Nd: LuAG crystal material with heterogeneous coating structure and preparation method of Nd: LuAG crystal material

Abstract

The invention discloses an Nd: LuAG crystal material with a heterogeneous coating structure and a preparation method thereof, the crystal material comprises an Nd: LuAG crystal, the surface of the Nd: LuAG crystal is coated with a layer of Sm: LuAG crystal, the doping concentration of Nd < 3 + > in the Nd: LuAG crystal is 0.5-10 at.%, and the doping concentration of Sm < 3 + > in the Sm: LuAG crystal is 0.5-10 at.%. During preparation, the Nd: LuAG crystal and the Sm: LuAG crystal are polished and cleaned, then the Sm: LuAG crystal is attached to the outer surface of the Nd: LuAG crystal to form a cladding structure, and the Nd: LuAG crystal material with the heterogeneous cladding structure is prepared by thermal bonding. The prepared Nd: LuAG crystal material with the heterogeneous coating structure can effectively inhibit parasitic oscillation and ASE effect of the Nd: LuAG crystal and improve the overall performance of the composite laser crystal, and the bonding of Sm: LuAG enhances the overall mechanical strength of the composite material, improves the bearing capacity to thermal load, and ensures the stable operation of the large-size Nd: LuAG crystal in a high-power laser.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-power solid lasers, and particularly relates to an Nd:LuAG crystal material with a heterogeneous coating structure and a preparation method thereof. Background Art

[0002] In the field of high-power solid lasers, neodymium-doped lutetium aluminum garnet (Nd:LuAG), as a gain medium with excellent laser performance, occupies a crucial position. Its remarkable advantages lie in its relatively high thermal conductivity, good mechanical strength, and stable optical properties, which make Nd:LuAG particularly suitable for high-power laser applications. Among them, the four-level structure of Nd³⁺ provides strong support for achieving high-efficiency laser operation, making it an ideal choice for high-repetition-rate and high-energy-output lasers.

[0003] However, when Nd:LuAG crystals are fabricated into large-sized crystals to meet the requirements of high-power lasers, their inherent drawbacks become obvious. Large-sized Nd:LuAG crystals are prone to being severely affected by parasitic oscillations and amplified spontaneous emission (ASE effect). These phenomena can lead to the ineffective dissipation of laser energy, thereby reducing the overall optical efficiency and even potentially causing system instability. Summary of the Invention

[0004] Aiming at the above deficiencies existing in the prior art, the purpose of the present invention is to provide an Nd:LuAG crystal material with a heterogeneous coating structure and a preparation method thereof, so as to solve the problems that large-sized Nd:LuAG crystals are susceptible to parasitic oscillations and ASE effect in high-power laser applications, resulting in ineffective dissipation of laser energy, reduction of optical efficiency, and even system instability.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: An Nd:LuAG crystal material with a heterogeneous coating structure includes an Nd:LuAG crystal, and the surface of the Nd:LuAG crystal is coated with a layer of Sm:LuAG crystal. The Nd 3+ doping concentration in the Nd:LuAG crystal is 0.5 - 10 at.%, and the Sm 3+ doping concentration in the Sm:LuAG crystal is 0.5 - 10 at.%.

[0006] The preparation method of the Nd:LuAG crystal material with a heterogeneous coating structure includes the following preparation steps: (1) Cut Nd:LuAG crystals and Sm:LuAG crystals into strip shapes, then polish all surfaces of the strip-shaped Nd:LuAG crystals and the bonding end faces of the Sm:LuAG crystals, and then clean the polished crystal materials and dry them for standby. (2) Take four dried Sm:LuAG crystals, symmetrically attach their bonding end faces to the surface of the Nd:LuAG crystal to form a cladding structure with both opposite end faces exposed, where one pair of symmetrically attached Sm:LuAG crystals is coplanarly aligned with the corresponding face of the Nd:LuAG crystal, and the other pair of symmetrically attached Sm:LuAG crystals is coplanarly aligned with the corresponding face of the Nd:LuAG crystal and the combined crystal formed by the Nd:LuAG crystal and the previously symmetrically attached Sm:LuAG crystals; use van der Waals force to closely bond the Sm:LuAG crystals and the Nd:LuAG crystals and the adjacent two Sm:LuAG crystals, and uniformly squeeze out the air bubbles and liquid remaining on the bonding end faces during the bonding process, and then place it under a vacuum degree of 1 - 3 Pa and keep it for 70 - 90 min. (3) Place the crystal material obtained in step (2) into a working furnace, evacuate the working furnace, and when the vacuum degree is less than 1×10 -3 Pa, perform a three-stage thermal diffusion treatment. First, slowly heat it to 850 - 1400 °C at a rate of 0.3 - 0.7 °C / min, then keep it at this temperature for 10 - 50 h, and finally slowly cool it to room temperature at a rate of 0.3 - 0.7 °C / min to obtain a Nd:LuAG crystal material with a heterogeneous cladding structure; during the thermal diffusion treatment, a pressure of 55 - 80 kgf / cm 2 is applied to the crystal material during both the heating and holding stages. Pressurizing the optical glue sample while heating can promote the contact and diffusion between the crystals and form a tighter bond. And the pressure should not be too large, otherwise it will cause deformation or damage to the bonding material, while too small pressure is not conducive to closer contact on the material surface, thus affecting the interfacial bonding strength of the crystals.

[0007] Further, in step (2), when attaching the Sm:LuAG crystals, first attach the Sm:LuAG crystals to two opposite attaching faces of the Nd:LuAG crystal and align the periphery of the attached Sm:LuAG crystals with the periphery of the Nd:LuAG crystal; then attach the Sm:LuAG crystals to the remaining two attaching faces of the Nd:LuAG crystal and align the periphery of the Sm:LuAG crystals attached to the remaining two faces with the periphery of the combined crystal formed by the Nd:LuAG crystal and the already attached Sm:LuAG crystals.

[0008] Further, in step (1), the flatness N of the polished surface of the crystal material is < 0.1λ, and the surface roughness Ra is < 0.5 nm. Uneven surfaces or impurities will cause incomplete contact of the crystal bonding surface, resulting in defects such as air bubbles and gaps on the bonding surface, thereby reducing the bonding strength. Controlling the flatness and surface roughness within this range can ensure the bonding strength and stability of thermal bonding.

[0009] Further, in step (1), the cleaning method is as follows: The polished crystal material is successively placed in deionized water, gasoline, and absolute ethanol for ultrasonic cleaning to remove the residues on the crystal surface.

[0010] Further, in step (2), the two exposed end faces are the opposite end faces of the plate-shaped Nd:LuAG crystal along the length direction or the width direction. In this way, the area of the exposed end faces can be made smaller, ensuring that when the high-power Nd:LuAG laser operates, the edge-cladding material Sm∶LuAG crystal can effectively reduce the consumption of the inversion population by ASE and parasitic oscillation, and increase the output efficiency of the laser.

[0011] Further, in step (2), the thicknesses of any pair of symmetrically attached Sm:LuAG crystals are the same. This can ensure the consistency of optical performance.

[0012] Further, in step (2), the thickness of the Sm:LuAG crystal symmetrically attached along the thickness direction of the Nd:LuAG crystal is less than the thickness of the Sm:LuAG crystal symmetrically attached along the length or width direction of the Nd:LuAG crystal. In this way, a smaller thickness and a larger length or width can be formed. At a smaller thickness, the pump light power density in the crystal can be increased during high-power pumping, and the rising value of the temperature can be reduced, reducing the negative impact caused by the thermal effect; while the larger length or width can increase the absorption length of the crystal and improve the absorption efficiency of the crystal, thereby increasing the optical-optical conversion efficiency of the laser.

[0013] Further, in step (1), both the Nd:LuAG crystal and the Sm:LuAG crystal are prepared by the horizontal directional crystallization method. Using the horizontal directional crystallization method for preparation is beneficial for preparing large-sized plate-shaped crystals to meet the requirements of high-power lasers.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses Sm:LuAG crystal as the cladding material and thermally bonds it with Nd:LuAG crystal to form a new type of bonded laser crystal. Since the two have the same matrix and similar structures, a stable connection can be formed during the bonding process, ensuring that the overall mechanical and optical properties of the crystal are not affected. Moreover, Sm:LuAG crystal has a strong absorption peak at 1064 nm. As the cladding material, it can suppress the parasitic oscillation and ASE effect of large-size Nd:LuAG crystal, enhance the pumping efficiency and energy output. In addition, the bonding of Sm:LuAG can also enhance the overall mechanical strength of the composite material and improve its tolerance to thermal load, thus ensuring the stable operation of large-size Nd:LuAG crystal in high-power lasers. This technology makes it possible to have large-size, low-loss, and high-efficiency laser working media, providing a reliable solution for the development of high-power lasers.

[0015] 2. During the process of preparing Nd:LuAG crystal material with a heterogeneous coating structure by thermal bonding in the present invention, the tight bonding between Nd:LuAG crystal and Sm:LuAG crystal is achieved through optical glue. The vacuum condition helps to remove air bubbles and liquids between the bonding surfaces, reducing the generation of bubbles and defects, thereby improving the quality and stability of the bonding. Moreover, the vacuum environment can also reduce oxidation and contamination, further improving the reliability of the bonding. After optical gluing, a three-stage thermal diffusion treatment is carried out, which can further promote the diffusion and bonding between crystals through high temperature and pressure to form a stable connection. During the heat treatment process, slow heating and cooling can ensure that the bonded crystals are heated evenly, avoiding cracking of the bonded crystals due to thermal shock, thereby preventing defects such as bubbles from appearing on the bonding surface and ensuring the quality of the bonded crystals. The holding stage can ensure that the bonded crystals are in a relatively stable and uniform temperature environment during heating, preventing excessive local temperature difference of the bonded crystals from affecting the bonding quality. Applying pressure to the optical glue sample during the heating process can promote the contact and diffusion between crystals, form a tighter bond, and further improve the strength and stability of the bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of the Nd:LuAG crystal material with a heterogeneous coating structure prepared by the present invention; Figure 2 are the three views of the Nd:LuAG crystal material with a heterogeneous coating structure prepared by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following combines specific embodiments to further describe in detail the specific implementation manners of the present invention.

[0018] Example 1 This example provides a preparation method of Nd:LuAG crystal material with a heterogeneous coating structure, including the following steps: S1. Material preparation: Select raw materials of 5N high-purity Lu2O3, Al2O3, Nd2O3 and Sm2O3, and fabricate Nd 3+ doped Nd:LuAG crystal with a doping concentration of 0.5 at.% and Sm 3+ doped Sm:LuAG crystal with a doping concentration of 0.5 at.%.

[0019] S2. Crystal cutting and processing: Cut the Nd:LuAG crystal and Sm:LuAG crystal into five plate-shaped crystals, and polish all surfaces of the plate-shaped Nd:LuAG crystal and the bonding end faces of the Sm:LuAG crystal to ensure that the flatness N of the crystal polished surface reaches 0.08λ and the surface roughness Ra reaches 0.4 nm to meet the usage requirements of the laser crystal. The sizes of the five plate-shaped crystals are as follows: one Nd:LuAG crystal with a size of 100 mm × 60 mm × 0.2 mm; four Sm:LuAG crystals, two of which have sizes of 100 mm × 60 mm × 0.7 mm; and the other two Sm:LuAG crystals have sizes of 5 mm × 60 mm × 1.6 mm.

[0020] S3. Crystal surface cleaning: Put the polished crystals into deionized water, gasoline, and absolute ethanol in sequence for ultrasonic cleaning to remove the residues on the crystal surface (such as organic substances like residual abrasives and polishing fluids), and then dry the crystals. Among them, deionized water is mainly used for pre-cleaning to remove the abrasives on the crystal surface, and gasoline and absolute ethanol are mainly used to further remove some organic pollutants.

[0021] S4, Optical bonding: Take four dried Sm:LuAG crystals, and symmetrically attach their bonding end faces to the surface of the Nd:LuAG crystal to form a cladding structure with both ends exposed. Among them, the corresponding faces of a pair of symmetrically attached Sm:LuAG crystals and the Nd:LuAG crystal are coplanar and aligned, and the corresponding faces of the other pair of symmetrically attached Sm:LuAG crystals and the Nd:LuAG crystal and the combined crystal formed by the previous pair of symmetrically attached Sm:LuAG crystals are coplanar and aligned. Specifically, when attaching, first attach two Sm:LuAG crystals with dimensions of 100mm×60mm×0.7mm to the two 100mm×60mm faces of the Nd:LuAG crystal respectively, and make the peripheries of the attached Sm:LuAG crystals align with the peripheries of the Nd:LuAG crystal. Then attach two Sm:LuAG crystals with dimensions of 5mm×60mm×1.6mm to the two 60mm×1.6mm faces formed after the combination of the Nd:LuAG crystal and the attached Sm:LuAG crystals respectively, and make the peripheries of the Sm:LuAG crystals after attaching to the 60mm×1.6mm faces align with the peripheries of the combined crystal formed by the Nd:LuAG crystal and the attached Sm:LuAG crystals. Use the van der Waals force to closely bond the Sm:LuAG crystal, the Nd:LuAG crystal, and the adjacent two Sm:LuAG crystals. During the bonding process, uniformly squeeze out the air bubbles and liquid remaining on the bonding end faces. Subsequently, place it in a vacuum device and maintain it at a vacuum degree of 3 Pa for 90 min. During the bonding process, keep two opposite end faces of the Nd:LuAG crystal exposed because if the exposed end faces of the Nd:LuAG crystal are also bonded, the pump light will first pass through the cladding Sm:LuAG crystal and then through the Nd:LuAG crystal, which will affect the absorption efficiency of the Nd:LuAG crystal for the pump light.

[0022] S5, Heat treatment of the bonded crystal: Place the optically bonded crystal in a vacuum hot press furnace, start the vacuum system, and when the vacuum degree reaches 8×10 -4 Pa, perform a three-stage thermal diffusion treatment, that is, first slowly heat up to 850 °C at a speed of 0.5 °C / min, keep it warm for 10 h, apply a pressure of 60 kgf / cm 2 to the crystal material during both the heating and holding stages, and finally slowly cool down to room temperature at a speed of 0.5 °C / min to obtain the Nd:LuAG crystal material with a hetero-coating structure.

[0023] The Nd:LuAG crystal material with a hetero-coating structure prepared in this embodiment has an inner core (Nd:LuAG crystal) with dimensions of 100mm×60mm×0.2mm, and the formed cladding structure (the structure formed after the Sm:LuAG crystal coats the Nd:LuAG crystal) has dimensions of 110mm×60mm×1.6mm; and the thicknesses of any pair of symmetrically attached Sm:LuAG crystals are the same.

[0024] The structure of the Nd:LuAG crystal material with a heterogeneous coating structure prepared by the present invention is as shown in Figure 1 , Figure 2 shown.

[0025] Example 2 This example provides a preparation method of a Nd:LuAG crystal material with a heterogeneous coating structure, including the following steps: S1. Material preparation: Select 5N high-purity Lu2O3, Al2O3, Nd2O3, and Sm2O3 raw materials, and use the horizontal directional crystallization method to prepare Nd 3+ :LuAG crystals with a doping concentration of 1 at.% and Sm 3+ :LuAG crystals with a doping concentration of 0.8 at.%.

[0026] S2. Crystal cutting and processing: Cut the Nd:LuAG crystal and the Sm:LuAG crystal into five plate-shaped crystals, and polish all surfaces of the plate-shaped Nd:LuAG crystal and the bonding end faces of the Sm:LuAG crystal to ensure that the flatness N of the crystal polished surface reaches 0.06λ and the surface roughness Ra reaches 0.3 nm to meet the usage requirements of the laser crystal. The sizes of the five plate-shaped crystals are as follows: one Nd:LuAG crystal with a size of 80 mm × 50 mm × 0.1 mm; four Sm:LuAG crystals, two of which have sizes of 80 mm × 50 mm × 0.45 mm each; and the other two Sm:LuAG crystals have sizes of 5 mm × 50 mm × 1 mm each.

[0027] S3. Crystal surface cleaning: Put the polished crystals into deionized water, gasoline, and absolute ethanol in sequence for ultrasonic cleaning to remove the residues on the crystal surface, and then dry the crystals.

[0028] S4, Optical bonding: Take four dried Sm:LuAG crystals, symmetrically attach their bonding end faces to the surface of the Nd:LuAG crystal to form a cladding structure with both ends exposed. Among them, the corresponding faces of a pair of symmetrically attached Sm:LuAG crystals and the Nd:LuAG crystal are coplanarly aligned, and the corresponding faces of the other pair of symmetrically attached Sm:LuAG crystals and the Nd:LuAG crystal and the combined crystal formed by the previous pair of symmetrically attached Sm:LuAG crystals are coplanarly aligned. Specifically, when attaching, first attach two Sm:LuAG crystals with dimensions of 80mm×50mm×0.45mm to the two 80mm×50mm faces of the Nd:LuAG crystal respectively, and align the peripheries of the attached Sm:LuAG crystals with the peripheries of the Nd:LuAG crystal. Then attach two Sm:LuAG crystals with dimensions of 5mm×50mm×1mm to the two 50mm×1mm faces formed after combining the Nd:LuAG crystal and the already attached Sm:LuAG crystals respectively, and align the peripheries of the Sm:LuAG crystals after attaching to the 50mm×1mm faces with the peripheries of the combined crystal formed by the Nd:LuAG crystal and the already attached Sm:LuAG crystals. Use van der Waals force to closely bond the Sm:LuAG crystal, the Nd:LuAG crystal, and two adjacent Sm:LuAG crystals. During the bonding process, evenly squeeze out the air bubbles and liquid remaining on the bonding end face. Subsequently, place it in a vacuum device and maintain it at a vacuum degree of 2 Pa for 70 min.

[0029] S5, Heat treatment of the bonded crystal: Place the optically bonded crystal in a vacuum hot pressing furnace, start the vacuum system. When the vacuum degree reaches 6×10 -4 Pa, perform a three-stage thermal diffusion treatment, that is, first slowly heat it to 1000 °C at a speed of 0.5 °C / min, then keep it at this temperature for 20 h. Apply a pressure of 65 kgf / cm 2 to the crystal material during both the heating and holding stages. Finally, slowly cool it to room temperature at a speed of 0.5 °C / min to obtain the Nd:LuAG crystal material with a heterogeneous cladding structure.

[0030] The Nd:LuAG crystal material with a heterogeneous cladding structure prepared in this embodiment has an inner core (Nd:LuAG crystal) with dimensions of 80mm×50mm×0.1mm, and the formed cladding structure (the structure formed after the Sm:LuAG crystal coats the Nd:LuAG crystal) has dimensions of 90mm×50mm×1mm; and the thicknesses of any pair of symmetrically attached Sm:LuAG crystals are the same.

[0031] In fact, when preparing the Nd:LuAG crystal material with a heterogeneous coating structure by using the method of the present invention, there are no strict requirements for the sizes of the Nd:LuAG crystal and the Sm:LuAG crystal, which can be selected according to market demands. Generally speaking, when the Nd:LuAG crystal material with a heterogeneous coating structure has a relatively large length and a relatively small thickness, the characteristic of the small thickness can make the pump light power density very high when the crystal is pumped at high power and can reduce the rising value of the temperature, reducing the negative impacts caused by the thermal effect; while the relatively large length can increase the absorption length of the crystal, improve the absorption efficiency of the crystal, and thus increase the optical-optical conversion efficiency of the laser. However, when increasing the length of the bonding surface, the relatively large bonding area puts forward higher requirements for the bonding quality of the crystal, which will increase the difficulty of the bonding process. In addition, for the thickness of the coating layer, under the condition of absorbing the same pump power (i.e., absorbing the same amount of heat), increasing the thickness of the coating layer is beneficial to improving the uniformity of the temperature distribution, but this will reduce the coupling efficiency. Therefore, comprehensive consideration can be made according to actual needs during application.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solution shall be covered by the scope of the claims of the present invention.

Claims

1. A Nd:LuAG crystal material with a heterogeneous coating structure, characterized in that: The Nd:LuAG crystal comprises a layer of Sm:LuAG crystal coated on the surface of the Nd:LuAG crystal. 3+ The doping concentration is 0.5-10 at.%, and the Sm in the Sm:LuAG crystal is 3+ The doping concentration is 0.5~10at.%.

2. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 1, characterized in that: The preparation steps include: (1) Cutting Nd:LuAG crystal and Sm:LuAG crystal into strips, then polishing all surfaces of the strip-shaped Nd:LuAG crystal and the bonding end face of the Sm:LuAG crystal, and then cleaning the polished crystal material, drying it and setting it aside; (2) Take four dried Sm:LuAG crystals and attach their bonding end faces symmetrically to the surface of a Nd:LuAG crystal to form a cladding structure with two opposite end faces exposed, wherein one symmetrically attached Sm:LuAG crystal is coplanarly aligned with the corresponding face of the Nd:LuAG crystal, and another symmetrically attached Sm:LuAG crystal is coplanarly aligned with the corresponding face of the combined crystal formed by the Nd:LuAG crystal and the previous symmetrically attached Sm:LuAG crystal; use van der Waals force to make the Sm:LuAG crystal and the Nd:LuAG crystal and the two adjacent Sm:LuAG crystals fit tightly together, and evenly squeeze out the air bubbles and liquid remaining on the bonding end faces during the bonding process, and then place it under a vacuum degree of 1~3Pa for 70~90min; (3) Placing the crystal material obtained in step (2) in a working furnace and evacuating the working furnace until the vacuum degree is less than 1×10 -3 Pa, a three-stage thermal diffusion treatment was performed, first slowly heating to 850-1400°C at a rate of 0.3-0.7°C / min, then keeping at this temperature for 10-50h, and finally slowly cooling to room temperature at a rate of 0.3-0.7°C / min, thus obtaining a Nd:LuAG crystal material with a heterogeneous coating structure; during the thermal diffusion treatment, 55-80kgf / cm 2 pressure.

3. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 2, characterized in that: In step (2), when attaching the Sm:LuAG crystal, first attach the Sm:LuAG crystal to two opposite attachment surfaces of the Nd:LuAG crystal and align the attached Sm:LuAG crystal around with the Nd:LuAG crystal around. Then, attach the Sm:LuAG crystal to the remaining two attachment surfaces of the Nd:LuAG crystal and align the attached Sm:LuAG crystal around with the combined crystal formed by the Nd:LuAG crystal and the attached Sm:LuAG crystal around.

4. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 2, characterized in that: In step (1), the polished surface flatness N<0.1λ and the surface roughness Ra<0.5nm of the polished crystal material.

5. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 2, characterized in that: In step (1), the cleaning method is: placing the polished crystal material in deionized water, gasoline, and anhydrous ethanol in turn for ultrasonic cleaning to remove residues on the crystal surface.

6. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 2, characterized in that: In step (2), the exposed two end faces are the opposite two end faces of the strip-shaped Nd:LuAG crystal along the length direction or along the width direction.

7. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 6, characterized in that: In step (2), the thickness of any symmetrically attached Sm:LuAG crystals is the same.

8. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 7, characterized in that: In step (2), the thickness of the Sm:LuAG crystal symmetrically attached along the thickness direction of the Nd:LuAG crystal is smaller than the thickness of the Sm:LuAG crystal symmetrically attached along the length or width direction of the Nd:LuAG crystal.

9. The method for preparing the Nd:LuAG crystal material with a heterogeneous coating structure according to claim 2, characterized in that: In step (1), the Nd:LuAG crystal and the Sm:LuAG crystal are both prepared by horizontal directional crystallization method.

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