A method for fine modification of the inside of a crystal based on double-beam focus interference

Abstract

The application discloses a method for fine modification of the interior of a crystal based on double-beam laser focus interference, and belongs to the field of laser precision machining. The method is realized by adjusting the divergence angle of double beams by using a laser shaping device to realize the overlap of focus A and focus B. The double foci overlap and interfere, and the interference phenomenon of the energy intensity alternately changing occurs in the focus overlap area; under the interference, laser energy is concentrated to the interference enhancement position, and the energy peak value can exceed the modification threshold of the material interior, and modification occurs; the size of the double-focus overlap area is compressed relative to the conventional single-focus area, and the modification by interference only occupies a part of the overlap area, and the size of the modification area is further compressed. Compared with the conventional single-focus modification area, the longitudinal size of the modification by the method can be compressed by at least 50%, and the precision of the micro-nano structure in the processed crystal is higher. According to the characteristics of the crystal material, laser parameters are selected, and scanning is carried out according to a preset track, modification points form a modification line, and then high-precision machining of a complex micro-nano structure in the crystal can be realized.

Description

A method for fine-tuning the interior of crystals based on dual-beam focal interferometry Technical Field

[0001] This invention belongs to the field of laser precision machining technology and relates to a method for finely modifying the interior of a crystal based on dual-beam focal interference. Background Technology

[0002] Crystal materials possess excellent optical, electrical, and mechanical properties, leading to their widespread application in aerospace, new energy, and electronic information fields. Semiconductor materials, in particular, such as silicon, silicon carbide, gallium arsenide, and diamond, play an irreplaceable role in microelectronics, resulting in enormous demand. Precision machining of the internal components of crystal materials is required for applications including waveguides, microchannels, and sensors. While two-photon polymerization (SPDP) is a relatively mature internal machining process, it is generally used for 3D printing of polymer materials. Conventional laser processing methods limit the precision required for machining the internal components of crystal materials.

[0003] Current conventional laser internal modification methods suffer from self-focusing due to aberrations and nonlinear effects generated during laser processing inside the crystal. This results in a large longitudinal extension of the modified region, limiting the processing accuracy inside the crystal. Summary of the Invention

[0004] To further improve the processing accuracy of micro- and nano-structures inside crystal materials, the present invention aims to provide a method for fine refining the internal structure of crystals based on dual-beam focal interference. Two beams are focused to the same position inside the crystal and interfere there. Refining occurs through interference, reducing the aberrations of the laser inside the crystal and the impact of self-focusing refining on processing accuracy. The refining point moves and scans according to a preset trajectory, forming a refining line, thereby achieving fine refining of the internal structure of the crystal.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention discloses a method for fine refining and processing the interior of a crystal based on dual-beam focal interference, comprising the following steps:

[0007] Step 1: The ultrafast laser performs spatial shaping and splits into two beams;

[0008] Step 2: Irradiate the interior of the crystal perpendicularly along the same longitudinal axis and focus at a predetermined depth. By adjusting the laser parameters, the focus of a single laser beam does not alter the crystal.

[0009] Step 3: After spatial shaping, beam 1 forms focal point A at a predetermined position. After spatial shaping, beam 2 is reflected from the bottom of the crystal and returns along the same path, forming focal point B at the same position. It overlaps with focal point A and interferes, forming a finely modified region.

[0010] Step 4: Move and scan along the set trajectory to form a modification line from the modified particles, thereby realizing the fabrication of micro-nano structures inside the crystal.

[0011] The specific implementation method of step three is as follows: The divergence angle is adjusted using a laser shaping device to achieve temporal and spatial overlap between focus A and focus B. The two focal points overlap and interfere, resulting in an interference phenomenon where energy intensity alternates in the overlapping region. Under interference, the laser concentrates most of its energy at the interference enhancement point, and its energy peak can exceed the material's internal modification threshold, thus causing modification. The size of the double-focal overlap region is compressed compared to conventional single-focal modification, while the interference-induced modification only occupies a portion of the overlap region. The modified region is further compressed, forming a finely modified region, resulting in higher precision in the micro / nano structure of the processed crystal.

[0012] Two-beam interference is achieved either by beam splitting, shaping, modulation, and focusing using the same laser system, or by synchronous focusing using two laser systems.

[0013] The crystal possesses properties such as high hardness and high brittleness; it can be penetrated by lasers of corresponding wavelengths, enabling internal modification via ultrafast lasers. The high hardness refers to a Mohs hardness greater than 7, and the high brittleness refers to an elongation at break under external force of less than 1%.

[0014] The crystals include silicon, silicon carbide, sapphire, gallium nitride, gallium arsenide, and diamond.

[0015] The trajectory can be set without restriction, and the required micro- and nano-structures can be fabricated according to actual needs.

[0016] The ultrafast laser refers to a laser pulse width in the femtosecond (10^-10) seconds. -15 (seconds) to picoseconds (10) -12 Lasers on the order of seconds.

[0017] Beneficial effects:

[0018] 1. The present invention discloses a method for fine modification of crystal based on dual-beam laser focus interference. The method uses two beams focused into the crystal to interfere and modify it. Compared with the conventional single-beam laser focus modification method, it can reduce the influence of laser aberrations and self-focusing on processing accuracy inside the crystal, realize fine modification of the crystal material, and facilitate high-precision processing of micro and nano structures inside the crystal.

[0019] 2. This invention discloses a method for finely modifying crystals based on dual-beam laser focus interference. It utilizes a laser shaping device to flexibly adjust the divergence angle, enabling simultaneous focusing of two beams at arbitrary depths within the crystal. The focal points of the two beams overlap and interfere. Under the interference effect, the laser concentrates most of its energy at the interference enhancement point, and its energy peak exceeds the modification threshold within the material, thus causing modification and ultimately achieving fine processing at different depths within the crystal material.

[0020] 3. This invention discloses a method for finely modifying crystals based on dual-beam laser focus interference. The size of the overlapping region of the dual-focus area is compressed compared to the conventional single-focus area, while the modification during interference only occupies a portion of the overlapping region, further compressing the modified region. The longitudinal dimension of the modified region using this method can be compressed by at least 50%, improving the precision of the modification and thus greatly enhancing the accuracy of the micro / nano structures within the processed crystal.

[0021] 4. The present invention discloses a method for fine modification of crystals based on dual-beam laser focus interference. The method selects appropriate laser parameters for modification according to the characteristics of the crystal material. It is applicable to the internal processing of various types of crystal materials and has a wide range of applications.

[0022] 4. The present invention discloses a method for finely modifying crystals based on dual-beam laser focus interference. The method involves moving and scanning along a preset trajectory, forming modification lines from the modified points, and achieving flexible modification by adjusting the laser parameters, which facilitates the processing of complex micro- and nano-structures. Attached Figure Description

[0023] Figure 1 is a schematic diagram of the process of a crystal fine modification method based on dual-beam laser focus interference according to the present invention;

[0024] Figure 2 is a schematic diagram of forming a finely modified region inside a SiC ingot using the method of the present invention.

[0025] Wherein: 1—Laser beam splitter A, 2—Laser beam splitter B, 3—Objective lens, 4—SiC ingot, 5—Dual-focus interference modification region, 6—Single-focus modification region, 7—Mirror, 8—Infrared camera, 9—Ultrafast laser, 10—Spatial light modulator.

[0026] Figure 3 is a schematic diagram of forming a fine modified surface inside a SiC ingot using the method of the present invention in the embodiment;

[0027] Wherein: 1—laser beam splitter A, 2—laser beam splitter B, 3—objective lens, 4—SiC ingot, 5—double-focus interference modification region.

[0028] Figure 4 is an experimental side view comparing the modification of the crystal interior using conventional methods and the method of the present invention. Detailed Implementation

[0029] To better illustrate the purpose and advantages of this invention, the following description, in conjunction with the accompanying drawings and examples, further clarifies the invention. The following embodiments are merely one example of the present invention and not all examples. The accompanying drawings are for illustrative purposes only, and their specific proportions can be adjusted according to design requirements.

[0030] This embodiment discloses a specific embodiment of the method of the present invention, which uses femtosecond laser to perform internal fine modification on SiC ingots. The sample used in the embodiment is a semi-insulating SiC ingot, and the laser used in the embodiment is a femtosecond laser with a wavelength of 1030nm.

[0031] As shown in Figure 1, this embodiment discloses a method for finely modifying crystals based on dual-beam laser focal interferometry. The specific implementation steps are as follows:

[0032] Step 1: The femtosecond laser is spatially shaped by a spatial light modulator (SLM) and split into two independent beams. The divergence angle, intensity distribution, phase, and polarization state of the laser beams are dynamically adjusted to adapt to the actual processing requirements.

[0033] Step 2: Irradiate the interior of the crystal perpendicularly along the same longitudinal axis and focus at a depth of 200 μm. By adjusting the laser parameters, the energy at the focal point of a single laser beam does not exceed the SiC modification threshold, thus not modifying the SiC ingot.

[0034] In step two, the laser's pulse width ranges from 200 fs to 20 ps, ​​its wavelength ranges from 355 nm to 1100 nm, and its laser power is adjustable from 0 to 20 W.

[0035] Step 3: After spatial shaping, beam 1 forms focal point A at a predetermined position 200 μm from the surface of the SiC ingot. After spatial shaping, beam 2 is reflected from the bottom surface of the crystal and returns along the same path, forming focal point B at the same position. It overlaps with focal point A and interferes, forming a fine modified particle region.

[0036] In step three, the divergence angle is adjusted using a spatial shaper to achieve temporal and spatial overlap between focus A and focus B. Under interference, an interference phenomenon with alternating energy intensities will occur in the overlapping area of ​​the focal points. The laser will concentrate most of its energy at the interference enhancement point, generating interference peaks and undergoing quality modification.

[0037] Step 4: By precisely controlling the femtosecond laser beam to move and scan along a preset trajectory, multiple modified points can be generated inside the SiC ingot. These modified points are connected to form modified lines, thereby precisely manufacturing a variety of micro and nano structures inside the SiC ingot.

[0038] Comparing the modified region processed using the method of the present invention with the single-focus modified region, the longitudinal modified dimension is reduced by at least 50%, which shows that the processing accuracy is significantly improved under the same processing conditions.

[0039] As shown in Figure 2, a fine-modification region is formed inside the SiC ingot 4 using the method of this invention. An ultrafast laser 9 is split into laser beam A and laser beam B by a spatial light modulator 10. Laser beams A and B undergo spatial shaping using the spatial light modulator 10 to correct aberrations. There is a pulse delay between the two laser beams, allowing them to simultaneously reach a depth of 200 μm inside the crystal. Laser beam A is perpendicularly irradiated into the crystal interior via a reflector 7 and an objective lens 3, forming a focal point A at a depth of 200 μm. Laser beam B is perpendicularly irradiated into the ingot interior via a reflector 7 and an objective lens 3, reflected from the bottom surface of the crystal, and returns along the same path, forming a focal point B at the same location. The processing is observed using an infrared camera 8 to accurately measure the distance to the laser focal points. After spatial shaping, focal points A and B overlap and interfere along the same longitudinal axis, forming a bifocal interference modification region 5. Compared to a single-focal modification region 6, the bifocal interference modification region 5 has a smaller longitudinal dimension.

[0040] As shown in Figure 3, laser beam splitters A and B are focused by objective lens 3 into the interior of a semi-insulating SiC ingot 4, with a focusing depth of 200 μm. After forming a dual-focus interference modification region 5 using the method of this invention, scanning modification is performed along the scanning trajectory at a scanning speed of 2000 μm / s. The scanning trajectory consists of multiple modification lines, around which microcracks are generated. The lines are spaced 50 μm apart, allowing the microcracks to extend and achieve full coverage, forming a modification surface. Subsequently, the method of this invention can be used to modify larger SiC ingots, and equal and opposite forces are applied to the upper and lower surfaces of the modified SiC ingot, causing the SiC wafer to peel off from the ingot.

[0041] Figure 4 shows an experimental side view comparing the modification of the crystal interior using conventional methods and the method of this invention. Since there is still room for optimization of the laser parameters, the longitudinal dimensional accuracy of the modification using the method of this invention is not optimal. Comparing the modification region dimensions of the two methods under the same laser parameters, the longitudinal dimension of the modification using the method of this invention is reduced by 50% compared to single-focus modification, resulting in a finer modification region.

[0042] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fine-tuning the interior of a crystal based on dual-beam focal interference, characterized in that: The process includes the following steps: Step 1: The ultrafast laser is spatially shaped and split into two beams; Step 2: The interior of the crystal is vertically irradiated along the same longitudinal axis and focused at a predetermined depth; by adjusting the laser parameters, the focus of a single laser beam does not alter the crystal; Step 3: After spatial shaping, laser beam A forms focus A at a predetermined position; laser beam B, after spatial shaping, is reflected from the bottom surface of the crystal and returns along the same path to form focus B, which overlaps with focus A and interferes, forming a finely modified region; The specific implementation method of Step 3 is to use a laser shaping device to adjust the divergence angle to achieve temporal and spatial alignment between focus A and focus B. Overlap; the two focal points overlap and interfere, and the energy intensity of the overlapping area changes alternately. Under the interference, the laser concentrates most of the energy at the interference enhancement point, and its energy peak exceeds the material's internal modification threshold, thus causing modification. The size of the double-focal overlapping area is compressed compared to the conventional single-focal area. The modification caused by interference only occupies a part of the overlapping area, and the modification area is further compressed to form a fine modification area, making the processed crystal's internal micro-nano structure more precise. Step 4: Move and scan according to the set trajectory, and the modification points form modification lines to realize the processing of the crystal's internal micro-nano structure.

2. The method for fine refining and processing the interior of a crystal based on dual-beam focal interference as described in claim 1, characterized in that: Two-beam interference is achieved by using the same laser system for beam splitting, shaping, modulation, and focusing.

3. The method for fine refining and processing the interior of a crystal based on dual-beam focal interference as described in claim 1, characterized in that: Two-beam interference is achieved by synchronous focusing of two laser systems.

4. The method for fine refining and processing the interior of a crystal based on dual-beam focal interference as described in claim 1, characterized in that: The crystal has high hardness and high brittleness, and can be penetrated by lasers of corresponding wavelengths to achieve internal modification by ultrafast lasers; the high hardness refers to a Mohs hardness greater than 7, and the high brittleness refers to an elongation at break under external force of less than 1%.

5. The method for fine refining and processing the interior of a crystal based on dual-beam focal interference as described in claim 1, characterized in that: The crystal includes silicon, silicon carbide, sapphire, gallium nitride, gallium arsenide, or diamond.

6. The method for fine refining and processing the interior of a crystal based on dual-beam focal interference as described in claim 1, characterized in that: The ultrafast laser has a pulse width range of 200 fs to 20 ps, ​​a wavelength range of 355 nm to 1100 nm, and a laser power range of 0 to 20 W.

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