Method for growing terbium lithium fluoride magneto-optical crystal by using fluxing agent

Abstract

The invention relates to a method for growing a terbium lithium fluoride magneto-optical crystal by using a fluxing agent. The process comprises the following steps: (1) fully mixing a fluxing agent with raw materials; (2) putting the mixture into a crucible, feeding the crucible into a high-temperature molten salt furnace, vacuumizing the furnace, and introducing protective gas; and (3) controlling the heating rate, heating until the mixture is completely molten, and keeping the temperature for several hours. And (4) slowly cooling until crystals are completely separated out. And (5) annealing to room temperature to obtain the terbium lithium fluoride crystal. Tests show that the terbium lithium fluoride crystal prepared by the method is good in quality, large in extinction ratio and high in damage threshold, has relatively high transmittance and relatively strong magneto-optical performance in wave bands of 505nm, 633nm, 880nm and 1064nm, and is expected to be practically applied to magneto-optical devices such as magneto-optical isolators, Faraday rotators and the like.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, specifically relating to a method for growing terbium lithium fluoride magneto-optical crystals using a flux. Background Technology

[0002] Magneto-optical devices, such as Faraday rotators and magneto-optical isolators, based on the Faraday effect of magneto-optical crystals, have wide applications in lasers, communications, and many other fields. Utilizing the unidirectional conductivity of magneto-optical crystals, damage to laser systems from reflected light can be effectively prevented, protecting critical components and improving laser output quality.

[0003] In recent years, with the continuous development of the laser and communication industries in the visible and near-infrared bands, the demand for corresponding magneto-optical devices has been increasing, and higher requirements have been placed on the quality of magneto-optical crystals. Currently, the traditional commercial magneto-optical crystal is terbium gallium garnet (TGG). TGG crystals have advantages such as a large Faraday rotation angle and a high Wilder constant, but their absorption loss and nonlinear coefficient are relatively large, making them difficult to use in high-power lasers of hundreds of watts and above.

[0004] Lithium terbium fluoride (LiTbF4, abbreviated as LTF) crystals have a tetragonal scheelite structure with the c-axis as the optical axis. They exhibit low absorption loss, a small nonlinear coefficient, and a negative thermo-optical coefficient, and possess a Wilder constant no less than that of TGG crystals, making them a high-performance magneto-optical crystal material. LTF crystals are used in high-power Faraday rotators and magneto-optical isolators, overcoming the problems of decreased isolation and deterioration of the pre-stage beam quality caused by the large absorption coefficient and rising temperature of traditional TGG crystals. However, LTF crystals are non-uniform melts, and terbium oxyfluoride (TbO) is easily formed during growth. x F 2-3x It is extremely difficult for it to grow. Summary of the Invention

[0005] This invention addresses existing technical problems by proposing a method for growing terbium lithium fluoride magneto-optical crystals using a flux. To achieve the above-mentioned objective, this invention adopts the following technical solution:

[0006] A method for growing lithium terbium fluoride magneto-optical crystals using a flux includes the following steps:

[0007] (1) Using a NaF-CaF2 system with a stoichiometric ratio of 1:1 as a flux, and high-purity LiF and TbF3 with a certain stoichiometric ratio as raw materials, they are thoroughly mixed.

[0008] (2) Place it in a platinum crucible and send it into a high-temperature molten salt furnace. Then, evacuate the furnace and introduce a protective gas.

[0009] (3) Set the program to control the heating rate so that the raw materials are completely melted and kept at a constant temperature for several hours to obtain a molten mixture of flux and lithium terbium fluoride.

[0010] (4) Set the program to control the cooling rate until LTF crystals are completely precipitated.

[0011] (5) After the crystal growth is completed, it is cooled and annealed until it reaches room temperature to obtain the crystal.

[0012] Furthermore, in step (1), the purity of the raw materials LiF and TbF3 is 99.999%, and the stoichiometric ratio is 1.5-1.7:1.

[0013] Furthermore, in step (2), the vacuum level is lower than 3 × 10⁻⁶. -3 Pa, the protective gas is high-purity argon.

[0014] Furthermore, in step (3), the heating rate is 40-50℃ / h, and the constant temperature time is 24-36 hours.

[0015] Furthermore, in step (4), the cooling rate is 1-3℃ / h.

[0016] Furthermore, in step (5), the cooling rate during annealing is 5℃ / h.

[0017] The flux-based growth process used in this invention is not limited to the parameters mentioned above and can be further optimized.

[0018] The beneficial effects of this invention are:

[0019] (1) The present invention uses a NaF-CaF2 system with a stoichiometric ratio of 1:1 as a flux, which effectively reduces the crystal growth temperature, greatly reduces the difficulty of crystal growth, and is conducive to the growth of large-size LTF crystals.

[0020] (2) Compared with the stoichiometry in LTF crystals, this invention appropriately increases the proportion of LiF and TbF3 in the raw materials and introduces a protective gas during the growth process, thus solving the problem that LTF crystals are non-uniform melts and produce terbium oxyfluoride (TbO3) during growth. x F 2-3x The problem is...

[0021] (3) According to the test, the LTF crystal prepared by the growth method of the present invention has a large extinction ratio and a high damage threshold. It also has high transmittance and strong magneto-optical performance in the 505nm, 633nm, 880nm and 1064nm bands. It is expected to be practically applied in magneto-optical devices such as magneto-optical isolators and Faraday rotators. Attached Figure Description

[0022] Figure 1The image shows the X-ray diffraction (XRD) pattern of an LTF crystal and its corresponding standard card.

[0023] Figure 2 This is the rocking curve of the LTF crystal.

[0024] Figure 3 This is the transmission spectrum of an LTF crystal.

[0025] Figure 4 This is a diagram of the LTF crystal extinction ratio testing setup.

[0026] Figure 5 This is a graph showing the laser damage threshold test of an LTF crystal.

[0027] Figure 6 The graph shows the Verdet constant of the LTF crystal at different wavelengths. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Implementation Case 1

[0030] A method for growing lithium terbium fluoride magneto-optical crystals using flux, the specific steps of which are as follows:

[0031] (1) Using a NaF-CaF2 system with a stoichiometric ratio of 1:1 as a flux, LiF and TbF3 with a purity of 99.999% as raw materials are fully mixed at a stoichiometric ratio of 1.6:1.

[0032] (2) Place it in a platinum crucible and send it into a high-temperature molten salt furnace, where the furnace is evacuated to a vacuum level below 3 × 10⁻⁶. -3 Pa, high-purity argon gas is introduced as a protective gas.

[0033] (3) Set the program to control the heating rate to 40℃ / h, so that the raw materials are completely melted and kept at a constant temperature for 36 hours to obtain a molten mixture of flux and lithium terbium fluoride.

[0034] (4) Set the program to control the cooling rate to 1℃ / h until LTF crystals are completely precipitated.

[0035] (5) After the crystal growth is completed, it is cooled and annealed at a rate of 5℃ / h until the LTF crystal is obtained after cooling to room temperature.

[0036] Implementation Case 2

[0037] A method for growing lithium terbium fluoride magneto-optical crystals using flux, the specific steps of which are as follows:

[0038] (1) Using a NaF-CaF2 system with a stoichiometric ratio of 1:1 as a flux, LiF and TbF3 with a purity of 99.999% as raw materials are fully mixed at a stoichiometric ratio of 1.7:1.

[0039] (2) Place it in a platinum crucible and send it into a high-temperature molten salt furnace, where the furnace is evacuated to a vacuum level below 3 × 10⁻⁶. -3 Pa, high-purity argon gas is introduced as a protective gas.

[0040] (3) Set the program to control the heating rate to 50℃ / h, so that the raw materials are completely melted and kept at a constant temperature for 40 hours to obtain a molten mixture of flux and lithium terbium fluoride.

[0041] (4) Set the program to control the cooling rate to 3℃ / h until LTF crystals are completely precipitated.

[0042] (5) After the crystal growth is completed, it is cooled and annealed at a rate of 5℃ / h until the LTF crystal is obtained after cooling to room temperature.

[0043] Sample characterization and performance testing

[0044] (1) After processing the LTF crystal obtained in Case 1, X-ray diffraction (XRD) was performed. The obtained XRD pattern and rocking curve are shown below. Figure 1 , Figure 2 As shown. The obtained crystal phase is consistent with the standard card PDF#04-006-0422, with no impurity peaks appearing. The full width at half maximum (FWHM) of the rocking curve in the edge region is 42″, and the full width at half maximum (FWHM) of the rocking curve in the center region is 25″, indicating that high-quality LTF crystals have been grown.

[0045] (2) After processing the LTF crystal obtained in Implementation Case 1, a transmittance test was performed, and the resulting transmittance curve is shown in Figure 1. Figure 3 As shown. Within the 400-1500nm range, excluding Tb... 3+ The ions exhibit an intrinsic absorption peak at 489 nm, while maintaining high transmittance in other wavelength ranges.

[0046] (3) After processing the LTF crystal obtained in Implementation Case 1, an extinction ratio test was performed, and the crystal was placed in an environment such as... Figure 4 In the optical path shown, green light with a wavelength of 510nm was used as the light source to test the extinction ratio of a crystal with a diameter of 5mm × 15mm. The extinction ratio of the obtained LTF crystal was 31dB.

[0047] (4) After processing the LTF crystal obtained in Case 1, a laser damage threshold (LIDT) test was performed, and the results are as follows: Figure 5 As shown. A 1064nm pulsed laser with a frequency of 1Hz and a pulse width of 10ns was used to perform LIDT testing on a double-polished LTF crystal, with a spot diameter of 0.25mm. The laser power flux was 0.401GW·cm⁻¹. -2 When the sample begins to show signs of damage, the LIDT of the sample is 4.01 J·cm⁻¹. -2 .

[0048] (5) After processing the LTF crystal obtained in Implementation Case 1, the Verdet constant was tested, and the results are as follows: Figure 6 As shown, under a magnetic field strength of approximately 300 mT, the Faraday deflection angle of the LTF crystal at a wavelength of 1064 nm is 35 rad·m. -1 The Faraday deflection angle at a wavelength of 880 nm is 70 rad·m. -1 The Faraday deflection angle at a wavelength of 633 nm is 117 rad·m. -1 The Faraday deflection angle at a wavelength of 505 nm is 160 rad·m. -1 The Verdet constant of the LTF crystal at 1064 nm was calculated to be 35 rad·T based on the Faraday effect formula. -1 ·m -1 The Verdet constant at 808 nm is 69 rad·T. -1 ·m -1 The Verdet constant at 633 nm is 110 rad·T. -1 ·m -1 At 505 nm, the value of the Verdet constant is 170 rad·T. -1 ·m -1 .

[0049] The foregoing detailed an embodiment of the present invention, but this description is merely the preferred embodiment and should not be construed as limiting the scope of the invention. All variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for growing a terbium lithium fluoride magneto-optic crystal by flux growth, characterized by: The method comprises the following steps: (1) mixing raw materials LiF and TbF3 in stoichiometric ratio with NaF-CaF2 system as flux in stoichiometric ratio of 1:

1. (2) placing the mixture in a platinum crucible and sending it into a high-temperature molten salt furnace, then vacuumizing the furnace and introducing a protective gas. (3) setting a program-controlled temperature rising rate to completely melt the raw materials, keeping constant temperature for several hours to obtain a molten mixture of flux and TbLiF4. (4) setting a program-controlled temperature falling rate until LTF crystals are completely precipitated. (5) after the crystal growth is completed, annealing the crystals by falling temperature, and obtaining the crystals after falling to room temperature.

2. The growing method of claim 1 : wherein: In step (1), the purity of raw materials LiF and TbF3 is 99.999%, and the stoichiometric ratio is 1.5-1.7:

1.

3. The growing method of claim 1 : wherein: In step (2), the vacuum degree is lower than 3 x 10 -3 Pa, and the protective gas is high-purity argon.

4. The growing method of claim 1 : wherein: In step (3), the temperature rising rate is 40-50℃ / h, and the constant temperature time is 24-36 hours.

5. The growing method of claim 1 : wherein: In step (4), the temperature falling rate is 1-3℃ / h.

6. The growth method of claim 1 : wherein: In step (5), the temperature falling rate during annealing is 5℃ / h.

7. Application of the TbLiF4 magneto-optical crystal grown according to claim 1 to magneto-optical devices such as magneto-optical isolators and Faraday rotators.

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