered. The seed light passes through a first quarter wave plate (4), passes through a plane reflector (5), is reflected, and passes through the first quarter wave plate (4) and the unpowered Pockels cell (3) again. At this time, the polarization state of the seed light is rotated by 90° and is reflected downward by the first polarization beam splitter (2). The Pockels cell (3) starts to be powered. In the second step, the seed light propagating downward is shaped by the first focusing lens (6), reflected by the second polarization beam splitter (7) and enters the four-way amplification part in the first direction; In the third step, after the seed light passes through the first laser crystal (8) in the first direction for the first time, it passes through the second quarter wave plate (9), is reflected by the first concave mirror (10), and passes through the first laser crystal (8) in the second direction for the second time, and the polarization state is changed at the same time. The seed light passes through the second polarization beam splitter (7), is reflected by the second concave mirror (11), passes through the first laser crystal (8) for the third time through the second polarization beam splitter (7), passes through the second quarter wave plate (9) in the first direction, is reflected by the first concave mirror (10), and passes through the first laser crystal (8) in the second direction for the fourth time. The polarization is restored, and the seed light is reflected and propagates upward when passing through the second polarization beam splitter (7). The fourth step is to pass through the first focusing lens (6) upwards, and be reflected by the first polarization beam splitter (2) to propagate in the first direction. At this time, the Pockels cell (3) is powered on, and the seed light is transmitted through the half-wave plate formed by the Pockels cell (3) and the first quarter-wave plate (4), and then reflected by the plane reflector (5) to pass through the half-wave plate for the second time. The polarization state remains unchanged, and the seed light continues to be amplified in the cavity. In the fifth step, when the gain reaches the target requirement, before the seed light passes through the Pockels cell (3) for the first time in the fourth step, the Pockels cell (3) is restored to a low level, and the seed passes through the first quarter wave plate (4), is reflected by the plane reflector (5), and passes through the first quarter wave plate (4) and the unpowered Pockels cell (3) again. At this time, the polarization state of the seed will cause it to be output outward through the first polarization beam splitter (2).

9. A laser multi-pass regenerative amplifier device, characterized in that: include: an oscillator, which generates the initial laser pulse; A pulse picker, which selects a single pulse from the laser pulses output by the oscillator so as to enter the six-pass regenerative amplifier for amplification; A six-pass regenerative amplifier, comprising a plurality of optical elements and a first pump source (12) and a second pump source (15), for amplifying selected laser pulses multiple times; the first pump source (12) provides energy to a first laser crystal (8) so that it can amplify laser pulses; the second pump source (15) provides energy to a second laser crystal (14) so ​​that it can amplify laser pulses; The plurality of optical elements include: a first polarization beam splitter (2), a Pockels cell (3), a first quarter wave plate (4), a plane reflector (5), a first focusing lens (6), a second polarization beam splitter (7), a second laser crystal (14), a second quarter wave plate (9), a first concave mirror (10), a second concave mirror (11), a second focusing lens (13), and a second laser crystal (14); A first polarization beam splitter (2) is used to split the selected laser pulse into two beams, which enter different paths respectively; Pockels cell (3), controlling the polarization state of the laser pulse; A first quarter wave plate (4) rotates the polarization state of the laser pulse by 90 degrees; A plane reflector (5) reflects the laser pulse back to the six-pass regeneration cavity; In the six-pass regeneration cavity, the following are arranged in order along the light propagation direction: a first quarter wave plate (4), a Pockels cell (3), a first polarization beam splitter (2), a first focusing lens (6), a second polarization beam splitter (7), a first laser crystal (8), a second quarter wave plate (9), a first concave mirror (10), a second quarter wave plate (9), a first laser crystal (8), a second polarization beam splitter (7), a second focusing lens (13), a second laser crystal (14), a second concave mirror (11), a second laser crystal (14), a second focusing lens (13), a second polarization beam splitter (7), a first laser crystal (8), a second quarter wave plate (9), a first concave mirror (10), a second quarter wave plate (9), and a first laser crystal (8); A six-pass regeneration cavity is obtained to pass through the gain medium six times in one circle; the high voltage duration of the pulse selector is adjusted so that the selected laser pulse is output from the six-pass regeneration cavity after obtaining 6N times of gain amplification; N is the high voltage duration divided by the time it takes for the pulse to go back and forth in the regeneration cavity.

10. A laser multi-pass regeneration amplification method, characterized in that: Using the laser multi-pass regeneration amplifier device as claimed in claim 9, the method specifically comprises: In the first step, a single laser pulse (1) passes through a first polarization beam splitter (2) in a first direction and enters a six-pass regeneration cavity. The Pockels cell (3) is not powered. The seed light passes through a first quarter wave plate (4), passes through a plane reflector (5), is reflected, and passes through the first quarter wave plate (4) and the unpowered Pockels cell (3) again. At this time, the polarization state of the seed light is rotated by 90° and is reflected downward by the first polarization beam splitter (2). The Pockels cell (3) starts to be powered. In the second step, the seed light propagating downward is shaped by the first focusing lens (6), reflected by the second polarization beam splitter (7) and enters the six-channel amplification part in the first direction; In the third step, after the seed light passes through the first laser crystal (8) in the first direction for the first time, it is reflected by the second quarter wave plate (9) and the first concave mirror (10), and the second quarter wave plate (9) passes through the first laser crystal (8) in the second direction for the second time, and the polarization state is changed at the same time. The seed light passes through the second polarization beam splitter (7) and the second focusing lens (13), passes through the second laser crystal (14) for the first time, and is reflected by the second concave mirror (11), passes through the second laser crystal (14) for the second time, passes through the second focusing lens (13) and the second polarization beam splitter (7), passes through the first laser crystal (8) for the third time, passes through the second quarter wave plate (9) and the first concave mirror (10) in the first direction, and the second quarter wave plate (9) passes through the first laser crystal (8) in the second direction for the fourth time, and the polarization is restored. When passing through the second polarization beam splitter (7), the seed light is reflected and propagates upward; The fourth step is to pass through the first focusing lens (6) upwards, and be reflected by the first polarization beam splitter (2) to propagate in the first direction. At this time, the Pockels cell (3) is powered on, and the seed light is transmitted through the half-wave plate formed by the Pockels cell (3) and the first quarter-wave plate (4), and then reflected by the plane reflector (5) to pass through the half-wave plate for the second time. The polarization state remains unchanged, and the seed light continues to be amplified in the cavity. In the fifth step, when the gain reaches the target requirement, before the seed light passes through the Pockels cell (3) for the first time in the fourth step, the Pockels cell (3) is restored to a low level, and the seed passes through the first quarter wave plate (4), is reflected by the plane reflector (5), and passes through the first quarter wave plate (4) and the unpowered Pockels cell (3) again. At this time, the polarization state of the seed will cause it to be output outward through the first polarization beam splitter (2).

Images