A bonded crystal and its preparation method

Abstract

The present invention discloses a bonded crystal and a preparation method thereof. By polishing the end faces of the crystals to be bonded, cleaning them and then fixing them together, heating the end faces to be bonded until they melt, and then slowly cooling until crystal growth is completed, and then annealing is carried out. The bonding position of the bonded crystal obtained by this method has a uniform transition, low thermal effect, is not prone to cracking, and significantly improves the laser efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal preparation, and in particular to a bonded crystal and a preparation method thereof. Background Art

[0002] A bonded crystal is a product in which a laser crystal and one or two pieces of homogeneous substrate materials are firmly bonded through a bonding technique. Experiments show that the bonded crystal can effectively reduce the temperature of the laser crystal, reduce the influence of the thermal lens effect caused by end-face deformation, improve the light-light conversion efficiency, increase the optical damage threshold, improve the output beam quality of the laser, and reduce the volume of the laser.

[0003] In the traditional crystal bonding process, by applying an external pressure perpendicular to the bonding surface, the two crystals to be bonded are tightly attached together, and then the temperature is raised to near the melting point, so as to realize the mutual penetration of ions at the bonding surface. This method has certain drawbacks. For example, the gas trapped in the bonding surface is difficult to diffuse out, and the uneven pressure easily causes tiny cracks on the bonding surface. In addition, the thermal effect near the bonding surface of the bonded crystal is still relatively significant, and the crystal is easily cracked. Therefore, it is necessary to design a new preparation method for bonded crystals. Summary of the Invention

[0004] To solve the above problems, the present invention provides a bonded crystal and a preparation method thereof.

[0005] In view of the problems existing in the prior art, the present invention provides the following technical solutions:

[0006] A preparation method for a bonded crystal, comprising:

[0007] Polishing the end faces of the crystals to be bonded, fixing them together after cleaning, heating the end faces to be bonded until melting, and slowly cooling until crystal growth is completed, and then annealing the obtained crystal to eliminate the thermal stress of the crystal.

[0008] Preferably, the bonded crystals are crystals of the same matrix and the same direction. Only crystals of the same matrix and the same direction can obtain a complete single crystal during dissolution and crystallization, thereby fundamentally avoiding problems such as birefringence and bubbles at the bonding interface, avoiding crystal cracking, and improving the quality of the laser beam.

[0009] Preferably, the preparation of the bonded crystal is carried out in a floating zone furnace.

[0010] Preferably, the rate of slow cooling is 0.1 - 0.5 °C / h. After the crystal at the bonding site melts, the doping medium in the crystal is evenly distributed in the melting zone. By growing the crystal through cooling, a single crystal can be obtained, enabling the doping concentration at the crystal bonding site to gradually change, forming a transition zone, thereby avoiding the accumulation of thermal effects at this location. In addition, at this cooling rate, high-quality crystals can be obtained.

[0011] Preferably, the annealing temperature is 70 - 90% of the crystal melting point. After crystal growth in a floating zone furnace, there are significant thermal stresses inside the crystal, which need to be eliminated through annealing to avoid cracking during subsequent processing and laser operation. Annealing at this temperature can ensure that the internal stress of the crystal is fully released while avoiding creep failure of the crystal.

[0012] Preferably, the annealing time is 24 - 72 h. Annealing within this time can release all the internal stress of the crystal.

[0013] Specifically, the crystals to be bonded are at least one of YAG and YVO 4 These crystals can be doped crystals or undoped crystals.

[0014] Preferably, the preparation of the bonded crystal is carried out in an air atmosphere.

[0015] As a general inventive concept, the present invention also provides a bonded crystal obtained by the above preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The preparation method of the bonded crystal in the present invention improves the existing preparation method of bonded crystals, eliminates the interface of the bonded crystal, and avoids problems such as stress, bubbles, and reduced efficiency caused by the existence of the bonding interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is a diagram of the laser slope efficiency of the bonded crystals prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following further elaborates on the technical solutions of the present invention through specific embodiments.

[0021] Example 1

[0022] An embodiment of the bonded crystal of the present invention. The preparation method of the bonded crystal in this embodiment is as follows:

[0023] Polish the end faces of <111>-oriented Nd:YAG and <111>-oriented YAG crystals, fix them together after cleaning, heat the end faces to be bonded to 1950 °C and melt them using a floating zone furnace, and slowly cool at a rate of 0.5 °C / h until crystal growth is completed. Then, anneal the obtained crystal in an annealing furnace at an annealing temperature of 1560 °C for 24 h to eliminate the thermal stress of the crystal.

[0024] The crystal prepared by the above method has no defects such as cracks and bubbles. The laser slope efficiency of the bonded crystal obtained in this embodiment is 28%.

[0025] Comparative Example 1

[0026] A preparation method of a bonded crystal, including:

[0027] Polish the end faces of <111>-oriented Nd:YAG and <111>-oriented YAG crystals, then closely attach the crystal surfaces together, put the whole into a vacuum device to evacuate, with a vacuum degree of 3 Pa, and maintain for 30 min; then put the crystal into a bonding furnace, evacuate, fill with nitrogen, and perform pressure pre-bonding at 20 °C, uniformly apply a pressure of 15 kg / cm 2 on the crystal surface, and keep for 2.5 hours; then raise the temperature to 600 °C, and uniformly apply 42 kg / cm 2 on the crystal surface, and keep for 1 hour; then cool down to 180 °C, and uniformly apply 50 kg / cm 2 on the crystal surface, and keep for 4 hours; finally raise the temperature to 1000 °C, uniformly apply 75 kg / cm 2 on the crystal surface, and keep for 1 hour, and then cool naturally to room temperature. Then, anneal the obtained crystal in an annealing furnace at an annealing temperature of 1560 °C for 24 h to eliminate the thermal stress of the crystal. The laser slope efficiency of the bonded crystal obtained in this comparative example is 23%.

[0028] Example 2

[0029] An embodiment of the bonded crystal of the present invention. The preparation method of the bonded crystal in this embodiment is as follows:

[0030] <100>-oriented Nd:YVO 4 and <100>-oriented YVO 4The crystal end faces are polished, fixed together after being cleaned, and the end faces to be bonded are heated to 1825 °C and melted using a floating zone furnace, and then slowly cooled at a rate of 0.1 °C / h until crystal growth is completed. After that, the obtained crystal is annealed in an annealing furnace at an annealing temperature of 1460 °C for 72 h to eliminate the thermal stress of the crystal.

[0031] The crystal prepared by the above method has no defects such as cracks and bubbles.

[0032] Comparative Example 2

[0033] The preparation method of the bonded crystal in this comparative example is as follows:

[0034] The end faces of <111>-oriented Nd:YAG and <111>-oriented YAG crystals are polished, fixed together after being cleaned, and the end faces to be bonded are heated to 1950 °C and melted using a floating zone furnace, and then slowly cooled at a rate of 0.6 °C / h until crystal growth is completed. After that, the obtained crystal is annealed in an annealing furnace at an annealing temperature of 1560 °C for 24 h to eliminate the thermal stress of the crystal.

[0035] The crystal prepared by the above method is cracked and the experiment fails.

[0036] Comparative Example 3

[0037] The preparation method of the bonded crystal in this comparative example is as follows:

[0038] The end faces of <100>-oriented Nd:YVO 4 and <100>-oriented YVO 4 crystals are polished, fixed together after being cleaned, and the end faces to be bonded are heated to 1825 °C and melted using a floating zone furnace, and then slowly cooled at a rate of 0.1 °C / h until crystal growth is completed. After that, the obtained crystal is annealed in an annealing furnace at an annealing temperature of 1180 °C for 72 h to eliminate the thermal stress of the crystal.

[0039] The crystal prepared by the above method cracks in the laser laboratory and the experiment fails.

[0040] Comparative Example 4

[0041] The preparation method of the bonded crystal in this comparative example is as follows:

[0042] The end faces of <111>-oriented Nd:YAG and <100>-oriented YAG crystals are polished, cleaned, and then fixed together. Using a floating zone furnace, the end faces to be bonded are heated to 1950 °C and melted, and then slowly cooled at a rate of 0.5 °C / h until crystal growth is completed. After that, the obtained crystal is annealed in an annealing furnace at an annealing temperature of 1560 °C for 24 h to eliminate the thermal stress of the crystal.

[0043] The crystal prepared by the above method cracked, and the experiment failed.

[0044] Comparative Example 5

[0045] The method for preparing the bonded crystal in this comparative example is as follows:

[0046] The end faces of <100>-oriented Nd:YVO 4 and <100>-oriented YVO 4 crystals are polished, cleaned, and then fixed together. Using a floating zone furnace, the end faces to be bonded are heated to 1825 °C and melted, and then slowly cooled at a rate of 0.1 °C / h until crystal growth is completed. After that, the obtained crystal is annealed in an annealing furnace at an annealing temperature of 1460 °C for 12 h to eliminate the thermal stress of the crystal.

[0047] The crystal prepared by the above method cracked in the laser laboratory, and the experiment failed.

[0048] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a bonded crystal, characterized in that, comprising: Polish the end faces of the crystals to be bonded, fix them together after cleaning, heat the end faces to be bonded until they melt, and then slowly cool them until crystal growth is completed. Then anneal the obtained crystals. The crystals to be bonded are crystals of the same matrix and the same direction. The rate of slow cooling is 0.1 - 0.5 °C / h. The annealing temperature is 70 - 90% of the melting point of the crystal. The annealing time is 24 - 72 h. The crystals to be bonded are at least one of YAG and YVO 4 in.

2. The method for preparing a bonded crystal according to claim 1, characterized in that, the preparation of the bonded crystal is carried out in a floating zone furnace.

3. The method for preparing a bonded crystal according to claim 1 or 2, characterized in that, the preparation of the bonded crystal is carried out in an air atmosphere.

4. A bonded crystal, characterized in that, it is prepared by using the preparation method according to any one of claims 1-3.

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