A multi-pass gain laser

Abstract

The present application relates to the technical field of laser, and especially relates to a multi-pass gain laser, comprising: a pump source, a beam shaping mirror group, a first mirror, a second mirror and an output coupling mirror arranged in sequence; laser is transmitted to the output coupling mirror after N times of reflection of optical path separation between the second mirror and the first mirror; the multi-pass gain laser further comprises a composite gain structure, and the composite gain structure comprises a high-thermal-conductivity part and a gain part, the gain part comprises N gain crystals connected in sequence, and the nth reflected light passes through the nth gain crystal; wherein, the high-thermal-conductivity part covers the surface of the gain part, and the high-thermal-conductivity part fills the interval region between the adjacent two gain crystals. The present application is at least beneficial to significantly improving the heat dissipation efficiency and ensuring that the laser has high gain and high output stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lasers, and particularly relates to a multi-pass gain laser. BACKGROUND

[0002] With the continuous growth of the demand for high-power mid-infrared lasers in the fields of industrial manufacturing, aerospace, laser medical treatment and the like, a Tm:YLF laser (a thulium-doped laser gain medium laser, whose substrate material is yttrium lithium fluoride) becomes one of the core technical routes due to its unique advantages. The output wavelength of the Tm:YLF laser covers a mid-infrared waveband of 1.9 μm~2.1 μm, is not only in an atmospheric transmission window, has low energy attenuation, and has moderate penetration depth to biological tissues and controllable thermal damage area, and has an irreplaceable position. In order to break through the power limitation of single-pass gain, a multi-pass gain structure is widely used, specifically, the laser beam passes through the Tm:YLF gain medium multiple times in the resonant cavity, the light path is increased in a limited cavity length, and the gain accumulation efficiency is significantly increased, which is a mainstream design way for realizing hundreds of watts of mid-infrared laser output at present.

[0003] However, the multi-pass gain structure, while improving the power, also brings a severe heat management challenge, because the thermal conductivity of the Tm:YLF crystal itself is low, about 6 W / (m·K) at room temperature, about 1 / 66 of the thermal conductivity of red copper and 1 / 366 of the thermal conductivity of diamond. When the light beam passes through the gain medium in a multi-pass way, a part of the energy injected by the pump source is not converted into laser energy, but is released in the form of heat energy in the gain medium crystal. Since the heat cannot be discharged in time, a significant temperature gradient along the light beam propagation direction and the radial direction will be formed in the gain medium crystal, and the highest temperature difference can reach tens or even hundreds of degrees Celsius. The problems caused by this heat accumulation are extremely destructive. On the one hand, the thermal stress generated by the temperature gradient will cause the distortion of the crystal lattice, leading to uneven refractive index distribution, and then inducing a serious thermal lens effect, that is, the beam waist radius and the divergence angle of the light beam in the cavity fluctuate with the change of the focal length of the thermal lens, which not only destroys the mode matching, but also causes the spot to diverge and the energy to be unevenly distributed, so that the beam quality factor M 2 rises from an ideal 1.0 to above 2.0, on the other hand, the long-term high-temperature environment will accelerate the fluorescence quenching of Tm 3+ ions, reduce the gain efficiency, and the difference in the thermal expansion coefficient between the gain medium crystal and the packaging structure will produce a continuous thermal stress, which may eventually cause the gain medium crystal to appear microcracks or even completely break, severely limiting the high-power continuous stable operation of the laser.

[0004] To solve the above problems, the prior art mainly relies on the traditional metal heat sink scheme, that is, the gain medium crystal is attached to the surface of the metal heat sink by mechanical clamping or heat-conducting glue, and is matched with a water-cooling channel or a forced air-cooling system. Although the thermal conductivity of the heat sink is high, the interfacial thermal resistance between the gain medium crystal and the heat sink becomes the key bottleneck of heat transfer. The mechanical attachment of the gain medium crystal and the metal heat sink also causes the existence of micron-level air gap at the attachment interface between them. The thermal conductivity of the air gap is only 0.026 W / (m·K). Even if heat-conducting glue is used, its thermal conductivity is in the range of 1 W / (m·K)~10 W / (m·K), which is much lower than the thermal conductivity of the gain medium crystal and the metal heat sink themselves. This causes the heat generated in the gain medium crystal to need to overcome a large interfacial resistance to be transferred to the heat sink, forming an inefficient heat dissipation state of "local high temperature of heat source and low temperature of idle heat sink". In addition, the in-plane heat conduction efficiency of a single metal heat sink is limited. When the pump power of the multi-pass gain structure is increased to more than 80W, the temperature distribution on the surface of the heat sink will be obviously uneven, and the temperature in the region close to the gain medium crystal will rise sharply, further weakening the heat dissipation effect. At this time, the insufficient heat dissipation capacity becomes the core bottleneck that restricts the laser to break through to the hundreds of watts level and maintain long-term stable output. Therefore, developing a heat management scheme that can directly reduce the interfacial thermal resistance between the gain medium crystal and the heat sink and build an efficient heat conduction has become an urgent technical demand for the development of multi-pass gain lasers to higher power and more stable performance. SUMMARY

[0005] Therefore, the present application aims to provide a multi-pass gain laser, which can significantly improve the heat dissipation efficiency and ensure the laser to have high gain and high output stability.

[0006] To achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0007] The application provides a multi-pass gain laser, comprising: a pump source, a beam shaping mirror group, a first mirror, a second mirror and an output coupling mirror arranged in sequence; wherein the pump source is used for emitting pump light, the pump light is shaped by the beam shaping mirror group, a preset part of the pump light transmits through the first mirror and is incident on the second mirror, and the laser formed between the second mirror and the first mirror transmits to the output coupling mirror after N times of reflection of optical path separation between the second mirror and the first mirror; the multi-pass gain laser further comprises a composite gain structure, the composite gain structure is located between the first mirror and the second mirror, and the composite gain structure comprises a high-thermal-conductivity part and a gain part, the gain part comprises N gain crystals connected in sequence, the N gain crystals correspond to the N times of reflection of the reflected light one by one, the nth gain crystal of the N gain crystals extends along the transmission light path of the nth time of reflection of the N times of reflection light, and the nth time of reflection light passes through the nth gain crystal; wherein the high-thermal-conductivity part covers the surface of the gain part, and the high-thermal-conductivity part fills the interval region between adjacent two gain crystals.

[0008] Further, the high-thermal-conductivity part comprises N+1 side thermal conduction units, 2 end surface thermal conduction units, 1 top surface thermal conduction unit and 1 bottom surface thermal conduction unit; the N gain crystals are arranged along a first direction, along the first direction, the interval region between adjacent two gain crystals has a corresponding one side thermal conduction unit, and the N gain crystals are provided with a corresponding one side thermal conduction unit on both sides in the first direction; the N gain crystals have a first side facing the first mirror and a second side facing the second mirror, and the 2 end surface thermal conduction units are located on the first side and the second side respectively; the N gain crystals have opposite top surface and bottom surface, the top surface thermal conduction unit is located on the top surface of the N gain crystals, and the bottom surface thermal conduction unit is located on the bottom surface of the N gain crystals.

[0009] Further, the high-thermal-conductivity part is bonded with the gain part and is connected seamlessly, the bonding interface thermal resistance of the high-thermal-conductivity part and the gain part is less than or equal to 5×10 -5 m 2 K / W.

[0010] Further, the material of the high-thermal-conductivity part is single crystal diamond with a thermal conductivity greater than 1800 W / (m·K), the gain part is thulium-doped gain medium, and the matrix material of the thulium-doped gain medium is yttrium lithium fluoride.

[0011] Further, a reference plane is defined to be perpendicular to the optical axis direction of the pump light shaped by the beam shaping mirror group, the reflection surface of the first mirror has a first included angle a with the reference plane, and the reflection surface of the second mirror has a second included angle θ with the reference plane, wherein a=(6 / 5)θ, the first included angle a is in the range of 3°-5°, and the second included angle θ is in the range of 3°-5°.

[0012] Further, N=6, the cavity length of the resonant cavity formed by the second mirror, the first mirror and the output coupling mirror is in the range of 280mm~320mm.

[0013] Further, the bottom of the composite gain structure is fixed to a red copper heat sink through a heat conduction connecting layer, the red copper heat sink has a water cooling channel inside, and the water cooling channel is connected with an external circulating water cooling system; wherein, the material of the red copper heat sink is oxygen-free red copper with purity ≥99.9%, the total length of the water cooling channel is greater than 500mm, the inner wall roughness of the water cooling channel is ≤0.8μm, the heat conduction connecting layer is an indium foil with thermal conductivity ≥80W / (m·K), and the bottom of the composite gain structure is embedded into the mounting groove of the red copper heat sink.

[0014] Further, the transmittance of the output coupling mirror at the wavelength band of 1.9μm~2.1μm is 20%, and the reflectivity of the output coupling mirror at the wavelength band of 1.9μm~2.1μm is 80%; the side of the first mirror away from the second mirror has an anti-reflection film for the pump light wavelength band.

[0015] Further, the size of the cross section of the gain crystal is 2mm×12mm, the light spot corresponding to the pump light after being shaped by the beam shaping lens group is a rectangular light spot, and the size of the rectangular light spot is 1mm×5mm.

[0016] Further, the pump source is a laser diode array, the output wavelength of the pump source is 792nm, and the output power adjustment range of the pump source is 0W~100W; the beam shaping lens group includes a first cylindrical lens, a second cylindrical lens and a third cylindrical lens arranged in sequence, wherein the first cylindrical lens is used to realize slow-axis collimation, the second cylindrical lens is used to realize pre-focusing in the fast-axis direction, and the third cylindrical lens is used to realize final focusing, the focal length of the first cylindrical lens is 100mm, the focal length of the second cylindrical lens is 80mm, and the focal length of the third cylindrical lens is 50mm.

[0017] Compared with the prior art, the application can achieve the following beneficial effects: the multi-pass gain laser provided by the application can realize the cooperation of efficient heat conduction and rapid heat dissipation through the composite gain structure including a high-thermal-conductivity part and a gain part, while maintaining high gain, the stability of the laser output power and the beam quality are improved.

[0018] Specifically, in the multi-pass gain laser provided by the application, when the pump source injects pump energy into the composite gain structure, the gain part absorbs the pump light and generates laser gain, and the energy not converted into laser is released in the form of heat energy through the high-thermal-conductivity part. Since there is a certain interval between the adjacent gain crystals, the high-thermal-conductivity part covers the surface of the gain part, the interval area has the high-thermal-conductivity part, and the high-thermal-conductivity part and the gain part are seamlessly bonded, the heat energy generated by each gain crystal can be quickly transferred to the surface of the composite gain structure through the high-thermal-conductivity lattice of the high-thermal-conductivity part. In addition, the composite gain structure is closely attached to the copper heat sink, which is conducive to achieving efficient heat dissipation in the composite gain structure. The heat is then taken away by the cooling liquid flowing at high speed inside the copper heat sink, forming a high-efficiency heat dissipation link of "heat generated by gain crystal-heat dissipation by high-thermal-conductivity part-heat removal by copper heat sink", which significantly reduces the temperature gradient in the gain crystal, and is conducive to inhibiting the thermal lens effect and thermal stress damage. Compared with the traditional metal heat sink scheme, the heat dissipation efficiency of the composite gain structure of the application is improved by 5 to 7 times. Under a pump power of 90W, the maximum temperature in the gain crystal is reduced by 40 to 60 degrees, the thermal lens focal length fluctuation can be controlled within ± 5%, and the beam quality factor M 2 is maintained between 1.6 and 1.8, and the output power stability per hour is less than or equal to 2%, providing an efficient and reliable technical solution for the thermal management of high-power mid-infrared lasers. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application and are incorporated herein for explanation along with the descriptions of the illustrative embodiments thereof. In the drawings:

[0020] Figure 1 A structural schematic diagram of the multi-pass gain laser according to the embodiments of the present application;

[0021] Figure 2 An exploded view of the composite gain structure according to the embodiments of the present application from two different perspectives, wherein, Figure 2 (a) in the above (a) is an exploded view of the remaining components in the composite gain structure from the perspective of the top thermal conduction unit on one side, without showing the top and bottom thermal conduction units; Figure 2 (b) in the above (b) is an exploded view of the remaining components in the composite gain structure from the perspective of the end thermal conduction unit on one side, without showing the end thermal conduction unit. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application.

[0023] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0024] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0025] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0027] Reference Figure 1 and Figure 2The application provides a multi-pass gain laser, comprising: a pump source 1, a beam shaping mirror group, a first mirror 5, a second mirror 7 and an output coupling mirror 8 arranged in sequence; wherein the pump source 1 is used for emitting pump light, the pump light is shaped by the beam shaping mirror group, a preset part of the pump light transmits through the first mirror 5 and is incident on the second mirror 7, and the laser formed between the second mirror 7 and the first mirror 5 transmits to the output coupling mirror 8 after N times of reflection of optical path separation between the second mirror 7 and the first mirror 5; the multi-pass gain laser further comprises a composite gain structure 6, the composite gain structure 6 is located between the first mirror 5 and the second mirror 7, and the composite gain structure 6 comprises a high-thermal-conductivity part 20 and a gain part 10, the gain part 10 comprises N gain crystals connected in sequence, the N gain crystals correspond to the N times of reflection of the reflected light one by one, the nth gain crystal of the N gain crystals extends along the transmission light path of the nth time of reflection of the N times of reflection, and the nth time of reflection light passes through the nth gain crystal; wherein the high-thermal-conductivity part 20 covers the surface of the gain part 10, and the high-thermal-conductivity part 20 fills the interval region between adjacent two gain crystals.

[0028] Wherein, n = 1, 2, … or N.

[0029] It should be noted that the N times of reflection makes the laser pass through the composite gain structure 6 N times, and each time through the composite gain structure 6 passes through the corresponding gain crystal.

[0030] Further, the high-thermal-conductivity part 20 comprises N+1 side thermal conduction units 21, 2 end thermal conduction units 22, 1 top thermal conduction unit 23 and 1 bottom thermal conduction unit 24; the N gain crystals are arranged along a first direction X, along the first direction X, the interval region between adjacent two gain crystals has a corresponding one side thermal conduction unit 21, and the N gain crystals are respectively provided with a corresponding one side thermal conduction unit 21 on both sides in the first direction X; the N gain crystals have a first side facing the first mirror 5 and a second side facing the second mirror 7, and the 2 end thermal conduction units 22 are respectively located on the first side and the second side; the N gain crystals have opposite top and bottom surfaces, the top thermal conduction unit 23 is located on the top surface of the N gain crystals, and the bottom thermal conduction unit 24 is located on the bottom surface of the N gain crystals. The application divides the high-thermal-conductivity part 20 into N+1 side thermal conduction units 21, 2 end thermal conduction units 22, 1 top thermal conduction unit 23 and 1 bottom thermal conduction unit 24, and the multi-segment bonding design between the plurality of thermal conduction units and the N gain crystals takes into account the high-thermal-conductivity performance and the processing feasibility.

[0031] In some embodiments, the N+1 side heat conduction units 21, the 2 end heat conduction units 22, the 1 top heat conduction unit 23 and the 1 bottom heat conduction unit 24 are all diamond, that is, the composite gain structure 6 provided by the application is a structure alternately bonded by multiple sections of diamond and multiple sections of gain crystal, and the heat generated by the gain crystal can be quickly conducted to the diamond from the periphery of the gain crystal, and then quickly conducted out through the diamond.

[0032] Further, the high-heat-conduction part 20 is bonded and seamlessly connected with the gain part 10, and the bonding interface thermal resistance between the high-heat-conduction part 20 and the gain part 10 is less than or equal to 5×10 -5 m 2 K / W. In this way, the heat accumulation of the gain medium crystal and the interface thermal resistance in the multi-pass gain process can be significantly reduced, the thermal lens effect and the beam quality degradation phenomenon can be effectively inhibited, and the output power stability and energy conversion efficiency of the laser can be improved.

[0033] In some embodiments, the bonding between the high-heat-conduction part 20 and the gain part 10 is achieved by the following process. The gain crystal and the high-heat-conduction part 20 are seamlessly connected by direct bonding after corresponding surface pretreatment. The surface pretreatment can be surface polishing treatment by plasma cleaning, and the polishing accuracy needs to be less than or equal to 0.1 μm.

[0034] Further, the material of the high-heat-conduction part 20 is single crystal diamond with a thermal conductivity greater than 1800 W / (m·K), and the gain part 10 is a thulium-doped gain medium, and the substrate material of the thulium-doped gain medium is yttrium lithium fluoride.

[0035] In some embodiments, the gain crystal is a light-transmitting crystal, the thickness of the gain crystal is 2 mm, and the doping concentration of thulium can be 2.5 at%.

[0036] In some embodiments, the thickness of each section of diamond can be 2 mm.

[0037] Further, a reference plane is defined perpendicular to the optical axis direction of the shaped pump light of the beam shaping mirror group, the reflecting surface of the first reflecting mirror 5 has a first included angle a with the reference plane, and the reflecting surface of the second reflecting mirror 7 has a second included angle θ with the reference plane, wherein a=(6 / 5)θ, the first included angle a is in the range of 3°~5°, and the second included angle θ is in the range of 3°~5°. It should be noted that the inclination direction of the reflecting surface of the first reflecting mirror 5 relative to the reference plane is the same as the inclination direction of the reflecting surface of the second reflecting mirror 7 relative to the reference plane, and the first included angle a is the smallest included angle between the reflecting surface of the first reflecting mirror 5 and the reference plane, and the second included angle θ is the smallest included angle between the reflecting surface of the second reflecting mirror 7 and the reference plane.

[0038] Further, N=6, the cavity length of the resonant cavity formed by the second mirror 7, the first mirror 5 and the output coupling mirror 8 is in the range of 280mm~320mm.

[0039] The six gain crystals are defined as the first gain crystal 11, the second gain crystal 12, the third gain crystal 13, the fourth gain crystal 14, the fifth gain crystal 15 and the sixth gain crystal 16, the second mirror 7 and the first mirror 5 are both full reflection mirrors, the reflectivity of the second mirror 7 and the first mirror 5 in the wavelength range of 1.9μm~2.1μm is greater than or equal to 99.9%, and the laser propagates in the resonant cavity along the path of the second mirror 7, the first gain crystal 11, the first mirror 5, the second gain crystal 12, the second mirror 7, the third gain crystal 13, the first mirror 5, the fourth gain crystal 14, the second mirror 7, the fifth gain crystal 15, the first mirror 5, the sixth gain crystal 16 to the output coupling mirror 8, thereby realizing multi-pass gain of 6 times through the gain crystal.

[0040] In some examples, the cavity length of the resonant cavity is controlled to be 300mm, so as to facilitate avoiding beam loss caused by long optical path while ensuring gain accumulation efficiency.

[0041] Further, the bottom of the composite gain structure 6 is fixed to the red copper heat sink through a heat-conducting connecting layer, the red copper heat sink has a water-cooling flow channel inside, and the water-cooling flow channel is connected with an external circulating water-cooling system; wherein, the material of the red copper heat sink is oxygen-free red copper with a purity greater than or equal to 99.9%, the total length of the water-cooling flow channel is greater than 500mm, the inner wall roughness of the water-cooling flow channel is less than or equal to 0.8μm, and the flow channel inner wall roughness is less than or equal to 0.8μm, so as to ensure that the flow rate of deionized water is greater than or equal to 1.5m / s under the pressure in the range of 0.3MPa~0.5MPa, reduce the flow resistance of the cooling liquid, and thereby maximize the heat exchange efficiency.

[0042] In some embodiments, the bottom of the composite gain structure 6 is embedded in the mounting groove of the red copper heat sink.

[0043] In some embodiments, the heat-conducting connecting layer is an indium foil with a thermal conductivity greater than or equal to 80W / (m·K).

[0044] In some embodiments, the flatness of the surface of the red copper heat sink in contact with the composite gain structure 6 is less than or equal to 0.05mm.

[0045] In some embodiments, the heat-conducting connecting layer is a low-temperature heat-conducting adhesive with a thermal conductivity greater than or equal to 8W / (m·K).

[0046] In some embodiments, the width of the water-cooling flow channel inside the red copper heat sink is in the range of 2mm~3mm, the depth of the water-cooling flow channel is in the range of 3mm~4mm, and the total length of the flow channel can be 550mm.

[0047] Further, the output coupling mirror 8 has a transmittance of 20% at a wavelength range of 1.9 μm to 2.1 μm, and a reflectance of 80% at the wavelength range of 1.9 μm to 2.1 μm; the first mirror 5 has an anti-reflection film for the pump light wavelength range on the side away from the second mirror 7.

[0048] Further, the gain crystal has a cross-sectional size of 2 mm x 12 mm, and the pump light is shaped into a rectangular spot with a size of 1 mm x 5 mm by the beam shaping lens group.

[0049] Further, the pump source 1 is a laser diode array, the output wavelength of the pump source 1 is 792 nm, and the output power of the pump source 1 is adjustable in a range of 0 W to 100 W; the beam shaping lens group includes the first cylindrical lens 2, the second cylindrical lens 3, and the third cylindrical lens 4 arranged in sequence, wherein the first cylindrical lens 2 is used to realize slow-axis collimation, the second cylindrical lens 3 is used to realize pre-focusing in the fast-axis direction, and the third cylindrical lens 4 is used to realize final focusing; the focal length of the first cylindrical lens 2 is 100 mm, the focal length of the second cylindrical lens 3 is 80 mm, and the focal length of the third cylindrical lens 4 is 50 mm.

[0050] The beam shaping lens group is used to realize efficient matching of the pump light and the gain crystal, and the pump light is shaped into a rectangular spot with a size of 1 mm x 5 mm by the synergistic effect of the cylindrical lenses in the beam shaping lens group, so as to match the pump light with the pump absorption area of all the gain crystals of the gain section 10.

[0051] In some embodiments, the gain crystal can be Tm 3+ The Tm:YLF crystal with a doping concentration of 2.5 at.% is processed into a light-transmitting crystal sheet with a thickness of 2 mm through directional cutting, precision grinding and polishing, the polishing precision of the light-transmitting surface of the gain crystal is controlled to be 0.08 μm, and the parallelism of the light-transmitting surface is ≤10'', so as to ensure that the laser transmission loss is lower than 0.1%. The high-thermal-conductivity part 20 can be high-thermal-conductivity single-crystal diamond with a thermal conductivity of ≥1800 W / (m·K), the single-crystal diamond is cut into 7 pieces of diamond sheets with a thickness of 2 mm as the side heat-conducting units 21, the single-crystal diamond is cut into 2 pieces of diamond sheets matching the front and rear end surfaces (with a size of 2 x 12 mm) of the 6 gain crystals as the end heat-conducting units 22, and the single-crystal diamond is cut into 2 pieces of diamond sheets matching the upper and lower bottom surfaces (with a size of 12 x 20 mm) as the top heat-conducting unit 23 and the bottom heat-conducting unit 24, the gain crystal and the diamond sheets are sequentially placed into a plasma cleaning machine to remove oil stains and oxide layers, so as to improve the bonding force of the bonding interface, the low-temperature bonding technology is adopted to bond the diamond sheets and the gain crystal together, a full-wrapping heat-conducting channel around the gain crystal is realized, and the heat generated by the gain crystal can be quickly conducted into the diamond from all directions.

[0052] In some embodiments, the first mirror 5 and the second mirror 7 are respectively installed on the optical adjustment frame on both sides of the composite gain structure 6 to realize the light path folding. The deflection angle a of the first mirror 5 and the deflection angle θ of the second mirror 7 can be calculated according to the geometric optics principle through the design constraint calculation of the cavity length, to ensure that the light beam stably propagates along the preset path.

[0053] In some embodiments, the output coupling mirror 8 can adopt a CaF2 substrate, and after coating treatment, the transmittance of the output coupling mirror 8 at a wavelength of 1908 nm is 20%, and the reflectivity is 80%, which takes into account the gain accumulation and laser output.

[0054] In some embodiments, the base size of the red copper heat sink is 50 mm x 30 mm x 10 mm.

[0055] In some embodiments, the prepared composite gain structure 6 can be tightly wrapped with an indium foil with a thickness of 0.1 mm. The indium foil has good thermal conductivity and deformation adaptability, can fill the small gap between the composite gain structure 6 and the red copper heat sink, further reduce the contact thermal resistance, and then embed the composite gain structure 6 wrapped with the indium foil into the mounting groove of the red copper heat sink, and tightly fit them by applying a pressure of 3N. The composite gain structure 6 is connected to the water circulating water cooler through a high-temperature resistant silica gel tube, and deionized water is selected as the cooling liquid. The working pressure can be set to 0.4 MPa, the flow rate is 1.6 m / s, the temperature control accuracy is ±0.1℃, and the heat dissipation system can continuously and efficiently operate. After starting the water circulating water cooler, when the temperature of the red copper heat sink is stabilized at 18℃, the pump source 1 is started. After the pump light is shaped by the beam shaping mirror group, it is vertically incident to the end face of the composite gain structure 6. After the gain crystal absorbs the pump light energy, the population inversion is realized, and the stimulated radiation is formed in the resonant cavity. The light beam first starts at the second mirror 7, and then passes through the first gain crystal 11, the first mirror 5, the second gain crystal 12, the second mirror 7, the third gain crystal 13, the first mirror 5, the fourth gain crystal 14, the second mirror 7, the fifth gain crystal 15, the first mirror 5, the sixth gain crystal 16, and reaches the output coupling mirror 8. The gain amplification is completed by passing through the gain crystal six times, and finally the continuous laser beam with a wavelength of 1908 nm is output from the output coupling mirror 8.

[0056] It should be understood that the various forms of flow shown above can be reordered, added to, or deleted from. For example, the steps described in the present disclosure can be executed in parallel, in sequence, or in a different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, and the present disclosure is not limited herein.

[0057] The above detailed description does not limit the scope of the application. Various modifications, combinations, sub-combinations and alternatives can be made to the detailed embodiment within the scope of the application. Any modification, equivalent replacement and improvement made without departing from the spirit and principle of the application shall fall within the scope of the application.

Claims

1. A multi-pass gain laser, characterized by, The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device.

2. The multi-pass gain laser of claim 1, wherein, The high thermal conductivity portion is bonded and seamlessly connected with the gain portion, and the bonding interface thermal resistance of the high thermal conductivity portion with the gain portion is less than or equal to 5 x 10 - 5 m 2 K / W.

3. The multi-pass gain laser of claim 1, wherein, The application relates to a multi-pass gain laser device.

4. The multi-pass gain laser of claim 1, wherein, The application relates to a multi-pass gain laser device.

5. The multi-pass gain laser of claim 1, wherein, The application relates to a multi-pass gain laser device.

6. The multi-pass gain laser of claim 1, wherein, The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. 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The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. 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The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application relates to a multi-pass gain laser device. The application The material of the red copper heat sink is oxygen-free red copper with purity greater than or equal to 99.9%, the total length of the water cooling flow channel is greater than 500 mm, the inner wall roughness of the water cooling flow channel is less than or equal to 0.8 μm, the thermal conductive connection layer is an indium foil with thermal conductivity greater than or equal to 80 W / (m·K), and the composite gain structure is embedded in the mounting groove of the red copper heat sink.

7. The multi-pass gain laser of claim 1, wherein, The output coupling mirror has a transmittance of 20% and a reflectivity of 80% in a wavelength range of 1.9 μm to 2.1 μm. The first reflector is provided with an anti-reflection film for the wavelength range of the pump light on the side away from the second reflector.

8. The multi-pass gain laser of claim 1, wherein, The gain crystal has a cross-section with a size of 2 mm x 12 mm, and the pump light is shaped into a rectangular light spot with a size of 1 mm x 5 mm by the beam shaping mirror group.

9. The multi-pass gain laser of claim 1, wherein, The pump source is a laser diode array, the output wavelength of the pump source is 792 nm, and the output power adjustment range of the pump source is 0 W to 100 W. The beam shaping mirror group comprises a first cylindrical lens, a second cylindrical lens and a third cylindrical lens arranged in sequence, wherein the first cylindrical lens is used to realize slow-axis collimation, the second cylindrical lens is used to realize pre-focusing in the fast-axis direction, and the third cylindrical lens is used to realize final focusing; the focal length of the first cylindrical lens is 100 mm, the focal length of the second cylindrical lens is 80 mm, and the focal length of the third cylindrical lens is 50 mm.

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