Double-crystal transverse electro-optical Q-switch

Abstract

The invention belongs to the technical field of laser devices, and relates to a bicrystal transverse electro-optical Q-switch which comprises two electro-optical crystals, electrodes, wires and a shell wrapping the electro-optical crystals. The electro-optical crystal is a potassium boron niobate crystal, the chemical formula of the electro-optical crystal is K3Nb3B2O12, the electro-optical crystal comprises a first electro-optical crystal and a second electro-optical crystal, the electro-optical crystal adopts a transverse electro-optical effect, and the first electro-optical crystal and the second electro-optical crystal have the same geometrical shape; the main axes of the first electro-optical crystal and the second electro-optical crystal mutually rotate by 90 degrees around the light passing direction. The electro-optical Q-switch is low in driving voltage, the driving voltage is reduced by 28%-95.6% compared with an existing commercialized electro-optical Q-switch under the condition that the crystal size is kept the same, and the important requirement of low-voltage driving electro-optical devices is met. The electro-optical Q-switch is simple in design, does not use a quarter-wave plate, is beneficial to miniaturized production, and has the advantages of being easy to industrialize and the like.

Description

Technical Field

[0001] This invention belongs to the field of laser device technology, specifically relating to a dual-crystal transverse electro-optic Q-switching switch based on potassium boron niobate crystal and its fabrication method. Background Technology

[0002] High-repetition-rate, narrow-pulse-width, and high-power lasers have broad application prospects in numerous fields such as industrial production, military, medicine, and scientific research. They play a crucial role, especially in laser military weapons applications such as laser fusion, laser ranging, and laser guidance, as well as in laser precision and ultra-precision machining. Q-switching technology is a practical technique for directly generating high-repetition-rate, narrow-pulse-width lasers. Among Q-switching techniques, electro-optic Q-switching features fast switching speed, strong turn-off capability, high precision, low energy jitter, and narrow pulse width, and has been widely used in fields requiring accurate and controllable high-quality pulsed lasers. The key component in electro-optic Q-switching is the electro-optic crystal.

[0003] Currently, the electro-optic Q-switching crystals that have achieved commercial applications mainly include KD2PO4 (DKDP), LiNbO3 (LN), KTiOPO4 (KTP), RbTiOPO4 (RTP), β-BaB2O4 (β-BBO), and La3Ga5SiO4. 14 (LGS), etc. These widely used commercial electro-optic crystals each have their advantages and can basically meet the application requirements of ordinary lasers. However, traditional electro-optic Q-switched crystals are generally large in size and require high modulation voltages due to their small electro-optic coefficients. For example, the maximum electro-optic coefficient of LN is γ. 33 =32pm / V, but in electro-optic Q-switched devices, its γ is usually used. 22 =6.8 pm / V, wavelength 1 μm, electro-optic crystal aspect ratio 1:1, its driving voltage is 3.6 kV. For electro-optic crystals with smaller electro-optic coefficients, LGS (2.3 pm / V) and BBO (2.2 pm / V), the driving voltage is even higher. In the 2 μm band, when the aspect ratio is adjusted to 1:1, the driving voltage of LGS is 32.5 kV and that of BBO is 49 kV. High driving voltages not only affect laser performance but also impose stringent requirements on safety and circuit design during use. To reduce the driving voltage of electro-optic Q-switches, traditional designs increase the aspect ratio l / d of the electro-optic crystal. However, this design requires increasing the light transmission length of the electro-optic crystal, which not only places higher demands on the growth technology of the electro-optic crystal and increases the cost of the electro-optic switch and even the laser, but also, as the length of the electro-optic crystal increases, the absorption of the crystal also affects the laser output power and the lifespan of the electro-optic Q-switcher.

[0004] Developing electro-optic crystals with larger electro-optic coefficients is another effective way to solve the problem of high drive voltage in electro-optic Q-switching switches. In 2021, Danpai et al. first discovered potassium boroniobate crystals (chemical formula K3Nb3B2O). 12 The electro-optic effect of potassium boroniobate was observed, and the electro-optic coefficient of the antiferroelectric phase potassium boroniobate crystal was measured to be 3.3 pm / V (Pai Shan et al., Electro-optic modulation in anon-centrosymmetric antiferroelectric crystal, J. Mater. Chem. C, 2021, 9, 9431-9435). In 2025, Lingfei Lv et al. prepared a ferroelectric phase of potassium boroniobate crystal and further increased its electro-optic coefficient to 50.14 pm / V (Lingfei Lv et al., A new-type electro-optic crystal: K3Nb3B2O). 12 (Journal of Materials, 2025, 11, 100991) This is greater than the current commercially available electro-optic crystals: LN crystal (32 pm / V), KDP crystal (10.5 pm / V), KTP crystal (36.3 pm / V), RTP crystal (33 pm / V), and β-BBO crystal (2.2 pm / V). Therefore, using potassium boroniobate crystals can yield electro-optic Q-switching devices with lower driving voltages. However, there are currently no reports on electro-optic Q-switching technology based on potassium boroniobate crystals. Summary of the Invention

[0005] To address the issues of large size and high Q-switching voltage in traditional electro-optic Q-switches, this invention provides a dual-crystal lateral electro-optic Q-switching switch based on potassium boron niobate crystals and its fabrication method.

[0006] The present invention specifically adopts the following technical solution:

[0007] This invention relates to a dual-crystal transverse electro-optic Q-switching switch, comprising two electro-optic crystals, electrodes, wires, and a shell encasing the electro-optic crystals. The electro-optic crystals are potassium boroniobate crystals with the chemical formula K3Nb3B2O. 12 Hereinafter referred to as KNBO. KNBO crystals possess two phases: a ferroelectric phase and an antiferroelectric phase. The antiferroelectric KNBO crystal, located in space group Pmc21, is a biaxial crystal. The ferroelectric KNBO crystal, located in space group P31m, is a uniaxial crystal.

[0008] The antiferroelectric KNBO crystal is a biaxial crystal with three principal refractive indices, denoted as N0, N1, N2, N3, N4, N5, N6, N7, N8, N9, N10 g N m N p And there are N g >Nm >N p The refractive index in the X direction of the optical principal axis is N. g The refractive index along the optical principal axis Y direction is N m The refractive index in the Z direction of the optical principal axis is N p Among them, the optical principal axis X direction is parallel to the crystallographic c-axis, the optical principal axis Y direction is parallel to the crystallographic a-axis, and the optical principal axis Z direction is parallel to the crystallographic b-axis.

[0009] The ferroelectric KNBO crystal is a uniaxial crystal with two principal refractive indices, denoted as N0 and N1 respectively. o N e And there are N o >N e The refractive index of the optical principal axes in the X and Y directions is N. o The refractive index in the Z direction of the optical principal axis is N e The optical principal axes X and Y are parallel to the crystallographic a and b axes, respectively, while the optical principal axis Z is parallel to the crystallographic c axis.

[0010] The electro-optic crystal includes a first electro-optic crystal and a second electro-optic crystal. The first electro-optic crystal and the second electro-optic crystal adopt a transverse electro-optic effect. Specifically, the applied electric field direction is along the Z-axis of the optical principal axis of the electro-optic crystal, and the light transmission direction is perpendicular to the Z-axis of the optical principal axis of the electro-optic crystal. The first electro-optic crystal and the second electro-optic crystal have the same geometric shape, such as a cuboid. The principal axes of the first electro-optic crystal and the second electro-optic crystal are rotated 90° around the light transmission direction. The lengths of the light transmission direction of the first electro-optic crystal and the second electro-optic crystal are equal and both are 5 to 100 mm.

[0011] The surface perpendicular to the light transmission direction of the electro-optic crystal is optically polished and coated with an anti-reflection film with a laser transmittance greater than 99% or left uncoated; the light transmission surface of the electro-optic crystal is square or rectangular with a side length of 1 to 20 mm.

[0012] The XY plane, perpendicular to the Z-axis of the electro-optic crystal, is coated with a metal film as an electrode. The electrode is connected to a wire, which extends out of the outer shell. The metal film is preferably a metal such as gold or titanium.

[0013] The outer shell is made of insulating material and is fixed to the electro-optic crystal, specifically using screws; the insulating material is plastic, plexiglass, or rubber.

[0014] The applicable repetition frequency for the transverse electro-optic Q-switching switch is 0.1Hz to 1000kHz.

[0015] The electro-optic Q-switching switch can be used in Q-switched lasers to achieve modulation of lasers from visible light to 3.3μm mid-infrared bands, thereby obtaining electro-optic modulated pulsed laser output.

[0016] The method for fabricating the dual-crystal lateral electro-optic Q-switching switch includes: oriented cutting of a KNBO crystal substrate into a cubic or cuboid shape according to the electro-optic application direction to obtain an electro-optic crystal; cutting two identical electro-optic crystals, specifically cuboids, at the center of the KNBO crystal placed horizontally along the light transmission direction; optically polishing the light transmission surfaces of the two electro-optic crystals respectively, and depositing anti-reflection coatings on the light transmission surfaces of the two electro-optic crystals; depositing electrode layers on the X and Y planes perpendicular to the Z direction of the optical principal axis of the two electro-optic crystals to obtain two electro-optic crystal elements with electrode layers; welding one end of two sets of wires to the electrode layers of the two electro-optic crystal elements respectively; rotating the principal axes of the two electro-optic crystals 90° relative to each other around the light transmission direction; and encapsulating and fixing them with a shell to obtain the KNBO dual-crystal lateral electro-optic Q-switching switch.

[0017] The working principle of the electro-optic Q-switching switch based on KNBO crystal is as follows:

[0018] When a voltage is applied across a KNBO crystal, the phase difference and the applied driving voltage satisfy the following relationship:

[0019]

[0020] In the formula, γ c Let n be the effective electro-optic coefficient of the KNBO crystal, n0 be the refractive index of the KNBO crystal at the working laser wavelength, l be the length of a single KNBO crystal in the light transmission direction, U be the voltage applied between the two electrodes, λ be the wavelength of the light wave, and d be the thickness between the two electrodes, i.e., the width of the KNBO crystal. As a Q-switching switch within the laser resonant cavity, the required phase difference is:

[0021]

[0022] Or the optical path difference is:

[0023]

[0024] Substituting equation (2) into equation (1), we obtain the voltage that should be applied across the two ends of the Q-switching switch device used in the laser resonant cavity:

[0025]

[0026] From equation (4), it can be seen that for a given KNBO, once the output wavelength λ of the laser is determined, the effective electro-optic coefficient γ cThe value of the refractive index n is fixed. When the length l of the KNBO crystal in the light transmission direction is constant, the voltage U applied to the KNBO crystal is proportional to the width d of the KNBO crystal, i.e., the distance d between the two electrodes. The smaller the width, the smaller the voltage required for the Q-switching switch to work. However, considering that a smaller width d of the KNBO crystal results in a smaller light transmission aperture, d cannot be infinitely small and is limited by the size of the beam cross-section. Therefore, the value of the KNBO crystal width d should be as small as possible while ensuring that the light transmission aperture meets the usage requirements.

[0027] When the width d of the KNBO crystal is constant, the voltage U applied to the KNBO crystal is inversely proportional to the length l in the light transmission direction. The larger l is, the smaller the voltage that needs to be applied to the KNBO crystal. However, since the larger l is, the greater the optical absorption and the lower the optical transmittance, the value of the length l of the KNBO crystal in the light transmission direction should be as large as possible, provided that the transmittance requirements of the laser resonator for the Q-switching device are met.

[0028] The beneficial effects of this invention include:

[0029] With the same crystal size, the potassium boroniobate crystal electro-optic Q-switched switch fabricated according to the present invention has a driving voltage that is only 62% of that of LN crystal, 21% of KDP crystal, 72% of KTP crystal, 66% of RTP crystal, and 4.4% of that of β-BBO crystal. That is, the electro-optic Q-switched switch fabricated using the present invention, while maintaining the same volume, reduces the driving voltage by 28%-95.6% compared to existing commercial electro-optic Q-switched switches. At the same operating voltage and the same aperture, the length of the electro-optic Q-switched switch device can be reduced by 28%-95.6%.

[0030] On the other hand, this invention provides specific light transmission direction, electric field application direction, and device fabrication method for KNBO crystals in the fabrication of electro-optic Q-switching devices, promoting the industrialization of KNBO crystals from materials to electro-optic devices. The electro-optic Q-switching switch of this invention has a simple design, does not use a quarter-wave plate, is conducive to miniaturization, and has advantages such as ease of industrialization. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of a dual-crystal electro-optic Q-switching switch based on potassium boroniobate crystal in Embodiment 1 or 2 of the present invention. Figure 1 .

[0032] Figure 2 This is a schematic diagram of the structure of a dual-crystal electro-optic Q-switching switch based on potassium boroniobate crystal in Embodiment 1 or 2 of the present invention. Figure 2 .

[0033] Figure 3This is a schematic diagram of the structure of a dual-crystal electro-optic Q-switching switch based on potassium boroniobate crystal in Embodiment 1 or 2 of the present invention. Figure 3 .

[0034] Figure 4 This is a schematic diagram of the structure of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal applied to a laser, as described in Embodiment 3 of the present invention. Figure 1 .

[0035] Figure 5 This is a schematic diagram of the structure of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal applied to a laser, as described in Embodiment 3 of the present invention. Figure 2 .

[0036] Figure 6 This is a schematic diagram of the structure of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal applied to a laser, as shown in Embodiment 4 of the present invention. Figure 1 .

[0037] Figure 7 This is a schematic diagram of the structure of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal applied to a laser, as shown in Embodiment 4 of the present invention. Figure 2 (The screws on the base are not shown in the picture.)

[0038] The image includes the following annotations:

[0039] 1-First electro-optic crystal, 2-Second electro-optic crystal, 3-Electrode, 4-Outer shell, 5-Wire, 6-Screw, 7-Connecting column, 8-Base. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] The KNBO crystal precursor of space group Pmc21 was prepared with reference to Chinese invention patent application publication number CN 112853467A (the space group Pmc21 in this invention and the P21ma in Chinese invention patent application publication number CN 112853467A represent the same space group crystal).

[0042] A new-type electro-optic crystal reference for KNBO crystal in space group P31m (Lingfei Lv et al., A new-type electro-optic crystal: K3Nb3B2O) 12(Prepared by Journal of Materials, 2025, 11, 100991).

[0043] Example 1

[0044] Using biaxial potassium boroniobate (K3Nb3B2O) in the antiferroelectric phase 12 KNBO (KNBO) crystals are used to fabricate a biaxial crystal electro-optic Q-switching switch for a wavelength λ = 633 nm.

[0045] A 40×6×5mm KNBO crystal primary crystal located in space group Pmc21 was obtained by directional cutting. 3 A cuboid electro-optic crystal has three edges parallel to the three optical principal axes of a KNBO crystal. The longest edge is parallel to the X-axis of the optical principal axis, and the shortest edge is parallel to the Z-axis. The X-axis is the light transmission direction, and the Z-axis is the direction in which the electric field is applied. Two identical cuboid crystals (a first electro-optic crystal and a second electro-optic crystal) are cut at the center of the KNBO crystal, which is placed horizontally along the X-axis. Each crystal measures 20 × 6 × 5 mm. 3 The light-transmitting surfaces of two cuboid crystals are precision optically polished, and a 633nm anti-reflection coating is deposited on the light-transmitting surfaces of the two cuboid crystals. Electrode layers are deposited on the XY planes of the two cuboid crystals to obtain two electro-optic crystal elements with electrode layers. One end of each of the two sets of wires 5 is welded to the electrode layers 3 of the two electro-optic crystal elements. The main axes of the first electro-optic crystal 1 and the second electro-optic crystal 2 are rotated 90° relative to each other around the light-transmitting direction, and then encapsulated with an insulating shell 4. After encapsulation, the wires 5 extend out of the shell 4 and are fixed with screws 6 to obtain a potassium boroniobate dual-crystal electro-optic Q-switching switch. Applying a voltage of approximately 1500V to the electro-optic Q-switching device can achieve a phase difference. The modulation can be used to obtain 633nm electro-optic modulated pulsed laser output.

[0046] Example 2

[0047] Using uniaxial potassium boroniobate (K3Nb3B2O) in the ferroelectric phase 12 KNBO (KNBO) crystals are used to fabricate a biaxial crystal electro-optic Q-switch for wavelengths up to 1064 nm.

[0048] A 40×6×5mm KNBO crystal primary crystal located in space group P31m was obtained by directional cutting. 3A cuboid electro-optic crystal has three edges parallel to the three optical principal axes of a KNBO crystal. The longest edge is parallel to the X-axis of the optical principal axis, and the shortest edge is parallel to the Z-axis. The X-axis is the light transmission direction, and the Z-axis is the direction in which the electric field is applied. Two identical cuboid crystals (a first electro-optic crystal and a second electro-optic crystal) are cut at the center of the KNBO crystal, which is placed horizontally along the X-axis. Each crystal measures 20 × 6 × 5 mm. 3 The light-transmitting surfaces of two cuboid crystals are precision optically polished, and a 1064nm anti-reflection coating is deposited on the light-transmitting surfaces of the two cuboid crystals. Electrode layers are deposited on the XY planes of the two cuboid crystals to obtain two electro-optic crystal elements with electrode layers. One end of each of the two sets of wires 5 is welded to the electrode layers 3 of the two electro-optic crystal elements. The main axes of the first electro-optic crystal 1 and the second electro-optic crystal 2 are rotated 90° relative to each other around the light-transmitting direction, and then encapsulated with an insulating shell 4. After encapsulation, the wires 5 extend out of the shell 4 and are fixed with screws 6 to obtain a potassium boroniobate dual-crystal electro-optic Q-switching switch. Applying a voltage of approximately 176V to the electro-optic Q-switching device can achieve a phase difference. The modulation can be used to obtain 1064nm electro-optic modulated pulsed laser output.

[0049] The electro-optic coefficient of the ferroelectric KNBO crystal is 50.14 pm / V, which is greater than that of existing commercial electro-optic crystals such as LN crystal (32 pm / V), KDP crystal (10.5 pm / V), KTP crystal (36.3 pm / V), RTP crystal (33 pm / V), and β-BBO crystal (2.2 pm / V). With the same crystal size, the driving voltage of the KNBO crystal electro-optic Q-switched switch fabricated according to this invention is only 62% of that of LN crystal, 21% of KDP crystal, 72% of KTP crystal, 66% of RTP crystal, and 4.4% of β-BBO crystal. Using the electro-optic Q-switched switch fabricated according to this invention, the driving voltage is reduced by 28%-95.6% compared to existing commercial electro-optic Q-switched switches while maintaining the same volume. At the same operating voltage and the same aperture, the length of the electro-optic Q-switched switch device can be reduced by 28%-95.6%.

[0050] Figure 1 and 2 These are schematic diagrams of the dual-crystal electro-optic Q-switching switch structures based on potassium boroniobate crystals in Embodiments 1 and 2 of the present invention. Figure 3 This is a side view schematic diagram of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal in Embodiments 1 and 2 of the present invention. In the figure, 1 is the first electro-optic crystal, 2 is the second electro-optic crystal, 3 is the electrode, 4 is the insulating shell, 5 is the wire, and 6 is the screw.

[0051] Example 3

[0052] Unlike Embodiments 1 or 2, four wires are connected to the connecting post 7, which is made of metal. The electro-optic Q-switching device can be fixed inside the laser via the connecting post 7. Figure 4 and 5 This is a schematic diagram of the structure of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal applied to a laser in Embodiment 3 of the present invention.

[0053] Example 4

[0054] Unlike Embodiments 1 or 2, a rectangular plastic plate is added below the electro-optic Q-switching switch as a base 8, making the entire electro-optic Q-switching switch convex in shape. Screw holes are provided at the four corners of the base, allowing the electro-optic Q-switching switch to be fixed inside the laser using screws. Figure 6 and 7 This is a schematic diagram of the structure of the dual-crystal electro-optic Q-switching switch based on potassium boron niobate crystal applied to a laser in Embodiment 4 of the present invention.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual crystal transverse electro-optic Q-switch, characterized in that, The application relates to a potassium boron niobate crystal, a potassium boron niobate crystal cell, a potassium boron niobate crystal cell array, and a potassium boron niobate crystal cell array system. 12 , The electro-optic crystal comprises a first electro-optic crystal (1) and a second electro-optic crystal (2), the first electro-optic crystal (1) and the second electro-optic crystal (2) adopt a transverse electro-optic effect, the first electro-optic crystal (1) and the second electro-optic crystal (2) have the same geometric shape; the main axes of the first electro-optic crystal (1) and the second electro-optic crystal (2) are rotated 90° relative to each other around the light transmission direction.

2. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, The potassium dideuterium borotriphosphate crystal is in a ferroelectric phase or an anti-ferroelectric phase. The antiferroelectric phase potassium niobate borate crystal is a biaxial crystal, wherein the optical principal axis X The refractive index in the direction of N g The optical principal axis Y The refractive index in the direction of N m The optical principal axis N p , N g > N m > N p ; The ferroelectric phase potassium niobate crystal is a uniaxial crystal, wherein the optical principal axis X direction and Y direction are N o , the optical principal axis Z direction and N e , N o > N e .

3. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, The direction of the applied electric field is along the optical principal axis of the electro-optic crystal Z The direction of the applied electric field is along the optical principal axis of the electro-optic crystal Z The direction of the applied electric field is along the optical principal axis of the electro-optic crystal 4. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, The first electro-optic crystal and the second electro-optic crystal have the same length of the light transmission direction and the length is 5-100 mm.

5. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, The surface of the electro-optic crystal perpendicular to the light transmission direction is optically polished, and the surface is coated with an anti-reflection film having a laser transmittance of greater than 99% or is not coated with a film; the light transmission surface of the electro-optic crystal is a square or a rectangle, and the side length is 1-20 mm.

6. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, perpendicular to the optical principal axis of the electro-optical crystal Z direction of XY a face, coated with a metal film layer as an electrode (3), which is connected to a lead (5) that extends out of the housing (4).

7. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, The shell (4) is made of an insulating material and is fixed to the electro-optic crystal.

8. A dual crystal transverse electro-optic Q-switching device according to claim 1, wherein, The electro-optic Q-switch is applicable to a repetition frequency of 0.1 Hz-1000 kHz.

9. Use of the electro-optic Q-switch of any one of claims 1-8 in the preparation of a Q-switched laser.

10. The method of claim 1, wherein the electro-optic Q-switch is prepared by the steps of: Comprising: ​ The potassium dideuterium borotriphosphate crystal is in a ferroelectric phase or an anti-ferroelectric phase. The surface of the electro-optic crystal perpendicular to the light transmission direction is optically polished, and the surface is coated with an anti-reflection film having a laser transmittance of greater than 99% or is not coated with a film; the light transmission surface of the electro-optic crystal is a square or a rectangle, and the side length is 1-20 mm. XY The optical axis of the two electro-optic crystals are perpendicular to each other Z The direction of the optical axis of the two electro-optic crystals is perpendicular to each other One end of the two groups of wires is welded to the electrode layer of the two electro-optic crystal elements, respectively. The electrode layer is plated on the surface of the two electro-optic crystals to obtain two electro-optic crystal elements plated with the electrode layer The main axes of the two electro-optic crystals are rotated 90° relative to each other around the light transmission direction. The shell is used for packaging and fixing, and the electro-optic Q-switch is obtained. ​

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