A ytterbium-doped potassium gadolinium tungstate four-crystal cascade high-gain laser amplifier

Abstract

The application belongs to the technical field of high-power ultrafast laser, and relates to a Yb-doped potassium tungstate gadolinium four-crystal cascade high-gain laser amplifier, which combines a polarization multiplexing pumping architecture with a four-crystal cascade gain module of four Yb:KGW crystal tetrablock combination, obtains high gain while keeping compact structure, amplifies milliwatt-level seed light to watt-level or tens of watt-level high-power and high-energy pulse output, and has comparable gain capacity to a regenerative amplifier; the four crystals are all Ng-cut, the Nm axes of the upper left and lower right two crystals are perpendicular to the horizontal plane, the Nm axes of the upper right and lower left two crystals are parallel to the horizontal plane, and each crystal is pumped by pumping light with the optimal polarization direction; the pumping light is injected from the left and right ends of the gain module, which is beneficial to the net gain state of the whole module; the signal light passes through the four crystals in turn along a U-shaped path, experiences different gain spectra in different crystals, and obtains a wider effective gain bandwidth after superposition, so that gain narrowing compensation is realized.

Description

Technical Field

[0001] This invention relates to the field of high-power ultrafast laser technology, and in particular to a cascaded high-gain laser amplifier using potassium ytterbium tungstate four-crystals. Background Technology

[0002] High-power ultrashort pulse lasers have wide applications in industrial precision machining, micro-nano manufacturing, biomedicine, and strong-field physics. Yb:KGW crystals, due to their wide emission bandwidth, high thermal conductivity, and large emission cross-section, have become the preferred gain medium for ultrashort pulse laser amplifiers. Compared to yttrium aluminum garnet (Yb:YAG) crystals, Yb:KGW has a wider emission spectrum, theoretically supporting shorter pulse widths.

[0003] Gain narrowing is a common physical limitation in laser amplifiers—as the seed light is amplified stage by stage in a cascade amplification process, the gain is highest near the center wavelength, and the spectral edges are gradually suppressed, resulting in a narrower output spectrum. Yb:KGW crystals have different emission spectral characteristics along their Nm and Np axes, with a significant shift in their emission peak positions. This characteristic provides a way to compensate for gain narrowing. By placing Yb:KGW crystals orthogonally, the signal light experiences gain spectra at different center wavelengths in the orientation, and their superposition yields a wider effective gain bandwidth.

[0004] Existing orthogonal crystal solutions typically employ a dual-crystal architecture. While this can achieve gain narrowing compensation, the pump structure often uses multiple independent pump crystals from semiconductor lasers (LDs), resulting in a large system size and high cost. Furthermore, if a Yb:KGW crystal is used as the gain medium, because it is a quasi-three-level system, the lower level has a certain thermal population at room temperature. In addition, the crystal has a large absorption cross-section. If a single-end pumping method is used to reduce system size, the pump light will attenuate rapidly along the crystal axis. The rear end of the crystal may become an absorption region due to the pump intensity falling below the laser threshold, not only failing to contribute gain but also absorbing signal light, directly reducing the overall laser gain.

[0005] In summary, there is an urgent need to design a laser amplifier that balances structural compactness, high gain, and gain narrowing compensation. Summary of the Invention

[0006] Therefore, the technical problem to be solved by this invention is how to design a laser amplifier that balances structural compactness, high gain, and gain narrowing compensation.

[0007] To solve the above technical problems, the present invention provides a cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals, comprising: The four-crystal cascaded gain module includes four Yb:KGW crystals arranged in a grid pattern to achieve a net gain state under the excitation of pump light; wherein the four Yb:KGW crystals include a first crystal, a second crystal, a third crystal, and a fourth crystal located at the lower right, lower left, upper left, and upper right positions of the grid pattern, respectively. The first pump module is located on the side of the second and third crystals away from the first and fourth crystals; it is used to output the first pump light and split the first pump light into two beams of orthogonal polarization, which are injected into the first pump points of the second and third crystals respectively, and the remaining first pump light after being absorbed by the second and third crystals is injected into the first pump points of the first and fourth crystals. The second pump module is located on the side of the first crystal and the fourth crystal away from the second crystal and the third crystal; it is used to output the second pump light and split the second pump light into two beams of orthogonal polarization, which are injected into the second pump points of the first crystal and the fourth crystal respectively, and the remaining second pump light after being absorbed by the first crystal and the fourth crystal is injected into the second pump points of the second crystal and the third crystal. The signal light amplification module includes a first dichroic mirror and a fourth dichroic mirror respectively disposed on the optical path of the second pump point of the beam injection into the first crystal and the fourth crystal, and a second dichroic mirror and a third dichroic mirror disposed on the optical path of the first pump point of the beam injection into the second crystal and the third crystal; it is used to amplify the seed light after it is injected from the first dichroic mirror by passing through the first crystal, the second crystal, the second dichroic mirror, the third dichroic mirror, the third crystal and the fourth crystal in sequence, and then output it after being reflected by the fourth dichroic mirror.

[0008] Preferably, the film systems of the first dichroic mirror, the second dichroic mirror, the third dichroic mirror, and the fourth dichroic mirror all have transmission characteristics in the pump light band; The films of the first, second, third, and fourth dichroic mirrors all exhibit reflective properties in the seed light band.

[0009] Preferably, the first crystal, the second crystal, the third crystal, and the fourth crystal are all Ng-cut; The Nm axis of the first crystal is perpendicular to the horizontal plane, thereby making the polarization direction of the first crystal match the S-polarized beam injected into its second pump point. The Nm axis of the second crystal is parallel to the horizontal plane, so that the polarization direction of the second crystal matches the P-polarized beam injected into its first pump point. The Nm axis of the third crystal is perpendicular to the horizontal plane, so that the polarization direction of the third crystal matches the S-polarized beam injected into its first pump point. The Nm axis of the fourth crystal is parallel to the horizontal plane, thereby making the polarization direction of the fourth crystal match the P-polarized beam injected into its second pump point.

[0010] Preferably, the first pump module includes: A first semiconductor laser is used to output a first pump light, and its output optical path is directly opposite the first pump point of the second crystal. A first collimating lens is disposed between the first semiconductor laser and the second crystal, and is used to collimate the first pump light; The first polarizing beam splitter is positioned between the first collimating lens and the second crystal to transmit and reflect the collimated first pump light, and output a P-polarized beam and an S-polarized beam. The first lower focusing lens is positioned between the first polarizing beam splitter and the second crystal, and is used to focus the P-polarized beam. The second polarizing beam splitter has its incident surface facing the exit surface of the S-polarized beam of the first polarizing beam splitter, and its exit surface facing the first pump point of the third crystal; it is used to reflect the S-polarized beam. The first upper focusing lens is positioned between the second polarizing beam splitter and the third crystal to focus the S-polarized beam.

[0011] Preferably, the second dichroic mirror is disposed between the first lower focusing lens and the second crystal, and is used to transmit the focused P-polarized beam to the first pump point of the second crystal, so that the remaining P-polarized beam after absorption by the second crystal is injected into the first pump point of the first crystal; and to reflect the seed light to the third dichroic mirror or the second crystal. The third dichroic mirror is positioned between the first upper focusing lens and the third crystal. It is used to transmit the focused S-polarized beam to the first pump point of the third crystal, so that the remaining S-polarized beam after absorption by the third crystal is injected into the first pump point of the fourth crystal; and to reflect the seed light to the second dichroic mirror or the third crystal.

[0012] Preferably, the second pump module includes: The second semiconductor laser is used to output the second pump light, and its output light path is directly opposite the second pump point of the fourth crystal. The second collimating lens is disposed between the second semiconductor laser and the fourth crystal, and is used to collimate the second pump light. The third polarizing beam splitter is positioned between the second collimating lens and the fourth crystal. It is used to transmit and reflect the collimated second pump light, and output P-polarized beam and S-polarized beam. The second upper focusing lens is positioned between the third polarizing beam splitter and the fourth crystal, and is used to focus the P-polarized beam. The fourth polarizing beam splitter has its incident surface facing the exit surface of the S-polarized beam of the third polarizing beam splitter, and its exit surface facing the second pump point of the first crystal; it is used to reflect the S-polarized beam. The second lower focusing lens is positioned between the fourth polarizing beam splitter and the first crystal, and is used to focus the S-polarized beam.

[0013] Preferably, the first dichroic mirror is disposed between the second lower focusing lens and the first crystal, and is used to transmit the focused S-polarized beam to the second pump point of the first crystal, so that the remaining S-polarized beam after absorption by the first crystal is injected into the second pump point of the second crystal; and to reflect the seed light or the light amplified by the four-crystal cascaded gain module to the first crystal or to reflect and output the light amplified by the four-crystal cascaded gain module. The fourth dichroic mirror is positioned between the second upper focusing lens and the fourth crystal. It is used to transmit the focused P-polarized beam to the second pump point of the fourth crystal, so that the remaining P-polarized beam after absorption by the fourth crystal is injected into the second pump point of the third crystal. It also reflects the light amplified by the four-crystal cascaded gain module to the fourth crystal or reflects and outputs the light amplified by the four-crystal cascaded gain module.

[0014] Preferably, it further includes: The first upper pump trap is located on the side of the second polarizing beam splitter away from the first upper focusing lens, and is used to absorb the P-polarized beam emitted from the second pump module that is not absorbed by the four-crystal cascaded gain module. The first downpump light trap is set on the side of the first polarizing beam splitter away from the second polarizing beam splitter, and is used to absorb the S-polarized beam emitted from the second pump module that is not absorbed by the four-crystal cascaded gain module. The second upper pump trap is set on the side of the third polarizing beam splitter away from the fourth polarizing beam splitter, and is used to absorb the S-polarized beam emitted from the first pump module that has not been absorbed by the four-crystal cascaded gain module. The second lower pump trap is located on the side of the fourth polarizing beam splitter away from the second lower focusing lens, and is used to absorb the P-polarized beam emitted from the first pump module that has not been absorbed by the four-crystal cascaded gain module.

[0015] Preferably, the feature is that it further includes a dual-channel extension structure, which specifically includes: The fifth polarizing beam splitter is positioned in the optical path of the seed light entering the first dichroic mirror. It is used to transmit the seed light in a P-polarized state to the first dichroic mirror, allowing it to pass sequentially through the first crystal, second crystal, second dichroic mirror, third dichroic mirror, third crystal, and fourth crystal for primary amplification. The primary amplified light in a P-polarized state is then output through the fourth dichroic mirror. The secondary amplified light in an S-polarized state output from the first dichroic mirror is reflected to output secondary amplified light. A quarter-glass slide is placed in the output optical path of the fourth dichroic mirror. It is used to perform polarization conversion on the primary amplified light in the P-polarized state output from the fourth dichroic mirror, and output the primary amplified light in the circularly polarized state. It also performs polarization conversion on the primary amplified light in the circularly polarized state returned from the first total reflection mirror, and outputs the primary amplified light in the S-polarized state to the fourth dichroic mirror. This allows the primary amplified light in the S-polarized state to be amplified twice in sequence through the fourth crystal, the third crystal, the third dichroic mirror, the second dichroic mirror, the second crystal, the first crystal, and the first dichroic mirror. The secondary amplified light in the S-polarized state is then output through the first dichroic mirror. The first total reflection mirror is positioned on the side of the quarter-plate furthest from the fourth dichroic mirror, and is used to return the circularly polarized, first-amplified light to the quarter-plate.

[0016] Preferably, it also includes a four-way extension structure, which specifically includes: The sixth polarization beam splitter is positioned in the optical path of the seed light injected into the fifth polarization beam splitter; it is used to transmit the seed light; and to reflect the S-polarized fourth-order amplified light output from the 1 / 2 glass slide, thus outputting fourth-order amplified light. A half-glass slide is placed between the sixth polarizing beam splitter and the fifth polarizing beam splitter to rotate the polarization direction of the P-polarized seed light transmitted by the sixth polarizing beam splitter; it also rotates the polarization direction of the fourth-amplified light emitted from the optical rotator to output the S-polarized fourth-amplified light. A rotator, positioned between the half-glass slide and the fifth polarizing beam splitter, is used to rotate the polarization direction of the seed light transmitted through the half-glass slide and output the P-polarized seed light to the fifth polarizing beam splitter; it also rotates the polarization direction of the fourth-order amplified P-polarized light output from the fifth polarizing beam splitter. The second total reflection mirror faces the secondary amplified light output surface of the fifth polarizing beam splitter; it is used to reflect the secondary amplified light to the fifth polarizing beam splitter so that the secondary amplified light can be amplified three and four times through the double-pass extension structure, thereby enabling the fifth polarizing beam splitter to output P-polarized four-times amplified light.

[0017] The potassium ytterbium tungstate quad-crystal cascaded high-gain laser amplifier provided in this application has the following advantages: 1. Four-crystal cascading is adopted to realize gain narrowing compensation and high-gain output, and support narrow-pulse-width large-energy pulses: four Yb:KGW crystals are combined into a "field-shaped" gain module, all four crystals are Ng-cut, with alternating crystal axis orientations (Nm axis alternating between horizontal and vertical), and the signal light sequentially passes through the four crystals along a "Ji-shaped" path. It experiences different gain spectra in different crystals, and a wider effective gain bandwidth is obtained after superposition, thereby realizing gain narrowing compensation and supporting pulse output with shorter pulse width; meanwhile, with the four-crystal cascading, the total gain is dispersed to four crystals, each crystal is injected with pump light and is in a net gain state, which avoids the problem that the rear end of a single long crystal becomes an absorption region because the pump intensity is lower than the threshold, and the total gain is significantly increased after the gains of all crystals are superimposed; in addition, the other end of each crystal also receives the remaining pump light after being absorbed by the adjacent orthogonal crystal, after this part of pump light is absorbed, the number of inverted particles is further increased, the problem of rear-end absorption region is further suppressed, and the gain is further improved;

[0018] 2. Aiming at the anisotropic characteristics of Yb:KGW crystals, the present application accurately matches the crystal axis orientations of the four crystals with the polarization direction of the injected pump light, so that the pump light is effectively absorbed in the four-crystal cascaded gain module. Cooperating with the polarization-multiplexed pump architecture, four-point pumping is realized by two semiconductor lasers through four polarization splitting prisms, which drives four-crystal cascading with a very small number of pumps, greatly reducing the volume and cost of the system; 3. A double-pass expansion structure and a four-pass expansion structure are designed to amplify seed light multiple times, so that milliwatt seed light can be directly amplified to high-power, large-energy pulse output of watt level or tens of watts level. The gain capability is comparable to that of a regenerative amplifier, and the resonant cavity and cavity dumping system required by a regenerative amplifier are not required, so the structure is simple, the cost is low, and the reliability is high. Description of Drawings

[0019] In order to make the content of the present invention easier to understand clearly, the following is a further detailed description of the present invention based on specific embodiments of the present invention and in combination with the accompanying drawings, wherein: Figure 1 is a schematic structural diagram of the ytterbium-doped potassium gadolinium tungstate four-crystal cascaded high-gain laser amplifier provided by the present application; Figure 2 is a top view of the crystal axis orientation of Yb:KGW crystal and the four-crystal cascaded gain module provided by the present application; wherein, Figure 2 (a) in it is a schematic diagram of the crystal orientation of Yb:KGW crystal with Nm axis parallel to the horizontal plane and the corresponding pump polarization, Figure 2 (b) in it is a schematic diagram of the crystal orientation of Yb:KGW crystal with Nm axis perpendicular to the horizontal plane and the corresponding pump polarization, Figure 2 (c) in it is a top view of the four-crystal cascaded gain module after four Yb:KGW crystals are combined in a field shape and a schematic diagram of the matching relationship between pump polarization; Figure 3 It is a schematic structural diagram of a four-crystal cascaded high-gain laser amplifier of ytterbium-doped potassium gadolinium tungstate with a two-pass expansion structure provided by the present application; Figure 4 It is a schematic structural diagram of a four-crystal cascaded high-gain laser amplifier of ytterbium-doped potassium gadolinium tungstate with a four-pass expansion structure provided by the present application; Description of the reference numerals in the drawings of the specification: 1. Four-crystal cascaded gain module; 11. First crystal; 12. Second crystal; 13. Third crystal; 14. Fourth crystal; 2. First pump module; 21. First semiconductor laser; 22. First collimating lens; 23. First polarization splitting prism; 24. First lower focusing lens; 25. Second polarization splitting prism; 26. First upper focusing lens; 3. Second pump module; 31. Second semiconductor laser; 32. Second collimating lens; 33. Third polarization splitting prism; 34. Second upper focusing lens; 35. Fourth polarization splitting prism; 36. Second lower focusing lens; 4. Signal light amplification module; 41. First dichroic mirror; 42. Second dichroic mirror; 43. Third dichroic mirror; 44. Fourth dichroic mirror; 51. First upper pump light trap; 52. First lower pump light trap; 53. Second upper pump light trap; 54. Second lower pump light trap; 61. Fifth polarization splitting prism; 62. Quarter-wave plate; 63. First total reflection mirror; 71. Sixth polarization splitting prism; 72. Half-wave plate; 73. Optical rotator; 74. Second total reflection mirror. Detailed Description of the Embodiments

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it. However, the given embodiments are not intended to limit the present invention.

[0021] The core idea of the present application is to combine the polarization splitting multiplexed pump architecture with a gain module formed by a field-shaped combination of four Yb:KGW crystals, and use the four-crystal cascade to achieve gain increase. All four Yb:KGW crystals are Ng-cut, with their crystal axes orientations arranged alternately, which accurately matches the polarization of the pump light; the signal light successively passes through the four crystals along a "zigzag" path, and the anisotropic gain characteristic of Yb:KGW crystals is used to achieve gain narrowing compensation, so as to obtain a wider gain bandwidth.

[0022] Please refer to Figure 1 , Figure 1 is a schematic structural diagram of the ytterbium-doped potassium gadolinium tungstate four-crystal cascaded high-gain laser amplifier provided by the present application, which specifically includes a four-crystal cascaded gain module 1, a first pump module 2, a second pump module 3 and a signal light amplification module 4.

[0023] The four-crystal cascaded gain module 1 comprises four Yb:KGW crystals combined in a grid shape, and is configured to achieve a net gain state under excitation of pump light. The four Yb:KGW crystals include a first crystal 11, a second crystal 12, a third crystal 13 and a fourth crystal 14 respectively located at the lower right, lower left, upper left and upper right positions of the grid shape.

[0024] It should be noted that the four Yb:KGW crystals are combined by splicing or bonding to form the four-crystal cascaded gain module 1.

[0025] Further, the first crystal 11, the second crystal 12, the third crystal 13 and the fourth crystal 14 are all Ng-cut; wherein Ng is the optical principal axis corresponding to the maximum principal refractive index of the indicatrix of a biaxial crystal, and Ng-cut means that the normal direction of the light-passing section of the crystal is parallel to the Ng optical principal axis.

[0026] The Nm axis of the first crystal 11 is perpendicular to the horizontal plane, so that the polarization direction of the first crystal 11 matches the S-polarized beam injected into its second pump point.

[0027] The Nm axis of the second crystal 12 is parallel to the horizontal plane, so that the polarization direction of the second crystal 12 matches the P-polarized beam injected into its first pump point.

[0028] The Nm axis of the third crystal 13 is perpendicular to the horizontal plane, so that the polarization direction of the third crystal 13 matches the S-polarized beam injected into its first pump point.

[0029] The Nm axis of the fourth crystal 14 is parallel to the horizontal plane, so that the polarization direction of the fourth crystal 14 matches the P-polarized beam injected into its second pump point.

[0030] Specifically, as Figure 2 shows a top view of the crystal axis orientation of the Yb:KGW crystal and the four-crystal cascaded gain module provided by the present application, wherein Figure 2 (a) in is a schematic diagram of the crystal orientation with the Nm axis parallel to the horizontal plane and the corresponding pump polarization, Figure 2 (b) in is a schematic diagram of the crystal orientation with the Nm axis perpendicular to the horizontal plane and the corresponding pump polarization, Figure 2 (c) in is a schematic diagram of the overall top view of the four-crystal cascaded gain module after the four crystals are combined in a grid shape and the pump polarization matching relationship. The present application uses four Yb:KGW crystals to combine and design the four-crystal cascaded gain module 1, and through the alternately oriented layout, each crystal is pumped by pump light with its optimal polarization direction.

[0031] It should be noted that the first pump points of the second crystal 12 and the third crystal 13 are both pump light injection points on the side away from the first crystal 11 and the fourth crystal 14, and the second pump points of the second crystal 12 and the third crystal 13 are both pump light injection points on the side close to the first crystal 11 and the fourth crystal 14; the first pump points of the first crystal 11 and the fourth crystal 14 are both pump light injection points on the side close to the second crystal 12 and the third crystal 13, and the second pump points of the first crystal 11 and the fourth crystal 14 are both pump light injection points on the side away from the second crystal 12 and the third crystal 13.

[0032] Specifically, in this application, the first crystal 11, the second crystal 12, the third crystal 13, and the fourth crystal 14 are of the same size and all adopt a low doping concentration design, thereby making the gain uniformly distributed along the length direction and reducing the heat load per unit length. At the same time, the four-crystal cascaded gain module 1 is mounted on the same water-cooled heat sink and dissipates heat through circulating cooling water. The design of injecting heat load from both ends by the four crystals and pump light disperses the heat load to all directions in space. Combined with the integrated water-cooled heat sink, the thermal effect is effectively mitigated.

[0033] The first pump module 2 is disposed on the side of the second crystal 12 and the third crystal 13 away from the first crystal 11 and the fourth crystal 14; it is used to output the first pump light and split the first pump light into two beams of orthogonal polarization, which are injected into the first pump points of the second crystal 12 and the third crystal 13 respectively, and the remaining first pump light after being absorbed by the second crystal 12 and the third crystal 13 is injected into the first pump points of the first crystal 11 and the fourth crystal 14.

[0034] Furthermore, such as Figure 1 As shown, the first pump module 2 includes a first semiconductor laser 21, a first collimating lens 22, a first polarizing beam splitter 23, a first lower focusing lens 24, a second polarizing beam splitter 25, and a first upper focusing lens 26.

[0035] The first semiconductor laser 21 is used to output the first pump light, and its output optical path is directly opposite the first pump point of the second crystal 12.

[0036] Specifically, the first semiconductor laser 21 is a semiconductor laser with fiber output, with an output wavelength of approximately 981 nm and a single-tube output power in the tens of watts range. Its output fiber is a multimode fiber, and the emitted light is unpolarized or low-polarization light.

[0037] The first collimating lens 22 is disposed between the first semiconductor laser 21 and the second crystal 12, and is used to collimate the first pump light.

[0038] The first polarizing beam splitter 23 is disposed between the first collimating lens 22 and the second crystal 12, and is used to transmit and reflect the collimated first pump light, and output P-polarized beam and S-polarized beam.

[0039] The first lower focusing lens 24 is disposed between the first polarizing beam splitter 23 and the second crystal 12, and is used to focus the P-polarized beam.

[0040] The incident surface of the second polarizing beam splitter 25 is directly opposite the exit surface of the S-polarized beam of the first polarizing beam splitter 23, and its exit surface is directly opposite the first pump point of the third crystal 13; it is used to reflect the S-polarized beam.

[0041] The first upper focusing lens 26 is positioned between the second polarizing beam splitter 25 and the third crystal 13 to focus the S-polarized beam.

[0042] The second pump module 3 is disposed on the side of the first crystal 11 and the fourth crystal 14 away from the second crystal 12 and the third crystal 13; it is used to output the second pump light and split the second pump light into two beams of orthogonal polarization, which are injected into the second pump points of the first crystal 11 and the fourth crystal 14 respectively, and the remaining second pump light after being absorbed by the first crystal 11 and the fourth crystal 14 is injected into the second pump points of the second crystal 12 and the third crystal 13.

[0043] Furthermore, such as Figure 1 As shown, the second pump module 3 includes a second semiconductor laser 31, a second collimating lens 32, a third polarizing beam splitter 33, a second upper focusing lens 34, a fourth polarizing beam splitter 35, and a second lower focusing lens 36.

[0044] The second semiconductor laser 31 is used to output the second pump light, and its output light path is directly opposite the second pump point of the fourth crystal 14.

[0045] Specifically, the second semiconductor laser 31 is a semiconductor laser with fiber output, with an output wavelength of approximately 981 nm and a single-tube output power in the tens of watts range. Its output fiber is a multimode fiber, and the emitted light is unpolarized or low-polarization light.

[0046] The second collimating lens 32 is disposed between the second semiconductor laser 31 and the fourth crystal 14, and is used to collimate the second pump light.

[0047] The third polarizing beam splitter 33 is positioned between the second collimating lens 32 and the fourth crystal 14 to transmit and reflect the collimated second pump light, outputting a P-polarized beam and an S-polarized beam.

[0048] The second upper focusing lens 34 is disposed between the third polarizing beam splitter 33 and the fourth crystal 14, and is used to focus the P-polarized beam.

[0049] The incident surface of the fourth polarizing beam splitter 35 is directly opposite the exit surface of the S-polarized beam of the third polarizing beam splitter 33, and its exit surface is directly opposite the second pump point of the first crystal 11; it is used to reflect the S-polarized beam.

[0050] The second lower focusing lens 36 is disposed between the fourth polarizing beam splitter 35 and the first crystal 11, and is used to focus the S-polarized beam.

[0051] The signal light amplification module 4 includes a first dichroic mirror 41 and a fourth dichroic mirror 44 respectively disposed on the optical path of the second pump point of the beam injection into the first crystal 11 and the fourth crystal 14, and a second dichroic mirror 42 and a third dichroic mirror 43 disposed on the optical path of the first pump point of the beam injection into the second crystal 12 and the third crystal 13; it is used to amplify the seed light after it is injected from the first dichroic mirror 1, by passing through the first crystal 11, the second crystal 12, the second dichroic mirror 42, the third dichroic mirror 43, the third crystal 13 and the fourth crystal 14 in sequence, and then output it after being reflected by the fourth dichroic mirror 44.

[0052] It should be noted that the first dichroic mirror 41, the second dichroic mirror 42, the third dichroic mirror 43, and the fourth dichroic mirror 44 are all dichroic mirrors with an incident angle of 45°; the film systems of the first dichroic mirror 41, the second dichroic mirror 42, the third dichroic mirror 43, and the fourth dichroic mirror 44 all have transmission characteristics for the pump light band; and the film systems of the first dichroic mirror 41, the second dichroic mirror 42, the third dichroic mirror 43, and the fourth dichroic mirror 44 all have reflection characteristics for the seed light band.

[0053] By employing a film system with high transmittance for the pump light band and high reflectance for the seed light band, the dichroic mirror can transmit the pump light to each crystal in the four-crystal cascaded gain module 1, while simultaneously reflecting the seed light to each crystal in the four-crystal cascaded gain module 1.

[0054] Furthermore, such as Figure 1 As shown, the second dichroic mirror 42 is disposed between the first lower focusing lens 24 and the second crystal 12, and is used to transmit the focused P-polarized beam to the first pump point of the second crystal 12, so that the remaining P-polarized beam after absorption by the second crystal 12 is injected into the first pump point of the first crystal 11; at the same time, it is also used to reflect the seed light to the third dichroic mirror 43 or the second crystal 12.

[0055] The third dichroic mirror 43 is disposed between the first upper focusing lens 26 and the third crystal 13, and is used to transmit the focused S-polarized beam to the first pump point of the third crystal 13, so that the remaining S-polarized beam after absorption by the third crystal 13 is injected into the first pump point of the fourth crystal 14; at the same time, it is also used to reflect the seed light to the second dichroic mirror 42 or the third crystal 13.

[0056] Furthermore, the first dichroic mirror 41 is disposed between the second lower focusing lens 36 and the first crystal 11, and is used to transmit the focused S-polarized beam to the second pump point of the first crystal 11, so that the remaining S-polarized beam after absorption by the first crystal 11 is injected into the second pump point of the second crystal 12; at the same time, it is also used to reflect the seed light or the light amplified by the four-crystal cascaded gain module 1 to the first crystal 11 or reflect and output the light amplified by the four-crystal cascaded gain module 1.

[0057] The fourth dichroic mirror 44 is disposed between the second upper focusing lens 34 and the fourth crystal 14. It is used to transmit the focused P-polarized beam to the second pump point of the fourth crystal 14, so that the remaining P-polarized beam after absorption by the fourth crystal 14 is injected into the second pump point of the third crystal 13. At the same time, it is also used to reflect the light amplified by the four-crystal cascaded gain module 1 to the fourth crystal 14 or to reflect and output the light amplified by the four-crystal cascaded gain module 1.

[0058] Specifically, the seed light is incident from below. The broadened femtosecond seed light (wavelength approximately 1030 nm) first enters the first dichroic mirror 41. After reflection by the first dichroic mirror 41, it enters the four-crystal cascaded gain module 1, passing sequentially along a "U"-shaped path through the first crystal 11, the second crystal 12, the second dichroic mirror 42, the third dichroic mirror 43, the third crystal 13, and the fourth crystal 14, achieving four-stage cascaded amplification. Finally, it is reflected by the fourth dichroic mirror 44 to output the amplified output light. The Yb:KGW crystal has different emission spectral characteristics on the Nm and Np axes, and its emission peak position is significantly shifted. During the seed light amplification process, the alternating orientation of the crystal axes of the four crystals—the Nm axis alternating between the horizontal and vertical planes—allows the seed light to experience different gain spectra in different crystals. After superposition, a wider effective gain bandwidth is obtained, achieving gain narrowing compensation and supporting broadband gain output. Furthermore, the pump light is injected from both ends of the four-crystal cascaded gain module 1. Each crystal receives matched polarization pump light (efficient absorption) from one end and the remaining pump light (inefficient absorption) after absorption by the adjacent orthogonal crystals at the other end. The pump light at the inefficient absorption end can still increase the number of inverted particles after absorption, which is more conducive to the four-crystal cascaded gain module 1 being in a net gain state as a whole and suppressing the quasi-three-level reabsorption problem.

[0059] Furthermore, such as Figure 1As shown, the cascaded high-gain laser amplifier with potassium ytterbium tungstate crystals also includes a first upper pump trap 51, a first lower pump trap 52, a second upper pump trap 53, and a second lower pump trap 54.

[0060] The first upper pump trap 51 is disposed on the side of the second polarizing beam splitter 25 away from the first upper focusing lens 26, and is used to absorb the P-polarized beam emitted from the second pump module 3 that is not absorbed by the four-crystal cascaded gain module 1.

[0061] Specifically, the second pump light output from the second semiconductor laser 31 is absorbed by the first upper pump light trap 51 after passing through the second collimating lens 32, the third polarizing beam splitter 33, the second upper focusing lens 34, the fourth dichroic mirror 44, the four-crystal cascaded gain module 1, the third dichroic mirror 43, the first upper focusing lens 26, and the second polarizing beam splitter 25.

[0062] The first down-pump light trap 52 is located on the side of the first polarizing beam splitter 23 away from the second polarizing beam splitter 25, and is used to absorb the S-polarized beam emitted from the second pump module 3 that is not absorbed by the four-crystal cascaded gain module 1.

[0063] Specifically, the second pump light output from the second semiconductor laser 31 is absorbed by the first downpump light trap 52 after passing through the second collimating lens 32, the third polarizing beam splitter 33, the fourth polarizing beam splitter 35, the second downfocusing lens 36, the first dichroic mirror 41, the four-crystal cascaded gain module 1, the second dichroic mirror 42, the first downfocusing lens 24, and the first polarizing beam splitter 23.

[0064] The second upper pump trap 53 is located on the side of the third polarizing beam splitter 33 away from the fourth polarizing beam splitter 35, and is used to absorb the S-polarized beam emitted from the first pump module 2 that is not absorbed by the four-crystal cascaded gain module 1.

[0065] Specifically, the first pump light output from the first semiconductor laser 21 is absorbed by the second upper pump light trap 53 after passing through the first collimating lens 22, the first polarizing beam splitter 23, the second polarizing beam splitter 25, the first upper focusing lens 26, the second dichroic mirror 42, the four-crystal cascaded gain module 1, the fourth dichroic mirror 44, the second upper focusing lens 34, and the third polarizing beam splitter 33.

[0066] The second lower pump trap 54 is located on the side of the fourth polarizing beam splitter 35 away from the second lower focusing lens 36, and is used to absorb the P-polarized beam emitted from the first pump module 2 that is not absorbed by the four-crystal cascaded gain module 1.

[0067] Specifically, the first pump light output from the first semiconductor laser 21 is absorbed by the second down-pump light trap 54 after passing through the first collimating lens 22, the first polarizing beam splitter 23, the first down-focusing lens 24, the second dichroic mirror 42, the four-crystal cascaded gain module 1, the first dichroic mirror 41, and the fourth polarizing beam splitter 35.

[0068] Four pump traps are respectively located outside the first pump module 2 and the second pump module 3 to absorb the remaining pump light that is not absorbed by the crystal. The remaining pump light emitted from the crystal passes through the corresponding dichroic mirror, is collimated by the focusing lens, and then enters the opposite polarization beam splitter. It is guided according to the polarization state to the corresponding pump trap for complete absorption, thus physically preventing it from returning to the semiconductor laser.

[0069] Furthermore, such as Figure 3 As shown, based on the ytterbium-doped potassium gadolinium four-crystal cascaded high-gain laser amplifier provided in the above embodiments, this application embodiment also adds a dual-pass extension structure, which specifically includes a fifth polarization beam splitter 61, a quarter glass plate 62, and a first total reflection mirror 63.

[0070] The fifth polarizing beam splitter 61 is positioned in the optical path of the seed light entering the first dichroic mirror 41; it is used to transmit the seed light, transmitting the seed light in a P-polarized state to the first dichroic mirror 41, so that it passes sequentially through the first crystal 11, the second crystal 12, the second dichroic mirror 42, the third dichroic mirror 43, the third crystal 13 and the fourth crystal 14 to achieve primary amplification, and outputs the P-polarized primary amplified light through the fourth dichroic mirror 44; it reflects the S-polarized secondary amplified light output by the first dichroic mirror 41 to output secondary amplified light.

[0071] A quarter-glass slide 62 is placed in the output optical path of the fourth dichroic mirror 44; it is used to perform polarization conversion on the primary amplified light of the P-polarized state output by the fourth dichroic mirror 44, and output the primary amplified light of the circularly polarized state; it also performs polarization conversion on the primary amplified light of the circularly polarized state returned by the first total reflection mirror 63, and outputs the primary amplified light of the S-polarized state to the fourth dichroic mirror 44, so that the primary amplified light of the S-polarized state passes through the fourth crystal 14, the third crystal 13, the third dichroic mirror 43, the second dichroic mirror 42, the second crystal 12, the first crystal 11, and the first dichroic mirror 41 in sequence to achieve secondary amplification, and outputs the secondary amplified light of the S-polarized state through the first dichroic mirror 41.

[0072] The first total reflection mirror 63 is positioned on the side of the quarter-plate 62 away from the fourth dichroic mirror 44, and is used to return the circularly polarized primary magnified light to the quarter-plate 62.

[0073] The specific optical path in the above dual-pass extended structure is as follows: the seed light, polarized in the P state, is incident from below, transmitted through the fifth polarizing beam splitter 61, and then enters the amplifier (i.e., sequentially passes through the first dichroic mirror 41, the first crystal 11, the second crystal 12, the second dichroic mirror 42, the third dichroic mirror 43, the third crystal 13, and the fourth crystal 14). After single-pass amplification, it is output as P-polarized amplified light through the fourth dichroic mirror 44. This P-polarized light is sequentially converted into circularly polarized light by the quarter-wave plate 62, and then passes through the first total reflection mirror 6... After reflection, the seed light passes through a quarter-wave plate 62 again to become S-polarized light, and then enters the amplifier in reverse (passing sequentially through the fourth dichroic mirror 44, the fourth crystal 14, the third crystal 13, the third dichroic mirror 43, the second dichroic mirror 42, the second crystal 12, the first crystal 11, and the first dichroic mirror 41), completing double-pass amplification. Finally, the S-polarized amplified light returns to the fifth polarization beam splitter 61. Since its polarization state becomes S-polarized, it is reflected by the fifth polarization beam splitter 61 and output as the final amplified output light. Specifically, double-pass means that the seed light passes through the four-crystal cascaded gain module 1 twice (each time it passes through the four-crystal cascaded gain module 1, it passes through the first crystal 11, the second crystal 12, the third crystal 13, and the fourth crystal 14). The gain is increased several times compared to the single-pass scheme. At the same time, the gain narrowing compensation effect accumulates, resulting in higher output energy and a wider gain bandwidth.

[0074] It should be noted that the phase delay accuracy of the quarter-wave plate 62 should meet the requirements, and the first total reflection mirror 63 has high reflectivity for the signal light wavelength.

[0075] Furthermore, such as Figure 4 As shown, based on the cascaded high-gain laser amplifier with a double-pass extended structure of potassium tungstate four crystals provided in the above embodiments, this application embodiment also designs a four-pass extended structure, which specifically includes a sixth polarization beam splitter 71, a half glass plate 72, a beam rotator 73, and a second total reflection mirror 74.

[0076] The sixth polarization beam splitter 71 is positioned in the optical path of the seed light injected into the fifth polarization beam splitter 61; it is used to transmit the seed light; and to reflect the S-polarized quadruple-amplified light output from the half-glass slide 72, thus outputting quadruple-amplified light.

[0077] A half-glass slide 72 is positioned between the sixth polarizing beam splitter 71 and the fifth polarizing beam splitter 61 to rotate the polarization direction of the P-polarized seed light transmitted through the sixth polarizing beam splitter 71; it also rotates the polarization direction of the 45° polarized quadruple-amplified light emitted from the optical rotator 73 to output S-polarized quadruple-amplified light.

[0078] The optical rotator 73 is positioned between the half-glass slide 72 and the fifth polarizing beam splitter 61. It is used to rotate the polarization direction of the seed light transmitted through the half-glass slide 72 and output the P-polarized seed light to the fifth polarizing beam splitter 61. It also rotates the polarization direction of the fourth-order amplified P-polarized light output by the fifth polarizing beam splitter 61.

[0079] The second total reflection mirror 74 faces the secondary amplified light output surface of the fifth polarizing beam splitter 61; it is used to reflect the secondary amplified light to the fifth polarizing beam splitter 61 so that the secondary amplified light can be amplified three times and four times through the double-pass extension structure, thereby enabling the fifth polarizing beam splitter 61 to output P-polarized four-times amplified light.

[0080] The specific optical path in the above four-way expansion structure is as follows: The seed light, polarized in a P-state, is incident vertically upwards from below onto the sixth polarizing beam splitter 71. After transmission, it passes sequentially through the half-wave plate 72 and the optical rotator 73, maintaining its P-polarized state. It then enters the fifth polarizing beam splitter 61 and, after transmission, enters the amplifier (i.e., sequentially passes through the first dichroic mirror 41, the first crystal 11, the second crystal 12, the second dichroic mirror 42, the third dichroic mirror 43, the third crystal 13, and the fourth crystal 14), completing the first amplification. Finally, it outputs P-polarized amplified light through the fourth dichroic mirror 44.

[0081] After the P-polarized amplified light is output from the amplifier, it passes sequentially through a quarter-wave plate 62 and a first total reflection mirror 63, changing its polarization state from P to S. It then returns to the amplifier via the same path (passing sequentially through a fourth dichroic mirror 44, a fourth crystal 14, a third crystal 13, a third dichroic mirror 43, a second dichroic mirror 42, a second crystal 12, a first crystal 11, and a first dichroic mirror 41), completing the second amplification and outputting S-polarized amplified light.

[0082] After the S-polarized amplified light returns to the fifth polarization beam splitter 61, it is reflected by the fifth polarization beam splitter 61 to the second total reflection mirror 74 due to its S polarization state. After being reflected by the second total reflection mirror 74, it returns along the same path and re-enters the fifth polarization beam splitter 61. It then returns along the same path to the amplifier (i.e., it passes through the first dichroic mirror 41, the first crystal 11, the second crystal 12, the second dichroic mirror 42, the third dichroic mirror 43, the third crystal 13, and the fourth crystal 14 in sequence), completing the third amplification. Finally, it outputs the S-polarized amplified light through the fourth dichroic mirror 44.

[0083] After the S-polarized amplified light is output from the amplifier, it passes through the quarter-wave plate 62 and the first total reflection mirror 63 in sequence, changing its polarization state from S to P. It then returns to the amplifier via the same path (passing through the fourth dichroic mirror 44, the fourth crystal 14, the third crystal 13, the third dichroic mirror 43, the second dichroic mirror 42, the second crystal 12, the first crystal 11, and the first dichroic mirror 41 in sequence), completing the fourth amplification and outputting the P-polarized amplified light.

[0084] After the P-polarized amplified light returns to the fifth polarization beam splitter 61, since its polarization state is P, it passes through the fifth polarization beam splitter 61 and then passes through the optical rotator 73 and the half-wave plate 72 in sequence. The polarization state changes from P to S. After being incident on the sixth polarization beam splitter 71, it is reflected and output as the final amplified light.

[0085] Specifically, the four-pass means that the seed light passes through the four-crystal cascaded gain module 1 four times (each time it passes through the four-crystal cascaded gain module 1, it will pass through the first crystal 11, the second crystal 12, the third crystal 13 and the fourth crystal 14). The gain is increased several times compared to the single-pass scheme, which can realize high-energy pulse output. At the same time, the gain narrowing compensation effect accumulates, supporting narrower pulse width output.

[0086] In this embodiment, the phase delay accuracy of the half-wave plate 72 should meet the requirements, the optical rotator 73 is used to cooperate with the half-wave plate 72 to control the maintenance and conversion of the polarization state, and the second total reflection mirror 74 has high reflectivity for the signal light wavelength.

[0087] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A cascaded high-gain laser amplifier using potassium ytterbium tungstate four-crystals, characterized in that, include: The four-crystal cascaded gain module includes four Yb:KGW crystals arranged in a grid pattern to achieve a net gain state under the excitation of pump light; wherein the four Yb:KGW crystals include a first crystal, a second crystal, a third crystal, and a fourth crystal located at the lower right, lower left, upper left, and upper right positions of the grid pattern, respectively. The first pump module is located on the side of the second and third crystals away from the first and fourth crystals; it is used to output the first pump light and split the first pump light into two beams of orthogonal polarization, which are injected into the first pump points of the second and third crystals respectively, and the remaining first pump light after being absorbed by the second and third crystals is injected into the first pump points of the first and fourth crystals. The second pump module is located on the side of the first crystal and the fourth crystal away from the second crystal and the third crystal; it is used to output the second pump light and split the second pump light into two beams of orthogonal polarization, which are injected into the second pump points of the first crystal and the fourth crystal respectively, and the remaining second pump light after being absorbed by the first crystal and the fourth crystal is injected into the second pump points of the second crystal and the third crystal. The signal light amplification module includes a first dichroic mirror and a fourth dichroic mirror respectively disposed on the optical path of the second pump point of the beam injection into the first crystal and the fourth crystal, and a second dichroic mirror and a third dichroic mirror disposed on the optical path of the first pump point of the beam injection into the second crystal and the third crystal; it is used to amplify the seed light after it is injected from the first dichroic mirror by passing through the first crystal, the second crystal, the second dichroic mirror, the third dichroic mirror, the third crystal and the fourth crystal in sequence, and then output it after being reflected by the fourth dichroic mirror.

2. The cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals according to claim 1, characterized in that, The film systems of the first, second, third, and fourth dichroic mirrors all exhibit transmission characteristics in the pump light band. The films of the first, second, third, and fourth dichroic mirrors all exhibit reflective properties in the seed light band.

3. The cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals according to claim 1, characterized in that, The first crystal, the second crystal, the third crystal, and the fourth crystal are all Ng-cut; The Nm axis of the first crystal is perpendicular to the horizontal plane, thereby making the polarization direction of the first crystal match the S-polarized beam injected into its second pump point. The Nm axis of the second crystal is parallel to the horizontal plane, so that the polarization direction of the second crystal matches the P-polarized beam injected into its first pump point. The Nm axis of the third crystal is perpendicular to the horizontal plane, so that the polarization direction of the third crystal matches the S-polarized beam injected into its first pump point. The Nm axis of the fourth crystal is parallel to the horizontal plane, thereby making the polarization direction of the fourth crystal match the P-polarized beam injected into its second pump point.

4. The cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals according to claim 1, characterized in that, The first pump module includes: A first semiconductor laser is used to output a first pump light, and its output optical path is directly opposite the first pump point of the second crystal. A first collimating lens is disposed between the first semiconductor laser and the second crystal, and is used to collimate the first pump light; The first polarizing beam splitter is positioned between the first collimating lens and the second crystal to transmit and reflect the collimated first pump light, and output a P-polarized beam and an S-polarized beam. The first lower focusing lens is positioned between the first polarizing beam splitter and the second crystal, and is used to focus the P-polarized beam. The second polarizing beam splitter has its incident surface facing the exit surface of the S-polarized beam of the first polarizing beam splitter, and its exit surface facing the first pump point of the third crystal; it is used to reflect the S-polarized beam. The first upper focusing lens is positioned between the second polarizing beam splitter and the third crystal to focus the S-polarized beam.

5. The cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals according to claim 4, characterized in that, The second dichroic mirror is positioned between the first lower focusing lens and the second crystal to transmit the focused P-polarized beam to the first pump point of the second crystal, so that the remaining P-polarized beam after absorption by the second crystal is injected into the first pump point of the first crystal; and to reflect the seed light to the third dichroic mirror or the second crystal. The third dichroic mirror is positioned between the first upper focusing lens and the third crystal. It is used to transmit the focused S-polarized beam to the first pump point of the third crystal, so that the remaining S-polarized beam after absorption by the third crystal is injected into the first pump point of the fourth crystal; and to reflect the seed light to the second dichroic mirror or the third crystal.

6. The potassium ytterbium tungstate four-crystal cascaded high-gain laser amplifier according to claim 4, characterized in that, The second pump module includes: The second semiconductor laser is used to output the second pump light, and its output light path is directly opposite the second pump point of the fourth crystal. The second collimating lens is disposed between the second semiconductor laser and the fourth crystal, and is used to collimate the second pump light. The third polarizing beam splitter is positioned between the second collimating lens and the fourth crystal. It is used to transmit and reflect the collimated second pump light, and output P-polarized beam and S-polarized beam. The second upper focusing lens is positioned between the third polarizing beam splitter and the fourth crystal, and is used to focus the P-polarized beam. The fourth polarizing beam splitter has its incident surface facing the exit surface of the S-polarized beam of the third polarizing beam splitter, and its exit surface facing the second pump point of the first crystal; it is used to reflect the S-polarized beam. The second lower focusing lens is positioned between the fourth polarizing beam splitter and the first crystal, and is used to focus the S-polarized beam.

7. The cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals according to claim 6, characterized in that, The first dichroic mirror is positioned between the second lower focusing lens and the first crystal. It is used to transmit the focused S-polarized beam to the second pump point of the first crystal, so that the remaining S-polarized beam after absorption by the first crystal is injected into the second pump point of the second crystal. It also reflects the seed light or the light amplified by the four-crystal cascaded gain module to the first crystal or reflects and outputs the light amplified by the four-crystal cascaded gain module. The fourth dichroic mirror is positioned between the second upper focusing lens and the fourth crystal. It is used to transmit the focused P-polarized beam to the second pump point of the fourth crystal, so that the remaining P-polarized beam after absorption by the fourth crystal is injected into the second pump point of the third crystal. It also reflects the light amplified by the four-crystal cascaded gain module to the fourth crystal or reflects and outputs the light amplified by the four-crystal cascaded gain module.

8. The potassium ytterbium tungstate-doped gadolinium four-crystal cascaded high-gain laser amplifier according to claim 6, characterized in that, Also includes: The first upper pump trap is located on the side of the second polarizing beam splitter away from the first upper focusing lens, and is used to absorb the P-polarized beam emitted from the second pump module that is not absorbed by the four-crystal cascaded gain module. The first downpump light trap is set on the side of the first polarizing beam splitter away from the second polarizing beam splitter, and is used to absorb the S-polarized beam emitted from the second pump module that is not absorbed by the four-crystal cascaded gain module. The second upper pump trap is set on the side of the third polarizing beam splitter away from the fourth polarizing beam splitter, and is used to absorb the S-polarized beam emitted from the first pump module that has not been absorbed by the four-crystal cascaded gain module. The second lower pump trap is located on the side of the fourth polarizing beam splitter away from the second lower focusing lens, and is used to absorb the P-polarized beam emitted from the first pump module that has not been absorbed by the four-crystal cascaded gain module.

9. The cascaded high-gain laser amplifier with potassium ytterbium tungstate four crystals according to any one of claims 1 to 8, characterized in that, It also includes a dual-channel expansion structure, which specifically includes: The fifth polarizing beam splitter is positioned in the optical path of the seed light entering the first dichroic mirror. It is used to transmit the seed light in a P-polarized state to the first dichroic mirror, allowing it to pass sequentially through the first crystal, second crystal, second dichroic mirror, third dichroic mirror, third crystal, and fourth crystal for primary amplification. The primary amplified light in a P-polarized state is then output through the fourth dichroic mirror. The secondary amplified light in an S-polarized state output from the first dichroic mirror is reflected to output secondary amplified light. A quarter-glass slide is placed in the output optical path of the fourth dichroic mirror. It is used to perform polarization conversion on the primary amplified light in the P-polarized state output from the fourth dichroic mirror, and output the primary amplified light in the circularly polarized state. It also performs polarization conversion on the primary amplified light in the circularly polarized state returned from the first total reflection mirror, and outputs the primary amplified light in the S-polarized state to the fourth dichroic mirror. This allows the primary amplified light in the S-polarized state to be amplified twice in sequence through the fourth crystal, the third crystal, the third dichroic mirror, the second dichroic mirror, the second crystal, the first crystal, and the first dichroic mirror. The secondary amplified light in the S-polarized state is then output through the first dichroic mirror. The first total reflection mirror is positioned on the side of the quarter-plate furthest from the fourth dichroic mirror, and is used to return the circularly polarized, first-amplified light to the quarter-plate.

10. The potassium ytterbium tungstate-doped gadolinium four-crystal cascaded high-gain laser amplifier according to claim 9, characterized in that, It also includes a four-way expansion structure, which specifically includes: The sixth polarization beam splitter is positioned in the optical path of the seed light injected into the fifth polarization beam splitter; it is used to transmit the seed light; and to reflect the S-polarized fourth-order amplified light output from the 1 / 2 glass slide, thus outputting fourth-order amplified light. A half-glass slide is placed between the sixth polarizing beam splitter and the fifth polarizing beam splitter to rotate the polarization direction of the P-polarized seed light transmitted by the sixth polarizing beam splitter; it also rotates the polarization direction of the fourth-amplified light emitted from the optical rotator to output the S-polarized fourth-amplified light. A rotator, positioned between the half-glass slide and the fifth polarizing beam splitter, is used to rotate the polarization direction of the seed light transmitted through the half-glass slide and output the P-polarized seed light to the fifth polarizing beam splitter; it also rotates the polarization direction of the fourth-order amplified P-polarized light output from the fifth polarizing beam splitter. The second total reflection mirror faces the secondary amplified light output surface of the fifth polarizing beam splitter; it is used to reflect the secondary amplified light to the fifth polarizing beam splitter so that the secondary amplified light can be amplified three and four times through the double-pass extension structure, thereby enabling the fifth polarizing beam splitter to output P-polarized four-times amplified light.

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