Yb:yag monocrystal laser slicing system and slicing method

Abstract

The application discloses a Yb:YAG monocrystal laser slicing system and a slicing method, and solves the technical problem that a large amount of material is lost in the process of cutting a crystal by using a mechanical slicing method, and a great amount of material is wasted in the process of preparing a crystal wafer; the application adopts a laser processing method, realizes large-size Yb:YAG crystal slicing, reduces crystal slicing loss, adopts a sound-light deflection scanning module to cooperate with synchronous movement of a platform, realizes efficient laser modification, and reduces the manufacturing cost of the crystal wafer; in addition, through optical field parameter control and optimization of the internal optical field distribution of the crystal, the generation of cracks in the isotropic Yb:YAG crystal is promoted, the cracks are constrained to expand in the modified layer, the laser modification of the isotropic crystal is realized, the crystal slicing with a surface roughness of less than 2.5 microns is realized by using external force to drive crack expansion, and the method can be further expanded to other types of crystal slicing fields.

Description

TECHNICAL FIELD

[0001] The application relates to a laser slicing method of a laser gain medium material, in particular to a Yb:YAG single crystal laser slicing system and slicing method. BACKGROUND

[0002] The gain medium is a key material in the field of solid-state lasers. Due to its uniform lattice structure, high thermal conductivity and wide transparency range in the visible and infrared spectrum, Yb:YAG crystal is often used as a substrate material for laser gain medium. However, the growth of high-quality Yb:YAG crystal doped with rare earth elements faces challenges in uniformity, purity, structural integrity, growth rate, internal stress and crack control, resulting in extremely high cost of growing high-quality single crystals that meet the requirements of laser performance. However, for the preparation of crystal thin slices in the preparation of thin slice gain devices, the traditional mechanical slicing method is still used, such as diamond wire, which causes a large amount of material loss (cutting width of about 300 mu m) in the cutting process, resulting in a great waste of materials in the preparation of crystal thin slices.

[0003] Compared with the traditional cutting method, the laser slicing does not have the additional slicing loss caused by the tool width in mechanical slicing, greatly improving the utilization rate of the crystal, and the generated debris and other pollutants are also greatly reduced. As a new technology, laser slicing technology has been applied to slicing of hard and brittle materials such as silicon carbide which is easy to be decomposed or vaporized by laser. Laser slicing technology usually produces less than 50 mu m of loss, significantly improving the material utilization rate and reducing the cost of crystal thin slice manufacturing. However, for Yb:YAG crystal laser gain medium material with stable structure, good thermal stability and isotropy, laser slicing has not been realized. SUMMARY

[0004] The purpose of the present application is to solve the technical problem of a large amount of material loss in the crystal cutting process by using mechanical slicing, resulting in a great waste of materials in the preparation of crystal thin slices, and to provide a Yb:YAG single crystal laser slicing system and slicing method.

[0005] In order to achieve the above-mentioned application purpose, the application adopts the following technical solutions:

[0006] The application provides a Yb:YAG monocrystal laser slicing system, which is characterized by comprising a laser and, sequentially arranged along a light path of the laser, a beam expander, an acousto-optic deflection scanning module, a focusing lens, a sleeve lens and a focusing objective lens; an exit end of the focusing objective lens is oppositely provided with an X-Y-Z displacement table, the X-Y-Z displacement table is used for placing a Yb:YAG crystal to be sliced and driving the Yb:YAG crystal to move in X, Y and Z directions; laser emitted by the laser sequentially passes through the beam expander, the acousto-optic deflection scanning module, the focusing lens, the sleeve lens and the focusing objective lens and is incident to the Yb:YAG crystal, and a cavity array is formed on an OXY plane at a same Z-axis position in the Yb:YAG crystal, and microcracks continuously extended between cavities in the cavity array are generated.

[0007] The X-Y-Z displacement table and the laser are both connected with a control computer, and the control computer is used for controlling the X-Y-Z displacement table to drive the Yb:YAG crystal to move at a uniform speed and setting laser emission parameters of the laser.

[0008] Further, the focusing objective lens comprises a plurality of lenses, and the spacing between the plurality of lenses is set according to an aberration correction method, which is used for compensating and optimizing a wavefront phase of the light beam emitted by the sleeve lens, further optimizing the light field distribution in the Yb:YAG crystal and obtaining a minimum depth cavity array.

[0009] Further, the laser emission parameters of the laser refer to pulse width, repetition frequency and single pulse energy of the laser.

[0010] Further, the pulse width ranges from 2 ps to 9 ps, the repetition frequency ranges from 50 kHz to 200 kHz, and the single pulse energy ranges from 0.2 muJ to 1 muJ.

[0011] Meanwhile, the application also provides a Yb:YAG monocrystal laser slicing method based on the Yb:YAG monocrystal laser slicing system, which is characterized by comprising the following steps.

[0012] Step 1, placing the Yb:YAG crystal on the X-Y-Z displacement table and adjusting the position of the Yb:YAG crystal to be opposite to the exit end of the focusing objective lens through the control computer, and adjusting the laser emission parameters of the laser through the control computer according to the thickness of the slice to be cut;

[0013] Step 2, adjusting the spacing between the beam expander, the acousto-optic deflection scanning module, the focusing lens, the sleeve lens and the focusing objective lens according to design requirements, turning on the laser to emit laser, and the laser passes through the beam expander, the acousto-optic deflection scanning module, the focusing lens, the sleeve lens and the focusing objective lens and is incident to the Yb:YAG crystal to scan, form a cavity array and generate microcracks continuously extended between cavities in the cavity array;

[0014] Step 3, control the X-Y-Z displacement table to move at a constant speed in the X-Y plane, form a uniformly distributed cavity array on the OXY plane in the Yb:YAG crystal at the same Z-axis position, and a continuously expanding micro-crack between each cavity in the cavity array, to obtain an internally modified Yb:YAG crystal;

[0015] Step 4, cool the modified Yb:YAG crystal by liquid nitrogen, the cooling temperature is-200℃ to-190℃, and the cooling time is 1min to 5min, the OXY plane of the cavity array of the modified Yb:YAG crystal in step 3 is cracked, to obtain a Yb:YAG crystal sheet.

[0016] Further, in step 1, the focusing objective lens comprises a plurality of lenses, the spacing between the plurality of lenses can be calculated and adjusted according to the aberration correction method, so as to optimize the internal light field distribution of the Yb:YAG crystal, and obtain a cavity array with the minimum depth.

[0017] Further, in step 1, the laser emission parameter is adjusted, specifically the pulse width, the repetition frequency and the single pulse energy of the laser emission are adjusted.

[0018] Wherein, the pulse width ranges from 2ps to 9ps, the repetition frequency ranges from 50kHz to 200kHz, and the single pulse energy ranges from 0.2uJ to 1uJ.

[0019] Further, in step 3, the spacing between adjacent cavities in the modified Yb:YAG crystal is 4um to 10um.

[0020] Further, in step 2, the laser is expanded by a beam expander and input into an acousto-optic deflection scanning module to form a high-speed scanning beam, the high-speed scanning beam sequentially passes through a focusing lens, a sleeve lens and a focusing objective lens for focusing, and the focused high-speed scanning beam scans to form a cavity array at the OXY plane position of the Yb:YAG crystal to be sliced, and continuously expanding micro-cracks are generated between each cavity in the cavity array. Further, the scanning direction of the focused high-speed scanning beam is perpendicular to the moving direction of the Yb:YAG crystal.

[0021] The beneficial effects of the present application are:

[0022] (1) The Yb:YAG single crystal laser slicing system and slicing method of the present application adopts a laser processing method, realizes large-size Yb:YAG crystal slicing, reduces crystal slicing loss, uses an acousto-optic deflection scanning module to cooperate with high-speed scanning of the Yb:YAG crystal, realizes efficient laser modification of the Yb:YAG crystal, and the laser slicing method adopted by the present application reduces the manufacturing cost of the Yb:YAG crystal sheet.

[0023] (2) The Yb:YAG single crystal laser slicing system and slicing method of the application optimizes the parameters of the focusing optical system in combination with the aberration correction method, minimizes the cavity depth, and can improve the crystal slicing precision.

[0024] (3) The Yb:YAG single crystal laser slicing system and slicing method of the application promotes the generation of cracks in the isotropic Yb:YAG crystal through light field parameter regulation and crystal internal light field distribution optimization, and the cracks are constrained to expand within the modified layer, realizing isotropic crystal laser modification. The cracks are driven to expand by external force to realize crystal slicing with a surface roughness of less than 2.5 μm. This method can be further expanded to other types of crystal slicing fields. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a structural schematic diagram of an embodiment of the Yb:YAG single crystal laser slicing system of the application;

[0026] Figure 2 is a processing principle diagram of an embodiment of the Yb:YAG single crystal laser slicing method of the application;

[0027] Figure 3 is a side view of the modified layer in the crystal in an embodiment of the Yb:YAG single crystal laser slicing method of the application.

[0028] In the figure, 1 is an X-Y-Z displacement table; 2 is a laser; 3 is a beam expander; 4 is a control computer; 5 is a focusing objective lens; 6 is an acousto-optic deflection scanning module; 7 is a Yb:YAG crystal; 8 is a focusing mirror; and 9 is a sleeve lens. DETAILED DESCRIPTION

[0029] The technical solutions of the application will be described clearly and completely below with reference to the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0030] The Yb:YAG single crystal laser slicing system provided in the embodiment is as shown in Figure 1 Fig. 1, and includes an X-Y-Z displacement table 1 for placing a Yb:YAG crystal 7. The X-Y-Z displacement table 1 can drive the Yb:YAG crystal 7 to move at a constant speed along the X axis, the Y axis or the Z axis. In the initial state, the initial position of the Yb:YAG crystal 7 can be adjusted to facilitate slicing of the Yb:YAG crystal 7.

[0031] In the embodiment, the laser 2, the beam expander 3, the acousto-optic deflection scanning module 6, the focusing lens 8, the sleeve lens 9 and the focusing objective 5 are sequentially arranged along the optical axis, the exit end of the focusing objective 5 is oppositely provided with the X-Y-Z displacement table 1, and the X-Y-Z displacement table 1 is used for placing the Yb:YAG crystal 7; the laser emitted by the laser 2 sequentially passes through the beam expander 3, the acousto-optic deflection scanning module 6, the focusing lens 8, the sleeve lens 9 and the focusing objective 5 and is incident to the Yb:YAG crystal 7, and a cavity array and continuously expanding microcracks are formed in the Yb:YAG crystal 7.

[0032] The beam expander 3 is used for expanding the incident laser, the expanded laser is incident to the acousto-optic deflection scanning module 6, based on the acousto-optic effect, an equal-phase grating can be formed, a high-speed scanning beam is obtained, the high-speed scanning beam sequentially passes through the focusing lens 8, the sleeve lens 9 and the focusing objective 5 and is focused, and then the Yb:YAG crystal 7 is scanned at high speed to form the cavity array and the continuously expanding microcracks.

[0033] The focusing lens, the sleeve lens and the focusing objective belong to a focusing system and are used for focusing the light beam, and the sleeve lens and the focusing objective belong to a conjugate system.

[0034] In the embodiment, the acousto-optic deflection scanning module 6 can effectively improve the scanning efficiency.

[0035] In the embodiment, the X-Y-Z displacement table 1 and the laser 2 are both connected with the control computer 4, the control computer 4 is used for controlling the X-Y-Z displacement table 1 to uniformly move the Yb:YAG crystal 7 and setting the laser parameter of the laser 2, and the laser emitted by the focusing objective 5 is used for layer-by-layer modification processing of the Yb:YAG crystal 7, wherein the pulse width, the repetition frequency and the single pulse energy of the laser 2 are adjusted by the control computer 4.

[0036] In the embodiment, one or more pulses are generated at one point by using the low pulse energy laser, the instantaneous high temperature generated by the high peak power laser generates the cavity array in the Yb:YAG crystal 7, the stress generated by the high pressure causes the modification area to generate cracks, the movement of the X-Y-Z displacement table 1 is matched, the equal-interval array processing is performed in the horizontal modification layer, the cavity and the continuous microcrack are induced to be generated, and the laser modification in the crystal is realized.

[0037] In the embodiment, the X-Y-Z displacement table 1 and the laser 2 are both connected with the control computer 4, the control computer 4 is used for controlling the X-Y-Z displacement table 1 to uniformly move the Yb:YAG crystal 7 and setting the laser parameter of the laser 2.

[0038] In this embodiment, during the laser focusing process, due to the mismatch of the refractive index between the Yb:YAG crystal 7 and the outside, the light rays with different entrance pupil radii are refracted to different positions of the optical axis, so that the focused spot changes from the symmetric distribution of the ellipsoidal shape to the long strip shape with very uneven energy distribution, the focused spot is obviously elongated, that is, the focal depth increases, and the cavity formed in the Yb:YAG crystal 7 is also elongated, which further leads to the reduction of the slicing accuracy. At the same time, the increase of the focal depth is not conducive to the generation and expansion of the cracks. Therefore, in order to improve the slicing accuracy of the Yb:YAG crystal 7, the focal spot depth needs to be compressed by using the aberration correction method, the distance between the beam expander 3, the acousto-optic deflection scanning module 6, the focusing lens 8, the sleeve lens 9 and the focusing objective lens 5 is optimized to compensate and optimize the wavefront phase, optimize the light field distribution inside the Yb:YAG crystal 7, realize high-quality focusing inside the Yb:YAG crystal 7, and form a cavity with the minimum depth in the Yb:YAG crystal 7. The cavity after the depth is shortened will form a continuous expansion of micro-cracks.

[0039] In this embodiment, there is a close relationship between the pulse width of the ultrafast laser and the thermal effect generated during processing, and the short pulse width of the ultrafast laser directly affects the thermal effect generated during processing. By adjusting the laser pulse width, the processing effect can be controlled. The larger the laser pulse width, the more obvious the thermal effect generated during processing, and more cracks can be generated. However, if the thermal effect is too large, the processing accuracy will be reduced. When the laser pulse width increases from 500 fs to 9 ps, the micro-cracks generated during the modification process are more obvious. A pulse width of 2 ps to 9 ps is selected for crystal modification. Therefore, in order to obtain a slice with a certain thickness, the laser parameters emitted by the laser 2 are controlled by the computer 4, specifically the pulse width, repetition frequency and single pulse energy of the laser emitted by the laser 2. The pulse width is in the range of 2 ps to 9 ps, the repetition frequency is in the range of 50 kHz to 200 kHz, and the single pulse energy is in the range of 0.2 μJ to 1 μJ.

[0040] In this embodiment, the pulse point spacing of the modification area, that is, the interval between adjacent cavities, is 4 μm to 10 μm, which can realize the continuous penetration of the modification layer cracks. Therefore, in the modified Yb:YAG crystal, the interval between adjacent cavities is 4 μm to 10 μm. According to the basic process exploration, the optimized laser parameters and pulse point spacing are used for layered modification processing of the complete Yb:YAG crystal 7, which can realize the modification of the large-size Yb:YAG crystal 7.

[0041] The embodiment also provides a Yb:YAG single crystal laser slicing method based on the above-mentioned Yb:YAG single crystal laser slicing system, which comprises the following steps:

[0042] Step 1, set the Yb:YAG crystal 7 on the X-Y-Z displacement table 1, and control the X-Y-Z displacement table 1 to move at a constant speed along the X-Y-Z direction by the control computer 4, adjust the position of the Yb:YAG crystal 7 to be opposite to the exit end of the focusing objective 5, and adjust the laser parameters emitted by the laser 2 according to the required thickness of the sliced sheet;

[0043] According to the aberration correction method, the spacing between the multiple lenses in the focusing objective 5 is calculated, and the positions of the multiple lenses are adjusted;

[0044] Step 2, as shown in Figure 2 , adjust the spacing between the beam expander, the acousto-optic deflection scanning module, the focusing lens, the sleeve lens, and the focusing objective according to the design requirements, turn on the laser to emit laser, and the laser passes through the beam expander, the acousto-optic deflection scanning module, the focusing lens, the sleeve lens, and the focusing objective, and is incident into the Yb:YAG crystal to scan, forming a cavity array and continuous expansion microcracks between each cavity in the cavity array, as shown in Figure 3 ;

[0045] Adjusting the laser parameters emitted by the laser 2 specifically refers to adjusting the pulse width, repetition frequency, and single pulse energy of the laser emitted by the laser 2;

[0046] Wherein, the pulse width ranges from 2ps to 9ps, the repetition frequency ranges from 50kHz to 200kHz, and the single pulse energy ranges from 0.2μJ to 1μJ.

[0047] Step 3, control the X-Y-Z displacement table to move at a constant speed in the X-Y plane, form a uniformly distributed cavity array on the OXY plane at the same Z-axis position in the Yb:YAG crystal, and continuous expansion microcracks between each cavity in the cavity array, and obtain the internally modified Yb:YAG crystal;

[0048] Control the X-Y-Z displacement table 1 to move the Yb:YAG crystal 7 at a constant speed in the X-Y plane, and the distance moved each time is 4μm-10μm.

[0049] The high-speed scanning beam formed by the acousto-optic deflection scanning module 6 is perpendicular to the X-Y movement direction.

[0050] Step 4, cool the modified Yb:YAG crystal 7 by liquid nitrogen, the cooling temperature is-200℃- -190℃, the cooling time is 1min-5min, the modified Yb:YAG crystal is cracked, and the Yb:YAG crystal sheet is obtained.

[0051] In this embodiment, in order to realize high-quality splitting, uniform external stress is introduced, crack propagation and complete splitting are realized by using liquid nitrogen cooling splitting process. The modified crystal is adhered to the aluminum metal block with epoxy resin, and after the epoxy resin is completely cured, the metal block is placed in liquid nitrogen, the metal cooling shrinkage causes the crystal to be connected, the end close to the metal is under pressure stress shrinkage, the internal stress of the crystal is unevenly distributed, which promotes the crack propagation produced by laser modification, and the complete splitting of the crystal with a diameter of 5mm-50mm is realized.

[0052] The Yb:YAG single crystal laser slicing system and slicing method in the above embodiment are used, the Φ12mm or Φ46mm Yb:YAG crystal ingot is placed on the X-Y-Z displacement table 1, the 1030nm laser with a pulse width of 9ps is used for internal modification of the crystal, the laser modification depth is adjusted to 700μm, the acousto-optic deflection scanning module 6 is used for high-speed scanning of the light beam to improve the modification efficiency, and the X-Y-Z displacement table 1 is moved to realize the internal modification of the crystal.

[0053] After the modification is completed, the crystal is adhered to the aluminum metal block, the metal is cooled by liquid nitrogen, the non-uniform stress field is generated in the crystal after the metal cooling shrinkage, which promotes the crack propagation produced by the internal laser modification of the crystal, and the slicing of the Φ12mm and Φ46mm Yb:YAG crystal is realized, and the slicing thickness error is less than 10μm.

[0054] The above is only a specific embodiment of the present application, and the effect of the related specific embodiment and the comparative example is compared, but the protection scope of the present application is not limited to this, any change or replacement within the technical scope disclosed in the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A Yb:YAG single-crystal laser slicing system, characterized in that: The laser (2) includes a beam expander (3), an acousto-optic deflection scanning module (6), a focusing lens (8), a sleeve lens (9), and a focusing objective (5) arranged sequentially along the output optical path of the laser (2). The output end of the focusing objective (5) is provided with an XYZ displacement stage (1), which is used to place the Yb:YAG crystal (7) to be sliced ​​and to drive the Yb:YAG crystal (7) to move in three dimensions in the X, Y, and Z directions. The laser emitted by the laser (2) passes through the beam expander (3), the acousto-optic deflection scanning module (6), the focusing lens (8), the sleeve lens (9), and the focusing objective (5) in sequence and is incident on the Yb:YAG crystal (7). A cavity array is formed on the OXY plane at the same Z-axis position in the Yb:YAG crystal (7), and microcracks are continuously extended between the cavities in the cavity array. The focusing objective (5) includes multiple lenses. The spacing between the multiple lenses is calculated and set according to the aberration correction method. It is used to compensate for and optimize the wavefront phase of the beam emitted from the sleeve lens (9), thereby optimizing the light field distribution inside the Yb:YAG crystal (7) and obtaining a minimum depth cavity array. The XYZ displacement stage (1) and the laser (2) are both connected to a control computer (4). The control computer (4) is used to control the XYZ displacement stage (1) to drive the Yb:YAG crystal (7) to move at a constant speed, and to set the laser emission parameters of the laser (2). The setting of laser emission parameters of laser (2) specifically refers to adjusting the pulse width, repetition rate and single pulse energy of laser emission of laser (2); The pulse width ranges from 2ps to 9ps, the repetition rate ranges from 50kHz to 200kHz, and the single pulse energy ranges from 0.2μJ to 1μJ.

2. A method for laser slicing Yb:YAG single crystals, characterized in that, Using the Yb:YAG single crystal laser slicing system as described in claim 1 includes the following steps: Step 1: Set the Yb:YAG crystal (7) on the XYZ displacement stage (1), and adjust the position of the Yb:YAG crystal (7) to face the output end of the focusing objective (5) by the control computer (4). Adjust the laser parameters emitted by the laser (2) by the control computer (4) according to the required thickness of the thin slice. Step 2: Adjust the spacing between the beam expander (3), acousto-optic deflection scanning module (6), focusing lens (8), sleeve lens (9), and focusing objective lens (5) according to the design requirements. Turn on the laser (2) to emit laser light. The laser light passes through the beam expander (3), acousto-optic deflection scanning module (6), focusing lens (8), sleeve lens (9), and focusing objective lens (5) and is incident on the Yb:YAG crystal (7) for scanning, forming a cavity array, and generating continuously expanding microcracks between the cavities in the cavity array. Step 3: Control the XYZ displacement stage (1) to move at a constant speed in the XY plane, and form a uniformly distributed cavity array on the OXY plane at the same Z-axis position in the Yb:YAG crystal (7), as well as microcracks that continuously extend between the cavities in the cavity array, to obtain the internally modified Yb:YAG crystal. Step 4: Cool the modified Yb:YAG crystal (7) with liquid nitrogen at a temperature of -200℃ to -190℃ for 1 min to 5 min. The modified Yb:YAG crystal will crack in the OXY plane where the cavity array described in step 3 is located, and obtain Yb:YAG crystal thin film.

3. The method for laser slicing Yb:YAG single crystals according to claim 2, characterized in that: In step 1, the focusing objective (5) includes multiple lenses. The spacing between the multiple lenses can be calculated and adjusted according to the aberration correction method to optimize the light field distribution inside the Yb:YAG crystal (7) and obtain a cavity array with the minimum depth.

4. The method for laser slicing Yb:YAG single crystals according to claim 2, characterized in that: In step 1, adjusting the laser emission parameters of the laser (2) specifically refers to adjusting the pulse width, repetition rate, and single pulse energy of the laser emitted by the laser (2); The pulse width ranges from 2ps to 9ps, the repetition rate ranges from 50kHz to 200kHz, and the single pulse energy ranges from 0.2μJ to 1μJ.

5. The method for laser slicing Yb:YAG single crystals according to claim 2, characterized in that: In step 3, the spacing between adjacent cavities in the modified Yb:YAG crystal is 4μm-10μm.

6. The method for laser slicing Yb:YAG single crystals according to claim 2, characterized in that: In step 2, the laser beam is expanded by the beam expander (3) and input into the acousto-optic deflection scanning module (6) to form a high-speed scanning beam. The high-speed scanning beam is focused by the focusing lens (8), the sleeve lens (9), and the focusing objective lens (5) in sequence. The focused high-speed scanning beam scans at the OXY plane position in the Yb:YAG crystal (7) where it needs to be sliced ​​to form a cavity array, and continuously expanding microcracks are generated between the cavities in the cavity array.

7. The method for laser slicing Yb:YAG single crystals according to claim 6, characterized in that: The scanning direction of the focused high-speed scanning beam is perpendicular to the moving direction of the Yb:YAG crystal (7).

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