CN113042884A - Femtosecond laser rotary type double-light-spot light beam micropore machining method - Google Patents
Femtosecond laser rotary type double-light-spot light beam micropore machining method Download PDFInfo
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- CN113042884A CN113042884A CN202110490885.8A CN202110490885A CN113042884A CN 113042884 A CN113042884 A CN 113042884A CN 202110490885 A CN202110490885 A CN 202110490885A CN 113042884 A CN113042884 A CN 113042884A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/0604—Shaping the laser beam, e.g. by masks or multi-focusing by a combination of beams
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
- B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
- B23K26/0624—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses using ultrashort pulses, i.e. pulses of 1ns or less
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
- B23K26/0648—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising lenses
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/08—Devices involving relative movement between laser beam and workpiece
- B23K26/083—Devices involving movement of the workpiece in at least one axial direction
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/36—Removing material
- B23K26/38—Removing material by boring or cutting
- B23K26/382—Removing material by boring or cutting by boring
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- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Mechanical Engineering (AREA)
- Laser Beam Processing (AREA)
Abstract
The invention relates to a femtosecond laser rotary type double-light-spot light beam micropore machining method, and belongs to the technical field of laser application. The method utilizes the spatial light modulator to load 0-pi phase, and carries out phase shaping on the incident femtosecond laser with Gaussian intensity distribution, and because different phases are applied to the left part and the right part of the incident Gaussian light field, a light field intensity dark region is formed in the middle area where the two parts are overlapped due to phase distortion, the original Gaussian beam is shaped into a double-spot beam; in the micropore machining process, the light field dark area at the center of the double-light-spot light beam is beneficial to the generated plasma to be sprayed from the position, so that the influence on subsequent laser pulse is reduced, the energy deposition efficiency is improved, and the micropore machining depth is increased.
Description
Technical Field
The invention relates to a femtosecond laser rotary type double-light-spot light beam micropore machining method, and belongs to the technical field of laser application.
Background
Micropores are very common structures, and high-quality micropore structures have extremely important application in various fields such as microfluidic chips, engine turbine blades, biosensing and the like. Conventional mechanical drilling, electric spark drilling and other modes are limited by the size of a machining device, and the machined microporous structure is shallow in depth and large in size and cannot meet requirements. The femtosecond laser has unique advantages when being used in a micropore machining process due to the characteristics of ultrafast and super-strong and the non-contact machining form of the femtosecond laser. However, the ultra-high peak intensity of femtosecond lasers also presents certain processing problems. During the femtosecond laser processing, the ultrahigh peak intensity of the laser leads to the generation of various forms of plasmas near a focus after the laser is focused, including plasmas generated by ionized air and material-steam plasmas generated in the phase change process of an ablative material. For non-transparent materials, the processing of deeper micropore structures can be realized only by adopting a traditional tapping method and matching with a moving focus, and the existence of plasma can seriously hinder the propagation of subsequent laser pulses and the eruption of fragments in the tapping type micropore processing process, so that the deposition of subsequent laser energy in the material is influenced, the phenomenon of deep saturation can be caused in the micropore processing process, and the depth of the micropore structures processed by femtosecond laser is greatly limited. The vacuum environment is adopted, so that air ionization can be avoided, eruption of material-steam plasma, debris and the like is facilitated, the problems can be relieved to a certain extent, however, the complexity of a processing system is greatly increased due to the introduction of the vacuum environment, the processing cost is increased, and the advantage that the femtosecond laser processing is not limited by the processing environment is lost. Therefore, a new processing method is needed to solve the problem that the plasma obstructs the deposition of laser energy during the femtosecond laser processing process, and realize the processing of the high depth-diameter ratio micropore structure on the non-transparent material.
Disclosure of Invention
The invention aims to solve the problems that the depth of a micropore structure processed on a non-transparent material by the existing femtosecond laser is limited and the use requirement cannot be met, and provides a femtosecond laser rotary type double-light-spot light beam micropore processing method;
the purpose of the invention is realized by the following technical scheme.
A femtosecond laser rotary type double-spot beam micropore processing method utilizes a spatial light modulator to load 0-pi phase to carry out phase shaping on incident femtosecond laser with Gaussian intensity distribution, and because different phases are applied to the left part and the right part of an incident Gaussian light field, a light field intensity dark zone is formed in the middle area of the superposition of the two parts due to phase distortion, the original Gaussian beam is shaped into a double-spot beam; in the micropore machining process, the light field dark area at the center of the double-light-spot light beam is beneficial to the generated plasma to be sprayed from the position, so that the influence on subsequent laser pulse is reduced, the energy deposition efficiency is improved, and the micropore machining depth is increased.
The computer controls real-time frame-by-frame switching of 0-pi phase diagrams distributed at different angles on the spatial light modulator, so that the double-spot light beam rotates along the central axis, the roundness of the hole can be improved, the laser repetition frequency is matched, and the sample is moved up and down by the translation table to process a circular deep hole structure.
The repetition frequency of the adopted laser cannot be lower than the frame conversion frequency of the phase diagram, and the frame conversion frequency of the phase diagram determines the rotation speed of the double-spot light beam, so that the micropore processing efficiency is determined.
The expression of the loaded 0- π phase is:
wherein tau k is the phase of the loaded kth phase diagram, theta is the polar angle of a polar coordinate, n is a positive integer, k is a natural number, and k is more than or equal to 0 and is less than n; the expression means that the angle of 2 pi is equally divided into n equal parts, and at the moment, n 0-pi phase diagrams with different angles are required to be switched to realize the rotation of the double-spot light beam, wherein k represents a distribution area with different phases of 0 and pi of a k-th phase diagram.
The method specifically comprises the following steps:
the method comprises the following steps: the femtosecond laser generates laser with Gaussian intensity distribution, and the energy of the laser is adjusted by the energy adjusting device;
step two: gaussian laser is incident on the reflective liquid crystal spatial light modulator at a small angle, and the incident Gaussian laser is shaped into a double-light-spot light beam by loading a required 0-pi phase on the spatial light modulator through a computer;
step three: through computer control, the 0-pi phase diagrams with different angle distributions are switched on the spatial light modulator in real time, and a rotary double-spot light beam is realized by matching with a certain pulse repetition frequency;
step four: the emitted rotary double-light-spot light beams are conveyed through a 4f system, so that the influence of diffraction on the integral light field in the transmission process is avoided;
step five: focusing the carried light field by adopting an objective lens, placing a sample at a focus, moving a translation table to enable the focus to gradually go deep into the sample, processing the sample, and obtaining the deep hole structure by adopting proper laser energy and frame changing speed.
Advantageous effects
1. The invention utilizes the spatial light modulator to carry out phase shaping on incident Gaussian laser to obtain double-spot light beams, and combines the function that the spatial light modulator can switch a phase diagram in real time to obtain rotary double-spot light beams.
2. The rotary double-light-spot light beam micropore processing method provided by the invention can avoid the problem of the non-circular micropore structure caused by the non-circular light spot or the laser linear polarization in the previous femtosecond laser micropore processing process, and improve the roundness of the micropore structure.
Drawings
FIG. 1 is a phase diagram of a beam shaper to be loaded and a shaped light field intensity distribution at a corresponding focus; FIG. 1(a) is a phase diagram requiring loading; FIG. 1(b) is the shaped light field intensity distribution at the corresponding focal point;
fig. 2 is a schematic diagram of the principle of the femtosecond laser rotary type double-spot beam micropore processing method provided by the invention.
Detailed Description
The invention is further described with reference to the following figures and examples.
Example 1
The amplification stage of the femtosecond laser generates a light beam with Gaussian intensity distribution, and the laser energy is adjusted by an energy adjusting device, wherein the energy adjusting device adopted in the embodiment is a continuously adjustable disc-shaped attenuation sheet, and the adopted laser energy is 50 mW. Gaussian beams are incident to the surface of a liquid crystal sheet of the reflective liquid crystal spatial light modulator at a small angle, and a 0-pi phase diagram is loaded on the spatial light modulator through a computer, so that double-spot beams are realized. Controlling the real-time switching of the 0-pi phase diagrams distributed at different angles on the spatial light modulator by using a computer program, wherein the corresponding expression of the loaded phase is as follows:
wherein, taukIs the phase of the loaded kth phase diagram, theta is the polar angle of a polar coordinate, n is a positive integer, k is a natural number, and k is more than or equal to 0 and less than n. The expression means that the angle of 2 pi is equally divided into n equal parts, and at the moment, n 0-pi phase diagrams with different angles are required to be switched to realize the rotation of the double-spot light beam, wherein k represents a distribution area with different phases of 0 and pi of a k-th phase diagram. In this example, n is 50, k is an integer between 0 and 50, and the laser repetition frequency is 1kHz, so as to generate a corresponding series of phase diagrams as shown in fig. 1 (a).
The rotating double-spot light beam reflected by the surface of the liquid crystal plate of the spatial light modulator sequentially passes through two identical plano-convex lenses, the distance between the two plano-convex lenses is equal to two times of focal length, the distance between the first plano-convex lens and the spatial light modulator is the focal length of the lens, at the moment, the two plano-convex lenses jointly form a 4f system to convey the shaped light beam to a focusing objective lens without diffraction, the objective lens is just arranged at the focal point of the second plano-convex lens, in the embodiment, the focal lengths of the two plano-convex lenses are both 600mm, the conveyed shaped light beam is focused by the focusing objective lens to form the double-spot light beam at the focal point, in the embodiment, the adopted focusing objective lens is a 20-time objective lens, the numerical aperture is 0.45, and the light field distribution of the. The sample is placed at the focus of an objective lens, 0-pi phase diagrams distributed at different angles are switched frame by frame, the sample is moved up and down by matching with a translation platform, the focus is moved up and down relative to the sample, and the femtosecond laser rotary type double-light-spot light beam micropore processing can be realized, wherein the frame number adopted in the example is 50Hz, namely 50 phase diagrams are switched per second, and the adopted sample is an aluminum sheet. The principle of the femtosecond laser rotary type double-light-spot light beam micropore machining method is schematically shown in fig. 2, and the generated plasma can be sprayed outwards from a light field dark area at the center preferentially, so that the deposition of laser energy is facilitated, and the processing of micropores with high depth-diameter ratio on a non-transparent material is realized.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A femtosecond laser rotary type double-light-spot light beam micropore processing method is characterized in that: loading a 0-pi phase by using a spatial light modulator, performing phase shaping on the incident femtosecond laser with Gaussian intensity distribution, wherein different phases are applied to the left part and the right part of the incident Gaussian light field, and a light field intensity dark region is formed in the middle area where the two parts are overlapped due to phase distortion, so that the original Gaussian beam is shaped into a double-spot beam; in the micropore machining process, the light field dark area at the center of the double-light-spot light beam is beneficial to the generated plasma to be sprayed from the position, so that the influence on subsequent laser pulse is reduced, the energy deposition efficiency is improved, and the micropore machining depth is increased.
2. The femtosecond laser rotary type double-spot beam micropore processing method according to claim 1, wherein: the computer controls real-time frame-by-frame switching of 0-pi phase diagrams distributed at different angles on the spatial light modulator, so that the double-spot light beam rotates along the central axis, the roundness of the hole can be improved, the laser repetition frequency is matched, and the sample is moved up and down by the translation table to process a circular deep hole structure.
3. The femtosecond laser rotary type double-spot beam micropore processing method according to claim 2, wherein: the repetition frequency of the adopted laser cannot be lower than the frame conversion frequency of the phase diagram, and the frame conversion frequency of the phase diagram determines the rotation speed of the double-spot light beam, so that the micropore processing efficiency is determined.
4. The femtosecond laser rotary type double-spot beam micropore processing method as claimed in claim 1 or 2, wherein: the expression of the loaded 0- π phase is:
wherein, taukIs the phase of the loaded kth phase diagram, theta is the polar angle of a polar coordinate, n is a positive integer, k is a natural number, and k is more than or equal to 0 and less than n; the expression means that the angle of 2 pi is equally divided into n equal parts, and at the moment, n 0-pi phase diagrams with different angles are required to be switched to realize the rotation of the double-spot light beam, wherein k represents a distribution area with different phases of 0 and pi of a k-th phase diagram.
5. The femtosecond laser rotary type double-spot beam micropore processing method as claimed in claim 1, 2 or 3, wherein: the method comprises the following steps:
the method comprises the following steps: the femtosecond laser generates laser with Gaussian intensity distribution, and the energy of the laser is adjusted by the energy adjusting device;
step two: gaussian laser is incident on the reflective liquid crystal spatial light modulator at a small angle, and the incident Gaussian laser is shaped into a double-light-spot light beam by loading a required 0-pi phase on the spatial light modulator through a computer;
step three: through computer control, the 0-pi phase diagrams with different angle distributions are switched on the spatial light modulator in real time, and a rotary double-spot light beam is realized by matching with a certain pulse repetition frequency;
step four: the emitted rotary double-light-spot light beams are conveyed through a 4f system, so that the influence of diffraction on the integral light field in the transmission process is avoided;
step five: focusing the carried light field by adopting an objective lens, placing a sample at a focus, moving a translation table to enable the focus to gradually go deep into the sample, processing the sample, and obtaining the deep hole structure by adopting proper laser energy and frame changing speed.
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2021
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