A rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal and a method of making the same

Abstract

The present application relates to a kind of rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal and its preparation method.The preparation method of the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal includes the following steps:(1) polishing, cleaning preparation rare earth doped alkaline earth fluoride RE:MF2 Crystal and alkaline earth fluoride MF2 Crystal pre-bonding piece of bonding surface;(2) RE:MF2 Crystal and MF2 Crystal pre-bonding piece is placed on the optical cement body with the direction of bonding surface opposite to each other with heat, pressure is applied to make the bonding surface of two crystals closely abut, obtain crystal optical cement pre-bonding piece;(3) crystal optical cement pre-bonding piece is fixed and by stainless steel spring perpendicular to bonding surface again 0.2-5MPa is applied pressure, MF2 Crystal powder is used to embed the crystal optical cement pre-bonding piece, heat treatment is carried out in muffle furnace at 400-650 ℃ temperature, obtain the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser crystal processing, and particularly relates to a rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal and a preparation method thereof. BACKGROUND

[0002] Alkaline earth fluoride (MF2) crystals have a face-centered cubic fluorite structure, are optically isotropic, have high thermal conductivity, a wide transmittance spectrum range, low effective phonon energy, and can be doped with high-concentration rare earth ions, and are therefore a kind of substrate crystal with excellent comprehensive performance. At present, rare earth doped alkaline earth fluoride (RE:MF2) crystals have achieved excellent laser performance in the visible light band, 1-micron near-infrared band and 2-3-micron mid-infrared band. In particular, in the mid-infrared band, Tm:SrF2 and Er:SrF2 crystals are the laser gain materials with the highest laser efficiency among the same type of crystals that have been reported.

[0003] However, the doping of rare earth ions will significantly reduce the thermal conductivity of the MF2 crystal, and the thermal expansion coefficient of the crystal is large, and under high-power optical pumping conditions, the thermal effect (including thermal lens and thermal stress birefringence) of the crystal will seriously deteriorate the quality of the generated laser beam, which is an important factor affecting its application in high-power lasers.

[0004] Since the undoped crystal has high thermal conductivity and extremely weak absorption of pump light, by bonding the doped crystal with the undoped crystal of the same substrate, the undoped crystal can act as a heat sink for the doped crystal, thereby improving the heat dissipation capacity of the pump end surface of the laser gain crystal element, and this scheme has been proven to significantly improve the thermal effect of the laser gain crystal. At present, there are documents and patents reporting the bonding process of rare earth doped crystals and pure crystals, including Nd:YAG / YAG, Nd:YVO4 / YVO4, Tm:LiYF4 / LiYF4, etc., but there is still a lack of effective process for RE:MF2 / MF2 crystal bonding. SUMMARY

[0005] In view of the above technical problems, the purpose of the present application is to provide a rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal and a preparation method thereof, so as to further prepare RE:MF2 / MF2 crystal bonded elements with high bonding strength and good optical uniformity.

[0006] In a first aspect, the present application provides a preparation method of a rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal, which comprises the following steps:

[0007] (1) polishing and cleaning the bonding surface to prepare a pre-bonding piece of a rare earth doped alkaline earth fluoride RE:MF2 crystal and an alkaline earth fluoride MF2 crystal;

[0008] (2) placing the RE:MF2 crystal and the pre-bonding piece of MF2 crystal in a direction that the bonding surfaces are opposite to each other on a light adhesive support, heating and applying pressure to make the bonding surfaces of the two crystals closely abut, to obtain a crystal light adhesive pre-bonding piece;

[0009] (3) fixing the crystal light adhesive pre-bonding piece and applying pressure of 0.2-5 MPa perpendicular to the bonding surface again by means of a stainless steel spring, embedding the crystal light adhesive pre-bonding piece with MF2 crystal powder, and heat treating in a muffle furnace at a temperature of 400-650 ℃, to obtain the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal.

[0010] Preferably, in step (1), the alkaline earth fluoride MF2 comprises CaF2, SrF2, BaF2, PbF2, and the doped rare earth element RE comprises at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y.

[0011] Preferably, in step (1), the pre-bonding surface is a square cross section with a side length ≤20 mm or a circular cross section with a diameter ≤Φ20 mm; preferably, the roughness of the polished bonding surface is less than 1 nm, and the flatness is less than λ / 10.

[0012] Preferably, in step (1), the cleaning process comprises: first ultrasonic cleaning in deionized water for 1-2 hours, then soaking in a 3-7 wt.% NaOH ethanol solution for 15-60 minutes, then cleaning with deionized water and then soaking in a 10-15 wt.% HCl aqueous solution for 10-60 minutes, and finally cleaning with ethanol and then spin-drying;

[0013] Preferably, the concentration of the NaOH ethanol solution is 4-5 wt.%, and the soaking time is 30 minutes; the concentration of the HCl aqueous solution is 10-13 wt.%, and the soaking time is 30 minutes.

[0014] Preferably, in step (2), the heating temperature is 100-110 ℃, and the heating time is 10-30 minutes, preferably 10-15 minutes.

[0015] Preferably, in step (2), the direction of the applied pressure is perpendicular to the bonding surface, and the applied pressure is 0.2-10 MPa, preferably 0.5-1 MPa.

[0016] Preferably, in step (3), the MF2 crystal powder used for embedding the crystal light adhesive pre-bonding piece has a particle size <1 mm.

[0017] Preferably, in step (3), the heat treatment process is: first heated to 400-650℃ at a heating rate of 2-10℃ / h, and then held for 10-30h, and then cooled to room temperature at a cooling rate of 1-5℃ / h, to complete the heat treatment and annealing of the crystal photo adhesive pre-bonding member.

[0018] In a second aspect, the present application provides a rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal obtained by the above preparation method.

[0019] Advantages

[0020] The rare earth doped alkaline earth fluoride crystal provided by the present application has high bonding strength and good optical uniformity, and the RE:MF2 / MF2 bonded crystal element prepared by the bonding process method of the pure alkaline earth fluoride crystal has high bonding strength and good optical uniformity; the heat treatment does not need to be carried out in high vacuum and fluorination conditions, and can effectively avoid oxidation of the bonded crystal, and the heat treatment and annealing of the bonded crystal are completed in one step, which greatly improves the bonding efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a physical photo of the crystal photo adhesive pre-bonding member after heat treatment in Example 1;

[0022] Figure 2 It is a photo of the Er:SrF2 / SrF2 bonded crystal element prepared after shaping in Example 1;

[0023] Figure 3 It is a photo of the Er:SrF2 / SrF2 bonded crystal element obtained in Comparative Example 1. DETAILED DESCRIPTION

[0024] The present application is further illustrated by the following examples, which should be understood as merely illustrative of the present application, but not limiting the present application.

[0025] Hereinafter, the preparation method of the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal provided by the present application is exemplarily described. The preparation method can include the following steps:

[0026] (1) Process the embryo materials of the rare earth doped alkaline earth fluoride RE:MF2 crystal and the alkaline earth fluoride MF2 crystal to the required size, and polish the bonding surfaces of the two crystals, and then clean to obtain a pre-bonding member;

[0027] (2) Place the pre-bonding member of the RE:MF2 crystal and the MF2 crystal on the photo adhesive support in a direction that the bonding surfaces are opposite to each other, and heat on a temperature-controlled hot plate, and at the same time, apply a pressure perpendicular to the bonding surfaces to make the bonding surfaces of the two crystals tightly abut and be coupled together by intermolecular forces, to obtain a crystal photo adhesive pre-bonding member;

[0028] (3) fixing the crystal photo-bonding piece and applying pressure of 0.2-5 MPa perpendicular to the bonding surface by means of stainless steel springs, embedding the crystal photo-bonding piece with MF2 crystal powder, and performing heat treatment at a temperature of 400-650°C in a muffle furnace to obtain the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal.

[0029] In some embodiments, in step (1), the alkaline earth fluoride MF2 can include CaF2, SrF2, BaF2, PbF2, and the doped rare earth element RE can include at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y; preferably, the doping molar percentage of the rare earth element in the rare earth doped alkaline earth fluoride RE:MF2 crystal can be 0.1-20%.

[0030] In some embodiments, in step (1), the pre-bonding surface can be a square cross-section with a side length of ≤20 mm or a circular cross-section with a diameter of ≤Φ20 mm; preferably, the roughness of the polished bonding surface is less than 1 nm, and the flatness is less than λ / 10. If the shape, roughness, and flatness of the bonding surface are not suitable, the photo-bonding effect will not be ideal, air holes will easily appear between the photo-bonding surfaces, or the photo-bonding strength will be low, and the photo-bonding will be opened during the heat treatment process.

[0031] In some embodiments, in step (1), the cleaning process can include: first, ultrasonic cleaning in deionized water for 1-2 hours, then soaking in a 3-7 wt.% NaOH ethanol solution for 15-60 minutes, then cleaning with deionized water and then soaking in a 10-15 wt.% HCl aqueous solution for 10-60 minutes, and finally cleaning with ethanol and then spin-drying; preferably, the concentration of the NaOH ethanol solution is 4-5 wt.%, and the soaking time is 30 minutes; the concentration of the HCl aqueous solution is 10-13 wt.%, and the soaking time is 30 minutes.

[0032] The cleaning process can promote the removal of particles and contaminants on the pre-bonding surface, and obtain a relatively ideal clean pre-bonding surface. If the cleaning process is not proper, the photo-bonding effect will not be ideal, air holes will easily appear between the photo-bonding surfaces, or the photo-bonding strength will be low, and the photo-bonding will be opened during the heat treatment process.

[0033] In addition, the crystal photo-bonding process can bond the pre-bonding surfaces together through intermolecular forces, so that a firm bond is formed through further heat treatment. Directly annealing after contacting the pre-bonding surfaces cannot achieve good bonding effect.

[0034] In some embodiments, in step (2), the temperature of the temperature-controlled hot plate can be 100-110℃, and the heating time on the temperature-controlled hot plate can be 10-30 minutes, preferably 10-15 minutes. By adjusting the temperature of the hot plate, water and organic solvents on the pre-bonding surface can be effectively removed. If the temperature / time is too short, the removal can be incomplete, and if the temperature / time is too long, the efficiency can be affected.

[0035] In some embodiments, in step (2), the pressure applied perpendicular to the bonding surface can be 0.2-10 MPa, preferably 0.5-1 MPa.

[0036] In some embodiments, in step (3), before the heat treatment, the crystal photo-adhesive pre-bonding piece can be embedded with MF2 crystal powder having a particle size of <1 mm.

[0037] It should be noted that, in general, fluorite crystals react with oxygen in the air when heated in air, which can reduce the optical quality of the crystals. Therefore, heat treatment of fluorite crystals is usually carried out in high vacuum or special atmosphere. However, the technical solution disclosed in the present application carries out heat treatment of the bonded crystal in air. On the one hand, the heat treatment temperature used in the present application is relatively low, and the reaction of MF2 crystal with oxygen is very slow at this temperature. On the other hand, by embedding the bonded crystal with MF2 crystal powder (which is more prone to react with oxygen), the oxidation of the bonded crystal by oxygen can be further reduced. Moreover, by limiting the particle size of the MF2 crystal powder to <1 mm, the embedding of the bonded crystal by the powder can be more compact, and the anti-oxidation effect can be better.

[0038] In some embodiments, in step (3), the heat treatment process can be: first heated to 400-650℃ at a heating rate of 2-10℃ / hour, held for 10-30 hours, and then cooled to room temperature at a cooling rate of 1-5℃ / hour, to complete the heat treatment and annealing of the crystal photo-adhesive pre-bonding piece.

[0039] The heat treatment temperature is related to the physical and chemical properties of the crystal itself (the melting point of MF2 crystal is about 1400℃). The lower heat treatment temperature proposed in the present application can achieve the bonding effect, while effectively avoiding the problem of crystal oxidation during heat treatment. If the heat treatment temperature is too low, the bonding strength can be low. If the heat treatment temperature is too high, the thermal stress on the bonding surface can be large, and the crystal can be oxidized. In addition, the heating / cooling rate should not be too fast, otherwise thermal stress can be formed in the crystal, leading to bonding failure.

[0040] In summary, the preparation method disclosed by the application performs heat treatment on fluoride crystals under air condition, effectively avoids oxidation of bonded crystals, and completes heat treatment and annealing of bonded crystals in one step, thereby improving bonding efficiency. The RE:MF2 / MF2 crystal bonded element obtained by the preparation method has high bonding strength and good optical uniformity. The conventional heat treatment of fluoride crystals is usually performed in vacuum or special atmosphere to prevent oxidation of the crystals. The method disclosed by the application performs heat treatment under air, and can be completed by using an ordinary muffle furnace, thereby having low requirement on equipment, low heat treatment cost and high efficiency. The bonding strength of the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal obtained by the preparation method is equivalent to that of a pure matrix crystal.

[0041] The following further illustrates the embodiments to explain the application in detail. It should be understood that the following embodiments are only used to further explain the application, and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the application all belong to the protection scope of the application. The specific process parameters and the like in the following examples are only one example in the appropriate range, that is, those skilled in the art can make appropriate selection in the range through the description herein, and are not limited to the specific values in the following examples. If not specifically indicated, the technical means used in the examples is the conventional means familiar to those skilled in the art.

[0042] Example 1

[0043] The preparation method of the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal provided in the embodiment includes the following steps:

[0044] (1) An inner circle cutting machine is used to cut the Er:SrF2 crystal and the pure SrF2 crystal into a square column crystal block with a size of 6mm*6mm*11mm, and a W50 and W20 CeO2 polishing liquid is used to coarsely and finely polish the pre-bonding end face, respectively, and the length of the crystal block is polished to 10mm; then a diamond polishing liquid is used to polish the bonding surface to a roughness of less than 1nm and a flatness of less than λ / 10; after the polished Er:SrF2 crystal and the pure SrF2 crystal pre-bonding piece are ultrasonically cleaned in deionized water for 1 hour, they are immersed in a 5wt.% NaOH ethanol solution for 30 minutes, cleaned with deionized water, and then immersed in a 12wt.% HCl aqueous solution for 30 minutes, finally cleaned with ethanol and dried, to obtain the pre-bonding piece;

[0045] (2) The Er:SrF2 crystal and the pure SrF2 crystal pre-bonding piece are placed on a photo adhesive support, and heated together on a temperature-controlled hot plate at 100℃ for 15 minutes, then a pressure of 0.5MPa is applied to the crystals to make the bonding surfaces tightly contact and form a photo adhesive, to obtain a crystal photo adhesive pre-bonding piece;

[0046] (3) Fix the Er:SrF2 / SrF2 crystal after optical cementing with stainless steel clamp, and apply 0.2 MPa pressure through spring vertical bonding surface, and place the whole in a cylindrical alumina crucible, and embed the Er:SrF2 / SrF2 crystal with SrF2 powder with particle size <1 mm, and cover the crucible cover; place the crucible in a muffle furnace, close the furnace cover after installing the insulation layer, heat the crucible to 500℃ at a heating rate of 10℃ / hour, keep constant temperature for 24 hours, then reduce to room temperature at a rate of 5℃ / hour, complete the heat treatment and annealing of the crystal optical cementing pre-bonding piece; grind the Er:SrF2 / SrF2 bonded crystal with W50 and W20 CeO2 grinding liquid respectively for coarse grinding and fine grinding, grind the cross section of the bonded crystal to 5mm×5mm, and obtain an Er:SrF2 / SrF2 bonded crystal with a size of 5mm×5mm×20mm and a length of 10mm for each of Er:SrF2 and SrF2.

[0047] Figure 1 It is the physical photo of the crystal optical cementing pre-bonding piece after completing the heat treatment in Example 1. As can be seen from the figure, the bonding surface is well bonded, and there is no edge opening problem, and the crystal is not obviously oxidized.

[0048] Figure 2 It is the photo of the Er:SrF2 / SrF2 bonded crystal element prepared after shaping in Example 1. As can be seen from the figure, the crystal bonding quality is good, the bonding surface interface is clear, and there is no air hole and opening problem in the whole bonding surface; the bonding strength is high, and the sample does not open after polishing and polishing.

[0049] Comparative Example 1

[0050] The preparation method of the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal provided in this comparative example refers to the example, the main difference is that in step (3), the heat treatment temperature is 700℃.

[0051] Figure 3 It is the photo of the Er:SrF2 / SrF2 bonded crystal element obtained in Comparative Example 1. As can be seen from the figure, there is obvious stress near the bonding interface, which is caused by the too high heat treatment temperature.

[0052] Although the content of the present application has been described in detail through the above preferred examples, it should be recognized that the above description should not be considered as a limitation of the present application. After reading the above content, various modifications and alternatives of the present application will be obvious to those skilled in the art. Therefore, the protection scope of the present application should be defined by the appended claims.

Claims

1. A method for producing a rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal, characterized by, The preparation method comprises the following steps: (1) polishing and cleaning bonding surfaces to prepare pre-bonded parts of rare earth doped alkaline earth fluoride RE:MF2 crystals and alkaline earth fluoride MF2 crystals; (2) placing the pre-bonded parts of RE:MF2 crystals and MF2 crystals on a photoresist supporting body in a direction that the bonding surfaces are oppositely attached, heating and applying pressure to make the bonding surfaces of the two crystals closely abut, and obtaining a crystal photoresist pre-bonded part; (3) fixing the crystal photoresist pre-bonded part, applying pressure of 0.2-5 MPa vertically to the bonding surface again by means of a stainless steel spring, embedding the crystal photoresist pre-bonded part with MF2 crystal powder, heating to 400-650 ℃ at a heating rate of 2-10 ℃ / h in a muffle furnace, keeping the temperature for 10-30 hours, and then reducing to room temperature at a rate of 1-5 ℃ / h, completing heat treatment and annealing of the crystal photoresist pre-bonded part, and obtaining the rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal.

2. The production method according to claim 1, characterized by, In step (1), the alkaline earth fluoride MF2 comprises CaF2, SrF2 and BaF2, and the doped rare earth element RE comprises at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y.

3. The production method according to claim 1, characterized by, In step (1), the pre-bonding surface is a square section with a side length of ≤20 mm or a circular section with a diameter of ≤Φ20 mm; the roughness of the polished bonding surface is less than 1 nm, and the flatness is less than λ / 10.

4. The method of claim 1, wherein, In step (1), the cleaning process comprises the following steps: first, ultrasonic cleaning in deionized water for 1-2 hours, then soaking in a 3-7 wt.% NaOH ethanol solution for 15-60 minutes, then cleaning with deionized water and then soaking in a 10-15 wt.% HCl aqueous solution for 10-60 minutes, and finally cleaning with ethanol and then spin-drying.

5. The preparation method according to claim 4, characterized in that, The concentration of the NaOH ethanol solution is 4-5 wt.%, and the soaking time is 30 minutes; the concentration of the HCl aqueous solution is 10-13 wt.%, and the soaking time is 30 minutes.

6. The method of claim 1, wherein, In step (2), the heating temperature is 100-110 ℃, and the heating time is 10-30 minutes.

7. The production method according to claim 6, wherein The heating time is 10-15 minutes.

8. The method of claim 1, wherein, In step (2), the pressure applying direction is perpendicular to the bonding surface, and the applied pressure is 0.2-10 MPa.

9. The production method according to claim 8, characterized by, The applied pressure is 0.5-1 MPa.

10. The method of claim 1, wherein, In step (3), the particle size of the MF2 crystal powder used for embedding the crystal photoresist pre-bonded part is <1 mm.

11. A rare earth doped alkaline earth fluoride / alkaline earth fluoride bonded crystal obtained by the preparation method according to claim 1.

Images