Laser multi-pass regeneration amplification device and method

Abstract

The present invention discloses a laser multi-pass regenerative amplification device and method. The device includes at least an oscillator, a pulse selector, and a multi-pass regenerative amplifier. A single laser pulse output by the oscillator is selected by the pulse selector at a set repetition frequency to enter the multi-pass regenerative cavity of the multi-pass regenerative amplifier. Polarization control is used to cause the selected laser pulse to travel back and forth through the multi-pass regenerative cavity four or six times for amplification through the laser gain medium. Adjusting the high-voltage duration of the pulse selector allows the selected laser pulse to be output from the multi-pass regenerative cavity after obtaining 4N or 6N times of gain amplification; N is the high-voltage duration divided by the time it takes the pulse to travel back and forth between the regenerative cavity and the laser. In the present invention, the multi-pass regenerative cavity design increases the number of amplifications of the laser pulse in a single round trip, thereby reducing the number of gain cycles required for saturation amplification and thereby increasing the repetition frequency of the regenerative amplifier. This can effectively improve gain extraction during the laser pulse regenerative amplification process.

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 practical needs. Short-pulse amplification technology is needed to amplify low-average-power laser pulses to target high-power laser pulses to meet application requirements in various fields.

[0003] Currently, the main amplification methods are

[0004] (1) Regenerative amplification: The Pockels cell can be used to easily 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 loss caused by the wave plate and the Pockels cell.

[0006] To meet the needs of researchers in fields such as laser processing, high-energy physics, precision measurement, and attosecond lasers, high-average-power femtosecond lasers must possess the characteristics of high power, high energy, and short pulses. Higher laser power and greater single-pulse energy result in faster processing rates, a wider range of materials that can be ablated, and more pronounced high-order nonlinear optical effects. Shorter pulses also broaden the spectrum, facilitating the generation of supercontinuums and producing cleaner processing boundaries.

[0007] The problems and drawbacks of the above technologies are as follows: For existing solutions, while the regenerative amplifier can fully extract the crystal gain as the number of gain turns increases, repeated passages through the Pockels cell and waveplate accumulate significant material dispersion, reducing the upper limit of the output pulse repetition frequency. The amplified spectrum width is also affected by the gain narrowing effect, resulting in a narrower spectrum. Multi-pass amplifiers offer less accumulated dispersion but weaker gain extraction capabilities, and they require extremely high optical control requirements. The beam's pointing stability after each pass through the laser crystal must be traced back to the oscillator, and the optical path becomes more difficult to adjust with increasing passes, increasing the beam quality requirements. The addition of an aperture required for non-collinear amplification reduces efficiency to 10% to 20%.

[0008] To combine the advantages of both amplification methods, some researchers have connected regenerative and multipass amplifiers in series, first using a more efficient regenerative amplifier to pre-amplify the seed pulse to the millijoule level, and then using single-stage or multi-stage multipass amplifiers with even less dispersion to amplify the pulse to tens of millijoules or even higher. This method significantly increases the energy of a single pulse while greatly increasing the system complexity and technical difficulty, making the constructed laser amplification device too large and complex. Laser amplifiers combining these two amplification schemes can achieve high peak power while maintaining gain and energy stability.

[0009] However, how to balance the cumulative dispersion of the regenerative amplifier and the difficulty of adjusting the multi-pass amplification optical path, fully extract the gain reduction and gain narrowing during 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 urgently need to solve. Summary of the Invention

[0010] In light of this, the present invention provides a multi-pass laser regenerative amplifier device and method. This device not only maintains the advantages of energy stability and low beam pointing requirements during regenerative amplification, but also reduces cumulative dispersion while maintaining the same number of amplifications, effectively addressing the issue of insufficient gain in high-pulse-energy and high-repetition-rate laser regenerative amplifiers. This method and device are not only simple to operate, scientifically sound, and effective, but also highly practical.

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

[0012] In a first aspect, an embodiment of the present invention provides a laser multi-pass regenerative 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 that it can enter the 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, enabling it to 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 mirror, 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, the following components are arranged in order along the direction of light propagation: 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 by passing 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 one circle, 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 mirror, 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. The Pockels cell starts to power up.

[0029] In the second step, the downward-propagating seed light 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, and passes through the first laser crystal for the third time through the second polarization beam splitter. The seed light 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 state is restored and the seed light is reflected and propagates upward when it passes through the second polarization beam splitter.

[0031] In the fourth step, the seed light passes through the first focusing lens and is 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 passes through the half-wave plate composed of the Pockels cell and the first quarter-wave plate. It is then reflected by the plane mirror and passes 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 regenerative amplifier device, comprising:

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

[0035] A pulse picker 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-channel regenerative amplifier, comprising a plurality of optical elements and a first pump source and a second pump source, is used to amplify selected laser pulses multiple times; the first pump source provides energy to a first laser crystal, enabling it to amplify laser pulses; the second pump source provides energy to a second laser crystal, enabling it to amplify laser pulses;

[0037] The plurality of optical elements include: a first polarization beam splitter, a Pockels cell, a first quarter wave plate, a plane mirror, 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 direction of light propagation, the following are arranged 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 by passing 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 travel back and forth to 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 passes through the first laser crystal is the same, and the polarization of the second and third passes through the first laser crystal is the same as the polarization of the first and second passes 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 achieves 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 achieves 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 and amplification method, using the laser multi-pass regeneration and 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 mirror, 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. The Pockels cell starts to power up.

[0052] In the second step, the downward-propagating seed light 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 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 and the second focusing lens, passes through the second laser crystal for the first time, is reflected by the second concave mirror, passes through the second laser crystal for the second time, passes through the second focusing lens and the second polarization beam splitter for the third time, passes through the first laser crystal in the first direction, 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 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] In the fourth step, the seed light passes through the first focusing lens and is 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 passes through the half-wave plate composed of the Pockels cell and the first quarter-wave plate. It is then reflected by the plane mirror and passes 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 solutions 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 during a round trip to the regenerative cavity, thereby achieving 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, ensuring the gain in the high pulse energy and high repetition rate laser regenerative amplifier.

[0058] In a four-pass regenerative amplifier, this invention optimizes the amplifier structure, moving from a simple cascaded regenerative amplifier and multi-pass amplifier to an embedded regenerative amplifier and multi-pass amplifier configuration. This utilizes a regenerative amplifier cavity to achieve energy stability and simple adjustability, while an embedded collinear multi-pass amplifier achieves high-efficiency amplification. While extracting the same gain, the accumulated dispersion is reduced, while also reducing the beam pointing stability requirement. Gain narrowing is suppressed by extracting gain from different crystal emission interfaces 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. Compared with a four-pass regenerative amplifier, the number of gain extractions per round is increased by 50%, and compared with a traditional general regenerative amplifier, the number of gain extractions per round is increased by 200%. This can achieve more efficient pulse amplification, reach the target power or pulse energy requirements more quickly, and achieve a 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any 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 This is 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 This is the pulse establishment process and output pulse situation of the regenerative six-pass amplifier of the present invention.

[0065] Figure 5The emission cross sections of the 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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0069] Example 1:

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

[0071] The four-way regenerative amplifier is composed of multiple optical elements and a first pump source 12, and is used to amplify the selected laser pulses multiple times; the first pump source 12 provides energy to the first laser crystal 8, enabling it to 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 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, 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 another 90 degrees.

[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 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 the 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. Combined with the polarization beam splitter and the first laser crystal, a "multi-pass" structure can be formed, 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.

[0085] 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 travel back and forth in the multi-pass regeneration cavity for one circle and pass through the laser gain medium for multiple amplifications. By adjusting the high-voltage duration of the pulse selector, the selected laser pulse can be output from the multi-pass regeneration cavity after receiving 4N (N is the high-voltage duration divided by the time it takes for the pulse to travel back and forth in the regeneration cavity) times of gain amplification.

[0086] The optical path of the four-pass regenerative amplifier device is specifically as follows: a single laser pulse 1 output by an oscillator is selected at a set repetition frequency by a pulse picker and enters a four-pass regenerative cavity. Within the four-pass regenerative cavity, along the direction of light propagation, the following sequence is followed: 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. This results in a multi-pass regenerative cavity with four passes through the gain medium. Adjusting the high-voltage duration of the pulse picker allows the selected laser pulse to be output from the multi-pass regenerative cavity after receiving 4N (N is the high-voltage duration divided by the time it takes the pulse to travel back and forth between the regenerative cavity) times of gain amplification.

[0087] That is, the four-pass regenerative cavity laser passes through the gain medium four times in one circle, twice with horizontal polarization and twice with vertical polarization. The polarization of the first and fourth passes is the same, and the polarization of the second and third passes is the same. Considering that the emission cross-section of the crystal is inconsistent under different polarization states, different polarization lights 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 multi-pass laser regenerative amplifier device provided by the present invention achieves multiple amplification of laser pulses through the design of a multi-pass regenerative cavity, effectively increasing the energy and power of the laser pulses. Furthermore, by controlling the polarization state and number of round trips of the laser pulses, the laser's central wavelength and spectral bandwidth can be adjusted, suppressing gain narrowing effects and ensuring the output pulse spectrum width.

[0089] Example 2:

[0090] The laser multi-pass regeneration amplification method provided by the embodiment of the present invention uses the laser multi-pass regeneration amplification device of Example 1. 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 mirror 5, and then 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 90° and 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 the seed light passes through the second polarization beam splitter 7, and is reflected by the second concave mirror 11. It 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" composed of 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, the Pockels cell 3 is restored to a low level before the seed light passes through the Pockels cell 3 for the first time in the fourth step. The seed 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 will cause it to pass through the first polarization beam splitter 2 and be output outward.

[0096] 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 axial directions. 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 rate of 10kHz, the pulse energy reaches 2.87mJ.

[0097] Example 3:

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

[0099] The six-pass regenerative amplifier is composed of multiple 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, enabling it to amplify the laser pulses; the second pump source 15 provides energy to the second laser crystal 14, enabling it to 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 another 90 degrees.

[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 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 the 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. Combining the polarization beam splitter and the first laser crystal and the second 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.

[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 travel back and forth in the multi-pass regeneration cavity for one circle and pass through the laser gain medium for multiple amplifications. By adjusting the high-voltage duration of the pulse selector, the selected laser pulse can be output from the multi-pass regeneration cavity after receiving 6N (N is the high-voltage duration divided by the time it takes for the pulse to travel back and forth in the regeneration cavity) times of gain amplification.

[0115] The optical path of the six-pass regenerative amplifier device is specifically as follows: a single laser pulse 1 output by an oscillator is selected at a set repetition frequency by a pulse picker and enters the six-pass regenerative cavity. Inside the six-pass regenerative cavity, along the direction of light propagation, the following 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. This results in a multi-pass regenerative cavity with six passes through the gain medium. By adjusting the high-voltage duration of the pulse picker, the selected laser pulse can be output from the multi-pass regenerative cavity after undergoing 6N rounds of gain amplification.

[0116] That is, the six-pass regenerative cavity laser makes a complete circuit through the gain medium six times. The first and fourth passes through first laser crystal 8 have the same polarization, while the second and third passes through first laser crystal 8 have the same polarization as the first and second passes through second laser crystal 14. The six-pass regenerative cavity not only utilizes light of different polarizations to increase the gain of different crystal emission cross sections, but also, by combining the two gain media in different placements, further achieves central wavelength and spectral bandwidth control based on the aforementioned four-pass regenerative amplification. Furthermore, by reducing the number of gain turns, the gain narrowing effect is suppressed, ensuring the output pulse spectrum width.

[0117] The laser multi-pass regenerative 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] Example 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. 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 then 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 90° and reflected downward by the first polarization beam splitter 2. 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 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 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 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.

[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" composed of 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, the Pockels cell 3 is restored to a low level before the seed light passes through the Pockels cell 3 for the first time in the fourth step. The seed 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 will cause it to pass through the first polarization beam splitter 2 and be output outward.

[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 As shown, 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 the re-amplification process. It can be used to solve the gain narrowing problem in the regenerative amplification process.

[0127] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0128] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser multi-pass regenerative 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 that it can enter the four-way regenerative amplifier for amplification; A four-way regenerative amplifier, comprising a plurality of optical elements and a first pump source (12), is used to amplify selected laser pulses multiple times; the first pump source (12) provides energy to a first laser crystal (8), enabling it to 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) splits the selected laser pulse into two beams, each entering a different path; 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 mirror (5) reflects the laser pulse back to the four-way regeneration cavity; In the four-way 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 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); a four-way regeneration cavity is obtained in which a circle passes through the gain medium four times; 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.

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. The 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. The 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 circle, twice with horizontal polarization and twice with vertical polarization; the polarization of the first and fourth passes is the same, and the polarization of the second and third passes is 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 the seed pulse 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 regenerative 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), and then reflects 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 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. At the same time, the polarization state is changed. 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), 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). 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 in the first direction. At this time, the Pockels cell (3) is powered on, and the seed light transmits the half-wave plate formed by the Pockels cell (3) and the first quarter-wave plate (4), and then is reflected by the plane reflector (5) and passes 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, the Pockels cell (3) is restored to a low level before the seed light passes through the Pockels cell (3) for the first time in the fourth step, 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 pass through the first polarization beam splitter (2) and be output outward.

9. A laser multi-pass regenerative 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 that it can enter the six-pass regenerative amplifier for amplification; A six-pass regenerative amplifier is composed of a plurality of optical elements and a first pump source (12) and a second pump source (15), and is used 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 second pump source (15) provides energy to a second laser crystal (14) 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 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) splits the selected laser pulse into two beams, each entering a different path; 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 mirror (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 by passing 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 travel back and forth to the regeneration cavity.

10. A laser multi-pass regeneration amplification method, characterized in that: Using the laser multi-pass regenerative amplifier device according to 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), and then reflects 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 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 at the same time, the polarization state changes, and 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 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), 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 the seed light passes through the second polarization beam splitter (7), it will be reflected and propagated upward; 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 in the first direction. At this time, the Pockels cell (3) is powered on, and the seed light transmits the half-wave plate formed by the Pockels cell (3) and the first quarter-wave plate (4), and then is reflected by the plane reflector (5) and passes 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, the Pockels cell (3) is restored to a low level before the seed light passes through the Pockels cell (3) for the first time in the fourth step, 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 pass through the first polarization beam splitter (2) and be output outward.

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