Concentration gradient doped surface gain type laser ceramic with composite structure and preparation method of concentration gradient doped surface gain type laser ceramic

Abstract

The invention discloses a concentration gradient doped surface gain type laser ceramic with a composite structure and a preparation method of the concentration gradient doped surface gain type laser ceramic. A middle layer of the concentration gradient doped surface gain type laser ceramic with the composite structure is a heat conduction layer not doped with active ions, and surface layers located on the two sides of the middle layer in the thickness direction of the middle layer are gain layers with the same structure and active ion concentration gradient. The gain layer is formed by arranging a plurality of gain units with the same thickness on the plane of the surface layer, and the active ion concentration of the gain unit located in the center of the arrangement direction in the multiple gain units is sequentially decreased to zero from the active ion concentration of the gain units at the two ends. Through the surface gain design, zigzag propagation of laser and pump light in the ceramic material can be realized, the gain layer is in direct contact with the lath cooling heat sink, and the heat effect in the lath is effectively compensated.

Description

Technical Field

[0001] The present invention relates to a concentration gradient doped surface layer gain type laser ceramic with a composite structure and a preparation method thereof, belonging to the technical field of ceramic materials. Background Art

[0002] An important development trend of advanced solid-state lasers is to obtain laser output with high power, high efficiency and excellent beam quality. Laser ceramics have the advantages of being easy to achieve large-size preparation to obtain higher-power laser output, high thermal conductivity, uniform doping of active ions and easy realization of composite structures, and are a gain medium material with great development prospects.

[0003] Since the 21st century, the output power of solid-state lasers has continuously achieved breakthroughs, from 10 kW to 100 kW. However, during the laser generation process, a large amount of heat will be generated because some pump light cannot be completely absorbed by the laser working medium. Therefore, the thermal effect of the laser gain medium severely restricts the further development of solid-state lasers. At this time, efficient heat dissipation and beam quality control have become the main research directions for improving the performance and continuous development of solid-state lasers. The corresponding improvements and innovations are mainly in the changes of the gain medium structure and the cooling method. From the perspective of the laser gain medium, designing a suitable composite structure laser gain medium to improve the thermal management ability of the laser gain medium, thereby improving the power, efficiency and laser beam quality of the laser. Therefore, composite structure laser gain medium materials have been widely studied.

[0004] In order to improve the thermal effect of solid-state lasers and further improve the heat dissipation ability of the gain medium, it is necessary to increase its surface area to volume ratio. The surface gain slab structure combines the advantages of both thin films and slabs. Laser and pump light can propagate in a zigzag optical path inside the material, and its gain thin layer is directly in contact with the heat sink, which can effectively compensate the thermal effect inside the slab. Therefore, it can meet the requirements of higher-power laser systems for gain media with low thermal distortion, high gain and high-power output.

[0005] The surface gain structure Yb:YAG laser material has achieved single-piece kW-level laser output, indicating that this structure has great research prospects in high-power solid-state lasers. However, at present, the research on this structure of laser ceramics is less, and like single crystals, it is combined by means of thermal bonding, which requires a laser-grade polished surface with high surface parallelism and high cleanliness. And there are large internal stresses in the bonding area, which is the area with the lowest strength in the material. Therefore, under high-power pumping conditions, the bonding surface is prone to fracture, which is a problem that multi-layer composite structure crystals are difficult to overcome. In addition, the overall preparation cycle of single crystal growth and bonding is long and the cost is high. Summary of the Invention

[0006] In view of the above problems, the present invention provides a novel composite structure concentration gradient doped surface layer gain type laser ceramic and a preparation method thereof. Through this surface gain design, zigzag propagation of laser and pump light inside the ceramic material can be achieved, and the gain layer is directly in contact with the plate cooling heat sink, effectively compensating for the thermal effect inside the plate. In addition, since the gain layer is gradient doped, the heat dissipation capacity and the uniformity of heat distribution of the gain medium under laser service conditions are effectively improved. Therefore, this laser ceramic can meet the requirements of higher power laser systems for the gain medium.

[0007] In a first aspect, the present invention provides a composite structure concentration gradient doped surface layer gain type laser ceramic. The intermediate layer of the composite structure concentration gradient doped surface layer gain type laser ceramic is a thermal conductivity layer doped with no active ions, and the surface layers located on both sides of the intermediate layer in the thickness direction of the intermediate layer are gain layers with the same structure and active ion concentration gradient. The gain layer is composed of a plurality of gain units with the same thickness arranged on the plane of the surface layer, and the active ion concentration of the gain unit located in the center of the arrangement direction among the plurality of gain units gradually decreases to zero towards the gain units at both ends.

[0008] Preferably, the active ions doped in the gain unit are selected from rare earth ions, and preferably, selected from Yb 3+ , Nd 3+ , Tm 3+ , Ho 3 + , Er 3+ or a combination of one or more of them.

[0009] Preferably, the matrix material of the gain unit is selected from one of YAG, LuAG, multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 , sesquioxide; preferably, the sesquioxide is Y2O3, Sc2O3, Lu2O3 or a solid solution thereof.

[0010] Preferably, the material of the thermal conductivity layer is selected from one of YAG, LuAG, multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 , sesquioxide; preferably, the sesquioxide is Y2O3, Sc2O3, Lu2O3 or a solid solution thereof. More preferably, the material of the thermal conductivity layer is the same as the matrix material of the gain layer.

[0011] Preferably, the shape of the gain unit in the arrangement direction is trapezoid or parallelogram.

[0012] Preferably, the doping concentration of the activator ions in the gain unit located at the center of the arrangement direction decreases in a stepwise or gradual manner towards the gain units at both ends.

[0013] Preferably, the doping concentration of the activator ions in the gain unit is within 30.0 at.%, preferably within 10.0 at.%.

[0014] Preferably, the doping concentration range of the activator ions in the gain unit having activator ions is 0.5 at.% to 30.0 at.%, preferably 0.5 at.% to 10.0 at.%.

[0015] Preferably, the thickness of the thermal conductivity layer is more than twice the thickness of the gain layer.

[0016] In a second aspect, the present invention provides a method for preparing a surface layer gain type laser ceramic with a concentration gradient doping in a composite structure. The preparation method includes: preparing a casting film as an intermediate layer and a surface layer respectively by using a casting forming technology, and then obtaining a surface layer gain type laser ceramic with a concentration gradient doping in a composite structure through film cutting, laminating, debinding, forming, and sintering.

[0017] Beneficial effects

[0018] Compared with traditional surface layer gain materials, the gain layer of the present invention is a structure with a gradient doping of activator ions, which can effectively improve the thermal management ability of the material and is more conducive to realizing high-power laser output. The surface layer gain ceramic prepared by the present invention using a casting forming technology combined with a sintering technology has no interface effect, the preparation process is simple, the cost is low, and it is more conducive to mass production. In addition, compared with the bonding technology, the preparation of a surface layer gain type laser ceramic with a concentration gradient doping in a composite structure can be simply and quickly realized by stacking and combining casting films with different doping concentrations through the casting forming technology. Description of the drawings

[0019] Figure 1 It is a schematic structural diagram of a one-step gradient doping surface layer gain type Yb:YAG ceramic prepared in Example 1; Figure 2 It is a physical photograph of a one-step gradient doping surface layer gain Yb:YAG ceramic sample prepared in Example 1 before annealing (a) and after annealing (b); Figure 3 It is a linear transmittance curve of a one-step gradient doping surface layer gain type Yb:YAG ceramic (with a thickness of 2 mm) prepared in Example 1; Figure 4 It is a micrograph of the thermally etched surface of a one-step gradient doping surface layer gain type Yb:YAG ceramic prepared in Example 1, where (a) is YAG; (b) is 1.9 at.% Yb:YAG; (c) is 3.7 at.% Yb:YAG; Figure 5 is the Yb distribution in the first - stage gradient - doped surface - gain Yb:YAG ceramic prepared in Example 1 3+ where (a) is the thickness direction; (b) is the length direction; Figure 6 is a schematic diagram of the second - stage gradient - doped surface - gain Yb:YAG ceramic structure prepared in Example 2; Figure 7 are the physical photos of the second - stage gradient - doped surface - gain Yb:YAG ceramic samples prepared in Example 2 before (a) and after (b) annealing; Figure 8 is the linear transmittance curve of the second - stage gradient - doped surface - gain Yb:YAG ceramic (with a thickness of 2 mm) prepared in Example 2; Figure 9 are the micro - morphological photos of the thermally etched surface of the second - stage gradient - doped surface - gain Yb:YAG ceramic prepared in Example 2, where (a) is YAG; (b) is 1.7 at.% Yb:YAG; (c) is 2.5 at.% Yb:YAG; (d) is 3.5 at.% Yb:YAG; Figure 10 is the Yb distribution in the second - stage gradient - doped surface - gain Yb:YAG ceramic prepared in Example 2 3+ where (a) is the thickness direction; (b) is the length direction. Detailed implementation manners

[0020] The present invention is further illustrated by the following implementation manners. It should be understood that the following implementation manners are only used to illustrate the present invention and do not limit the present invention.

[0021] In the middle layer of the concentration gradient doped surface layer gain type laser ceramic of the composite structure according to the present invention, there is a thermal conductivity layer without doped active ions. On both sides of the middle layer in the thickness direction of the middle layer, there are gain layers with the same structure and active ion concentration gradient. That is, on both sides of the middle layer in the thickness direction of the middle layer, there are gain layers doped with active ions with the same structure and components and concentration gradient. Each of the gain layers is composed of a plurality of gain units with the same thickness arranged on the plane of the surface layer. Among the multiple gain units, the active ion concentration of the gain unit located in the center of the arrangement direction decreases sequentially to zero towards the gain units at both ends. That is to say, among the multiple gain units, the gain unit located in the center of the arrangement direction has the highest active ion concentration, and the active ion concentrations of the gain units at both ends of the arrangement direction are zero. Through this surface gain design, the zigzag propagation of laser and pump light inside the material can be realized, and the gain layer is directly in contact with the slab cooling heat sink, effectively compensating for the thermal effect inside the slab. In addition, since the gain layer is doped with active ions in a gradient manner, the heat dissipation capacity and the uniformity of the thermal distribution of the gain medium under the laser service conditions are effectively improved. Therefore, this laser ceramic can meet the requirements of higher power laser systems for the gain medium.

[0022] The way that the active ion concentration of the gain unit located in the center of the arrangement direction among the multiple gain units increases sequentially towards the gain units at both ends is not applicable to the present invention.

[0023] The gradient of the active ion concentration of the gain unit located in the center of the arrangement direction among the multiple gain units decreasing sequentially towards the gain units at both ends is N + 1 gradients. Including but not limited to this, N can be selected from integers less than 10. Those skilled in the art can adjust the number of gradients according to needs. In specific embodiments, the number of N is 1 and 2 respectively.

[0024] Preferably, the decreasing trend of the active ion concentration of the gain unit located in the center of the arrangement direction among the multiple gain units towards the gain units at both ends is the same. That is, the decreasing gradient of the active ion concentration of the gain unit located in the center of the arrangement direction among the multiple gain units towards each end at both ends is the same.

[0025] The arrangement direction is the length direction of the gain layer. In a specific embodiment, the arrangement direction is the length direction of the gain layer, that is, the input direction of the pump light.

[0026] The active ions doped in the gain units are selected from rare earth ions. Preferably, selected from Yb 3+ , Nd 3+ , Tm 3+ , Ho 3+, Er 3+ One or a combination of several of the above. The active ions can be used in quasi-three-level or four-level laser systems. The energy level structure is simple, it is easy to achieve population inversion, the theoretical quantum efficiency is high, and it is easier to achieve laser output.

[0027] The matrix material of the gain unit is selected from one of YAG, LuAG, multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 , sesquioxide. The multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 is a material obtained by substituting one or several of Lu, Gd, Sc, Ga for the YAG matrix for optimization. Sesquioxides include, but are not limited to, common laser matrix materials such as Y2O3, Sc2O3, Lu2O3 or their solid solutions.

[0028] The material of the thermal conduction layer is selected from one of YAG, LuAG, multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 , sesquioxide. The multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 is a material obtained by substituting one or several of Lu, Gd, Sc, Ga for the YAG matrix for optimization. Sesquioxides include, but are not limited to, common laser matrix materials such as Y2O3, Sc2O3, Lu2O3 or their solid solutions.

[0029] The shape of the gain unit (in the arrangement direction) is trapezoidal or parallelogram. In a specific embodiment, the shape of the gain unit in the arrangement direction is parallelogram.

[0030] The active ion concentration of the gain unit is within 30 at.%, preferably within 10.0 at.%. If the active ion concentration of the gain unit exceeds the above range, serious thermal effects and luminescence quenching will occur.

[0031] As an example, the active ion concentration range of the gain unit with active ions is 0.5 at.% to 30 at.%, preferably 0.5 at.% to 10.0 at.%.

[0032] The thickness of the thermal conduction layer is more than twice the thickness of the gain layer. This can achieve better thermal conduction ability and heat dissipation ability of surface direct cooling. Preferably, the thickness of the gain layer is the same as the thickness of the gain unit.

[0033] For a gain layer with uniformly doped surface-activated ions, the absorbed pump power density decreases exponentially along the pump direction. In the case of double-sided pumping, the center of the gain medium along the pump direction cannot be fully pumped, reducing the energy storage capacity of the material. By designing a gradient doping for the gain layer, the absorption coefficient and the absorbed pump power density in the middle region are increased, and the total energy storage density of the overall material is increased. In addition, the difference in the pump absorption intensity inside the material decreases with gradient doping, and the temperature gradient of the gain medium under high-power pumping conditions also further decreases, which is beneficial to alleviating the thermal effect problem.

[0034] The present invention also provides a method for preparing a surface gain type laser ceramic with a concentration gradient doping of the above composite structure. The tape casting technology is used to prepare tape cast films as the intermediate layer and the surface layer respectively, and then through film cutting, laminating, debinding, forming, sintering, (annealing), a surface gain type laser ceramic with a concentration gradient doping of the composite structure is obtained. Annealing treatment can also be carried out after sintering. As an example, the annealing temperature is 1750 °C, the pressure is normal pressure, the atmosphere is air atmosphere, and the heat preservation is 20 h.

[0035] The present invention uses the tape casting technology combined with the sintering technology to prepare a surface gain type laser ceramic with a concentration gradient doping of the composite structure. Since the bonding technology is not used, on the one hand, there is no weak interface caused by bonding, and on the other hand, the cost of laser-grade polishing of the bonding interface is saved.

[0036] In the tape casting process, the initial raw material powder can be first prepared into a slurry, and then the slurry is tape cast into a tape cast film. The initial raw material powder can be a commercial oxide powder weighed and formulated according to the stoichiometric ratio, or a phase-forming powder of different components prepared by a wet chemical method. Film cutting, laminating, debinding, forming, sintering, etc. are conventional processes in the art. Those skilled in the art can make selections according to needs.

[0037] The present invention has a sandwich structure in the non-pumping route direction, with better heat dissipation ability, which is more conducive to realizing high-power laser output. Moreover, the present invention uses tape casting, and compared with gel casting, the tape casting has higher precision and is easier to control the structure. In addition, compared with gradient rods, the strip prepared by the present invention has better heat dissipation ability, and a surface heat dissipation structure is realized on the basis of gradient doping, having greater structural advantages.

[0038] In summary, the present invention uses the tape casting technology combined with the sintering technology to prepare a novel composite structure surface gain laser ceramic with a concentration gradient doping. Compared with the single crystal gain medium prepared by using the bonding technology, the ceramic gain medium prepared by the present invention does not require multiple laser-grade polishings for bonding, saving costs, and there is no weak interface formed by bonding, having a higher laser damage threshold and being more suitable for high-power laser output. Moreover, compared with direct dry pressing, it can better control the thickness of the gain layer and the heat conduction layer and the uniformity of the green body.

[0039] The following are further examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples.

[0040] Example 1

[0041] Prepare an undoped YAG thin film. Using yttrium oxide (Y2O3) and alumina (Al2O3) as raw materials, according to Y3Al5O 12 Precisely weigh a total of 60 g of the raw material powder, add it to a high-purity alumina ball milling tank, add tetraethyl orthosilicate (TEOS) accounting for 0.8 wt% of the raw material powder and magnesium oxide (MgO) accounting for 0.08 wt% as sintering aids, use herring oil (0.6 g) as a dispersant, and use anhydrous ethanol (13 g) and xylene (13 g) as a mixed solvent. Ball mill the above raw material powder, sintering aids, dispersant and mixed solvent for 12 h for uniform mixing and dispersion. Subsequently, add the binder polyvinyl butyral (PVB, 4.8 g), plasticizer butyl benzyl phthalate (BBP, 2.4 g) and polyethylene glycol 400 (PEG-400, 2.4 g) for secondary ball milling and mixing for 16 h to obtain a casting slurry with moderate viscosity. Debubble the slurry in a vacuum degassing machine for 5 min. Use a casting machine to prepare a cast film, and control the distance between the doctor blade and the carrier tape at 300 μm. Pour the slurry into the slurry tank, start the motor, set the casting rate at 100 mm / min, and carry out casting at room temperature. Take down the dried cast film from the casting machine and seal it for standby.

[0042] Refer to the same process to prepare a Yb 3+ -doped YAG thin film. The difference is only that: using yttrium oxide (Y2O3), alumina (Al2O3), ytterbium oxide (Yb2O3) as raw materials, according to Yb x Y (3-x) Al5O 12 (x = 1.9, 3.7) composition to precisely weigh the raw material powder.

[0043] Figure 1 Figure 25 is a schematic structural diagram of a one-step gradient-doped surface gain type Yb:YAG ceramic prepared in Example 1. The middle layer is a YAG thermal conductivity layer, and the units of the upper surface layer are Yb 3+Yb:YAG gain layer with doping concentrations of 0 at.%, 1.9 at.%, 3.7 at.%, 1.9 at.%, and 0 at.%. The lower surface layer is the same as the upper surface layer.

[0044] Arrange and stack the cast films according to the above structural design. The stacked cast films are placed in an oven and heated to 70 °C to make the PVB, which serves as the binder, reach its glass transition temperature. Then, a vertical pressure of 40 MPa is applied on a tablet press. After cooling, a complete green body is obtained. The green body is degreased in a muffle furnace. The degreasing regime is set to slowly rise from room temperature to 600 °C and hold for 10 h. After cooling to room temperature with the furnace, the green body is taken out of the muffle furnace. The degreased green body has no organic residue and no cracks. The degreased green body is cold isostatically pressed at 250 MPa for 5 min. The cold isostatically pressed green body is put into a vacuum sintering furnace for sintering. The sintering conditions are: the holding temperature is 1750 °C, the holding time is 30 h, and the vacuum degree in the vacuum sintering furnace is better than 1×10 -3 Pa. Subsequently, the ceramic is annealed under the conditions of 1750 °C, 200 MPa, Ar atmosphere, and holding for 3 h. Finally, the opposite sides of the sample are polished to obtain a one-step gradient-doped surface layer gain type Yb:YAG ceramic.

[0045] Figure 2 This is a physical photo of the one-step gradient-doped surface layer gain type Yb:YAG ceramic prepared in Example 1 of the present invention.

[0046] Figure 3 This is the linear transmittance curve (thickness: 2 mm) of the one-step gradient-doped surface layer gain type Yb:YAG ceramic prepared in Example 1. The dashed part is the high-doping region. The solid part is the low-doping region. Different doping concentration regions all have high linear transmittance. The linear transmittance of the high-doping concentration region at 1100 nm is 82.9%, and the linear transmittance of the low-doping concentration region at 1100 nm is 83.6%.

[0047] Figure 4 This is the micrograph of the thermally etched surface of the one-step gradient-doped surface layer gain type Yb:YAG ceramic prepared in Example 1 (thermal etching: heat-treat the double-sided polished ceramic in a muffle furnace at 1450 °C for 3 h). No obvious pores and second phases are observed in different regions. The average grain sizes of the YAG, 1.9 at.% Yb:YAG, and 3.7 at.% Yb:YAG regions are 32.1 μm, 33.7 μm, and 30.5 μm in sequence.

[0048] Figure 5 This is the Yb 3+ distribution in the one-step gradient-doped surface layer gain Yb:YAG ceramic: (a) thickness direction; (b) length direction. In the thickness direction, the test region is the high-doping concentration region, and Yb3+ There are signals at both ends, and the middle of the ceramic is a signal-free area. In the length direction, for the halved ceramic, the Yb on the ceramic surface 3+ The distributed signals are in three stages, namely no signal, low signal, and high signal. This is consistent with the structure of the designed one-step gradient doped ceramic.

[0049] A 940 nm laser diode array (LDA) is used as the pump source and double-sided pumping is carried out. The ceramic and the pump source share water cooling, and a plano-concave cavity is used as the resonant cavity for experiments. It is found that a 1030 nm laser output with high average power and high beam quality can be obtained.

[0050] Example 2

[0051] Prepare undoped YAG thin films. Using yttrium oxide (Y2O3) and alumina (Al2O3) as raw materials, according to Y3Al5O 12 A total of 60 g of raw material powder is accurately weighed according to the composition, added to a high-purity alumina ball milling tank, 0.8 wt% of tetraethyl orthosilicate (TEOS) and 0.08 wt% of magnesium oxide (MgO) are added as sintering aids, herring oil (0.6 g) is used as a dispersant, and anhydrous ethanol (13 g) and xylene (13 g) are used as a mixed solvent. The above raw material powder, sintering aid, dispersant and mixed solvent are ball milled for 12 h for uniform mixing and dispersion. Subsequently, a binder polyvinyl butyral (PVB, 4.8 g), a plasticizer butyl benzyl phthalate (BBP, 2.4 g) and polyethylene glycol 400 (PEG-400, 2.4 g) are added for secondary ball milling and mixing for 16 h to obtain a casting slurry with moderate viscosity. The slurry is defoamed in a vacuum defoamer for 5 min. A casting film is prepared using a casting machine, and the distance between the doctor blade and the carrier tape is controlled at 300 μm. The slurry is poured into the slurry tank, the motor is started, the casting rate is set at 100 mm / min, and casting is carried out at room temperature. The dried casting film is taken off the casting machine and sealed for standby.

[0052] Refer to the same process to prepare Yb-doped 3+ YAG thin films. The difference is only that: using yttrium oxide (Y2O3), alumina (Al2O3), ytterbium oxide (Yb2O3) as raw materials, according to Yb x Y (3-x) Al5O 12 (x = 1.7, 2.5, 3.5) to accurately weigh the raw material powder.

[0053] Figure 6 is a schematic structural diagram of the two-step gradient doped surface gain type Yb:YAG ceramic prepared in Example 2 of the present invention. The middle layer is the YAG thermal conductivity layer, and the units on the upper surface layer are Yb in turn 3+The Yb:YAG gain layer with doping concentrations of 0 at.%-1.7 at.%-2.5 at.%-3.5 at.%-2.5 at.%-1.7 at.%-0 at.%. The lower surface layer is the same as the upper surface layer.

[0054] Figure 7 This is a physical photo of the two-step gradient doped surface layer gain type Yb:YAG ceramic prepared in Example 2 of the present invention. It can be seen that the structure of the prepared physical ceramic is consistent with the schematic Figure 1 one. The middle layer is an undoped thermal conduction layer. The gain layers on the upper and lower surface layers located in the middle layer have seven gain units. The middle gain unit has the darkest color, and the colors of the gain units extending to both sides gradually become lighter, and the two ends are undoped end caps.

[0055] Figure 8 This is the linear transmittance curve (thickness is 2 mm) of the two-step gradient doped surface layer gain type Yb:YAG ceramic prepared in Example 2. The long dashed line part is the high doping region. The short dashed line part is the medium doping region. Different doping concentration regions all have high linear transmittance. The linear transmittance of the high concentration doping region at 1100 nm is 84.5%, the linear transmittance of the medium concentration doping region at 1100 nm is 84.4%, and the linear transmittance of the low concentration doping region at 1100 nm is 84.5%.

[0056] Figure 9 This is the microscopic morphology photo of the thermally etched surface of the two-step gradient doped surface layer gain type Yb:YAG ceramic prepared in Example 2 (thermal etching: heat-treat the double-sided polished ceramic in a muffle furnace at 1450 °C for 3 h). No obvious pores and second phases are observed in different regions. The average grain sizes of the YAG, 1.7 at.% Yb:YAG, 2.5 at.% Yb:YAG, and 3.5 at.% Yb:YAG regions are 30.3 μm, 30.7 μm, 32.6 μm, and 34.7 μm in turn.

[0057] Figure 10 This is the Yb 3+ distribution in the two-step gradient doped surface layer gain Yb:YAG ceramic: (a) thickness direction; (b) length direction. In the thickness direction, the test area is the high concentration doping area, and Yb 3+ has signals at both ends, and there is no signal area in the middle of the ceramic. In the length direction, the Yb 3+ distribution signal has five segments, there is no signal at both left and right ends, and the doping layer signal is distributed in the order of low, medium, and high from one end to the center. It is proved that the structure of the prepared one-step gradient doped ceramic is consistent with the design.

[0058] Example 3

[0059] Prepare undoped YAG thin films. Using yttrium oxide (Y2O3) and alumina (Al2O3) as raw materials, according to Y3Al5O 12 Precisely weigh a total of 60 g of the raw material powders according to the composition, add tetraethyl orthosilicate (TEOS) accounting for 0.8 wt% of the raw material powders and magnesium oxide (MgO) accounting for 0.08 wt% of the raw material powders as sintering aids, use polyester (0.5 g) as a dispersant, and use absolute ethanol (13 g) and methyl ethyl ketone (13 g) as a mixed solvent. Ball-mill the above powders, sintering aids, dispersant, and mixed solvent for 12 h for uniform mixing and dispersion. Subsequently, add a composite binder of polyacrylic acid (2 g) and methyl ethyl ketone (2 g) and butyl benzyl phthalate (1 g) as a plasticizer, and perform secondary ball-milling and mixing for 24 h to obtain a casting slurry with moderate viscosity. Debubble the slurry in a vacuum degassing machine for 5 min. Use a casting machine to prepare a cast film, and control the distance between the doctor blade and the carrier tape at 300 μm. Pour the slurry into the slurry tank, start the motor, set the casting rate at 100 mm / min, and perform casting at room temperature. Take down the dried cast film from the casting machine and seal it for standby.

[0060] Refer to the same process to prepare Yb-doped 3+ YAG thin films. The difference is only that: using yttrium oxide (Y2O3), alumina (Al2O3), and ytterbium oxide (Yb2O3) as raw materials, according to Yb x Y (3-x) Al5O 12 (x = 1.9, 3.7) precisely weigh the raw material powders according to the composition.

[0061] The laser ceramic structure design of this example is the same as that of Example 1.

[0062] Arrange and stack the cast films according to the above structure design. Place the arranged and stacked cast films in an oven and heat up to 70 °C to make the PVB as the binder reach its glass transition temperature, and then place it on a tablet press to apply a vertical pressure of 40 MPa. After cooling, a complete green body is obtained. Debind the green body in a muffle furnace. The debinding system is set to slowly rise from room temperature to 600 °C and hold for 10 h. After cooling to room temperature with the furnace, take out the green body from the muffle furnace. There is no organic residue and no crack in the debound green body. Cold isostatically press the debound green body at 250 MPa and hold the pressure for 5 min. Put the cold isostatically pressed green body into a vacuum sintering furnace for sintering. The sintering conditions are: the holding temperature is 1750 °C, the holding time is 30 h, and the vacuum degree in the vacuum sintering furnace is better than 1×10 -3 Pa. Subsequently, anneal the ceramic under the conditions of 1750 °C, 200 MPa, Ar atmosphere, and hold for 3 h. Finally, polish the opposite side of the sample to obtain a stepped gradient-doped surface gain-type Yb:YAG ceramic.

[0063] Example 4

[0064] Reference "Preparation and Property Optimization of Yb:YAG Nanopowders and Transparent Ceramics by Wet Chemical Method" (Liu Yumin, Jiangsu University) prepared YAG powders by the co - precipitation method. Undoped YAG thin films were prepared. Using the prepared YAG powders (35 g) as raw materials, they were added to a high - purity alumina ball - milling tank. Herring oil (0.8 g) was used as a dispersant, and absolute ethanol (12 g) and xylene (12 g) were used as a mixed solvent. The above - mentioned powders, sintering aids, dispersant, and mixed solvent were ball - milled for 12 h for uniform mixing and dispersion. Subsequently, the binder polyvinyl butyral (PVB, 4.8 g), plasticizer butyl benzyl phthalate (BBP, 2.4 g), and polyethylene glycol 400 (PEG - 400, 2.4 g) were added for secondary ball - milling and mixing for 16 h to obtain a casting slurry with a moderate viscosity. The slurry was degassed in a vacuum degassing machine for 5 min. A casting film was prepared using a casting machine, and the distance between the doctor blade and the carrier tape was controlled at 500 μm. The slurry was poured into the slurry tank, the motor was started, and the casting rate was set at 100 mm / min. The casting was carried out at room temperature. The dried casting film was taken off the casting machine and sealed for standby.

[0065] Refer to the process of Example 1 to prepare doped Yb 3+ doped YAG thin films. Using yttrium oxide (Y2O3), aluminum oxide (Al2O3), ytterbium oxide (Yb2O3) as raw materials, according to Yb x Y (3-x) Al5O 12 (x = 1.9, 3.7) to accurately weigh the raw material powders.

[0066] The laser ceramic structure design of this example is the same as that of Example 1.

[0067] Arrange and stack the casting films according to the above - mentioned structure design. The arranged and stacked casting films were placed in an oven and heated to 70 °C to make PVB, which is used as a binder, reach its glass transition temperature. Then, a vertical pressure of 40 MPa was applied on a tablet press. After cooling, a complete green body was obtained. The green body was debound in a muffle furnace. The debinding regime was set to slowly rise from room temperature to 600 °C and hold for 10 h. After cooling to room temperature with the furnace, the green body was taken out of the muffle furnace. There was no organic residue and no crack in the debound green body. The debound green body was cold isostatically pressed at 250 MPa for 5 min. The cold - isostatically - pressed green body was put into a vacuum sintering furnace for sintering. The sintering conditions were: the holding temperature was 1800 °C, the holding time was 20 h, and the vacuum degree in the vacuum sintering furnace was better than 1×10 -3 Pa. Subsequently, the ceramic was annealed under the conditions of 1750 °C, 200 MPa, Ar atmosphere, and holding for 3 h. Finally, the sample was polished on the opposite side to obtain a stepped - gradient - doped surface - gain - type Yb:YAG ceramic.

Claims

1. A concentration-gradient doped surface gain type laser ceramic with a composite structure, characterized in that, The intermediate layer of the concentration gradient doped surface layer gain type laser ceramic of the composite structure is a thermal conduction layer without doped active ions. The surface layers on both sides of the intermediate layer in the thickness direction of the intermediate layer are gain layers with the same structure and active ion concentration gradient. The gain layer is composed of a plurality of gain units with the same thickness arranged on the plane of the surface layer. The active ion concentration of the gain unit located in the center of the arrangement direction among the plurality of gain units decreases to zero in sequence towards the active ion concentrations of the gain units at both ends.

2. The concentration gradient doped surface layer gain type laser ceramic of the composite structure according to claim 1, characterized in that, The activation ions doped in the gain unit are selected from rare earth ions, preferably Yb 3+ 、Nd 3+ 、Tm 3+ 、Ho 3+ , Er 3+ One or a combination of the following.

3. The concentration gradient doped surface layer gain type laser ceramic of the composite structure according to claim 1 or 2, characterized in that, The matrix material of the gain unit is selected from one of YAG, LuAG, multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 , and one of sesquioxides; preferably, the sesquioxide is Y2O3, Sc2O3, Lu2O3 or a solid solution thereof.

4. The concentration-gradient doped surface layer gain type laser ceramic of the composite structure according to any one of claims 1 to 3, characterized in that, The material of the thermal conduction layer is selected from one of YAG, LuAG, multi-component garnet (Y, Lu, Gd)3(Al, Sc, Ga)5O 12 , and one of sesquioxides; preferably, the sesquioxide is Y2O3, Sc2O3, Lu2O3 or a solid solution thereof.

5. The concentration gradient doped surface layer gain type laser ceramic of the composite structure according to any one of claims 1 to 4, characterized in that, The shape of the gain unit in the arrangement direction is trapezoidal or parallelogram.

6. The concentration gradient doped surface layer gain type laser ceramic of the composite structure according to any one of claims 1 to 5, characterized in that, The active ion concentration of the gain unit located in the center of the arrangement direction among the plurality of gain units decreases towards the active ion concentrations of the gain units at both ends in a stepwise or gradual manner.

7. The concentration-gradient doped surface layer gain type laser ceramic of the composite structure according to any one of claims 1 to 6, characterized in that, The active ion concentration of the gain unit is within 30.0 at.%, preferably within 10.0 at.%.

8. The concentration gradient doped surface layer gain type laser ceramic of the composite structure according to any one of claims 1 to 7, characterized in that, The range of the active ion concentration of the gain unit with active ions is 0.5 at.% to 30.0 at.%, preferably 0.5 at.% to 10.0 at.%.

9. The concentration-gradient doped surface layer gain type laser ceramic of the composite structure according to any one of claims 1 to 8, characterized in that, The thickness of the thermal conduction layer is more than twice the thickness of the gain layer.

10. The preparation method of the concentration gradient doped surface layer gain type laser ceramic with a composite structure according to any one of claims 1 to 9, characterized in that, The preparation method includes: respectively preparing casting films as the intermediate layer and the surface layer by the tape casting technology, and then obtaining the concentration gradient doped surface layer gain type laser ceramic of the composite structure through film cutting, laminating, debinding, shaping, and sintering.

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