Cascade amplifier and laser generating device

Abstract

The invention provides a cascade amplifier and a laser generation device, and the cascade amplifier comprises N stages of multi-optical-path amplification units which achieve the amplification of a to-be-amplified light beam based on a multi-optical-path pool and a gain medium; and the N-1-stage optical coupling unit is used for converting the light spot size of the light beam to be amplified amplified by the front-stage multi-optical-path amplification unit and coupling the light beam to be amplified to the rear-stage multi-optical-path amplification unit, and converting the light spot size of the pump light beam which is not absorbed by the rear-stage multi-optical-path amplification unit and coupling the light beam to the front-stage multi-optical-path amplification unit. According to the invention, a multi-stage amplification structure is adopted, pumping light beams are fully utilized, and high pulse energy and high pulse peak power can be realized; meanwhile, confocal of the multi-optical-path amplification unit is ensured based on the doping concentration and / or thickness of the gain medium sheet; the cross-section of the light beam at the location of the optical component is also increased such that the pulse peak power density and pulse energy density at the location of the optical component are maintained below a damage threshold, thereby protecting the optical component.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optics, in particular to a cascade amplifier and a laser generating device. BACKGROUND

[0002] Material processing with short or ultrashort pulsed lasers has become more and more widespread, which has the advantages of precision and flexibility. High productivity requires high average power, which is the product of pulse repetition rate and pulse energy. According to the application and system technology, high average power can only be achieved when the laser beam has high pulse energy and medium-high pulse repetition rate. High pulse energy combined with short or ultrashort pulses results in high pulse peak power density or high pulse energy density. For example, high peak pulse power density and high pulse energy density can cause coating damage, optical device damage, stimulated Raman scattering, stimulated Brillouin scattering, nonlinear effects (causing changes or degradation in the temporal and spatial characteristics of the laser beam, or even damaging optical devices, including but not limited to self-phase modulation, Kerr lens, self-focusing), etc. It is necessary to control the pulse peak power density and pulse energy density as much as possible to avoid damaging the optical device. In addition, there is a problem that the pump beam cannot be fully utilized in the module for power and energy amplification, and the amplification capacity is limited.

[0003] Therefore, how to fully utilize the pump beam while protecting the optical device and improve the performance of the device has become one of the problems to be solved by those skilled in the art.

[0004] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely describing the technical scheme of the present application and facilitating the understanding of those skilled in the art. The above technical scheme cannot be considered as known to those skilled in the art only because it is described in the background section of the present application. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a cascade amplifier and a laser generating device, which are used to solve the problems of optical device damage caused by excessive pulse peak power density and pulse energy density, and insufficient utilization of pump beam in the prior art.

[0006] To achieve the above-mentioned purpose and other related purposes, the present application provides a cascade amplifier, which at least comprises:

[0007] N-stage multi-optical path amplification unit and N-1-stage optical coupling unit, N is a natural number greater than or equal to 2;

[0008] Each multi-optical-path amplification unit amplifies the to-be-amplified light beam based on a multi-optical-path pool and a gain medium arranged in the corresponding multi-optical-path pool; the to-be-amplified light beam enters each multi-optical-path amplification unit in turn for step-by-step amplification, and the pump light beam enters each multi-optical-path amplification unit in turn in the opposite direction of the to-be-amplified light beam to excite the gain medium;

[0009] Each optical coupling unit is arranged on an optical path between two adjacent multi-optical-path amplification units, and is used for converting and coupling the spot size of the to-be-amplified light beam amplified by the previous multi-optical-path amplification unit into the next multi-optical-path amplification unit, and converting and coupling the spot size of the pump light beam not completely absorbed by the next multi-optical-path amplification unit into the previous multi-optical-path amplification unit; wherein the spot size in the previous multi-optical-path amplification unit is smaller than the spot size in the next multi-optical-path amplification unit.

[0010] Optionally, N is set to 2; the first multi-optical-path amplification unit includes three reflection components, at least one of the first reflection component, the second reflection component and the third reflection component has a gain medium sheet with a light beam amplification function; wherein the first reflection component is arranged opposite to the second reflection component and the third reflection component, respectively, and the three reflection components are arranged in focus to form a first White multi-optical-path pool structure.

[0011] The second multi-optical-path amplification unit includes three reflection components, at least one of the fourth reflection component, the fifth reflection component and the sixth reflection component has a gain medium sheet with a light beam amplification function; wherein the fourth reflection component is arranged opposite to the fifth reflection component and the sixth reflection component, respectively, and the three reflection components are arranged in focus to form a second White multi-optical-path pool structure.

[0012] More optionally, the first reflection component includes a first concave curved mirror.

[0013] More optionally, the second reflection component includes a second concave curved mirror and a first gain medium sheet arranged in front of the second concave curved mirror; the light transmission surface of the first gain medium sheet is a plane.

[0014] More optionally, the second reflection component includes a first optical element;

[0015] The first optical element includes a gain dielectric sheet and a positive lens located in front of the corresponding gain dielectric sheet. The coating on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be magnified and the pump beam, and the coating on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the positive lens are both coated with a high-transmission coating for the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the gain dielectric sheet are both planar. The effective focal length of the gain dielectric sheet and the corresponding positive lens in the first optical element is equal to the radius of curvature of the first concave curved mirror.

[0016] Alternatively, the first optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the first optical element is convex, the second light-transmitting surface is planar, and the focal length of the first optical element is equal to the radius of curvature of the first concave curved mirror; or, the first light-transmitting surface of the first optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the first optical element is set such that the effective focal length of the beam to be amplified after passing through the first optical element twice is equal to half the radius of curvature of the first concave mirror.

[0017] Alternatively, the third reflective component includes a third concave curved mirror and a second gain dielectric sheet disposed in front of the third concave curved mirror; the light-transmitting surface of the second gain dielectric sheet is a plane.

[0018] Alternatively, the third reflective component may include a second optical element;

[0019] The second optical element includes a gain dielectric sheet and a positive lens located in front of the corresponding gain dielectric sheet. The coating on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be magnified and the pump beam, while the coating on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the positive lens are coated with high-transmission coatings for the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the gain dielectric sheet are planar. The effective focal length of the gain dielectric sheet and the corresponding positive lens in the second optical element is equal to the radius of curvature of the first concave curved mirror.

[0020] Alternatively, the second optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the second optical element is convex, the second light-transmitting surface is planar, and the focal length of the second optical element is equal to the radius of curvature of the first concave curved mirror; or, the first light-transmitting surface of the second optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the second optical element is set such that the effective focal length of the beam to be amplified after passing through the second optical element twice is equal to half the radius of curvature of the first concave mirror.

[0021] Alternatively, the fourth reflective component may include a fourth concave curved mirror.

[0022] Alternatively, the fifth reflective component includes a fifth concave curved mirror and a third gain dielectric sheet disposed in front of the fifth concave curved mirror; the light-transmitting surface of the third gain dielectric sheet is a plane.

[0023] Alternatively, the fifth reflective component may include a third optical element;

[0024] The third optical element includes a gain medium sheet and a positive lens located in front of the corresponding gain medium sheet. The coating on the first light-transmitting surface of the gain medium sheet is highly transparent to the beam to be magnified and the pump beam, and the coating on the second light-transmitting surface of the gain medium sheet is highly reflective to the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the positive lens are both coated with high-transmission coatings for the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the gain medium sheet are both planar. The effective focal length of the gain medium sheet and the corresponding positive lens in the third optical element is equal to the radius of curvature of the fourth concave curved mirror.

[0025] Alternatively, the third optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the third optical element is convex, the second light-transmitting surface is planar, and the focal length of the third optical element is equal to the radius of curvature of the fourth concave curved mirror; or, the first light-transmitting surface of the third optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the third optical element is set such that the effective focal length of the beam to be amplified after passing through the third optical element twice is equal to half the radius of curvature of the fourth concave mirror.

[0026] Alternatively, the sixth reflective component includes a sixth concave curved mirror and a fourth gain dielectric sheet disposed in front of the sixth concave curved mirror; the light-transmitting surface of the fourth gain dielectric sheet is a plane.

[0027] Alternatively, the sixth reflective component may include a fourth optical element;

[0028] The fourth optical element includes a gain dielectric sheet and a positive lens located in front of the corresponding gain dielectric sheet. The coating on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be magnified and the pump beam, while the coating on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the positive lens are coated with high-transmission coatings for the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the gain dielectric sheet are planar. The effective focal length of the gain dielectric sheet and the corresponding positive lens in the fourth optical element is equal to the radius of curvature of the fourth concave curved mirror.

[0029] Alternatively, the fourth optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the fourth optical element is convex, the second light-transmitting surface is planar, and the focal length of the fourth optical element is equal to the radius of curvature of the fourth concave curved mirror; or, the first light-transmitting surface of the fourth optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the fourth optical element is set such that the effective focal length of the beam to be amplified after passing through the fourth optical element twice is equal to half the radius of curvature of the fourth concave mirror.

[0030] Alternatively, the radius of curvature of the concave mirror used in the first White multi-path cell structure is less than or equal to the radius of curvature of the concave mirror used in the second White multi-path cell structure.

[0031] Alternatively, the positive lens is mounted on the shifting unit, and the effective focal length of the corresponding optical element is adjusted by shifting the positive lens, so that the thermal lens is compensated in the corresponding multi-pass cell structure.

[0032] Alternatively, the second light-transmitting surface of each optical element is attached to the corresponding heat sink.

[0033] Alternatively, when both the second and third reflective components are provided with gain dielectric sheets, the product of the doping concentration and the thickness of the gain dielectric sheet in the second reflective component and the product of the doping concentration and the thickness of the gain dielectric sheet in the third reflective component are set such that the power absorbed by the gain dielectric sheets in the second and third reflective components is equal.

[0034] And / or, when both the fifth and sixth reflective components are provided with gain dielectric sheets, the product of the doping concentration and the thickness of the gain dielectric sheet in the fifth reflective component and the product of the doping concentration and the thickness of the gain dielectric sheet in the sixth reflective component are set such that the power absorbed by the gain dielectric sheets in the fifth and sixth reflective components is equal.

[0035] Alternatively, at least one optical coupling unit may further convert the beam to be amplified by the preceding multi-path amplification unit into a first astigmatic beam, which is collimated in the YZ plane and focused in the XZ plane, with its focal point in the focal plane of the subsequent multi-path amplification unit; or the first astigmatic beam is collimated in the XZ plane and focused in the YZ plane, with its focal point in the focal plane of the subsequent multi-path amplification unit.

[0036] Among them, the X-axis, Y-axis and Z-axis are perpendicular to each other, and the Z-axis is the direction of beam propagation.

[0037] Alternatively, the cascaded amplifier further includes an astigmatic element disposed at the input end of the beam to be amplified in the first-stage multi-path amplification unit, which converts the beam to be amplified into a second astigmatic beam. The second astigmatic beam is collimated in the YZ plane and focused in the XZ plane, with its focal point within the focal plane of the first-stage multi-path amplification unit; or the second astigmatic beam is collimated in the XZ plane and focused in the YZ plane, with its focal point within the focal plane of the first-stage multi-path amplification unit.

[0038] Among them, the X-axis, Y-axis and Z-axis are perpendicular to each other, and the Z-axis is the direction of beam propagation.

[0039] Optionally, at least one optical coupling unit may also include a Faraday isolator.

[0040] Optionally, the output end of the beam to be amplified in the last stage multi-path amplification unit is also provided with a first beam splitter, which is used to separate the amplified beam and couple it out.

[0041] Optionally, the pump beam output end of the first-stage multi-path amplification unit is further provided with a second beam splitter, which is used to separate the pump beam that has not been absorbed.

[0042] To achieve the above and other related objectives, the present invention also provides a laser generating apparatus, the laser generating apparatus comprising at least:

[0043] Laser and the aforementioned cascaded amplifier;

[0044] The cascaded amplifier is located at the output end of the laser and is used to amplify the laser emitted by the laser.

[0045] As described above, the cascaded amplifier and laser generating device of the present invention have the following beneficial effects:

[0046] The cascaded amplifier and laser generator of the present invention adopt a multi-stage amplification structure, making full use of the pump beam to achieve high pulse energy and high pulse peak power; at the same time, based on ensuring the confocality of the multi-optical-path amplification units by adjusting the doping concentration and / or thickness of the gain dielectric sheet, the performance of the cascaded amplifier is improved.

[0047] The cascaded amplifier and laser generator of the present invention increase the cross-section of the beam at the locations of lenses, mirrors, gain media sheets and other optical components. In this way, while achieving high pulse energy and high pulse peak power, the pulse peak power density and pulse energy density at the locations of optical components (e.g., lenses, mirrors and gain media sheets) can be kept below the threshold of damage or the threshold of undesirable nonlinear effects, thereby protecting the optical components from damage. Attached Figure Description

[0048] Figure 1 The diagram shown is a structural schematic of one type of cascaded amplifier according to the present invention.

[0049] Figure 2 The diagram shown is a cross-sectional view of the rectangular planar sheet of the present invention.

[0050] Figure 3 The image shown is a side view of the rectangular planar sheet of the present invention.

[0051] Figure 4 The diagram shown is a cross-sectional view of the circular planar sheet of the present invention.

[0052] Figure 5 The image shown is a side view of the circular planar sheet of the present invention.

[0053] Figure 6 The diagram shows a schematic of an optical element of the present invention mounted on a heat sink.

[0054] Figure 7 This is a schematic diagram of another structure of the cascaded amplifier of the present invention.

[0055] Figure 8 This is a schematic diagram of another side structure of the optical element of the present invention.

[0056] Figure 9 Displayed as Figure 8 A schematic diagram of the structure of optical components mounted on a heat sink.

[0057] Figure 10 The diagram shows another side view of the optical element of the present invention.

[0058] Figure 11 Displayed as Figure 10 A schematic diagram of the structure of optical components mounted on a heat sink.

[0059] Figure 12 A schematic diagram showing a single-fold astigmatic beam.

[0060] Figure 13 The diagram shows the cross-section of the astigmatic beam and the aperture array on the first or fourth reflective component of the present invention.

[0061] Figure 14 The diagram shows the cross-section of the astigmatic beam and the aperture array on the focal plane of the present invention.

[0062] Figure 15 The diagram shows the cross-section of the astigmatic beam and the aperture array on the second, third, fifth, or sixth reflective component of the present invention.

[0063] Figure 16 The diagram shown is a structural schematic of the laser generating device of the present invention.

[0064] Component designation explanation

[0065] 1 Cascade Amplifier

[0066] 11 First Multi-Path Amplification Unit

[0067] 111 First Reflection Component

[0068] 112 Second Reflection Component

[0069] 113 Third Reflection Component

[0070] 11a First concave curved mirror

[0071] 11b Second concave curved mirror

[0072] 11c First Gain Dielectric Piece

[0073] 11d Third Concave Surface Mirror

[0074] 11e Fourth Gain Dielectric Piece

[0075] 110 focal plane

[0076] 12 Second Multi-Path Amplification Unit

[0077] 121 Fourth Reflector Component

[0078] 122 Fifth Reflector Component

[0079] 123 Sixth Reflection Component

[0080] 12a Fourth concave curved mirror

[0081] 12b Fifth concave curved mirror

[0082] 12c Third Gain Dielectric Chip

[0083] 12d Sixth Concave Surface Mirror

[0084] 12e Fourth Gain Dielectric Piece

[0085] 120 focal plane

[0086] 13 Optical coupling units

[0087] 14 Astigmatism Element

[0088] 15-Aperture Array

[0089] 151 Through Hole

[0090] 16 Pump Beam Generator

[0091] 161 Pump Source

[0092] 162 Optical Devices

[0093] 17 First Beam Spectroscope

[0094] 2 Second Multi-Path Amplification Unit

[0095] 3. Planar thin sheet

[0096] 31 Gain dielectric substrate

[0097] 32. Film layer on the first light-transmitting surface of the gain dielectric film

[0098] 33. Film layer on the second light-transmitting surface of the gain dielectric film

[0099] 4. Radiator

[0100] 5 Positive Lens

[0101] 601-609 Cross-section of astigmatic beam Detailed Implementation

[0102] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0103] Please see Figures 1-16 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0104] This invention provides a cascaded amplifier with the advantages of large cross-section, high efficiency and high gain, which can achieve high pulse energy and high pulse peak power without causing damage to the coating, optical devices, stimulated Raman scattering, stimulated Brillouin scattering, nonlinear effects and other effects.

[0105] like Figure 1 As shown, the present invention provides a cascaded amplifier 1, comprising:

[0106] The system comprises an N-stage multi-path amplification unit and an N-1-stage optical coupling unit, where N is a natural number greater than or equal to 2. Each multi-path amplification unit amplifies the beam to be amplified based on a multi-path cell and a gain medium disposed in the corresponding multi-path cell. The beam to be amplified sequentially enters each multi-path amplification unit for progressive amplification, while the pump beam enters each multi-path amplification unit sequentially in the opposite direction to the beam to be amplified to excite the gain medium. Each optical coupling unit is disposed on the optical path between two adjacent multi-path amplification units. It is used to convert the spot size of the beam to be amplified by the preceding multi-path amplification unit and couple it to the subsequent multi-path amplification unit. It also converts the spot size of the pump beam that is not completely absorbed by the subsequent multi-path amplification unit and couples it to the preceding multi-path amplification unit. The spot size in the preceding multi-path amplification unit is smaller than the spot size in the subsequent multi-path amplification unit.

[0107] In this embodiment, N is set to 2, which includes two multi-path amplification units and one optical coupling unit, namely, a first multi-path amplification unit 11, a second multi-path amplification unit 12, and an optical coupling unit 13. In practical use, the number of cascaded multi-path amplification units can be set as needed. The invention is described below based on a two-stage cascaded structure:

[0108] like Figure 1 As shown, the first multi-path amplification unit 11 achieves first-stage amplification of the beam to be amplified based on a multi-path cell and a gain medium disposed in the multi-path cell. The second multi-path amplification unit 12 achieves second-stage amplification of the beam to be amplified based on a multi-path cell and a corresponding gain medium in the multi-path cell. The gain medium is excited by the pump beam. The beam to be amplified has a diameter d1 in the gain medium of the first multi-path amplification unit 11, and a diameter d2 in the gain medium of the second multi-path amplification unit 12, where d1 < d2.

[0109] Specifically, in this embodiment, the first multi-path amplification unit 11 includes three reflective components, denoted as first reflective component 111, second reflective component 112, and third reflective component 113. At least one of the first reflective component 111, second reflective component 112, and third reflective component 113 has a gain medium sheet with beam amplification function. The first reflective component 111 is disposed opposite to the second reflective component 112 and the third reflective component 113, and the three reflective components are confocal to form a first White multi-path cell structure. The second multi-path amplification unit 12 includes three reflective components, denoted as fourth reflective component 121, fifth reflective component 122, and sixth reflective component 123. At least one of the fourth reflective component 121, fifth reflective component 122, and sixth reflective component 123 has a gain medium sheet with beam amplification function. The fourth reflective component 121 is disposed opposite to the fifth reflective component 122 and sixth reflective component 123, and the three reflective components are confocal to form a second White multi-path cell structure. It should be noted that in this embodiment, the first multi-path amplification unit 11 and the second multi-path amplification unit 12 have the same structure, both adopting the White multi-path cell structure; in actual use, the structures of the first multi-path amplification unit 11 and the second multi-path amplification unit 12 can also be set differently, including but not limited to the White multi-path cell structure and the Herriot multi-path cell structure, and are not limited to this embodiment.

[0110] As an example, such as Figure 1As shown, the first reflecting component 111 includes a first concave curved mirror 11a, the second reflecting component 112 includes a second concave curved mirror 11b and a first gain dielectric sheet 11c, and the third reflecting component 113 includes a third concave curved mirror 11d and a second gain dielectric sheet 11e. For simplicity, an XYZ coordinate system is introduced; the Z-axis is parallel to the beam propagation direction, and multiple optical paths propagate through multiple reflections in the XZ plane, while the YZ plane is perpendicular to the XZ plane. The second concave curved mirror 11b and the third concave curved mirror 11d are located on the same side (at the same position on the Z-axis) and are positioned opposite to the first concave curved mirror 11a in the Z-axis direction; therefore, the first concave curved mirror 11a, the second concave curved mirror 11b, and the third concave curved mirror 11d are arranged confocally, and the confocal surface 110 is the central plane of the first multi-path amplification unit 11. The first gain medium plate 11c is disposed in front of the second concave curved mirror 11b, and the second gain medium plate 11e is disposed in front of the third concave curved mirror 11d. The light-transmitting surfaces of the first gain medium plate 11c and the second gain medium plate 11e are planar. The pump beam excites the first gain medium plate 11c and the second gain medium plate 11e, and the pump beam and the beam to be amplified pass through the first gain medium plate 11c and the second gain medium plate 11e multiple times. Similarly, the fourth reflection component 122 includes a fourth concave curved mirror 12a, the fifth reflection component 122 includes a fifth concave curved mirror 12b and a third gain medium plate 12c, and the sixth reflection component 123 includes a sixth concave curved mirror 12d and a fourth gain medium plate 12e; the structure is the same as that of the first multi-path amplification unit 11, and will not be described in detail here; the confocal surface 120 of the fourth concave curved mirror 12a, the fifth concave curved mirror 12b, and the sixth concave curved mirror 12d is the central plane of the second multi-path amplification unit 12. Among them, the first concave curved mirror 11a, the second concave curved mirror 11b, and the third concave curved mirror 11d have the same first radius of curvature R1, and the fourth concave curved mirror 12a, the fifth concave curved mirror 12b, and the sixth concave curved mirror 12d have the same second radius of curvature R2; the radius of curvature of the concave mirrors used in the first White multi-path cell structure is less than or equal to the radius of curvature of the concave mirrors used in the second White multi-path cell structure (i.e., the first radius of curvature R1 is less than or equal to the second radius of curvature R2). More specifically, each gain dielectric sheet is a planar thin sheet 3 structure (both the first and second light-transmitting surfaces are planar). In one example, such as Figure 2 and Figure 3 As shown, the cross-section of the planar sheet 3 is rectangular. The long side of the planar sheet 3 is a, the short side is b, and the thickness is d. The ratio of the short side to the thickness is greater than 10, i.e., b / d > 10. In another example, as... Figure 4 and Figure 5As shown, the cross-section of the planar thin plate 3 is circular. The diameter of the planar thin plate 3 is D, and the thickness is d. The ratio of diameter to thickness is greater than 10, i.e., D / d > 10. When the gain medium is solid, pumping can be performed optically. Preferably, a diode laser is used for pumping. Furthermore, when using a planar thin plate structure for the gain medium, the pump radiation can be coupled into the gain medium plate perpendicularly or at a small angle.

[0111] Based on this, as another example, a gain dielectric sheet is coated; in this case, the first reflective assembly 111 includes a first concave curved mirror 11a, the second reflective assembly 112 includes a first optical element, and the third reflective assembly 113 includes a second optical element; similarly, the fourth reflective assembly 121 includes a fourth concave curved mirror 12a, the fifth reflective assembly 122 includes a third optical element, and the sixth reflective assembly 123 includes a fourth optical element. Wherein, as... Figure 6 As shown, each optical element includes a gain medium sheet 31 and a positive lens 5 located in front of the corresponding gain medium sheet. The shape and size of the gain medium sheet 31 are the same as the planar thin sheet in the previous example. The first light-transmitting surface (the side near the first concave curved mirror 11a or the fourth concave curved mirror 12a) and the second light-transmitting surface (the side away from the first concave curved mirror 11a or the fourth concave curved mirror 12a) are both planar. The film layer 32 of the first light-transmitting surface of the gain medium sheet 31 is highly transparent to the beam to be magnified and the pump beam. The film layer 33 of the second light-transmitting surface of the gain medium sheet 31 is highly reflective to the beam to be magnified and the pump beam. The second light-transmitting surface acts as a planar reflecting mirror (at this time, it is not necessary to set the second concave curved mirror 11b, the third concave curved mirror 11d, the fifth concave curved mirror 12b and the sixth concave curved mirror 12d). The first light-transmitting surface and the second light-transmitting surface of the positive lens 5 are both provided with high-transmission films for the beam to be magnified and the pump beam.

[0112] It should be noted that the gain dielectric sheet 31 and other optical components (such as the beam splitter) in the multi-path cell structure may experience thermal lensing due to high power loads. This thermal lensing effect varies with power; to reduce its impact, operating parameters such as power / energy are significantly limited. To address this issue, the present invention mounts the positive lens 5 on a shifting unit (not shown in the figure), and shifts the positive lens 5 (e.g., by shifting the positive lens 5...) Figure 6 As indicated by the double arrows, changing the distance between the positive lens 5 and the gain medium sheet 31 adjusts the effective focal length of the corresponding optical element, thereby compensating for the thermal lensing effect in the corresponding multi-pass cell structure. The positive lens 5 can be a single lens or a lens group; at least one lens in the lens group is mounted on a shifting unit, and the focal length of the lens group can be changed by shifting the lenses in the lens group; as an example, the lens group consists of concave lenses and convex lenses, which have similar absolute focal length values.

[0113] Furthermore, such as Figure 6 As shown, as another example, the second light-transmitting surface of the optical element is attached to the heat sink 4 so that the heat generated in the optical element is dissipated and carried away by the heat sink 4 for effective cooling. In this case, heat conduction is one-dimensional, and the direction of heat conduction and the temperature gradient in the optical element are almost parallel to the occurrence of the amplified beam. Therefore, the gain dielectric sheet does not produce a thermal lensing effect, and the beam propagation is determined only by the passive optical devices used (such as mirrors and lenses). The positive lens 5, the optical element, and the heat sink 4 constitute the reflecting assembly.

[0114] like Figure 7 The following is based on Figure 6 In the cascaded amplifier formed by the reflective components shown, the light beam passes through the positive lens 5 and the corresponding optical element twice with each reflection. At this time, assuming that the gain medium does not have a thermal lensing effect, the focal length of the positive lens 5 is set to be almost equal to the radius of curvature of the corresponding concave surface mirror (the first concave surface mirror 11a or the fourth concave surface mirror 12a). Assuming that the gain medium has a thermal lensing effect, the focal length of the positive lens 5 is set such that the effective focal length of the thermal lens formed by the positive lens 5 and the corresponding optical element is equal to the radius of curvature of the corresponding concave surface mirror. That is, the effective focal lengths of the first optical element and the corresponding positive lens, and the second optical element and the corresponding positive lens are equal to the radius of curvature of the first concave surface mirror 11a, and the effective focal lengths of the third optical element and the corresponding positive lens, and the fourth optical element and the corresponding positive lens are equal to the radius of curvature of the fourth concave surface mirror 12a.

[0115] To reduce the number of optical elements, the gain dielectric sheet 31 can be designed to have a convex, curved incident surface and a flat exit surface, such as... Figure 8 As shown, as another example, each optical element is composed of a gain dielectric sheet 31. The film layer 32 on the first light-transmitting surface of the gain dielectric sheet 31 is highly transparent to the beam to be amplified and the pump beam, and the film layer 33 on the second light-transmitting surface of the gain dielectric sheet 31 is highly reflective to the beam to be amplified and the pump beam. The first light-transmitting surface of each optical element is convex, and the second light-transmitting surface is planar. The focal length of the first and second optical elements is equal to the radius of curvature of the first concave curved mirror 11a; the focal length of the third and fourth optical elements is equal to the radius of curvature of the fourth concave curved mirror 12a. Figure 9 As shown, the second light-transmitting surface of the optical element is further attached to the heat sink 4.

[0116] As another example, the shape of the gain dielectric sheet 31 is set as a meniscus lens. For example... Figure 10As shown, each optical element is composed of a gain dielectric sheet 31. The film layer 32 on the first light-transmitting surface of the gain dielectric sheet 31 is highly transparent to the beam to be amplified and the pump beam, while the film layer 33 on the second light-transmitting surface of the gain dielectric sheet 31 is highly reflective to the beam to be amplified and the pump beam. The first light-transmitting surface of each optical element is concave, and the second light-transmitting surface is convex. Since the gain dielectric sheet 31 is very thin, the radii of curvature of the two surfaces can be chosen to be the same. The radii of curvature of the first and second optical elements are set such that the effective focal length of the beam to be amplified after passing through the first and second optical elements twice is equal to half the radius of curvature of the first concave curved mirror 11a. The radii of curvature of the third and fourth optical elements are set such that the effective focal length of the beam to be amplified after passing through the third and fourth optical elements twice is equal to half the radius of curvature of the fourth concave curved mirror 12a. Furthermore, in order to cool the optical elements, a heat sink 4 with a concave curved contact surface is used. The second light-transmitting surface of the optical element is attached to the heat sink 4, as shown below. Figure 11 As shown, ideally, the concave curved contact surface of the heat sink 4 has the same radius of curvature as the convex surface of the optical element.

[0117] It should be noted that, for ease of explanation, the second, third, fifth, and sixth reflective components are set to have the same structure in this embodiment; in actual use, the structure of each reflective component in different multi-path amplification units may be different, and the structure of each reflective component in the same multi-path amplification unit may also be different, and is not limited to this embodiment.

[0118] like Figure 1 As shown, the optical coupling unit 13 is disposed in the optical path between the first multi-path amplification unit 11 and the second multi-path amplification unit 12. It is used to convert the spot size of the beam to be amplified by the first multi-path amplification unit 11 and couple it into the second multi-path amplification unit 12. It also converts the spot size of the pump beam that is not completely absorbed by the second multi-path amplification unit 12 and couples it into the first multi-path amplification unit 11.

[0119] Specifically, since the spot sizes in the first multi-path amplification unit 11 and the second multi-path amplification unit 12 are different, the optical coupling unit 13 has the function of beam cross-section size conversion to meet the requirements of beam coupling; in this embodiment, the spot size in the first multi-path amplification unit 11 is smaller than the spot size in the second multi-path amplification unit 12.

[0120] Furthermore, the optical coupling unit 13 is also equipped with a Faraday isolator to limit the propagation direction of the beam, preventing the beam to be amplified emitted from the first multi-path amplification unit 11 from re-entering the first multi-path amplification unit 11, and preventing the pump beam emitted from the second multi-path amplification unit 12 from re-entering the second multi-path amplification unit 12. For cases where N is greater than 2, Faraday isolators can be installed in each level of the optical coupling unit, or only partially as needed; details will not be elaborated here.

[0121] like Figure 1 and Figure 7 As shown, the beam to be amplified sequentially enters the first multi-path amplification unit 11 and the second multi-path amplification unit 12 for first-stage amplification and second-stage amplification. The pump beam sequentially enters the second multi-path amplification unit 12 and the first multi-path amplification unit 11 to excite the gain medium, thereby generating gain in the gain medium. Since the pump beam enters the second multi-path amplification unit 12 first, it is first absorbed by the gain medium in the second multi-path amplification unit 12, resulting in a higher gain for the second multi-path amplification unit 12. The remaining pump beam then enters the first multi-path amplification unit 11 and is fully absorbed. However, since the gain medium in the first multi-path amplification unit 11 absorbs relatively less pump beam, the resulting gain is relatively lower. In the cascaded amplifier of this invention, the gain of the second multi-path amplification unit 12 is greater than that of the first multi-path amplification unit 11, thus making full use of the pump beam. Furthermore, within the same multi-path amplification unit, the order in which the pump beam enters the gain medium varies. Relatively speaking, the gain medium (or optical element) excited earlier absorbs more power, resulting in different thermal lensing effects between the two gain mediums within the same multi-path amplification unit. For example, the thermal lensing effect of the gain medium in the third reflection assembly is greater than that in the second reflection assembly, and the thermal lensing effect of the gain medium in the sixth reflection assembly is greater than that in the fifth reflection assembly. To make the thermal lensing effects of the two gain mediums (or optical elements) within the same multi-path amplification unit the same, in... Figure 1 and Figure 7In the illustrated scheme, the product of the doping concentration and thickness of the gain dielectric sheet in the second reflective component and the product of the doping concentration and thickness of the gain dielectric sheet in the third reflective component are set such that the power absorbed by the gain dielectric sheets in the second and third reflective components is equal; as an example, the product of the doping concentration and thickness of the gain dielectric sheet in the second reflective component is equal to the product of the doping concentration and thickness of the gain dielectric sheet in the third reflective component. Similarly, the products of the doping concentration and thickness of the gain dielectric sheet in the fifth reflective component and the product of the doping concentration and thickness of the gain dielectric sheet in the sixth reflective component are set such that the power absorbed by the gain dielectric sheets in the fifth and sixth reflective components is equal; as an example, the product of the doping concentration and thickness of the gain dielectric sheet in the fifth reflective component is equal to the product of the doping concentration and thickness of the gain dielectric sheet in the sixth reflective component.

[0122] In free propagation, an astigmatic beam has a circular power density distribution in each plane, with the beam waist (focal point) being the same size and located in the same position within the two perpendicular planes (XZ and YZ planes). In this case, the power density is inversely proportional to the square of the beam diameter. A compact optical structure would result in extremely high power density in the focal plane (110, 120) of this invention; high pulse peak power density and pulse energy density lead to localized heating and ionization of the air, resulting in beam quality and performance losses, which limits the achievable peak pulse power and pulse energy. Therefore, to reduce pulse peak power density and pulse energy density, the beam to be amplified can be converted into an astigmatic beam before coupling to a multipath cell; an astigmatic beam can be converted into a simple astigmatic beam by using devices including, but not limited to, cylindrical optics (e.g., cylindrical lenses, cylindrical mirrors, or prisms). Figure 1 and Figure 7As shown, the optical coupling unit 13 also converts the beam to be amplified by the first multi-path amplification unit 11 into a first astigmatic beam. The first astigmatic beam is collimated in the YZ plane and focused in the XZ plane, with its focal point in the focal plane of the second multi-path amplification unit 12; or the first astigmatic beam is collimated in the XZ plane and focused in the YZ plane, with its focal point in the focal plane of the second multi-path amplification unit 12 (for cases where N is greater than 2, each stage of the optical coupling unit can convert the beam to be amplified by the previous multi-path amplification unit into an astigmatic beam. In this case, the focal point of the astigmatic beam is in the focal plane of the subsequent multi-path amplification unit; partial conversion is also possible as needed, which will not be elaborated here). The cascaded amplifier 1 also includes an astigmatic element 14, which is disposed at the input end of the beam to be amplified in the first multi-path amplification unit 11 (i.e., the first-stage multi-path amplification unit when N is greater than 2). The astigmatic element 14 converts the beam to be amplified into a second astigmatic beam. The second astigmatic beam is collimated in the YZ plane and focused in the XZ plane, with its focal point within the focal plane of the first multi-path amplification unit 11 (i.e., the first-stage multi-path amplification unit when N is greater than 2); or the second astigmatic beam is collimated in the XZ plane and focused in the YZ plane, with its focal point within the focal plane of the first multi-path amplification unit 11 (i.e., the first-stage multi-path amplification unit when N is greater than 2). The X, Y, and Z axes are mutually perpendicular, with the Z axis representing the beam propagation direction. Figure 12 As shown, this is a single-astigmatic beam that propagates along the Z-axis. In the XZ plane, the beam waist dσx0 is located at point Z0x, and in the YZ plane, the beam waist dσy0 is located at point Z0y. A single-astigmatic beam can significantly reduce the power density on optical devices and at the focal point. For example... Figure 13 The figures shown are cross-sections 601, 602, and 603 of the astigmatic beam on the first reflecting component 111 or the fourth reflecting component 121, as shown. Figure 14 The figures shown are cross-sections 604, 605, 606, and 607 of the astigmatic beam on the focal plane 110 or 120, as shown. Figure 15 The cross-sections 608 and 609 of the astigmatic beam on the second reflecting component 112, the third reflecting component 113, the fifth reflecting component 122, or the sixth reflecting component 123 are shown; it can be seen that the beam has a large cross-section in the reflecting plane. Furthermore, to improve beam quality, one or more aperture arrays 15 can be used in a multi-path cell; the aperture array has a beam aperture 151, the geometry of which is adapted to the beam cross-section of the corresponding beam passage location, including but not limited to being set to 1.2 to 2 times the corresponding beam cross-section. As an example, the aperture array is positioned in one of the mirror surfaces and / or near the focal planes 110 and 120; as... Figure 13 As shown, the aperture array 15 is disposed on the mirror surface of the first reflective assembly 111 or the fourth reflective assembly 121; asFigure 14 As shown, the aperture array 15 is positioned near the focal plane 110 or 120; as Figure 15 As shown, the aperture array 15 is disposed on the mirror surface of the second reflective component 112, the third reflective component 113, the fifth reflective component 122, or the sixth reflective component 123.

[0123] like Figure 1 and Figure 7 As shown, in this embodiment, the cascaded amplifier also includes a pump beam generator 16. The laser emitted by the pump source 161 in the pump beam generator 16 forms a pump beam through the optical device 162, so that the pump beam on the gain dielectric sheet has a size that is equivalent to or the same as the beam to be amplified.

[0124] In this embodiment, to simplify the separation of the beam to be amplified and the pump beam, it is advantageous that the two beams are coupled into the multi-path cell in an antiparallel manner. Furthermore, the output end (input end) of the beam to be amplified of the second multi-path amplification unit 12 (which is the last stage multi-path amplification unit for cases where N is greater than 2) is also provided with a first beam splitter 17. The first beam splitter 17 is used to separate the amplified beam and couple it out. The beam splitter 17 transmits the pump beam and reflects the amplified beam; thus, the pump beam can be coupled into the multi-path cell, while the amplified beam is separated and reflected. Similarly, the output end (input end) of the pump beam of the first multi-path amplification unit 11 (which is the first stage multi-path amplification unit for cases where N is greater than 2) can also be provided with a second beam splitter (not shown in the figure). The second beam splitter transmits the beam to be amplified and reflects the pump beam; thus, the beam to be amplified can be coupled into the multi-path cell, while the unabsorbed pump beam is separated and reflected.

[0125] In the cascaded amplifier of this invention, the first light-transmitting surfaces of the second, third, fifth, and sixth reflective components have high transmittance for both the beam to be amplified and the pump beam, while the second light-transmitting surfaces have high reflectivity for both. Therefore, the beam to be amplified and the pump beam propagate in opposite parallel directions, resulting in overlap and maximizing amplification. As an example, a laser oscillator can be implemented based on the cascaded amplifier of this invention. In a multi-path cell, by appropriately adjusting the incident direction and position of the beam, and adjusting the curvature and position of the reflectors, a 4xN channel can be generated in the multi-path cell, where N is an integer. To amplify the beam, one or more gain media can be arranged within the multi-path cell.

[0126] like Figure 16 As shown, the present invention also provides a laser generating device, including: the cascade amplifier 1 and the laser 2 of the present invention; the cascade amplifier 1 is disposed at the output end of the laser 2 and is used to amplify the laser emitted by the laser 2.

[0127] In summary, this invention provides a cascaded amplifier and a laser generating device, comprising: N-stage multi-optical-path amplification units and N-1-stage optical coupling units, where N is a natural number greater than or equal to 2; each stage of the multi-optical-path amplification unit amplifies the beam to be amplified based on a multi-optical-path cell and a gain medium disposed in the corresponding multi-optical-path cell; the beam to be amplified sequentially enters each multi-optical-path amplification unit for progressive amplification, and a pump beam enters each multi-optical-path amplification unit sequentially in the opposite direction to the beam to be amplified to excite the gain medium; each optical coupling unit is disposed on the optical path between two adjacent stages of the multi-optical-path amplification unit, used to convert the spot size of the beam to be amplified by the preceding stage multi-optical-path amplification unit and couple it to the following stage multi-optical-path amplification unit, and also to convert the spot size of the pump beam that is not completely absorbed by the following stage multi-optical-path amplification unit and couple it to the preceding stage multi-optical-path amplification unit; wherein, the spot size in the preceding stage multi-optical-path amplification unit is smaller than the spot size in the following stage multi-optical-path amplification unit. N is a natural number greater than or equal to 2. The cascaded amplifier and laser generator of this invention employ a multi-stage amplification structure, fully utilizing the pump beam to achieve high pulse energy and high pulse peak power. Simultaneously, by ensuring confocality of the multi-path amplification units through the doping concentration and / or thickness of the gain dielectric sheet, the performance of the cascaded amplifier is improved. Furthermore, the cross-section of the beam at the locations of the lens, mirror, gain dielectric sheet, and other optical components is increased. Thus, while achieving high pulse energy and high pulse peak power, the pulse peak power density and pulse energy density at the locations of optical components (e.g., lenses, mirrors, and gain dielectric sheets) can be kept below the threshold of damage or the threshold of undesirable nonlinear effects, thereby protecting the optical components from damage. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0128] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A cascaded amplifier, characterized in that, The cascaded amplifier includes at least: N-level multi-path amplification units and N-1-level optical coupling units, where N is a natural number greater than or equal to 2; Each multi-path amplification unit amplifies the beam to be amplified based on a multi-path cell and a gain medium disposed in the corresponding multi-path cell. The beam to be amplified enters each multi-path amplification unit in sequence for step-by-step amplification, and the pump beam enters each multi-path amplification unit in the opposite direction to the beam to be amplified to excite the gain medium. Each optical coupling unit is disposed on the optical path between two adjacent multi-path amplification units. It is used to convert the spot size of the beam to be amplified by the preceding multi-path amplification unit and couple it to the following multi-path amplification unit. It also converts the spot size of the pump beam that is not completely absorbed by the following multi-path amplification unit and couples it to the preceding multi-path amplification unit. The spot size in the preceding multi-path amplification unit is smaller than the spot size in the following multi-path amplification unit.

2. The cascaded amplifier according to claim 1, characterized in that: N is set to 2; the first multi-path amplification unit includes three reflective components, at least one of the first reflective component, the second reflective component and the third reflective component having a gain medium sheet with beam amplification function; wherein, the first reflective component is respectively arranged opposite to the second reflective component and the third reflective component, and the three reflective components are confocal to form a first White multi-path cell structure; The second multi-path amplification unit includes three reflective components, at least one of which, including the fourth, fifth, and sixth reflective components, has a gain dielectric sheet with beam amplification function; wherein, the fourth reflective component is respectively arranged opposite to the fifth and sixth reflective components, and the three reflective components are confocal to form a second White multi-path cell structure.

3. The cascaded amplifier according to claim 2, characterized in that: The first reflective component includes a first concave curved mirror.

4. The cascaded amplifier according to claim 2, characterized in that: The second reflective component includes a second concave curved mirror and a first gain dielectric sheet disposed in front of the second concave curved mirror; the light-transmitting surface of the first gain dielectric sheet is a plane.

5. The cascaded amplifier according to claim 3, characterized in that: The second reflective component includes a first optical element; The first optical element includes a gain dielectric sheet and a positive lens located in front of the corresponding gain dielectric sheet. The coating on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be magnified and the pump beam, and the coating on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the positive lens are both coated with a high-transmission coating for the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the gain dielectric sheet are both planar. The effective focal length of the gain dielectric sheet and the corresponding positive lens in the first optical element is equal to the radius of curvature of the first concave curved mirror. Alternatively, the first optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the first optical element is convex, the second light-transmitting surface is planar, and the focal length of the first optical element is equal to the radius of curvature of the first concave curved mirror; or, the first light-transmitting surface of the first optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the first optical element is set such that the effective focal length of the beam to be amplified after passing through the first optical element twice is equal to half the radius of curvature of the first concave mirror.

6. The cascaded amplifier according to claim 2, characterized in that: The third reflective component includes a third concave curved mirror and a second gain medium sheet disposed in front of the third concave curved mirror; the light-transmitting surface of the second gain medium sheet is a plane.

7. The cascaded amplifier according to claim 3, characterized in that: The third reflective component includes a second optical element; The second optical element includes a gain dielectric sheet and a positive lens located in front of the corresponding gain dielectric sheet. The coating on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be magnified and the pump beam, while the coating on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the positive lens are coated with high-transmission coatings for the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the gain dielectric sheet are planar. The effective focal length of the gain dielectric sheet and the corresponding positive lens in the second optical element is equal to the radius of curvature of the first concave curved mirror. Alternatively, the second optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the second optical element is convex, the second light-transmitting surface is planar, and the focal length of the second optical element is equal to the radius of curvature of the first concave curved mirror; or, the first light-transmitting surface of the second optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the second optical element is set such that the effective focal length of the beam to be amplified after passing through the second optical element twice is equal to half the radius of curvature of the first concave mirror.

8. The cascaded amplifier according to claim 2, characterized in that: The fourth reflective component includes a fourth concave curved mirror.

9. The cascaded amplifier according to claim 2, characterized in that: The fifth reflective component includes a fifth concave curved mirror and a third gain medium sheet disposed in front of the fifth concave curved mirror; the light-transmitting surface of the third gain medium sheet is a plane.

10. The cascaded amplifier according to claim 8, characterized in that: The fifth reflective component includes a third optical element; The third optical element includes a gain medium sheet and a positive lens located in front of the corresponding gain medium sheet. The coating on the first light-transmitting surface of the gain medium sheet is highly transparent to the beam to be magnified and the pump beam, and the coating on the second light-transmitting surface of the gain medium sheet is highly reflective to the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the positive lens are both coated with high-transmission coatings for the beam to be magnified and the pump beam. The first and second light-transmitting surfaces of the gain medium sheet are both planar. The effective focal length of the gain medium sheet and the corresponding positive lens in the third optical element is equal to the radius of curvature of the fourth concave curved mirror. Alternatively, the third optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the third optical element is convex, the second light-transmitting surface is planar, and the focal length of the third optical element is equal to the radius of curvature of the fourth concave curved mirror; or, the first light-transmitting surface of the third optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the third optical element is set such that the effective focal length of the beam to be amplified after passing through the third optical element twice is equal to half the radius of curvature of the fourth concave mirror.

11. The cascaded amplifier according to claim 2, characterized in that: The sixth reflective component includes a sixth concave curved mirror and a fourth gain dielectric sheet disposed in front of the sixth concave curved mirror; the light-transmitting surface of the fourth gain dielectric sheet is a plane.

12. The cascaded amplifier according to claim 8, characterized in that: The sixth reflective component includes a fourth optical element; The fourth optical element includes a gain dielectric sheet and a positive lens located in front of the corresponding gain dielectric sheet. The coating on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be magnified and the pump beam, while the coating on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the positive lens are coated with high-transmission coatings for the beam to be magnified and the pump beam. Both the first and second light-transmitting surfaces of the gain dielectric sheet are planar. The effective focal length of the gain dielectric sheet and the corresponding positive lens in the fourth optical element is equal to the radius of curvature of the fourth concave curved mirror. Alternatively, the fourth optical element may be composed of a gain dielectric sheet, wherein the film layer on the first light-transmitting surface of the gain dielectric sheet is highly transparent to the beam to be amplified and the pump beam, and the film layer on the second light-transmitting surface of the gain dielectric sheet is highly reflective to the beam to be amplified and the pump beam; wherein the first light-transmitting surface of the fourth optical element is convex, the second light-transmitting surface is planar, and the focal length of the fourth optical element is equal to the radius of curvature of the fourth concave curved mirror; or, the first light-transmitting surface of the fourth optical element is concave, the second light-transmitting surface is convex, and the radius of curvature of the fourth optical element is set such that the effective focal length of the beam to be amplified after passing through the fourth optical element twice is equal to half the radius of curvature of the fourth concave mirror.

13. The cascaded amplifier according to any one of claims 2-12, characterized in that: The radius of curvature of the concave mirror used in the first White multi-path cell structure is less than or equal to the radius of curvature of the concave mirror used in the second White multi-path cell structure.

14. The cascaded amplifier according to claim 5, 7, 10 or 12, characterized in that: The positive lens is mounted on the shifting unit. By shifting the positive lens, the effective focal length of the corresponding optical element is adjusted, so that the thermal lens is compensated in the corresponding multi-pass cell structure.

15. The cascaded amplifier according to claim 5, 7, 10 or 12, characterized in that: The second light-transmitting surface of each optical element is attached to the corresponding heat sink.

16. The cascaded amplifier according to any one of claims 2-12, characterized in that: When both the second and third reflective components are provided with gain dielectric sheets, the product of the doping concentration and the thickness of the gain dielectric sheet in the second reflective component and the product of the doping concentration and the thickness of the gain dielectric sheet in the third reflective component are set to make the power absorbed by the gain dielectric sheets in the second and third reflective components equal. And / or, when both the fifth and sixth reflective components are provided with gain dielectric sheets, the product of the doping concentration and the thickness of the gain dielectric sheet in the fifth reflective component and the product of the doping concentration and the thickness of the gain dielectric sheet in the sixth reflective component are set such that the power absorbed by the gain dielectric sheets in the fifth and sixth reflective components is equal.

17. The cascaded amplifier according to any one of claims 1-12, characterized in that: At least one optical coupling unit also converts the beam to be amplified after being amplified by the preceding multi-path amplification unit into a first astigmatic beam. The first astigmatic beam is collimated in the YZ plane and focused in the XZ plane, with its focal point in the focal plane of the subsequent multi-path amplification unit; or the first astigmatic beam is collimated in the XZ plane and focused in the YZ plane, with its focal point in the focal plane of the subsequent multi-path amplification unit. Among them, the X-axis, Y-axis and Z-axis are perpendicular to each other, and the Z-axis is the direction of beam propagation.

18. The cascaded amplifier according to any one of claims 1-12, characterized in that: The cascaded amplifier further includes an astigmatic element disposed at the input end of the beam to be amplified in the first-stage multi-path amplification unit, which converts the beam to be amplified into a second astigmatic beam. The second astigmatic beam is collimated in the YZ plane and focused in the XZ plane, with its focal point within the focal plane of the first-stage multi-path amplification unit; or the second astigmatic beam is collimated in the XZ plane and focused in the YZ plane, with its focal point within the focal plane of the first-stage multi-path amplification unit. Among them, the X-axis, Y-axis and Z-axis are perpendicular to each other, and the Z-axis is the direction of beam propagation.

19. The cascaded amplifier according to claim 1, characterized in that: At least one optical coupling unit also includes a Faraday isolator.

20. The cascaded amplifier according to claim 1, characterized in that: The final stage of the multi-path amplification unit is also equipped with a first beam splitter at the beam output end. The first beam splitter is used to separate the amplified beam and couple it out.

21. The cascaded amplifier according to claim 1, characterized in that: The pump beam output end of the first-stage multi-path amplification unit is also equipped with a second beam splitter, which is used to separate the pump beam that has not been absorbed.

22. A laser generating device, characterized in that, The laser generating device includes at least: a laser and a cascaded amplifier as described in any one of claims 1-21; The cascaded amplifier is located at the output end of the laser and is used to amplify the laser emitted by the laser.

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