Laser single crystal optical fiber doped with ions in gradient mode and preparation method of laser single crystal optical fiber

Abstract

The invention discloses a laser single crystal optical fiber doped with ions in a gradient manner and a preparation method of the laser single crystal optical fiber, when the single crystal optical fiber is prepared, firstly, raw materials with different doping concentrations are uniformly mixed respectively, then the raw materials are pressed into sheets respectively, the sheets are pressed for the second time to enhance compactness, then the pressed sheets are sintered to obtain a polycrystal material, and the polycrystal material is sintered to obtain the laser single crystal optical fiber doped with ions in a gradient manner. The preparation method comprises the following steps: respectively grinding a polycrystalline material until the polycrystalline material passes through a 400-mesh sieve, filling polycrystalline material powder into a strip balloon in a gradient segmentation manner, compacting and sealing, pressing and sintering to obtain a ceramic material rod, cutting the ceramic material rod into a ceramic square rod, and performing seeding growth by adopting a laser heating base method and taking the ceramic square rod as a source material rod to obtain the gradient ion-doped laser single crystal optical fiber. Compared with the prior art that the laser single crystal fiber doped with the ions in the gradient mode is prepared through a welding process, the method is low in process difficulty, welding interface diameter fluctuation does not need to be accurately controlled, the yield is high, the procedure is simple, and the production efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of laser crystal materials, and in particular to a gradient ion-doped laser single crystal optical fiber and a preparation method thereof. Background Art

[0002] As the core component that promotes the development and application of all-solid-state lasers, the performance of laser crystals is crucial. However, when using diode lasers for single-end pumping, uniformly doped laser crystals face a significant problem: due to the absorption characteristics of the activated ions, the pump light intensity decays exponentially along the longitudinal direction of the crystal. This characteristic causes the absorption intensity of the entire gain medium to the pump light to be unevenly distributed, with the part close to the pump light source absorbing more strongly, so the thermal effect is also more significant, while the end far from the pump light source is relatively light.

[0003] Under high-power pumping conditions, this problem of uneven heat distribution becomes particularly prominent. The front end of the laser crystal absorbs more pump light, resulting in strong thermal lensing and thermally induced birefringence effects, which may even cause laser thermal damage. These thermal effects severely limit the ability of solid-state lasers to achieve higher power and higher beam quality.

[0004] In order to meet the thermal management challenges of laser crystals, researchers have tried a variety of solutions. On the one hand, the thermal effect is reduced by increasing the surface heat dissipation area of ​​the laser crystal, such as developing new crystal structures such as slab crystals, disk crystals and single crystal optical fibers. These designs aim to increase the contact area between the crystal and the cooling medium, thereby improving the efficiency of heat conduction. On the other hand, the thermal lens effect is compensated by designing laser crystals with curvature to reduce its impact on the laser beam quality.

[0005] However, these improvements do not fundamentally solve the problem of uneven heat distribution inside the laser crystal due to uniform doping. To further alleviate this problem, researchers have explored bonding methods using laser crystals with different doping concentrations. This method changes the doping concentration distribution inside the crystal, making the absorption of pump light in the crystal more uniform, which is expected to improve the uneven heat distribution. However, the bonding process has extremely strict requirements on parameters such as crystal surface finish, cleanliness, temperature, time and pressure, resulting in high preparation costs and difficult process technology. In addition, the surface area and volume of the crystal prepared by bonding technology are relatively small, which limits its heat dissipation capacity, so the entire laser crystal still has the problem of poor thermal effect.

[0006] CN116200818A discloses a method for growing a single crystal optical fiber with a continuous gradient distribution of doped ions, comprising: cutting at least two homogeneous crystals or ceramics with different doped ion concentrations and a homogeneous crystal or ceramic without doped ions into square rods; selecting the square rod without doped ions as a first seed crystal, selecting the square rod doped with a first ion concentration as a first source rod, and performing a first forward growth of the single crystal optical fiber by a laser heating base method; when the single crystal optical fiber doped with the first ion concentration grows to a required length, adding a square rod doped with a second ion concentration as a source rod for fusion splicing to continue the first forward growth of the single crystal optical fiber, and repeating N times until each single crystal optical fiber with doped ions grows to a required length; and sequentially performing a first reverse growth, a second forward growth and a second reverse growth on the obtained fused single crystal optical fibers with different doped ion concentrations to obtain a single crystal optical fiber with a continuous gradient distribution of doped ions. This method was used to obtain single-crystal optical fiber with gradient ion doping, which solved the problem of relatively small surface area and volume of the crystal prepared by the bonding process. However, the process required precise control of the diameter fluctuation of the fusion interface, which was difficult and easily led to a decrease in the yield. In addition, the preparation process was complicated and the production efficiency was low. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a gradient-doped ion laser single crystal fiber and a preparation method thereof, so as to solve the problems of high process difficulty, low yield, complex preparation process and low production efficiency in the prior art.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a gradient ion-doped laser single crystal optical fiber comprises the following steps:

[0010] S1. The target laser single crystal fiber is composed of at least two sections, each section has the same doping element, and the two adjacent sections have different doping concentrations, and the doping concentration of each section is uniformly distributed; there is a transition section between the two adjacent sections, the doping element of the transition section remains unchanged, and the doping concentration changes gradiently from one section to the other, according to the doping concentration requirements of each section of the target laser single crystal fiber, the raw materials are weighed according to the stoichiometric ratio of each section of the laser single crystal fiber; the transition section is not considered when preparing the materials in sections; there is a transition section between different ion doping concentrations in the laser single crystal fiber grown by the laser heating base method, and the transition section forms a continuous gradient doping, which is more conducive to the uniform absorption of pump light by the optical fiber and the improvement of local laser thermal damage. Since the transition section is very short (less than 1 mm), it is not considered when preparing the materials in sections, and a transition section is formed between the two sections after preparation according to this method.

[0011] S2, mixing different raw materials in the same section evenly to obtain raw materials with different doping concentrations;

[0012] S3, pressing the mixed raw materials with different doping concentrations into sheets respectively, sealing and evacuating, and then performing secondary pressing to enhance density;

[0013] S4, sintering the pressed tablets to form polycrystalline materials with different doping concentrations;

[0014] S5, grinding the sintered polycrystalline materials with different doping concentrations respectively until they pass through a standard sorting sieve with a particle size of 400 mesh;

[0015] S6, loading polycrystalline powders with different doping concentrations into long balloons in sections according to a gradient, compacting and sealing the sections one by one;

[0016] S7, pressing the loaded balloon under high pressure to form a plurality of ceramic rods doped with different concentrations;

[0017] S8, performing secondary sintering on the ceramic rod to improve density, and cutting it into rectangular ceramic square rods;

[0018] S9, adopting a laser heating base method, using the ceramic square rod as a source rod, and growing a laser single crystal optical fiber with gradient ion doping by controlling the growth rate and the feeding rate;

[0019] S10. Annealing the grown single crystal optical fiber to eliminate residual stress.

[0020] Further, the gradient segmentation in step S6 is one of the following forms:

[0021] (a) Single-end gradient: doping concentration changes continuously from low to high;

[0022] (b) Gradient at both ends: the doping concentration increases from low to high and then decreases to low.

[0023] Furthermore, the laser single crystal fiber in step S1 is an oxide, a sesquioxide or a mixed sesquioxide, including Re:YAG, Re:GAGG, Re:YSGG, Re:Y 2 O 3 、Re:Al 2 O 3 or Re:YScO 3 At least one of the following, wherein Re is Er 3+ 、Tm 3 + 、Ho 3+ 、Nd 3+ Cr 3+ 、Dy 3+ 、Ti 3+ or Yb 3+ One or more of the above, and the total concentration of doped ions does not exceed 50at.%.

[0024] Furthermore, the pressure of the secondary pressing in step S3 and the high-pressure pressing in step S7 is 200-250 MPa, and the pressing time is 10-15 minutes.

[0025] Furthermore, in steps S4 and S8, the sintering temperature is 1400° C. to 1600° C., the heating rate is 24 to 30 hours to reach the target temperature, after being kept constant for 48 to 50 hours, it is cooled to room temperature over 24 to 30 hours.

[0026] Furthermore, the growth rate of the laser heating susceptor method in step S9 is 30-60 mm / h, and the feeding speed is 10-20 mm / h.

[0027] Furthermore, in step S8, the side length of the cross section of the ceramic square rod is 0.7-2 mm.

[0028] Furthermore, the laser heating susceptor method in step S9 includes multiple drawing processes, and the single crystal optical fiber after the initial drawing is drawn for the second time to reduce the diameter and increase the length.

[0029] Further, in step S9, when the laser heating susceptor method is used to seed the ceramic square rod, the diameter of the seed crystal is smaller than the side length of the cross section of the ceramic square rod.

[0030] A gradient ion-doped laser single crystal optical fiber is prepared by the above method, has a diameter of 20-2000 μm, a doping ion concentration gradient of a single end gradient or a two end gradient, and a total doping ion concentration of no more than 50 at.%.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention designs a gradient doping of the ceramic rod, and the doping ion concentration of the obtained laser single crystal fiber changes gradiently along the longitudinal direction (single-end or two-end gradient), so that the pump light absorption distribution is more uniform. Compared with the traditional uniformly doped crystal, this method effectively alleviates the thermal lens effect and thermally induced birefringence caused by the exponential decay of the pump light intensity, thereby reducing the risk of local thermal damage and improving the stability and beam quality of high-power lasers. Compared with the prior art of preparing gradient-doped ion laser single crystal fibers through a fusion process, the process difficulty of the present invention is lower, there is no need to accurately control the fluctuation of the diameter of the fusion interface, the yield rate is higher, the process is simple, and the production efficiency is high.

[0033] 2. The present invention can design a variety of concentration gradient forms (such as single-end increasing, two-end increasing-decreasing) according to actual needs, and supports single doping or multi-ion co-doping. By adjusting the raw material ratio and the segmented loading order, the doping concentration (0-50at.%) of different sections can be accurately controlled to meet the diverse laser wavelength and power requirements. And the laser single crystal fiber with gradient doping distribution at both ends can be more fully and effectively pumped by a double-ended pump source, which is conducive to obtaining more efficient pump source absorption efficiency and higher laser power.

[0034] 3. The present invention improves the density of the ceramic rod through secondary pressing and segmented sintering process, reduces the pores and impurity defects in the crystal growth process, and improves the optical uniformity and mechanical strength of the final single crystal optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the growth of single crystal optical fiber with gradient ion doping of the present invention;

[0036] Reference numerals: 1. CO 2 Laser; 2. Beam expansion collimator; 3. Beam ring-changing device; 4. Focusing reflector; 5. Plane reflector; 6. Seed crystal; 7. Melting zone; 8. Doped ceramic rod; 9. Undoped ceramic rod. DETAILED DESCRIPTION

[0037] The specific implementation modes of the present invention are further described in detail below in conjunction with specific examples.

[0038] Example 1

[0039] This embodiment provides a method for preparing a YAG-1.0at.%Yb:YAG-YAG single crystal optical fiber. The YAG-1.0at.%Yb:YAG-YAG single crystal optical fiber has a double-end gradient change and is divided into three sections. 3+ The doping concentrations are 0, 1 at.%, and 0, respectively. The doping ions in each section of the single crystal optical fiber are evenly distributed, and a transition section is formed at the junction of two adjacent sections, and the doping ion concentration changes gradually. The following steps are included:

[0040] 1. Preparation of ceramic rods

[0041] (1) Raw material ratio and pressing

[0042] According to the chemical formula Y 3 Al 5 O 12 The stoichiometric ratio of Y 2 O 3 、Al 2 O 3The powder raw materials have a purity of 99.999% and a total mass of 200 g, and YAG powder is obtained after mixing.

[0043] According to the chemical formula Yb 0.03 Y 0.97 Al 5 O 12 The stoichiometric ratio of Yb 2 O 3 , Y 2 O 3 、Al 2 O 3 Powder raw materials, the purity of which is 99.999%, the total mass is 500g, and Yb 3+ Yb:YAG powder with a doping concentration of 1 at.%.

[0044] The YAG powder and Yb:YAG powder were pressed into sheets by an isostatic press, then put into sealed bags and evacuated, and then put into a 200 MPa hydraulic press for secondary pressing. The pressing lasted for 15 minutes and the sheets were taken out to obtain YAG tablets and Yb:YAG tablets, respectively.

[0045] (2) Sintering and grinding

[0046] The YAG pressed tablets and Yb:YAG pressed tablets were placed in a pre-cleaned alumina crucible, and then sintered in a muffle furnace. The sintering process was to heat up to 1500°C for 24 hours, keep the temperature constant for 48 hours, and then cool to room temperature for 24 hours. After sintering, YAG polycrystalline material and Yb:YAG polycrystalline material were obtained. The YAG polycrystalline material and Yb:YAG polycrystalline material were placed in a pre-cleaned agate mortar and ground thoroughly until all the polycrystalline materials passed through a sieve with a particle size of 400 mesh, and YAG polycrystalline powder and Yb:YAG polycrystalline powder were obtained respectively.

[0047] (3) Gradient loading and molding

[0048] YAG polycrystalline powder and Yb:YAG polycrystalline powder are loaded into a long balloon that has been cleaned and dried in advance. The loading order is to first load 1cm of YAG polycrystalline powder, then load 3cm of Yb:YAG polycrystalline powder, and finally load 1cm of YAG polycrystalline powder. At the same time, during the powder loading process, a glass rod should be continuously used to extend into the balloon longitudinally to compact it to avoid the problem of uneven diameter and poor density of the ceramic rods prepared later. After the loading is completed, the balloon mouth is sealed. Then the loaded balloon is placed in a 200MPa hydraulic press and pressed for 10min. After taking it out, the balloon is removed and sintered. The sintering procedure is to heat up to 1500℃ for 24h, keep the temperature constant for 48h, and then cool to room temperature for 24h. After sintering, a ceramic rod is obtained. The process of secondary grinding, pressing and sintering is to ensure that the ceramic rod has better density. Finally, the sintered ceramic rod is cut into multiple ceramic square rods with a side length of 1mm and a length of 5cm by an inner circle cutting machine, and ultrasonically cleaned for 20min. The reason for cutting the ceramic rod into smaller ceramic square rods is that due to the limitation of the laser spot diameter, the side length of the cross section of the ceramic square rod should not be greater than 2mm, otherwise the top of the rod will be difficult to completely melt and seeding growth will not be achieved. Compared with cutting into ceramic round rods, cutting into ceramic square rods is simpler.

[0049] 2. Growth of single crystal optical fiber by laser heating pedestal method

[0050] (1) Initial drawing

[0051] like Figure 1 As shown, the cut ceramic square rods (including doped ceramic rods 8 and undoped ceramic rods 9) are used as source rods and fixed to the feeding device, with a size of Φ0.5×30mm 3 The YAG single crystal fiber is fixed to the pulling device as the seed crystal 6. Move the feeding device upward so that the top of the ceramic square rod is at the focus of the focusing reflector 4, and turn on the CO 2 Laser 1, the laser beam passes through the beam expansion collimator 2 and the beam ring-changing device 3 in sequence, and then irradiates the plane reflector 5 in parallel. After 90° reflection, it irradiates the focusing reflector 4. After 45° reflection, the beam is focused at the focal point; the power is slowly increased until the top of the ceramic square rod is melted into a bulb shape, and then the seed crystal 6 is slowly moved downward to contact the molten zone 7. After the molten zone 7 is stable, the seed crystal is pulled upward at a pulling speed of 30mm / h, and the ceramic square rod is fed upward at a feeding speed of 10mm / h, and finally a size of Φ0.632×85.6mm is grown. 3 YAG-1.0at.%Yb:YAG-YAG single crystal optical fiber.

[0052] (2) Secondary drawing

[0053] The grown YAG-1.0at.%Yb:YAG-YAG single crystal optical fiber was drawn again, with an upward pulling speed of 180mm / h and an upward feeding speed of 30mm / h, and a size of Φ0.232×237.5mm was grown. 3 After drawing, the single crystal fiber is placed in a muffle furnace for annealing to eliminate the internal stress of the single crystal fiber and reduce defects.

[0054] Example 2

[0055] This embodiment provides a gradient doped Ti:Al 2 O 3 A method for preparing a single crystal optical fiber, wherein the gradient doped Ti:Al 2 O 3 Single crystal fiber, single-end gradient change, divided into 5 sections, each section Ti 3+ The doping concentrations are 0.05at.%, 0.1at.%, 0.2at.%, 0.3at.%, and 0.35at.%, respectively. The doping ions in each section of the single crystal optical fiber are evenly distributed, and a transition section is formed at the junction of two adjacent sections, and the doping ion concentration changes gradually. The following steps are included:

[0056] 1. Preparation of ceramic rods

[0057] (1) Raw material ratio and pressing

[0058] According to the chemical formula Ti 0.001 Al 1.999 O 3 The stoichiometric ratio of Ti 2 O 3 、Al 2 O 3 Powder raw materials, the purity of which is 99.999%, the total mass is 100g, and Ti is obtained after mixing 3+ Ti:Al doping concentration of 0.05at.% 2 O 3 powder.

[0059] According to the chemical formula Ti 0.002 Al 1.998 O 3 The stoichiometric ratio of Ti 2 O 3 、Al 2 O 3 Powder raw materials, the purity of which is 99.999%, the total mass is 100g, and Ti is obtained after mixing 3+ Ti:Al doping concentration of 0.1at.% 2 O 3 powder.

[0060] According to the chemical formula Ti 0.004 Al 1.996 O 3 The stoichiometric ratio of Ti 2 O 3 、Al 2 O 3 Powder raw materials, the purity of which is 99.999%, the total mass is 100g, and Ti is obtained after mixing 3+ Ti:Al doping concentration of 0.2at.% 2 O 3 powder.

[0061] According to the chemical formula Ti 0.006 Al 1.994 O 3 The stoichiometric ratio of Ti 2 O 3 、Al 2 O 3 Powder raw materials, the purity of which is 99.999%, the total mass is 100g, and Ti is obtained after mixing 3+ Ti:Al doping concentration of 0.3at.% 2 O 3 powder.

[0062] According to the chemical formula Ti 0.007 Al 1.993 O 3 The stoichiometric ratio of Ti 2 O 3 、Al 2 O 3 Powder raw materials, the purity of which is 99.999%, the total mass is 100g, and Ti is obtained after mixing 3+ Ti:Al doping concentration of 0.35at.% 2 O 3 powder.

[0063] Five different Ti 3+ Doping concentration of Ti:Al 2 O 3 The powders were pressed into sheets, then put into sealed bags and evacuated, and then put into a 200MPa hydraulic press for secondary pressing. After pressing for 15 minutes, the powders were taken out to obtain five different Ti 3+ Doping concentration of Ti:Al 2 O 3 Tablet pressing.

[0064] (2) Sintering and grinding

[0065] 5 different Ti 3+Doping concentration of Ti:Al 2 O 3 The tablets were placed in a pre-cleaned alumina crucible and sintered in a muffle furnace. The sintering process was to heat up to 1600°C for 24 hours, keep the temperature constant for 48 hours, and then cool to room temperature for 24 hours. After sintering, 5 different Ti 3+ Doping concentration of Ti:Al 2 O 3 Polycrystalline material. 5 different Ti 3+ Doping concentration of Ti:Al 2 O 3 The polycrystalline materials were put into a pre-cleaned agate mortar and ground thoroughly until all the polycrystalline materials passed through a 400-mesh sieve, and 5 different Ti 3+ Doping concentration of Ti:Al 2 O 3 Polycrystalline powder.

[0066] (3) Gradient loading and molding

[0067] 5 different Ti 3+ Doping concentration of Ti:Al 2 O 3 The polycrystalline powder is loaded into a long balloon that has been cleaned and dried in advance, and the loading order is 0.05at.%Ti:Al 2 O 3 、0.1at.%Ti:Al 2 O 3 、0.2at.%Ti:Al 2 O 3 、0.3at.%Ti:Al 2 O 3 、0.35at.%Ti:Al 2 O 3 , each Ti:Al 2 O 3 The length of the polycrystalline powder is 1 cm. At the same time, during the powder loading process, a glass rod should be continuously inserted into the balloon longitudinally to compact it to avoid the uneven diameter and poor density of the ceramic rods prepared later. After the loading is completed, the balloon mouth is sealed. Then the loaded balloon is placed in a 200MPa hydraulic press and pressed for 10 minutes. After taking it out, the balloon is removed and sintered. The sintering procedure is to heat up to 1600℃ for 24 hours, keep the temperature constant for 48 hours, and then cool to room temperature for 24 hours. After sintering, the ceramic rod is obtained. The process of secondary grinding, pressing and sintering is to ensure that the ceramic rod has better density. Finally, the sintered ceramic rod is cut into multiple ceramic square rods with a side length of 0.7mm and a length of 5cm using an inner circle cutting machine, and ultrasonically cleaned for 20 minutes.

[0068] 2. Growth of single crystal optical fiber by laser heating pedestal method

[0069] The cut ceramic square rod is used as the source rod and fixed to the feeding device with a size of Φ0.38×30mm 3 Al 2 O 3 The single crystal fiber is fixed to the pulling device as a seed crystal. The feeding device is moved upward so that the top of the ceramic square rod is at the focus of the focusing reflector. The CO 2 The laser is used to focus the beam at the focal point; the power is slowly increased until the top of the ceramic square rod is melted into a bulb shape, and then the seed crystal is slowly moved downward to contact the molten zone. After the molten zone is stable, the seed crystal is pulled upward at a pulling speed of 50mm / h, and the ceramic square rod is fed upward at a feeding speed of 15mm / h. The final growth is a Φ0.427×80mm 3 0.05~0.35at.%Ti:Al 2 O 3 Single crystal optical fiber. After drawing, the single crystal optical fiber is placed in a muffle furnace for annealing to eliminate the internal stress of the single crystal optical fiber and reduce the generation of defects.

[0070] Example 3

[0071] This embodiment provides a method for preparing a gradient-doped Er,Cr:YSGG single crystal optical fiber. The gradient-doped Er,Cr:YSGG single crystal optical fiber has a single-end gradient change and is divided into five sections. The doping concentration of each section is 0; Er 3+ :15at.%Cr 3 + :1at.%;Er 3+ :25at.%Cr 3+ :2at.%;Er 3+ :30at.%Cr 3+ :3at.%;Er 3+ :35at.%Cr 3+ :4at.% Each section of the single crystal optical fiber is doped with ions evenly distributed, and a transition section is formed at the junction of two adjacent sections, and the doped ion concentration changes gradually. The following steps are included:

[0072] 1. Preparation of ceramic rods

[0073] (1) Raw material ratio and pressing

[0074] According to the chemical formula Y 2.93 Sc 1.43 Ga 3.64 O 12 The stoichiometric ratio of Y 2 O 3 Sc 2 O3 , Ga 2 O 3 The powder raw materials have a purity of 99.999% and a total mass of 150 g, and are mixed to obtain YSGG powder.

[0075] According to the chemical formula Er 0.4395 Cr 0.0364 Y 2.4905 Sc 1.43 Ga 3.6036 O 12 Weigh Er in the stoichiometric ratio 2 O 3 Cr 2 O 3 , Y 2 O 3 Sc 2 O 3 , Ga 2 O 3 Powder raw materials, purity of 99.999%, total mass of 150g, after mixing, Er 3+ The doping concentration is 15at.%, Cr 3+ The doping concentration of Er,Cr:YSGG powder is 1at.% and 0.1at.%.

[0076] According to the chemical formula Er 0.7325 Cr 0.0507 Y 2.1975 Sc 1.4157 Ga 3.6036 O 12 Weigh Er in the stoichiometric ratio 2 O 3 Cr 2 O 3 , Y 2 O 3 Sc 2 O 3 , Ga 2 O 3 Powder raw materials, purity of 99.999%, total mass of 150g, after mixing, Er 3+ The doping concentration is 25at.%, Cr 3+ Er,Cr:YSGG powder with a doping concentration of 2at.%.

[0077] According to the chemical formula Er 0.879 Cr 0.0871 Y 2.051 Sc 1.4157 Ga 3.5672 O 12 Weigh Er in the stoichiometric ratio 2 O 3 Cr2 O 3 , Y 2 O 3 Sc 2 O 3 , Ga 2 O 3 Powder raw materials, purity of 99.999%, total mass of 150g, after mixing, Er 3+ The doping concentration is 30at.%, Cr 3+ Er,Cr:YSGG powder with a doping concentration of 3at.%.

[0078] According to the chemical formula Er 1.0255 Cr 0.1014 Y 1.9045 Sc 1.4014 Ga 3.5672 O 12 Weigh Er in the stoichiometric ratio 2 O 3 Cr 2 O 3 , Y 2 O 3 Sc 2 O 3 , Ga 2 O 3 Powder raw materials, purity of 99.999%, total mass of 150g, after mixing, Er 3+ The doping concentration is 35at.%, Cr 3+ The doping concentration of Er,Cr:YSGG powder is 4at.%.

[0079] An isostatic press was used to press Er,Cr:YSGG powders with five different doping concentrations into sheets, then put them into sealed bags and evacuated, and then put them into a 200MPa hydraulic press for secondary pressing. The pressing lasted for 15 minutes and the sheets were taken out to obtain Er,Cr:YSGG tablets with five different doping concentrations.

[0080] (2) Sintering and grinding

[0081] The Er,Cr:YSGG tablets with 5 different doping concentrations were placed in a pre-cleaned alumina crucible, and then sintered in a muffle furnace. The sintering process was to heat up to 1400°C for 24 hours, keep the temperature constant for 48 hours, and then cool to room temperature for 24 hours. After sintering, 5 Er,Cr:YSGG polycrystalline materials with different doping concentrations were obtained. The Er,Cr:YSGG polycrystalline materials with 5 different doping concentrations were placed in a pre-cleaned agate mortar and ground thoroughly until all the polycrystalline materials passed through a sieve with a particle size of 400 mesh, and 5 Er,Cr:YSGG polycrystalline powders with different doping concentrations were obtained.

[0082] (3) Gradient loading and molding

[0083] Five kinds of Er,Cr:YSGG polycrystalline powders with different doping concentrations were loaded into the long balloons that were cleaned and dried in advance. The loading order was YSGG, 15at.% Er, 1at.% Cr: YSGG, 25at.% Er, 2at.% Cr: YSGG, 30at.% Er, 3at.% Cr: YSGG, 35at.% Er, 4at.% Cr: YSGG, and the length of each polycrystalline powder was 1 cm. At the same time, during the powder loading process, a glass rod should be continuously inserted into the balloon from the longitudinal direction to compact it to avoid the problems of uneven diameter and poor density of the ceramic rods prepared later. After the loading is completed, the balloon mouth is sealed. Then the loaded balloon is placed in a 200MPa hydraulic press and pressed for 15 minutes. After taking it out, the balloon is removed and sintered. The sintering procedure is to increase the temperature to 1400℃ for 24 hours, keep the temperature constant for 48 hours, and then cool it to room temperature for 24 hours. After sintering, a ceramic material rod is obtained. The process of secondary grinding, pressing and sintering is to ensure that the ceramic rod has better density. Finally, the sintered ceramic rod is cut into multiple ceramic square rods with a side length of 1.5 mm and a length of 5 cm by an internal circle cutting machine, and ultrasonically cleaned for 25 minutes.

[0084] 2. Growth of single crystal optical fiber by laser heating pedestal method

[0085] The cut ceramic square rod is used as the source rod and fixed to the feeding device with a size of Φ0.38×30mm 3 The YAG single crystal fiber is fixed to the pulling device as the seed crystal. Move the feeding device upward so that the top of the ceramic square rod is at the focus of the focusing reflector, and turn on the CO 2 The laser is used to focus the beam at the focal point; the power is slowly increased until the top of the ceramic square rod is melted into a bulb shape, and then the seed crystal is slowly moved downward to contact the molten zone. After the molten zone is stabilized, the seed crystal is pulled upward at a pulling speed of 60mm / h, and the ceramic square rod is fed upward at a feeding speed of 20mm / h. The final growth is a Φ0.712×95.6mm 3 0~35at.%Er, 0~4at.%Cr:YSGG single crystal optical fiber. After drawing, the single crystal optical fiber is placed in a muffle furnace for annealing to eliminate the internal stress of the single crystal optical fiber and reduce the generation of defects.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a gradient ion-doped laser single crystal fiber, characterized in that: The following steps are involved: S1. The target laser single crystal fiber is composed of at least two sections, each section has the same doping element, the two adjacent sections have different doping concentrations, and the doping concentration of each section is evenly distributed; there is a transition section between the two adjacent sections, the doping element of the transition section remains unchanged, and the doping concentration changes gradually from one section to the other. According to the doping concentration requirements of each section of the target laser single crystal fiber, the raw materials are weighed according to the stoichiometric ratio of each section of the laser single crystal fiber; the transition section is not considered when preparing the materials in sections; S2, mixing different raw materials in the same section evenly to obtain raw materials with different doping concentrations; S3, pressing the mixed raw materials with different doping concentrations into sheets respectively, sealing and evacuating, and then performing secondary pressing to enhance density; S4, sintering the pressed tablets to form polycrystalline materials with different doping concentrations; S5, grinding the sintered polycrystalline materials with different doping concentrations respectively until they pass through a standard sorting sieve with a particle size of 400 mesh; S6, loading polycrystalline powders with different doping concentrations into long balloons in sections according to a gradient, compacting and sealing the sections one by one; S7, pressing the loaded balloon under high pressure to form a plurality of ceramic rods doped with different concentrations; S8, performing secondary sintering on the ceramic rod to improve density, and cutting it into rectangular ceramic square rods; S9, adopting a laser heating base method, using the ceramic square rod as a source rod, and growing a laser single crystal optical fiber with gradient ion doping by controlling the growth rate and the feeding rate; S10. Annealing the grown single crystal optical fiber to eliminate residual stress.

2. The method for preparing a gradient ion-doped laser single crystal fiber according to claim 1, characterized in that: The gradient segmentation in step S6 is one of the following forms: (a) Single-end gradient: doping concentration changes continuously from low to high; (b) Gradient at both ends: the doping concentration increases from low to high and then decreases to low.

3. The method for preparing a gradient ion-doped laser single crystal fiber according to claim 1, characterized in that: The laser single crystal fiber in step S1 is an oxide, a sesquioxide or a mixed sesquioxide, including at least one of Re:YAG, Re:GAGG, Re:YSGG, Re:Y2O3, Re:Al2O3 or Re:YScO3, wherein Re is Er 3+ 、Tm 3+ 、Ho 3+ 、Nd 3+ Cr 3+ 、Dy 3+ 、Ti 3+ or Yb 3+ One or more of the above, and the total concentration of doped ions does not exceed 50at.%.

4. The method for preparing a gradient ion-doped laser single crystal fiber according to claim 1, characterized in that: The pressure of the secondary pressing in step S3 and the high-pressure pressing in step S7 is 200-250 MPa, and the pressing time is 10-15 minutes.

5. The method for preparing a gradient ion-doped laser single crystal optical fiber according to claim 1, characterized in that: In steps S4 and S8, the sintering temperature is 1400° C. to 1600° C., and the heating rate is 24 to 30 hours to reach the target temperature. After maintaining the temperature for 48 to 50 hours, the temperature is lowered to room temperature over 24 to 30 hours.

6. The method for preparing a gradient ion-doped laser single crystal fiber according to claim 1, characterized in that: The growth rate of the laser heating susceptor method in step S9 is 30-60 mm / h, and the feeding speed is 10-20 mm / h.

7. The method for preparing a gradient ion-doped laser single crystal fiber according to claim 1, characterized in that: The side length of the cross section of the ceramic square rod in step S8 is 0.7-2 mm.

8. The method for preparing a gradient ion-doped laser single crystal fiber according to claim 1, characterized in that: The laser heating susceptor method in step S9 includes multiple drawing processes, and the single crystal optical fiber after the initial drawing is drawn for the second time to reduce the diameter and increase the length.

9. The method for preparing a gradient ion-doped laser single crystal optical fiber according to claim 1, characterized in that: In step S9, when the laser heating susceptor method is used to seed the ceramic square rod, the diameter of the seed crystal is smaller than the side length of the cross section of the ceramic square rod.

10. A gradient ion-doped single crystal laser fiber, characterized in that: The nanostructured ...

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