CN117600647A - Acousto-optic dynamic focusing module and three-dimensional scanning system - Google Patents
Acousto-optic dynamic focusing module and three-dimensional scanning system Download PDFInfo
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/33—Acousto-optical deflection devices
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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
- B23K26/082—Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
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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
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
Abstract
The invention discloses an acousto-optic dynamic focusing module and a three-dimensional scanning system. The acousto-optic dynamic focusing module comprises a plurality of optical components and a focusing field lens, wherein the optical components and the focusing field lens are sequentially arranged along an optical path, and the optical components comprise a first acousto-optic deflector, a first concave parabolic mirror, a second concave parabolic mirror and a second acousto-optic deflector; the concave surfaces of the first concave parabolic mirror and the second concave parabolic mirror are oppositely arranged; an aberration correcting lens group is arranged between any two optical components; an aberration correcting lens group is arranged between any two optical components; the first acousto-optic deflector and the second acousto-optic deflector are used for deflecting the focus of the laser focused by the focusing field lens along the light path direction through the change of the refractive index of the first acousto-optic deflector and the second acousto-optic deflector. The invention adopts the acousto-optic deflector to carry out dynamic focusing, so that the focusing frequency along the direction of the light path can be increased to the MHz level, the speed of three-dimensional scanning is increased, and the focusing performance of the system is greatly improved.
Description
Technical Field
The invention belongs to the field of laser processing, and particularly relates to an acousto-optic dynamic focusing module and a three-dimensional scanning system.
Background
With the continuous development of laser processing technology, in order to improve the processing speed, higher requirements are placed on the dynamic focusing speed of laser. The laser scanning device is a key for changing the focusing speed of the laser, and the highest response frequency of the laser scanning device directly affects the focusing speed of the laser. Laser scanning devices can be divided into two main categories: mechanical scanning device and diffraction scanning device. The mechanical scanning device directly changes the light beam along the axis through the linear motion of the motor or generates an optical path difference before focusing through the circular motion of the motor, so as to change the focusing position of the light beam. For the mechanical scanning device, the response frequency is the order of KHz, the focusing speed of m/s order can be realized, and the mechanical scanning device comprises a galvanometer, a prism, a Galileo transmission type dynamic focusing module, an off-axis parabolic mirror reflection type dynamic focusing module and the like. The diffraction scanning device changes the refractive index of a medium by utilizing the principles of liquid crystal birefringence, electro-optic effect or acousto-optic effect and the like, thereby realizing the deflection of light beams, including a liquid crystal deflector, an acousto-optic deflector and the like. In order to increase the processing speed and achieve rapid focusing of the laser light, some researchers have used diffractive scanning devices instead of mechanical scanning devices.
For example, patent CN115735158A discloses "an apparatus and a method for controlling focusing of a laser beam". The patent receives a laser beam into an acousto-optic deflector, and by providing an acoustic wave to the acousto-optic deflector, a grating is built into the crystal and deflection of the laser beam is achieved. The rate of change of the acoustic wave frequency is adjusted during the microscan so as to create an acoustic wave frequency difference within the width of the laser beam in a direction parallel to the microscan, the frequency difference causing a desired focusing of the laser beam in a direction parallel to the microscan. The disadvantage of this approach is that dynamic focusing with frequency differences, the speed of the sound wave frequency change over time can interfere with the frequency differences, thereby affecting the focusing of the laser beam in the scan direction. In addition, the non-linear scanning in the scanning process also affects the scanning speed change, so that the position change in the laser scanning process is not a linear function which changes with time, and the dynamic focusing error is enlarged.
Patent CN202199931U discloses a laser scanning device for processing micro-circular holes based on acousto-optic effect, which is characterized in that an acousto-optic modulator is arranged between a plane reflector and a laser, two acousto-optic deflectors are arranged below a reflecting laser beam of the reflector, and nonlinear variation of acoustic wave frequency in an acousto-optic crystal is controlled through the two acousto-optic deflectors which are mutually perpendicular, so that deflection angle of a diffracted laser beam is changed, and dynamic focusing of the laser beam is realized. However, the dynamic focusing range is limited because the laser beam directly passes through the two acousto-optic deflectors and then is focused after passing through the parallel flat plate. In addition, since the two acousto-optic deflectors are fixed in position, the incident beam has limited change in direction after transmission, the bragg condition cannot be fully satisfied, and the diffraction efficiency is also reduced.
Patent CN217412799U discloses a "galvanometer field lens type laser processing system based on an acousto-optic deflector", which comprises an acousto-optic deflector and a galvanometer, wherein the acousto-optic deflector has two acousto-optic deflection structures, namely an X-axis acousto-optic deflection structure and a Y-axis acousto-optic deflection structure, which are sequentially connected in series, and the two structures are matched with the galvanometer to realize scanning of light beams in two-dimensional angles, thereby realizing dynamic focusing. However, since the deflected laser has a larger diameter, the acousto-optic deflector deflects the transmitted laser at a smaller angle, so that the 0 th and 1 st diffraction lights are required to be distinguished by a focusing mirror and a diaphragm, the 1 st laser used for processing is not fixed in the deflected angle, and the laser cannot pass through the diaphragm beyond the screening range, so that the laser processing range is smaller.
Disclosure of Invention
Aiming at the prior art, the invention aims to provide a three-dimensional scanning device, method and system based on acousto-optic dynamic focusing. The system aims to solve the problems that the existing system is large and heavy in size, low in scanning speed, low in laser three-dimensional scanning machining precision, and difficult to realize step machining, and the like.
In order to achieve the above object, in a first aspect, the present invention provides an acousto-optic dynamic focusing module for a three-dimensional scanning system, the acousto-optic dynamic focusing module including a plurality of optical components and focusing field lenses sequentially arranged along an optical path;
the plurality of optical components comprise a first acousto-optic deflector, a first concave parabolic mirror, a second acousto-optic deflector and a focusing field lens, and the concave surfaces of the first concave parabolic mirror and the second concave parabolic mirror are oppositely arranged;
an aberration correcting lens group is arranged between any two optical components;
the first acousto-optic deflector (2-1) and the second acousto-optic deflector (2-5) are used for deflecting the focus of the laser focused by the focusing field lens (4) along the light path direction through the change of the refractive index of the first acousto-optic deflector and the second acousto-optic deflector.
Preferably, the materials of the first acousto-optic deflector and the second acousto-optic deflector are optical anisotropic materials, the acousto-optic diffraction quality factor of the optical anisotropic materials on laser with target wavelength is larger than 1.5, the maximum acousto-optic diffraction efficiency is larger than 80%, and the reflectivity on ultrasound is smaller than 10%.
As a further preferred, the optically anisotropic material is lead molybdate, tellurium dioxide, lithium niobate or fused silica.
Preferably, piezoelectric transducers are arranged on the side surfaces of the first acousto-optic deflector and the second acousto-optic deflector, which are perpendicular to the light path of the laser; the piezoelectric transducer is used for generating pressure under the drive of ultrasound, so that the refractive indexes of the first acousto-optic deflector and the second acousto-optic deflector in the direction perpendicular to the light path are periodically changed to form a grating, and the focus of the laser focused by the focusing field lens is deflected along the light path direction.
As a further preferred aspect, the piezoelectric transducer is coated with a film layer on the side where the piezoelectric transducer is disposed, and the film layer is made of gold, silver, aluminum, epoxy resin or benzene benzoate.
Preferably, the acousto-optic dynamic focusing module further comprises a radio frequency generator and a power amplifier;
the output end of the radio frequency generator is connected with the input end of the power amplifier and is used for generating ultrasonic waves; and the output end of the power amplifier is connected with the input end of the piezoelectric transducer and is used for amplifying the power of the ultrasonic wave.
According to another aspect of the present invention, there is also provided a three-dimensional scanning system including the above acousto-optic dynamic focusing module; the three-dimensional scanning system further comprises a two-dimensional scanning device, wherein the two-dimensional scanning device is used for deflecting the focus of the laser focused by the focusing field lens in a plane direction perpendicular to the light path.
Preferably, the two-dimensional scanning device is a galvanometer disposed behind the optical path of the second acoustic deflection.
Preferably, the three-dimensional scanning system further comprises a controller and a memory; the output end of the controller is directly or indirectly connected with the input ends of the first acousto-optic deflector, the second acousto-optic deflector and the two-dimensional scanning device;
the controller is used for applying control signals to the two acousto-optic deflectors and/or the two-dimensional scanning device according to the processing instruction, so that the focus of the laser deflects in the direction along the light path and/or the plane direction perpendicular to the light path; the output end of the memory is connected with the input end of the controller, and the memory is used for storing programs executed by the controller.
Preferably, the laser is arranged at the forefront end of the optical path and is used for emitting laser.
In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:
1. the invention provides an acousto-optic dynamic focusing module; different from the structure adopting a vibrating mirror or a mechanical arm in the prior art, the invention adopts a first acousto-optic deflector, a double parabolic mirror system and a second acousto-optic deflector to form an acousto-optic dynamic focusing module; due to the '0 inertia' characteristic of the acousto-optic deflector, the focusing frequency along the direction of the light path can be increased from KHz to MHz, and the speed of three-dimensional scanning is increased, so that the focusing performance of the system is greatly improved; the focusing frequency of the acousto-optic deflector to the light beam can reach the MHz level, so that step-type processing which cannot be realized by the traditional focusing device can be realized;
2. the invention provides an aberration correction lens group in an acousto-optic dynamic focusing module, which is positioned between any two adjacent optical components arranged along an optical path of the acousto-optic dynamic focusing module and is used for reducing optical path differences between other light rays in an off-axis optical path and central light rays of each off-axis light ray, so as to correct aberration generated in a dynamic focusing process, and further improve the three-dimensional scanning range compared with the prior art;
3. besides adopting an acousto-optic dynamic focusing module, the three-dimensional scanning system also preferably adopts a two-dimensional scanning device to form a two-dimensional scanning module, so as to realize the plane scanning processing function of the laser focusing position;
4. a piezoelectric transducer is arranged on the side surfaces of the first acousto-optic deflector and the second acousto-optic deflector, which are perpendicular to the light path of the laser; the piezoelectric transducer is used for generating pressure under the drive of ultrasound, and can rapidly adjust the laser focus position along the optical axis to realize a dynamic focusing function;
during actual processing, the first acousto-optic deflector and the second acousto-optic deflector are cooperatively deflected; firstly, deflecting two acousto-optic deflectors by the same angle through a piezoelectric transducer, and dynamically adjusting a focal plane focused by laser to a required Z-axis position; then controlling the two-dimensional scanning device according to the processing pattern, and carrying out laser pattern scanning processing on the focal plane, thereby realizing the function of high-speed and high-precision dynamic focusing laser three-dimensional processing; the invention simplifies the complexity of the control device, reduces the accumulated error of the device, increases the laser three-dimensional scanning processing precision and the external interference resistance, further improves the speed of adjusting the laser focus position to be more than 100m/s, is at least 10 times of the prior art, and improves the laser three-dimensional scanning processing efficiency.
Drawings
FIG. 1 is a schematic diagram of a three-dimensional scanning system based on acousto-optic dynamic focusing;
FIG. 2 is a schematic diagram of a dynamic focusing function in a device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of two-dimensional scanning of a system in an apparatus according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a system in a device according to an embodiment of the present invention for dynamic focusing and two-dimensional scanning simultaneously;
FIG. 5 is a schematic diagram illustrating the optical path deflection performed by the acousto-optic deflector in the device according to the embodiment of the present invention;
the same reference numbers are used throughout the drawings to reference like elements or structures, wherein:
the device comprises a 1-laser, a 2-1-first acousto-optic deflector, a 2-2-first concave parabolic mirror, a 2-3-second concave parabolic mirror, a 2-4-aberration correcting mirror group, a 2-5-second acousto-optic deflector, a 3-two-dimensional scanning device, a 4-focusing field lens, a 5-controller, a 6-1-focal plane and a 6-2-focusing plane.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention discloses an acousto-optic dynamic focusing module for a three-dimensional scanning system, which comprises a plurality of optical components, wherein the optical components are sequentially arranged along an optical path, and each optical component comprises a first acousto-optic deflector 2-1, a first concave parabolic mirror 2-2, a second concave parabolic mirror 2-3, a second acousto-optic deflector 2-5 and a focusing field lens 4; the concave surfaces of the first concave parabolic mirror 2-2 and the second concave parabolic mirror 2-3 are oppositely arranged, and an aberration correcting lens group 2-4 is arranged between any two optical components and is used for reducing optical path differences between other light rays in the off-axis optical path and central light rays of each off-axis light ray, so as to correct aberration generated in a dynamic focusing process, as shown in fig. 1. For convenience of description, in fig. 1 to 4, the direction along the optical path is taken as the Z direction, the direction perpendicular to the paper surface is taken as the X direction, and the vertical direction is taken as the Y direction.
In some embodiments, the sides of the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 perpendicular to the optical path are provided with piezoelectric transducers; the piezoelectric transducer is used for generating pressure under the drive of radio frequency, so that the refractive indexes of the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 in the direction perpendicular to the light path are periodically changed to form a grating, and the light path is deflected;
a focusing field lens 4 is further arranged on the light path behind the second optical deflector 2-5, and the scanning focusing field lens 4 is used for focusing the light beam; in some embodiments, the focusing field lens 4 is a plano-convex lens, a convex-plano lens, or other lens group that may be used for focusing.
The acousto-optic deflector uses an optically anisotropic material such as an optically uniaxial crystal or an optically biaxial crystal of lead molybdate, tellurium dioxide, lithium niobate, fused silica, or the like. The laser with the target wavelength lambda needs to have higher acousto-optic diffraction quality factor and acousto-optic diffraction efficiency, and when ultrasound is injected into an acousto-optic deflector, the reflected ultrasound power is less than 10%, and the absorbed ultrasound power is more than 90%; taking fused quartz as an example, the acousto-optic diffraction quality factor M2=1.51@632.8nm can reach diffraction efficiency of more than 80% after being injected with ultrasonic power of 5-10W; because the acoustic impedance of the piezoelectric crystal is inconsistent with the acoustic impedance of the acousto-optic crystal, the transition from the acoustic impedance of the piezoelectric crystal to the acoustic impedance of the acousto-optic crystal can be realized by plating a thin layer with different acoustic impedances on the side of the acousto-optic deflector, on which the piezoelectric transducer is arranged, and the process is called an impedance matching process; materials for the acoustic impedance thin layer include, but are not limited to, gold, silver, aluminum, epoxy, benzene benzoate, or the like.
Since the deflection angle Δθ of the acousto-optic deflector is typically greater than 0.5 °, the frequency f of the corresponding injected ultrasound should be such that
Where λ is the target wavelength and v is the speed of sound.
The bandwidth of the acousto-optic deflector of the laser under the target wavelength is more than 3db, so that the dynamic focusing range of the dynamic focusing system is more than the time bandwidth product T.BW.
The formula of the time-bandwidth product is as followsWherein d represents the aperture of the light passing beam (i.e. the diameter of the laser beam), T represents the response time, B represents the pulse width of the pulse, W represents the spectral width, and Δθ max Indicating the maximum deflection angle.
The acousto-optic dynamic focusing module further comprises a waveform generator, a radio frequency generator and a power amplifier; the output end of the waveform generator is connected with the input end of the radio frequency generator and is used for generating an electric signal for controlling the radio frequency generator; the output end of the radio frequency generator is connected with the input end of the power amplifier and is used for generating an ultrasonic signal; the power amplifier is connected with the piezoelectric transducer and is used for amplifying the power of the ultrasonic signal.
Wherein, the relation between diffraction efficiency eta and power is as follows;
where ζ represents the acoustically induced phase shift and ζ represents the phase mismatch;
the acoustic phase shift ζ satisfies
Where λ is the target wavelength, n i And n d The refractive indexes of the incident light and the diffracted light are respectively, p is the effective acousto-optic coefficient of the acousto-optic deflector, S is the strain caused by ultrasonic waves in the acousto-optic deflector, and L represents the acousto-optic interaction length.
Phase mismatch ζ satisfies
Wherein Δf represents the frequency offset of the driving signal, Δf π When the DC voltage on the electro-optic electrode is zero, U represents the DC voltage, and U is the frequency offset of the driving signal necessary for reducing the diffraction efficiency to zero π When the frequency offset of the driving electric signal is zero, a direct current voltage which is required to be applied to the electro-optical electrode for reducing the diffraction efficiency to zero is v, v denotes the sound velocity, h denotes the length of the crystal along the direction of the direct current electric field, and γ denotes the effective electro-optical coefficient.
Through the structure, acousto-optic dynamic focusing can be realized in the z-axis direction of an object to be processed, but focal point movement in an XY plane is required to be combined with the two-dimensional scanning device 3 to form a three-dimensional scanning system. The two-dimensional scanning device 3 is used for adjusting the focus of the acousto-optic dynamic focusing module in the XY plane. For example, in some embodiments a galvanometer 3 may be positioned behind the second acoustic deflector 2-5, with the galvanometer adjusted to deflect the optical path in the plane X, Y; the three-dimensional scanning system further comprises a laser 1, wherein the laser 1 is arranged at the forefront end of the light path and is used for emitting laser.
The three-dimensional scanning system can also comprise a controller 5 and a memory;
the first output end of the controller 5 is directly or indirectly connected with the first acousto-optic deflector and the second acousto-optic deflector, and is used for sending out control signals according to processing instructions, and finally converting the control signals into signals capable of enabling refractive indexes of the first acousto-optic deflector and the second acousto-optic deflector to deflect in the direction perpendicular to the light path through devices such as a piezoelectric transducer or a power amplifier, and further enabling the laser focus to deflect in the Z-axis direction; the second output end of the controller 5 is connected with the two-dimensional scanning device 3, so that the two-dimensional scanning device 3 is controlled to deflect the focus on the XY plane, and a three-dimensional machining process is realized.
The output end of the memory is connected with the input end of the controller and is used for storing instructions executed by the controller.
The control method of the three-dimensional scanning system provided by the invention comprises the following steps:
dynamic focusing stage: when the acousto-optic deflector is driven by radio frequency, the crystal of the acousto-optic deflector generates sound wave by a piezoelectric transducer and the like, so that the structure of the crystal material generates recoverable and periodic spatial change, the laser beam emitted by the laser 1 deflects, and the deflection degree depends on the change period of the structure of the crystal material. Therefore, by changing the frequency of the input radio frequency signal, the deflection angle of the laser beam can be changed. The first acousto-optic deflector and the second acousto-optic deflector are controlled to synchronously deflect by inputting radio frequency signals, the deflection angles of the first acousto-optic deflector and the second acousto-optic deflector are the same, the directions of the two deflection angles are opposite, the controller 5 can calculate the Z-axis coordinate of the laser focus at the next moment according to a built-in program, and control signals corresponding to the deflection angles of the first acousto-optic deflector and the second acousto-optic deflector under the coordinate are sent to the piezoelectric transducer of the first acousto-optic deflector and the second acousto-optic deflector, so that the divergence angle of a laser beam before entering the focusing field lens 4 is changed, and the dynamic focusing function of the laser is realized;
two-dimensional scanning: dynamically adjusting a focal plane of laser focusing to a required Z-axis position, namely calculating X, Y-axis coordinates of the laser focus at the next moment according to a processed workpiece, and sending a control signal corresponding to the coordinates to a two-dimensional scanning device 3 to realize a scanning processing function in an XY two-dimensional plane;
example 1
Fig. 1 is a schematic structural diagram of a three-dimensional scanning system based on acousto-optic dynamic focusing according to embodiment 1 of the present invention. As shown in fig. 1, the device mainly comprises a laser 1, an acousto-optic dynamic focusing module 2, a two-dimensional scanning device 3, a focusing field lens 4, a controller 5 and a focal plane 6-1; wherein the focusing field lens 4 adopts a scanning focusing field lens, and the two-dimensional scanning device 3 adopts a vibrating lens 3 arranged behind the second acoustic deflector 2-5.
The acousto-optic dynamic focusing module 2 includes: the optical system comprises a first acousto-optic deflector 2-1, a first parabolic mirror 2-2, a second parabolic mirror 2-3, an aberration correcting lens group 2-4 and a second acousto-optic deflector 2-5.
The first parabolic mirror 2-2 and the second parabolic mirror 2-3 are concave parabolic mirrors having the same focal length. The first parabolic mirror 2-2 and the second parabolic mirror 2-3 are symmetrically arranged, and the central axes are coincident. The polarization centers of the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-4 are respectively positioned at the focuses of the first parabolic mirror 2-2 and the second parabolic mirror 2-3. The optical path deflection axes of the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-4 are parallel to each other and are perpendicular to the central axis of the double parabolic mirror system.
As shown in fig. 1, after the laser beam is emitted through the laser 1 and enters the first acousto-optic deflector 2-1 and exits from the first acousto-optic deflector 2-1, the polarization center of the first acousto-optic deflector 2-1 coincides with the focal point of the first parabolic mirror 2-2, and the deflection angle of the first acousto-optic deflector 2-1 can be controlled by the optical path deflection axis perpendicular to the YZ plane, so that the incident laser beam is reflected to the first parabolic mirror 2-2. Since the center of the first acousto-optic deflector 2-1 is located at the parabolic focus position of the first parabolic mirror 2-2, the direction of the optical axis exiting from the first parabolic mirror 2-2 is always a direction parallel to the central axis of the first parabolic mirror 2-2, the second parabolic mirror 2-3 and the first parabolic mirror 2-2 are mirror-placed with their central optical axes coincident, regardless of the rotation angle of the first acousto-optic deflector 2-1. The center of polarization of the second acoustic deflector 2-5 coincides with the focal point of the second parabolic mirror 2-3, and the optical path deflection axis is perpendicular to the YZ plane, and since the center of the second acoustic deflector 2-5 is located at the parabolic focal point position of the second parabolic mirror 2-3, the laser beam emitted from the second parabolic mirror 2-3 always enters the center of polarization of the second acoustic deflector 2-5. The laser beam on the second optical deflector 2-5 will be emitted to the center of the two-dimensional scanning device 3, and the laser beam emitted from the two-dimensional scanning device 3 will enter the scan focusing field lens 4 located right behind the two-dimensional scanning device 3, and finally be focused on the focal plane 6-1 located below the scan focusing field lens 4.
Fig. 2 is a schematic diagram of a dynamic focusing function in the device provided by the embodiment of the present invention, as shown in fig. 2, further, when the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 deflect at the same size and in opposite directions, the optical paths among the first acousto-optic deflector 2-1, the first parabolic mirror 2-2, the second parabolic mirror 2-3 and the second acousto-optic deflector 2-5 are changed, so that the laser divergence angle on the second acousto-optic deflector 2-5 is changed. Since the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 deflect by the same angle, the position focused on the optical axis moves after scanning the focusing field lens 4. Therefore, by synchronously deflecting the deflection angles of the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5, the optical path distance among the first acousto-optic deflector 2-1, the first parabolic mirror 2-2, the second parabolic mirror 2-3 and the second acousto-optic deflector 2-5 can be changed, so that the size of the laser divergence angle is changed, the position (from the focal plane 6-1 to the focusing plane 6-2) of the laser focus on the optical axis is quickly adjusted, and the function of quick dynamic focusing is realized.
An aberration correcting lens group is arranged between any two adjacent optical components (2-1 and 2-2, 2-2 and 2-3, 2-3 and 2-5) or between 2-5 and 3, 3 and 4) arranged along the optical path of the acousto-optic dynamic focusing module, and is used for reducing optical path differences between other light rays in the off-axis optical path and central light rays of each off-axis light ray, so as to correct aberration generated in the dynamic focusing process, and in the embodiment, the arrangement position of the aberration correcting lens group between 2-3 and 2-5 is selected, as shown in fig. 1 to 5.
Fig. 3 is a schematic diagram of a two-dimensional scanning function in the device provided by the embodiment of the present invention, as shown in fig. 3, further, when the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 are stationary, a two-dimensional scanning plane can be determined. When the light beam enters the two-dimensional scanning device 3, the controller 5 adjusts the two-dimensional scanning device 3 through signals, so that the light path deflects in the two-dimensional scanning device 3 in the two directions X, Y, and the laser focus performs two-dimensional scanning in the two directions X, Y in a focal plane determined by the acousto-optic adjustment Jiao Mokuai.
Fig. 4 is a schematic diagram of a device system provided in the embodiment of the present invention for simultaneously performing dynamic focusing and two-dimensional scanning, as shown in fig. 4, as known from the description of the dynamic focusing function and the two-dimensional scanning function in the embodiment of the present invention, if the system is to perform dynamic focusing and two-dimensional scanning simultaneously, first, a large reverse Δθ angle such as deflection is required by the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 simultaneously, and the two-dimensional scanning device 3 is stationary, so as to realize that the laser focusing position moves from the focal plane 6-1 to the focusing plane 6-2 along the optical axis direction; then, the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 are stationary, the two-dimensional scanning device 3 deflects the optical path X, Y in two directions, and the focused laser beams are controlled to perform XY plane scanning processing within the scanning range of the focal plane 6-2. After the scanning processing of the focal plane 6-2 is finished, the focal plane where the focusing position of the laser is located can be changed again by controlling the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5, the two-dimensional scanning device 3 is controlled to cooperatively deflect, X, Y, Z coordinates of a scanning pattern of a workpiece to be processed in space are calculated and converted into control signals by the controller 5 in the actual three-dimensional processing process, and the control signals of dynamic focusing and two-dimensional scanning are synchronously sent by the controller 5, so that the dynamic focusing scanning processing of the laser in the three-dimensional space is realized.
Wherein the deflection angle Δθ satisfies:
λ is the beam wavelength, f is the acoustic frequency, v is the speed of the acoustic wave in the acousto-optic deflector; the deflection angle of the acousto-optic converter can be adjusted by adjusting the frequency
Fig. 5 is a schematic working diagram of the first acousto-optic deflector 2-1 and the second acousto-optic deflector 2-5 in actual use in the device provided by the embodiment of the invention, when light emitted by the laser 1 enters the first acousto-optic deflector 2-1, the controller 5 calculates the Z coordinate of the focusing position of the laser, converts the Z coordinate into a corresponding control signal, drives the inside of the first acousto-optic deflector 2-1 to generate sound waves, and causes the density of the first acousto-optic deflector 2-1 to change under pressure driving. So that a variable, periodic spatial variation in the refractive index of the material of the first acousto-optic deflector 2-1 is produced, forming a grating-like structure, the period of which can be increased or decreased. By adjusting the control signal, the optical path can be deflected by a deflection angle corresponding to the Z-coordinate in the first acousto-optic deflector 2-1.
The working principle of the first acousto-optic deflector 2-1 is the same, when the light path passes through the first parabolic mirror 2-2, the second parabolic mirror 2-3 and the aberration correction mirror group 2-4, the light enters the second acousto-optic deflector 2-5 at the same incident angle as the emergent angle of the first acousto-optic deflector 2-1, at the moment, the Z coordinate of the focusing position of the laser is calculated through the controller 5 and is converted into a corresponding control signal, and the internal density of the second acousto-optic deflector 2-5 is driven to change by pressure. The refractive index of the material of the second acoustic deflector 2-5 is made to vary, periodically and spatially, to form a grating-like structure, and the period of the grating can vary. By adjusting the control signal, the optical path can be deflected by a corresponding angle in the second acoustic deflector 2-5.
Two-dimensional scanning: dynamically adjusting a focal plane of laser focusing to a required Z-axis position, namely calculating X, Y-axis coordinates of the laser focus at the next moment according to a processing procedure, and sending a control signal corresponding to the coordinates to a two-dimensional scanning device to realize a scanning processing function in an XY two-dimensional plane;
it will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. An acousto-optic dynamic focusing module for a three-dimensional scanning system comprises a plurality of optical components which are sequentially arranged along the light path of laser, and is characterized in that the optical components comprise a first acousto-optic deflector (2-1), a first concave parabolic mirror (2-2), a second concave parabolic mirror (2-3), a second acousto-optic deflector (2-5) and a focusing field lens (4); the concave surfaces of the first concave parabolic mirror (2-2) and the second concave parabolic mirror (2-3) are oppositely arranged;
an aberration correcting lens group (2-4) is arranged between any two optical components;
the first acousto-optic deflector (2-1) and the second acousto-optic deflector (2-5) are used for deflecting the focus of the laser focused by the focusing field lens (4) along the light path direction through the change of the refractive index of the first acousto-optic deflector and the second acousto-optic deflector.
2. The acousto-optic dynamic focusing module according to claim 1, wherein the material of the first acousto-optic deflector (2-1) and the second acousto-optic deflector (2-5) is an optically anisotropic material, the acousto-optic diffraction quality factor of the optically anisotropic material for laser light is larger than 1.5, the maximum acousto-optic diffraction efficiency is larger than 80%, and the reflectivity for ultrasound light is smaller than 10%.
3. The acousto-optic dynamic focusing module according to claim 2, wherein the optically anisotropic material is lead molybdate, tellurium dioxide, lithium niobate or fused silica.
4. The acousto-optic dynamic focusing module according to claim 1, characterized in that piezoelectric transducers are provided on the sides of the first acousto-optic deflector (2-1) and the second acousto-optic deflector (2-5) perpendicular to the optical path of the laser light; the piezoelectric transducer is used for generating pressure on the first acousto-optic deflector (2-1) and the second acousto-optic deflector (2-5) under the driving of ultrasound, so that the refractive index of the first acousto-optic deflector (2-1) and the refractive index of the second acousto-optic deflector (2-5) are changed.
5. The acousto-optic dynamic focusing module according to claim 4, wherein the piezoelectric transducer is coated with a film layer on a side where the piezoelectric transducer is disposed, and the film layer is made of gold, silver, aluminum, epoxy or benzene benzoate.
6. The acousto-optic dynamic focusing module according to claim 4, further comprising a radio frequency generator and a power amplifier;
the output end of the radio frequency generator is connected with the input end of the power amplifier and is used for generating ultrasonic waves; and the output end of the power amplifier is connected with the input end of the piezoelectric transducer and is used for amplifying the power of the ultrasonic wave.
7. A three-dimensional scanning system comprising an acousto-optic dynamic focusing module according to any of claims 1-6, further comprising a two-dimensional scanning device (3), said two-dimensional scanning device (3) being adapted to deflect the focal point of the laser light focused by the focusing field lens (4) in a plane direction perpendicular to the optical path.
8. The three-dimensional scanning system according to claim 7, characterized in that the two-dimensional scanning device (3) is a galvanometer arranged behind the optical path of the second acoustic deflector (2-5).
9. The three-dimensional scanning system of claim 7, further comprising a controller (5) and a memory;
the controller (5) is used for directly or indirectly applying control signals to the two acousto-optic deflectors and/or the two-dimensional scanning device (3) according to processing instructions so that the focus of the laser deflects in the direction along the light path and/or the plane direction perpendicular to the light path;
the output end of the memory is connected with the input end of the controller, and the memory is used for storing programs executed by the controller.
10. The three-dimensional scanning system according to claim 7, further comprising a laser (1), the laser (1) being disposed at a forefront end of the optical path for emitting laser light.
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