Growth preparation method of laser self-frequency-doubling crystal

Abstract

The invention discloses a growth preparation method of a laser self-frequency-doubling crystal. The growth preparation method comprises the following steps: S1, preparing a rare earth calcium borate oxide crystal melt; fixing a seed crystal on a lifting device, and enabling the seed crystal to be in contact with the surface of the melt so as to ensure good initial contact and a growth starting point; slowly lifting the seed crystal, and controlling the lifting speed and the temperature gradient, so that the crystal stably grows; temperature oscillation parameters are set, the temperature oscillation parameters comprise the amplitude, the frequency and the period of temperature change, and ultrasonic assistance is introduced in each temperature oscillation period in a staged mode; when each temperature oscillation period is finished, performing seed crystal reentry operation; and after the predetermined growth cycle is completed, naturally cooling the growth equipment, taking out the crystal, cleaning and drying the crystal, and machining the crystal to prepare the laser self-frequency-doubling crystal. According to the growth preparation method of the laser self-frequency-doubling crystal, a seed crystal reentry method and a temperature oscillation method are combined, and ultrasonic assistance is introduced, so that the growth efficiency and the crystal quality are improved.

Description

Technical Field

[0001] The invention relates to the technical field of crystal growth, and in particular to a method for growing and preparing a laser self-frequency doubling crystal. Background Art

[0002] Laser self-doubling crystal is an optical material that can realize the conversion of fundamental frequency light to second harmonic within a single material. It has a wide range of applications, especially in green and yellow lasers. The traditional frequency doubling process usually requires the use of two different crystals to generate fundamental frequency light and second harmonic respectively. The self-doubling crystal integrates laser emission and nonlinear optical frequency doubling functions into one crystal, simplifying the structure of the laser system and improving the stability and reliability of the system.

[0003] Traditional crystal growth methods, such as the Czochralski method and the crucible descent method, have certain limitations in the preparation of high-quality laser self-doubling crystals. Traditional methods may introduce dislocations, bubbles and other microscopic defects inside the crystal, which will seriously affect the optical properties of the crystal, leading to increased light scattering and absorption, thereby reducing the doubling efficiency. The presence of impurities will also change the local chemical environment of the crystal, causing unnecessary optical absorption or scattering, further weakening its performance. Due to the difference in temperature gradient and cooling rate, traditional methods are prone to generate stress and strain inside the crystal, especially during rapid cooling, which can cause the crystal to deform or crack. Internal stress can affect the optical uniformity and mechanical strength of the crystal, reducing its long-term stability and reliability. In order to ensure crystal quality, traditional methods often use slower growth rates, but this increases production cycle and cost. Increasing the growth rate may lead to more defects and sacrifice crystal quality.

[0004] Therefore, it is necessary to improve a method for growing and preparing a laser self-frequency doubling crystal in the prior art to solve the above problems. Summary of the invention

[0005] The present invention overcomes the shortcomings of the prior art and provides a method for growing and preparing a laser self-frequency doubling crystal, aiming to solve the problem of improving the growth efficiency and quality of the crystal in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for growing and preparing a laser self-frequency doubling crystal, comprising:

[0007] S1, preparing a calcium borate oxy-rare earth salt crystal melt;

[0008] S2, fixing the seed crystal on the pulling device, the seed crystal contacts the melt surface to ensure good initial contact and growth starting point;

[0009] S3, slowly lift the seed crystal, control the pulling speed and temperature gradient, and make the crystal grow steadily;

[0010] S4, setting temperature oscillation parameters, including: the amplitude, frequency and period of temperature change, introducing ultrasonic assistance in stages within each temperature oscillation period; performing seed crystal re-entry operation at the end of each temperature oscillation period;

[0011] S5. After the predetermined growth cycle is completed, the growth equipment is cooled naturally, the crystal is taken out for cleaning and drying, and the crystal is mechanically processed to prepare a laser self-frequency doubling crystal.

[0012] In a preferred embodiment of the present invention, in step S1, the preparation method of calcium borate rare earth salt crystals is:

[0013] Boric acid, calcium oxide and rare earth oxide are selected as raw materials for preparation, wherein the molar ratio of H3BO3, CaO, Nd2O3, Tb4O7 and CeO2 is: 1: 6-6.5: 0.02-0.03: 0.005-0.015: 0.01-0.03;

[0014] Grind the raw materials according to the molar ratio and mix them. Put the mixed powder into a crucible and heat it in a high-temperature furnace to 1100-1300℃ to completely melt it. Connect a vacuum pump and reduce the pressure to 10 -2 -10 -13 The support allows the gas dissolved in the melt to escape, forming a stable melt without bubbles, and then high-purity inert gas is introduced to restore normal pressure.

[0015] In a preferred embodiment of the present invention, in step S2,

[0016] S21, using an ultrasonic cleaner and a high-purity solvent to thoroughly clean and dry the seed crystal to remove impurities and contaminants on the surface;

[0017] S22, fixing the seed crystal on the pulling device so that the seed crystal can move freely in the vertical direction, and the melt is below the seed crystal;

[0018] S23. Slowly lower the seed crystal so that the tip of the seed crystal contacts the melt surface. The seed crystal stays on the melt surface for 3-5 minutes to make the melt surface temperature evenly distributed. Rotate the seed crystal at a speed of 1-3 rpm so that the melt forms a more uniform wetting layer on the seed crystal surface, thereby promoting the stability of initial crystal growth.

[0019] In a preferred embodiment of the present invention, in step S3, the seed crystal is slowly lifted to gradually leave the melt surface, and the pulling speed is 0.5-5 mm / h; the temperature gradient between the melt surface and the seed crystal is kept constant, and the temperature gradient is 1-5°C / cm.

[0020] In a preferred embodiment of the present invention, in step S4, the frequency of each oscillation cycle is 2-3 times / day, and a complete oscillation cycle includes a heating stage, a heat preservation stage and a cooling stage, with a total duration of 9-12 hours.

[0021] In a preferred embodiment of the present invention, in step S4, for the calcium borate rare earth salt crystal, the temperature variation range of the melt near the crystal growth interface is ±10°C.

[0022] In a preferred embodiment of the present invention, the melt temperature near the crystal growth interface is increased by 2°C at a rate of 0.5°C / h during the heating stage, and then enters the insulation stage where the temperature remains constant, and finally the temperature is reduced by 2°C at a rate of 0.5°C / h to complete a complete oscillation cycle.

[0023] In a preferred embodiment of the present invention, the ultrasonic wave with a frequency of 40-60kHz and a power density of 1-3W / cm 2 ;

[0024] The heat preservation stage uses ultrasonic waves with a frequency of 20-40kHz and a power density of 0.5-1.5W / cm 2 ;

[0025] During the cooling stage, the ultrasonic frequency is 20-40kHz, and the temperature is reduced by 0.5-1W / cm per hour. 2 until the ultrasound stops.

[0026] In a preferred embodiment of the present invention, in step S4, after the cooling stage is over, the seed crystal is re-entered, and the seed crystal is lowered to a depth of 2-5 mm in the melt at a speed of 0.5-1 mm / min, and the seed crystal is allowed to stay in the melt for 1-3 minutes to ensure full contact with the melt and repair the growth interface, and then the seed crystal is lifted back to its original position at a speed of 1-2 mm / min. The frequency of seed crystal re-entry is 1-3 times / day.

[0027] In a preferred embodiment of the present invention, in step S4, after the seed crystal is restored to its original position, the temperature is oscillated again to start a new oscillation cycle.

[0028] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0029] (1) The present invention proposes a method for growing and preparing laser self-frequency doubling crystals, which combines the seed crystal re-entry method and the temperature oscillation method, and introduces ultrasonic assistance to improve the growth efficiency and crystal quality. The specific technical scheme includes: preparing a calcium borate rare earth salt crystal melt; fixing the seed crystal on a pulling device after cleaning and drying, and ensuring that the seed crystal is in good contact with the melt surface; slowly lifting the seed crystal, controlling the pulling speed and temperature gradient, so that the crystal grows smoothly; setting the temperature oscillation parameters, and introducing ultrasonic assistance in stages within each temperature oscillation cycle, and performing a seed crystal re-entry operation at the end of the cycle; after completing the predetermined growth cycle, naturally cooling the growth equipment, taking out the crystal for cleaning, drying and mechanical processing, and finally preparing a high-quality laser self-frequency doubling crystal.

[0030] (2) The present invention realizes multiple optimizations in the crystal growth process by combining the seed crystal re-entry method and the temperature oscillation method and introducing ultrasonic assistance; the seed crystal re-entry method ensures the continuity and directionality of crystal growth and reduces internal defects; the temperature oscillation method optimizes the internal stress distribution of the crystal by periodically changing the temperature, thereby improving the uniformity and quality of the crystal; the ultrasonic assistance promotes the uniform distribution of solutes in the melt and enhances the stability of the growth interface; the combination of these three directly improves the growth efficiency and quality of the crystal, and compared with the prior art, further achieves the effect of high-efficiency and high-quality growth of laser self-doubling crystals.

[0031] (3) The present invention optimizes the initial conditions and growth environment of crystal growth by precisely controlling the contact, rotation and pulling processes of the seed crystal in steps S2 and S3. The thorough cleaning and drying of the seed crystal removes impurities and contaminants on the surface, ensuring the purity of crystal growth. The residence and rotation of the seed crystal on the melt surface promote the uniform wetting of the melt on the seed crystal surface, improving the stability of initial crystal growth. The slow and constant pulling speed and temperature gradient ensure the uniformity and integrity of the internal structure of the crystal, effectively reducing defects such as bubbles and cracks during the crystal growth process, and improving the overall quality of the crystal.

[0032] (4) The present invention achieves fine control over the crystal growth process by introducing temperature oscillation and ultrasonic assistance in step S4. The temperature oscillation affects the formation and quality of the crystal by periodically changing the temperature of the growth environment; the ultrasonic assistance promotes the uniform distribution of the solute in the melt by generating cavitation effect and microjets; the different combined application of the two in the heating, insulation and cooling stages not only accelerates the redissolution and uniform distribution of the solute, but also maintains the stability of the growth interface, so that the crystal can grow in a more optimized environment. Compared with the prior art, the combination of this step significantly improves the growth efficiency and optical properties of the crystal.

[0033] (5) In step S1 of the present invention, the accuracy and uniformity of the crystal composition are ensured by precisely controlling the molar ratio of the raw materials and the smelting process. Boric acid, calcium oxide and rare earth oxide are selected as the raw materials for preparation, and their molar ratio is strictly set. Then, the gas in the melt is removed through high-temperature smelting and vacuum treatment, forming a stable and bubble-free melt. This step is combined with the subsequent crystal growth step to ensure that the crystal can continuously and stably obtain the required components during the growth process, achieve a high degree of uniformity and purity of the crystal composition, and further improve the optical properties of the crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 is a flow chart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0038] Application Overview:

[0039] Laser self-doubling crystals are a type of composite functional crystals with unique properties. They not only have laser activity, but also exhibit significant nonlinear optical effects. They can directly convert the fundamental laser emitted by the laser into doubled-frequency light, including green and yellow lasers, through nonlinear optical effects. Traditional crystal growth methods, such as the pulling method and the crucible descent method, have certain limitations in the preparation of high-quality laser self-doubling crystals.

[0040] The seed crystal re-entry method is a crystal growth technology that reintroduces pre-prepared seed crystals into the molten crystal raw materials to guide the crystal to grow in a predetermined direction and reduce internal defects. Due to the influence of factors such as heat exchange and material diffusion between the seed crystal and the melt, the crystal growth will be uneven. The temperature oscillation method is a technology that affects the growth rate and crystal structure of the crystal by periodically changing the growth temperature of the crystal. It controls the state of the growth interface and can optimize the internal stress distribution of the crystal, but it will cause fluctuations in the crystal growth rate, increase the growth time, and reduce efficiency.

[0041] Therefore, the present application proposes a method for preparing a self-frequency doubling crystal that combines the seed crystal re-entry method and the temperature oscillation method, introduces ultrasonic assistance, improves the growth efficiency, and achieves high-quality and high-efficiency growth of laser self-frequency doubling crystals.

[0042] Exemplary methods:

[0043] like Figure 1 As shown, a method for growing and preparing a laser self-frequency doubling crystal comprises the following steps:

[0044] S1, preparing a calcium borate oxy-rare earth salt crystal melt;

[0045] S2, fixing the seed crystal on the pulling device, the seed crystal contacts the melt surface to ensure good initial contact and growth starting point;

[0046] S3, slowly lift the seed crystal, control the pulling speed and temperature gradient, and make the crystal grow steadily;

[0047] S4, setting temperature oscillation parameters, including: the amplitude, frequency and period of temperature change, introducing ultrasonic assistance in stages within each temperature oscillation period; performing seed crystal re-entry operation at the end of each temperature oscillation period;

[0048] S5. After the predetermined growth cycle is completed, the growth equipment is cooled naturally, the crystal is taken out for cleaning and drying, and the crystal is mechanically processed to prepare a laser self-frequency doubling crystal.

[0049] Calcium borate rare earth salt crystal is a composite crystal material composed of boric acid, calcium oxide and rare earth elements; it has a high second harmonic generation efficiency and can achieve effective conversion of fundamental frequency light to second harmonic within a single material; rare earth elements include one or more elements of neodymium, terbium and cerium as rare earth ions doped into calcium borate rare earth salt crystals, and these rare earth elements can produce frequency doubling effects of yellow and green lasers under specific conditions.

[0050] Neodymium ions can achieve green light output through a four-level system in certain matrices; terbium ions have a strong green light emission line near 545nm; cerium ions can have a broad emission band in the ultraviolet to visible light range, including the green light region. By selecting the type and doping ratio of rare earth elements, the nonlinear optical properties of the crystal can be optimized, thereby achieving high-efficiency laser frequency doubling output.

[0051] In step S1, the preparation method of calcium borate rare earth salt crystals is:

[0052] Boric acid, calcium oxide and rare earth oxide are selected as raw materials for preparation, wherein the molar ratio of H3BO3, CaO, Nd2O3, Tb4O7 and CeO2 is: 1: 6-6.5: 0.02-0.03: 0.005-0.015: 0.01-0.03;

[0053] Grind the raw materials thoroughly and mix them according to the required molar ratio to ensure that the raw materials are pure and evenly distributed. Put the mixed powder into a crucible and heat it in a high-temperature furnace to 1100-1300℃ to completely melt it. Connect a vacuum pump and reduce the gas pressure to 10 -2 -10 -13 The melt is supported by a pressure regulator to allow the gas dissolved in the melt to escape, forming a stable melt without bubbles. High-purity inert gas, including argon or helium, is then introduced to restore the pressure to normal to prevent the melt from contacting with air.

[0054] Seed crystal refers to the material used to guide crystal growth. During the crystal growth process, the seed crystal provides an initial crystallization template to ensure that it grows along a specific path, thereby obtaining high-quality crystals with ideal optical and mechanical properties.

[0055] Select high-quality single crystals that are consistent with the melt composition as seed crystals, and give priority to seed crystals cut from existing high-quality crystals to ensure the best match; then the crystals finally prepared in this application can be used to cut and obtain seed crystals to reduce costs; the selected seed crystals are required to be of good quality, free of cracks and inclusions.

[0056] In step S2,

[0057] S21. Use an ultrasonic cleaner and a high-purity solvent to thoroughly clean and dry the seed crystal to remove surface impurities and contaminants; the high-purity solvent includes ethanol and acetone;

[0058] S22, fixing the seed crystal on the pulling device so that the seed crystal can move freely in the vertical direction, and the melt is below the seed crystal;

[0059] S23, slowly lower the seed crystal so that the tip of the seed crystal contacts the surface of the melt, and the seed crystal stays on the surface of the melt for 3-5 minutes to make the surface temperature of the melt evenly distributed and ensure that the heat exchange between the seed crystal and the melt reaches a balance; rotate the seed crystal at a speed of 1-3 rpm so that the melt forms a more uniform wetting layer on the surface of the seed crystal, promote the stability of the initial crystal growth, and avoid the generation of bubbles or impurities;

[0060] In step S3, the seed crystal is slowly lifted so that the seed crystal gradually leaves the melt surface, and the pulling speed is 0.5-5 mm / hour; the temperature distribution in the furnace is ensured to be uniform through the heating element and the cooling system, and the temperature gradient between the melt surface and the seed crystal should be kept constant, and the temperature gradient is 1-5°C / cm.

[0061] The rotation operation in S2 helps the melt to form a uniform wetting layer on the surface of the seed crystal. Maintaining a constant pulling speed and temperature gradient in S3 further promotes the uniformity and integrity of the internal structure of the crystal, allowing the crystal to maintain a consistent growth pattern throughout the growth cycle, reducing or avoiding the generation of defects such as bubbles and cracks.

[0062] During the growth process of laser self-frequency doubling crystals, the temperature oscillation method is introduced to optimize the growth conditions of the crystals, thereby improving the quality and performance of the crystals; the temperature oscillation method affects the formation and quality of the crystals by periodically changing the temperature of the growth environment.

[0063] During the temperature oscillation process, the solute concentration in the melt will change periodically. When the temperature rises, the solubility of the melt increases, and some of the precipitated substances will dissolve back into the melt; when the temperature drops, these solutes will recrystallize and grow along the direction of the lowest energy on the crystal surface. The redistribution of solutes can reduce the compositional heterogeneity inside the crystal and help form a more uniform crystal structure.

[0064] During the temperature oscillation process, tiny thermal stress fluctuations are generated at the solid-liquid interface, which helps to maintain a stable growth interface, making the crystal growth regular and smooth, and reducing the possibility of unexpected branching or twisted growth; for calcium borate rare earth salt crystals, the temperature oscillation method allows the crystals to grow better along the predetermined optimal phase matching direction, thereby improving their optical properties.

[0065] In step S4, for calcium borate rare earth salt crystals, the temperature variation of the melt near the crystal growth interface is ±10°C; the frequency of each oscillation cycle is 2-3 times / day, and a complete oscillation cycle includes a heating stage, a heat preservation stage and a cooling stage, and the total duration is generally 9-12 hours; in the heating stage, the temperature is increased by 2°C at a rate of 0.5°C / h, and then enters the heat preservation stage, the temperature remains unchanged, and finally the temperature is reduced by 2°C at a rate of 0.5°C / h to complete a complete oscillation cycle;

[0066] Ultrasonic assistance is introduced at different stages of each oscillation cycle. When ultrasonic waves propagate in the melt, cavitation effect will occur, that is, tiny bubbles will be formed and quickly collapse. In this process, strong microjets and shock waves will be generated, which will help the solutes in the melt to be more evenly distributed, thereby reducing the compositional heterogeneity inside the crystal.

[0067] The heating stage needs to accelerate the re-dissolution of the solute. The ultrasonic wave with a frequency of 40-60kHz and a power density of 1-3W / cm2 is used in the heating stage. 2 , helps maintain solution homogeneity and promotes solute redissolution without inducing excessive turbulence;

[0068] The main purpose of the insulation stage is to maintain the uniformity of the melt. The ultrasonic wave with a frequency of 20-40kHz and a power density of 0.5-1.5W / cm 2 , low-intensity ultrasound can prevent local concentration differences and avoid unnecessary interference with the crystal growth interface;

[0069] The cooling stage is the key period for the crystal to grow in a stable environment. The ultrasonic frequency in the cooling stage is 20-40kHz, and it decreases by 0.5-1W / cm per hour. 2 Until the ultrasound stops, avoid the thermal shock that may be caused by the sudden cessation of ultrasound, so that the crystal can grow freely in a stable and undisturbed environment.

[0070] In step S4, after the cooling stage is over, the seed crystal is re-entered, and the seed crystal is slowly lowered to a depth of 2-5 mm in the melt at a speed of 0.5-1 mm / min, and the seed crystal is allowed to stay in the melt for 1-3 minutes to ensure full contact with the melt and repair the growth interface, and then the seed crystal is slowly lifted back to its original position at a speed of 1-2 mm / min. The frequency of seed crystal re-entry is 1-3 times / day; after returning to its original position, normal temperature oscillation is restored and a new oscillation cycle begins.

[0071] Ultrasonic assistance significantly improves the quality of crystals during temperature oscillation by promoting uniform distribution of solutes and enhancing interface stability; at the same time, it accelerates the dissolution process and optimizes growth conditions, effectively improving the growth efficiency of crystals.

[0072] In step S5, the growth device and the crystal inside are cooled naturally to room temperature to avoid thermal stress and possible cracks caused by rapid cooling.

[0073] When the growth equipment is completely cooled, the crystal is taken out and placed in a high-purity solvent for cleaning to remove melt residues, impurities and contaminants attached to the crystal surface. The cleaned crystal is placed in a dryer or blown dry with nitrogen; the crystal is mechanically processed according to the application requirements of the crystal.

[0074] Embodiment 1

[0075] A method for growing and preparing a laser self-frequency doubling crystal, comprising:

[0076] Select the raw materials: boric acid, calcium oxide, neodymium oxide, terbium oxide, cerium oxide, and the molar ratio is 1:6.25:0.025:0.01:0.02; grind the raw materials thoroughly and mix them evenly; put the mixed powder into a crucible, heat it in a high-temperature furnace to 1200℃ and completely melt it, connect a vacuum pump, and reduce the pressure to 10 -3 Torr; introduce high-purity argon gas to restore normal pressure;

[0077] Use an ultrasonic cleaner and ethanol to thoroughly clean and dry the seed crystal; fix the seed crystal on the lifting device to ensure that the seed crystal can move freely in the vertical direction, and there is melt below the seed crystal; slowly lower the seed crystal so that the tip of the seed crystal contacts the melt surface, and the seed crystal stays on the melt surface for 4 minutes; rotate the seed crystal at a speed of 2 rpm for 2 minutes;

[0078] The seed crystal is slowly lifted to gradually leave the melt surface. The pulling speed is 2 mm / h. The temperature gradient between the melt surface and the seed crystal is kept constant at 3 °C / cm.

[0079] The temperature oscillation parameters were set as follows: the melt temperature variation near the crystal growth interface was ±10°C; the frequency of each oscillation cycle was 2 times / day, and a complete oscillation cycle included a heating stage, a heat preservation stage, and a cooling stage, with a total duration of 10.5 hours.

[0080] Specifically: during the heating phase, the temperature was raised by 2°C at a rate of 0.5°C / h; during the insulation phase, the temperature remained constant for 6 hours; and finally, the temperature was lowered by 2°C at a rate of 0.5°C / h.

[0081] During the heating stage, the frequency was 50kHz and the power density was 2W / cm 2 The ultrasonic wave lasts throughout the whole heating stage. During the heat preservation stage, the frequency of the ultrasonic wave is 30kHz and the power density is 1W / cm 2 The ultrasonic wave lasts throughout the whole heat preservation stage. In the cooling stage, the ultrasonic wave frequency is 30kHz and the power density is 1W / cm 2 Initially, reduce by 0.5W / cm per hour 2 Until the ultrasound stops;

[0082] After the cooling stage, the seed crystal is re-entered: the seed crystal is slowly lowered to a depth of 3 mm in the melt at a speed of 0.75 mm / min, stayed for 2 minutes, and then slowly lifted back to its original position at a speed of 1.5 mm / min. The seed crystal re-entry frequency is 2 times / day.

[0083] After completing all the scheduled growth cycles, turn off the heating element and allow the growth equipment and the crystal inside to cool down naturally to room temperature. The cooling process lasts for 24 hours. The crystal is placed in high-purity ethanol for cleaning for 30 minutes and then blown dry with nitrogen. The crystal is mechanically processed, such as cutting and polishing, to prepare a laser self-doubling crystal with a specific shape and size.

[0084] Embodiment 2

[0085] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0086] The raw material ratio is: 1:6:0.02:0.005:0.01;

[0087] Embodiment 3

[0088] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0089] The raw material ratio is: 1:6.5:0.03:0.015:0.03;

[0090] Embodiment 4

[0091] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0092] The seed crystal re-entry frequency is once per day;

[0093] Embodiment 5

[0094] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the second embodiment are not described in detail, and the difference between this embodiment and the second embodiment is that;

[0095] The seed crystal re-entry frequency is once per day;

[0096] Embodiment 6

[0097] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the third embodiment are not described in detail, and the difference between this embodiment and the third embodiment is that;

[0098] The seed crystal re-entry frequency is once per day;

[0099] Embodiment 7

[0100] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0101] The seed crystal re-entry frequency is 3 times / day;

[0102] Embodiment 8

[0103] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in Example 2 are not described in detail, and the difference between this embodiment and Example 2 is that;

[0104] The seed crystal reentry frequency is 3 times / day;

[0105] Embodiment 9

[0106] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the third embodiment are not described in detail, and the difference between this embodiment and the third embodiment is that;

[0107] The seed crystal reentry frequency is 3 times / day;

[0108] Embodiment 10

[0109] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0110] The temperature gradient is 1°C / cm;

[0111] Embodiment 11

[0112] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0113] The temperature gradient was 2°C / cm;

[0114] Embodiment 12

[0115] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0116] The temperature gradient was 4°C / cm;

[0117] Embodiment 13

[0118] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0119] The temperature gradient was 5°C / cm;

[0120] Embodiment 14

[0121] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the first embodiment are not described in detail, and the difference between this embodiment and the first embodiment is that;

[0122] The heating and cooling speed is 1℃ / h;

[0123] Embodiment 15

[0124] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the tenth embodiment are not described in detail, and the difference between this embodiment and the tenth embodiment is that;

[0125] The heating and cooling speed is 1℃ / h;

[0126] Embodiment 16

[0127] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the eleventh embodiment are not described in detail, and the difference between this embodiment and the eleventh embodiment is that;

[0128] The heating and cooling rate is 1℃ / h;

[0129] Embodiment 17

[0130] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in Example 12 are not described in detail, and the difference between this embodiment and Example 12 is that;

[0131] The heating and cooling rate is 1℃ / h;

[0132] Embodiment 18

[0133] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in the thirteenth embodiment are not described in detail, and the difference between this embodiment and the thirteenth embodiment is that;

[0134] The heating and cooling speed is 1℃ / h;

[0135] Comparative Example 1

[0136] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in Example 1 are not described in detail, and the difference between this comparative example and Example 1 is that;

[0137] This comparison did not use ultrasound assistance;

[0138] Comparative Example 2

[0139] A method for growing and preparing a laser self-frequency doubling crystal, the same points as those in Example 1 are not described in detail, and the difference between this comparative example and Example 1 is that;

[0140] This comparison does not use the temperature oscillation method and ultrasound assistance;

[0141] Experimental Example 1

[0142] This experiment selected Examples 1 to 9 to conduct experiments, and tested the second harmonic generation efficiency, light absorption and transmittance of the self-frequency doubling crystal; and conducted an optical evaluation on the prepared crystal;

[0143] Table 1 Optical evaluation of Examples 1 to 9

[0144]

[0145]

[0146] Experimental data show that different raw material molar ratios have a significant effect on the growth efficiency, absorption coefficient and transmittance of the crystal. The raw material molar ratio determines the chemical composition of the crystal, which in turn affects the physical and optical properties of the crystal. Changes in the seed crystal re-entry frequency may affect the crystal quality during the crystal growth process. Seed crystal re-entry can promote crystal growth and improve the integrity and uniformity of the crystal. Different re-entry frequencies may lead to different crystal growth speeds and qualities, thus affecting the final optical properties.

[0147] Experimental Example 2

[0148] This experiment selected Examples 1, 10 to 18, and Comparative Examples 1 and 2 to conduct tests, and tested the second harmonic generation efficiency, light absorption and transmittance of the self-doubling crystal, as well as the preparation time required for preparing crystals of the same size. The quality of the crystal prepared in Example 1 after 72 hours was used as the basis, and the time required for preparing crystals of the same quality by other methods was calculated; the prepared crystals were optically evaluated;

[0149] Table 2 Optical evaluation of Examples 1, 10 to 18, and Comparative Examples 1 and 2

[0150]

[0151]

[0152] Example 1 exhibits the best SHG efficiency, the lowest absorption coefficient and the highest transmittance among all temperature gradients, which indicates that the temperature gradient of 3°C / cm is helpful to maintain a stable growth interface and reduce stress and defects inside the crystal.

[0153] Temperature gradient is one of the key factors affecting crystal growth. A higher temperature gradient may lead to faster crystal growth, but it may also increase stress and defects inside the crystal, thus affecting the optical properties of the crystal. On the contrary, a lower temperature gradient may promote more uniform crystal growth and reduce defects, but it may reduce the growth rate and increase the preparation time. The heating and cooling rates will also affect the growth quality of the crystal. A faster heating / cooling rate will lead to uneven temperature distribution inside the crystal, affecting the uniformity of crystal growth and thus affecting the optical properties. A slower rate may help maintain a more uniform temperature distribution and promote uniform crystal growth, but it will increase the preparation time.

[0154] Ultrasonic assistance can improve the uniformity and quality of crystal growth. Examples using ultrasonic assistance generally show higher SHG efficiency and transmittance, and lower absorption coefficient, which indicates that ultrasonic assistance helps reduce defects and stress inside the crystal and improve the optical properties of the crystal.

[0155] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for growing and preparing a laser self-frequency doubling crystal, characterized in that: Includes steps: S1, preparing a calcium borate oxy-rare earth salt crystal melt; S2, fixing the seed crystal on the pulling device, the seed crystal contacts the melt surface to ensure good initial contact and growth starting point; S3, slowly lift the seed crystal, control the pulling speed and temperature gradient, and make the crystal grow steadily; S4, setting temperature oscillation parameters, including: the amplitude, frequency and period of temperature change, introducing ultrasonic assistance in stages within each temperature oscillation period; performing seed crystal re-entry operation at the end of each temperature oscillation period; S5. After the predetermined growth cycle is completed, the growth equipment is cooled naturally, the crystal is taken out for cleaning and drying, and the crystal is mechanically processed to prepare a laser self-frequency doubling crystal.

2. The method for growing and preparing a laser self-frequency doubling crystal according to claim 1, characterized in that: In step S1, the preparation method of calcium borate rare earth salt crystals is: Boric acid, calcium oxide and rare earth oxide are selected as raw materials for preparation, wherein the molar ratio of H3BO3, CaO, Nd2O3, Tb4O7 and CeO2 is: 1: 6-6.5: 0.02-0.03: 0.005-0.015: 0.01-0.03; Grind the raw materials according to the molar ratio and mix them. Put the mixed powder into a crucible and heat it in a high-temperature furnace to 1100-1300℃ to completely melt it. Connect a vacuum pump and reduce the pressure to 10 -2 -10 -13 The support allows the gas dissolved in the melt to escape, forming a stable melt without bubbles, and then high-purity inert gas is introduced to restore normal pressure.

3. The method for growing and preparing a laser self-frequency doubling crystal according to claim 1, characterized in that: In step S2, S21, using an ultrasonic cleaner and a high-purity solvent to thoroughly clean and dry the seed crystal to remove impurities and contaminants on the surface; S22, fixing the seed crystal on the pulling device so that the seed crystal can move freely in the vertical direction, and the melt is below the seed crystal; S23. Slowly lower the seed crystal so that the tip of the seed crystal contacts the melt surface. The seed crystal stays on the melt surface for 3-5 minutes to make the melt surface temperature evenly distributed. Rotate the seed crystal at a speed of 1-3 rpm so that the melt forms a more uniform wetting layer on the seed crystal surface, thereby promoting the stability of initial crystal growth.

4. The method for growing and preparing a laser self-frequency doubling crystal according to claim 1, characterized in that: In step S3, the seed crystal is slowly lifted to gradually leave the melt surface, and the pulling speed is 0.5-5 mm / h; the temperature gradient between the melt surface and the seed crystal is kept constant, and the temperature gradient is 1-5°C / cm.

5. The method for growing and preparing a laser self-frequency doubling crystal according to claim 1, characterized in that: In step S4, the frequency of each oscillation cycle is 2-3 times / day, and a complete oscillation cycle includes a heating stage, a heat preservation stage and a cooling stage, with a total duration of 9-12 hours.

6. The method for growing and preparing a laser self-frequency doubling crystal according to claim 5, characterized in that: In step S4, for the calcium borate rare earth salt crystal, the temperature variation range of the melt near the crystal growth interface is ±10°C.

7. The method for growing and preparing a laser self-frequency doubling crystal according to claim 5, characterized in that: During the heating stage, the melt temperature near the crystal growth interface was raised by 2°C at a rate of 0.5°C / h, and then entered the insulation stage where the temperature remained constant. Finally, the temperature was lowered by 2°C at a rate of 0.5°C / h to complete a complete oscillation cycle.

8. The method for growing and preparing a laser self-frequency doubling crystal according to claim 5, characterized in that: The heating stage uses ultrasonic waves with a frequency of 40-60kHz and a power density of 1-3W / cm 2 ; The heat preservation stage uses ultrasonic waves with a frequency of 20-40kHz and a power density of 0.5-1.5W / cm 2 ; During the cooling stage, the ultrasonic frequency is 20-40kHz, and the temperature is reduced by 0.5-1W / cm per hour. 2 until the ultrasound stops.

9. The method for growing and preparing a laser self-frequency doubling crystal according to claim 5, characterized in that: In step S4, after the cooling stage is over, the seed crystal is re-entered, and the seed crystal is lowered to a depth of 2-5 mm in the melt at a speed of 0.5-1 mm / min, and the seed crystal is allowed to stay in the melt for 1-3 minutes to ensure full contact with the melt and repair the growth interface, and then the seed crystal is lifted back to its original position at a speed of 1-2 mm / min. The frequency of seed crystal re-entry is 1-3 times / day.

10. The method for growing and preparing a laser self-frequency doubling crystal according to claim 9, characterized in that: In step S4, after the seed crystal is restored to its original position, the temperature is oscillated again to start a new oscillation cycle.

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