Multi-focal-length laser focusing system and method

Abstract

The invention discloses a multi-focal-length laser focusing system and method, and belongs to the technical field of photoelectrons and lasers. The multi-focal-length laser focusing system comprises a laser beam splitting unit, a light path conversion unit and a laser multi-focal-length focusing unit. The laser beam splitting unit is used for splitting an incident laser beam; the light path conversion unit collimates the plurality of beam splitting lasers and stretches the collimated laser beams; the laser multi-focal-length focusing unit comprises a first acousto-optic driving source and a first acousto-optic device, the first acousto-optic driving source sequentially generates a plurality of chirp signals with adjustable energy, and the first acousto-optic device forms a plurality of acoustic sub-gratings with different grating intervals; and the acoustic sub-grating performs focusing with different focal lengths on the split light beams which are shaped by the light path conversion unit. By adjusting the angle and the intensity of the beam splitting laser and the number and the chirp rate of the chirp signals, the focusing number and the focusing focal length of the beam splitting laser are controlled. The adjustable multi-beam multi-focal-length focusing is realized, and the size of the device is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronics and laser technology, and more specifically, relates to a multi-focal length laser focusing system and method. Background Art

[0002] In the field of laser processing, with the rapid development of high-end manufacturing industries such as aerospace and precision medical equipment, the demand for efficient and precise processing of complex curved parts is becoming increasingly urgent. Traditional laser processing technology mainly uses a single beam with a fixed focal length optical system. This solution has obvious limitations when processing free-form surfaces. When the surface curvature of the workpiece changes greatly, the operator has to frequently adjust the processing platform or the laser focus position, resulting in low processing efficiency and difficulty in ensuring the stability of processing accuracy. Especially in micron-level precision processing scenarios, slight deviations in focal length will lead to uneven energy density distribution, which directly affects the processing quality. This single-point serial processing mode has become one of the main bottlenecks restricting the development of laser processing technology towards efficiency and intelligence.

[0003] Although the optical system with fixed focal length has a simple structure, it is completely unable to adapt to the processing requirements of variable curvature surfaces. In order to meet the needs of complex surface processing, existing technologies have attempted to improve it through dynamic focusing or multi-beam parallel processing. The dynamic focusing system usually adopts a mechanical zoom lens group or a galvanometer scanning system. Although it can achieve continuous adjustment of the focal length, it has problems such as slow response speed and easy wear of moving parts. Multi-beam solutions often rely on the combination of multiple independent lasers and optical systems, which not only greatly increases the cost and volume of the equipment, but also brings new problems such as poor consistency of beam parameters and complex system calibration. More importantly, these improvement solutions still face technical challenges such as complex optical path design, low energy utilization, and the inability to independently control the focus characteristics of each sub-beam when realizing multi-focal length and multi-beam collaborative processing. It is difficult to meet the needs of modern manufacturing for high-efficiency and high-precision laser processing.

[0004] In the prior art, there is a problem that the existing laser focusing device has a single focal length and cannot achieve simultaneous focusing of multiple focal lengths. Summary of the Invention

[0005] In view of the defects of the related art, the purpose of the present invention is to provide a multi-focal length laser focusing system and method, which aims to solve the problem that the existing laser focusing device has a single focal length and cannot achieve simultaneous focusing of multiple focal lengths.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a multi-focal length laser focusing system, comprising: a laser beam splitting unit, an optical path conversion unit, and a laser multi-focal length focusing unit;

[0007] The laser beam splitting unit is used to split the incident laser beam;

[0008] The optical path transformation unit includes a collimator and a cylindrical mirror; the collimator is used to collimate multiple split laser beams; the cylindrical mirror is used to stretch the collimated laser beam;

[0009] The laser multi-focal length focusing unit includes a first acousto-optic driving source and a first acousto-optic device, wherein the first acousto-optic driving source is used to sequentially generate a plurality of chirp signals with adjustable energy, and the first acousto-optic device is used to form a corresponding acoustic sub-grating according to each chirp signal, so as to focus each split laser beam output by the optical path conversion unit at a different focal length.

[0010] The laser beam splitting unit is further used to adjust the angle and intensity of the split laser beam; the first acousto-optic driving source is further used to adjust the number and chirp rate of the chirp signal, thereby controlling the number of focused split laser beams and the focused focal length.

[0011] Optionally, the laser beam splitting unit includes a second acousto-optic driving source and a second acousto-optic device having a Bragg diffraction effect;

[0012] The second acousto-optic driving source is used to generate signals of different frequencies and superimpose them to obtain a superimposed frequency signal;

[0013] The second acousto-optic device forms an acoustic grating with adjustable split beam intensity under the action of the superimposed frequency signal, which is used to cause the incident laser beam to undergo Bragg diffraction at different diffraction angles to obtain a one-dimensional laser beam splitting array.

[0014] Optionally, the second acousto-optic driving source includes a second signal generator and a second radio frequency power amplifier; the second signal generator is used to generate signals of different frequencies and superimpose them to obtain a superimposed frequency signal; the superimposed frequency signal is represented by a superposition of a series of cosine functions with different frequencies; the second radio frequency power amplifier is used to amplify the superimposed frequency signal;

[0015] The second acousto-optic device includes a second piezoelectric transducer and a second acousto-optic interaction medium; the second piezoelectric transducer is a piezoelectric crystal sheet attached to the second acousto-optic interaction medium, and is used to generate mechanical vibration under the drive of the superimposed frequency signal generated by the second acousto-optic driving source, acting on the second acousto-optic interaction medium to form an acoustic grating with adjustable splitting beam intensity; the second acousto-optic interaction medium is used to cause the incident laser beam to undergo Bragg diffraction at different diffraction angles, thereby obtaining a one-dimensional laser beam splitting array.

[0016] Optionally, the second acousto-optic driving source is used to adjust the number of frequency superpositions in the superposition frequency signal, thereby controlling the number of laser beam splittings.

[0017] Optionally, the second acousto-optic interaction medium is any one of fused quartz, quartz crystal, tellurium oxide or lead molybdate.

[0018] Optionally, the laser beam splitting unit is a diffraction optical element DOE;

[0019] The diffractive optical element DOE is used to split an incident laser beam into multiple beams.

[0020] Optionally, the acoustic modulator sub-grating formed by the chirp signal in the acousto-optic crystal matches each corresponding split light beam, so that each corresponding split light beam is located at the center of the acoustic modulator sub-grating formed by the chirp signal.

[0021] Optionally, the superimposed frequency signal generated by the laser beam splitting unit is the same as the switching frequency of the multiple chirp signals generated by the laser multi-focal length focusing unit; the laser pulses generated by the laser beam splitting unit are synchronized with the switching of the chirp signals;

[0022] The superimposed frequency signal generated by the laser beam splitting unit is synchronized with the chirp signal generated by the laser multi-focal length focusing unit.

[0023] In a second aspect, the present invention further provides a multi-focal length laser focusing method, which is applied to the multi-focal length laser focusing system as described in any one of the first aspects, comprising:

[0024] S1. Setting parameters of the laser beam splitting unit based on the target deflection angle and target spot intensity of the split laser beam;

[0025] S2. Based on the target number of output split laser beams and the target focal length of the focus, determine the number and chirp rate of chirp signals generated by the laser multifocal focusing unit, and set parameters for the laser multifocal focusing unit;

[0026] S3. The incident laser beam is incident on the multi-focal length laser focusing system, and light spots having the target number and respectively focused at the target focal length are output.

[0027] Optionally, also include:

[0028] By adjusting the angles between the split laser beams and the corresponding chirp signals of different lengths, multi-focal length focusing with unequal intervals is generated.

[0029] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0030] 1. The present invention provides a multi-focal length laser focusing system, comprising a laser beam splitting unit, an optical path conversion unit, and a laser multi-focal length focusing unit. The laser beam splitting unit can adjust the laser beam splitting, and the laser multi-focal length focusing unit can adjust the focal length of the beam by adjusting the chirp rate of the chirp signal. The split laser beams passing through the laser beam splitting unit pass through acoustic gratings formed by different chirp rates, thereby achieving multi-beam multi-focal length focusing. At the same time, multi-focal length focusing can be achieved without multiple sets of focusing mirrors. This solves the technical problem that existing laser focusing devices have a single focal length and cannot achieve simultaneous focusing of multiple focal lengths. Multi-beam multi-focal length focusing is achieved, and the size of the device is reduced. At the same time, the optical path is easily adjusted, and the operation is simple.

[0031] 2. The present invention provides a multi-focal laser focusing system. The laser beam splitting unit generates a superimposed frequency signal. By adjusting the number of superimposed frequency signals, the number of split laser beams can be adjusted, thereby adjusting the number of final multi-focal focused beams. By adjusting the frequency interval of the superimposed frequency, the splitting angle can be adjusted, thereby adjusting the position of the final multi-focal focused beam. By adjusting the intensity of the superimposed frequency signal, the intensity of the split laser beam can be adjusted. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic structural diagram of another multi-focal length laser focusing system provided by an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of the principle of a multi-focal length laser focusing system provided by an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of a laser beam splitting unit provided in an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of laser multi-focal focusing provided by an embodiment of the present invention;

[0036] Figure 5 A schematic diagram of unequally spaced laser multi-focal length focusing generated by a multi-focal length laser focusing system provided by an embodiment of the present invention;

[0037] Figure 6 A schematic diagram of any number of laser multi-focal focusing generated by a multi-focal laser focusing system provided by an embodiment of the present invention;

[0038] Figure 7 A schematic structural diagram of another multi-focal length laser focusing system provided by an embodiment of the present invention.

[0039] In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein: 1-laser beam splitting unit; 2-optical path conversion unit; 3-laser multi-focal length focusing unit; 101-second signal generator; 102-second RF power amplifier; 103-second piezoelectric transducer; 104-second acousto-optic interaction medium; 201-collimating mirror; 202-cylindrical mirror; 301-first signal generator; 302-first RF power amplifier; 303-first piezoelectric transducer; 304-first acousto-optic interaction medium. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0041] The contents involved in the above embodiment are described below in conjunction with a preferred embodiment.

[0042] Example 1

[0043] like Figure 1 As shown, the present invention provides a multi-focal length laser focusing system, comprising: a laser beam splitting unit 1, an optical path conversion unit 2 and a laser multi-focal length focusing unit 3;

[0044] The laser beam splitting unit 1 is used to split the incident laser beam;

[0045] The optical path transformation unit 2 includes a collimator 201 and a cylindrical mirror 202; the collimator 201 is placed behind the laser beam splitting unit 1 and is used to collimate multiple split laser beams; the cylindrical mirror 202 is placed behind the collimator 201 and receives the collimated laser beam and stretches the collimated laser beam;

[0046] The laser multi-focal length focusing unit 3 includes a first acousto-optic driving source and a first acousto-optic device. The first acousto-optic driving source is used to sequentially generate a plurality of chirp signals with adjustable energy. The first acousto-optic device is used to form a corresponding acoustic sub-grating according to each chirp signal to focus each split laser beam output by the side switching unit 2 at different focal lengths.

[0047] The laser beam splitting unit 1 is also used to adjust the angle of the split laser and the intensity of the split laser; the first acousto-optic driving source is also used to adjust the number and chirp rate of the chirp signal, thereby controlling the number of focused split lasers and the focused focal length.

[0048] like Figure 1As shown, the incident laser is split into multiple split laser beams by the laser beam splitting unit 1, and the optical path conversion unit 2 collimates and stretches the multiple split laser beams to obtain multiple processed split laser beams; when the incident laser is incident on the laser beam splitting unit 1, the first acousto-optic driving source in the laser multi-focal length focusing unit 3 is set according to the preset focusing number and focal length to generate multiple chirp signals, and multiple acoustic control sub-gratings with different grating spacings are formed in the first acousto-optic device. Each acoustic control sub-grating processes an incident split laser beam and focuses it to a preset focus to obtain focused light spots with different focal lengths. Among them, the number of split lasers generated by the incident laser passing through the laser beam splitting unit 1, the deflection angle of each split laser, and the intensity of each split laser can all be adjusted; in the laser multi-focal length focusing unit 3, one chirp signal corresponds to a focus of one focal length, and this focal length can be the same. The focused light spot corresponds to a split beam, and the number of focuses is equal to the number of loaded chirp signals. The number of chirp signals and the chirp rate are adjustable, so the number of focuses and the focused focal length are correspondingly adjustable.

[0049] The present invention provides a multi-focal-length laser focusing system capable of simultaneously forming multiple independently controllable focused light spots in space, with the focal length parameters of each spot quickly and precisely adjusted. This device should overcome the limitations of traditional mechanical zoom systems, significantly improving system response speed and reliability while maintaining machining accuracy. This approach will truly meet the industrial demand for efficient and precise machining of complex curved surfaces, and advance laser machining technology towards intelligent and flexible applications.

[0050] In a specific embodiment, if Figure 2 As shown, optionally, the laser beam splitting unit 1 includes a second acousto-optic driving source and a second acousto-optic device with Bragg diffraction effect;

[0051] The second acousto-optic driving source is used to generate signals of different frequencies and superimpose them to obtain a superimposed frequency signal;

[0052] The second acousto-optic device forms an acoustic grating with adjustable split beam intensity under the action of the superimposed frequency signal, which is used to cause the incident laser beam to undergo Bragg diffraction at different diffraction angles to obtain a one-dimensional laser beam splitting array.

[0053] Optionally, the second acousto-optic driving source includes a second signal generator 101 and a second RF power amplifier 102; the second signal generator 101 is used to generate signals of different frequencies and superimpose them to obtain a superimposed frequency signal; the superimposed frequency signal is represented by a superposition of a series of cosine functions with different frequencies; the second RF power amplifier 102 is used to amplify the superimposed frequency signal;

[0054] The second acousto-optic device includes a second piezoelectric transducer 103 and a second acousto-optic interaction medium 104; the second piezoelectric transducer 103 is a piezoelectric crystal sheet attached to the second acousto-optic interaction medium 104, and is used to generate mechanical vibration under the drive of the superimposed frequency signal generated by the second acousto-optic driving source, acting on the second acousto-optic interaction medium 104 to form an acoustic grating with adjustable splitting beam intensity; the second acousto-optic interaction medium 104 is used to cause the incident laser beam to undergo Bragg diffraction at different diffraction angles, thereby obtaining a one-dimensional laser beam splitting array.

[0055] The laser beam splitting unit 1 works based on the acousto-optic effect of the crystal. Figure 3 As shown in the figure, under the influence of ultrasound, the refractive index of the acousto-optic crystal changes periodically, equivalent to a grating. Consequently, the acousto-optic deflector can generate a diffracted beam at a certain angle. In the acousto-optic deflector, a piezoelectric transducer is attached to one side of the acousto-optic crystal. This converts mechanical vibrations into ultrasonic oscillations, which are then transmitted to the acousto-optic crystal. This results in a periodic distribution of the acousto-optic crystal's refractive index, forming a diffraction grating. At this point, the speed of light is much greater than the speed of sound. Therefore, the grating generated by the ultrasonic oscillations can be considered a relatively stationary grating, achieving diffraction of the beam.

[0056] A plurality of superimposed frequency signals are set at the second signal generator 101, and the expression of the driving signal is:

[0057]

[0058] Where N represents the N-song superimposed frequency signal acting on the acousto-optic device, a i represents the waveform intensity of each input frequency, Indicates the phase of the input waveform.

[0059] N different input frequencies f i They are:

[0060]

[0061] Wherein, f0 is the operating center frequency of the corresponding acousto-optic device, and Δf is the frequency interval between adjacent input frequencies of the acousto-optic device.

[0062] The drive signal generated by the second signal generator 101 passes through the RF power amplifier and acts on the second piezoelectric transducer 103, which is a metal sheet attached to the second acousto-optic interaction medium 104. This causes mechanical vibration, which acts on the second acousto-optic interaction medium 104 to form an energy-adjustable acoustic grating. The incident light is deflected by the ultrasonic field, forming a split diffraction beam. The deflection angle Δθ satisfies:

[0063]

[0064] Where λ is the wavelength of the incident laser beam, and v is the propagation velocity of the acoustic wave in the acousto-optic interaction medium.

[0065] By adjusting the number N of input frequencies, the number of focused beams is adjusted; by adjusting the frequency interval Δf between adjacent input frequencies of the acousto-optic device, the deflection angle Δθ of the beam is adjusted; by adjusting the amplitude a of the driving signal i , adjust the intensity of the split laser.

[0066] In order to achieve multi-focal focusing of equally spaced laser beams, the frequency interval of the driving signal is set constant to achieve equally spaced beam splitting.

[0067] The first acousto-optic driving source in the laser multi-focal focusing unit 3 includes a first signal generator 301 and a first radio frequency power amplifier 302. The first acousto-optic device in the laser multi-focal focusing unit 3 includes a first piezoelectric transducer 303 and a first acousto-optic interaction medium 304. The laser multi-focal focusing unit 3 is used to focus the split laser beams to achieve multi-focal focusing.

[0068] The first signal generator 301 is used to generate multiple chirp signals with different chirp rates, and the first RF power amplifier 302 is used to amplify the chirp signals. The first piezoelectric transducer 303 is a piezoelectric crystal slice attached to the first acousto-optic interaction medium 304, which is used to generate mechanical vibration under the drive of the chirp signal generated by the first acousto-optic driving source, and act on the first acousto-optic interaction medium 304 in turn. The sound waves propagate along the first acousto-optic interaction medium 304 in turn, and different acoustic gratings are formed in different positions of the first acousto-optic interaction medium 304 in turn. The split laser beam passes through the acoustic gratings formed by the driving signals with different chirp rates to form different focuses.

[0069] The laser multi-focal focusing unit 3 works based on the acousto-optic effect of the crystal. Figure 4 As shown, in order to achieve focusing of the split beam, the first signal generator 301 sets a chirp signal. The frequency of the chirp drive signal generated by the first signal generator 301 is:

[0070] f i =αt+f c

[0071] Among them, the driving frequency of the chirp signal gradually increases with time, where f c is the initial value of the driving frequency, α is the chirp rate, and the chirp rate is calculated as follows:

[0072]

[0073] Where f is the frequency of the RF signal, f minis the minimum value of the RF signal, T is the period of chirp scanning;

[0074] The driving waveform signal of the acousto-optic device is expressed as:

[0075]

[0076] The chirp signal is input sequentially, so that at a certain moment, different positions in the acousto-optic device sequentially receive the corresponding chirp signal. The stretched light beam incident on the multi-focal length focusing unit 3 passes through the acousto-optic interaction crystal, where the acoustic field frequency gradually increases with time. Since the acoustic field frequency gradually increases with time and propagates along the acousto-optic interaction crystal, the acoustic field frequencies at different acousto-optic interaction regions are different. The incident stretched laser beam will form diffracted light with different diffraction angles. The deflection angle of the diffracted light at a specific position at a certain moment is calculated as follows:

[0077]

[0078] Where x is the position of the chirp frequency at time t.

[0079] Since the deflection angles of diffracted light at different positions are different, the diffracted light beam can be focused. The focal length is calculated as follows:

[0080]

[0081] Among them, θ e and θ b are the deflection angles of the incident light at the beginning and end of the chirp signal propagation, respectively.

[0082] Chirp signals with different chirp rates are sequentially set in the acousto-optic device in the multi-focal focusing unit 3. These chirp signals sequentially move along the first acousto-optic interaction crystal 304. Therefore, multiple acoustic gratings with different chirp rates exist in the first acousto-optic interaction crystal 304. The split beams at different positions pass through the acoustic gratings formed by different chirp rates, thereby achieving multi-focal focusing.

[0083] At the same time, a pulsed laser is used as the light source, and the repetition frequency of the pulsed laser is the same as the switching frequency of multiple chirp signals in the laser multi-focal length focusing unit 3, so that each time the split beam laser is incident on the acousto-optic interaction medium 304, it can be incident on the acoustic grating formed by different chirp rate driving signals. The laser pulse is synchronized with the switching of the chirp signal to achieve stable multi-focal length focusing.

[0084] In the embodiment of the present invention, since the driving signal of the acousto-optic splitting unit 1 is adjustable and the chirp signal of the acousto-optic focusing unit 3 is adjustable, the embodiment of the present application can flexibly adjust the focal length and position of the split laser to achieve multi-focal length focusing at different positions.

[0085] Based on the above embodiment, optionally, the superimposed frequency signal generated by the laser beam splitting unit 1 is the same as the switching frequency of the multiple chirp signals generated by the laser multi-focal length focusing unit 3; the laser pulses generated by the laser beam splitting unit 1 are synchronized with the switching of the chirp signals;

[0086] The superimposed frequency signal generated by the laser beam splitting unit 1 is time-synchronized with the chirp signal generated by the laser multi-focal length focusing unit 3 .

[0087] To achieve multifocal focusing of the beam, pulsed lasers are used as light sources, loaded sequentially and synchronized to ensure that each pulse of laser light arrives at the laser multifocal focusing unit 3 and simultaneously loads the acoustic wave at the specified location. The repetition rate of the pulsed laser is the same as the switching frequency of the multiple chirp signals in the laser multifocal focusing unit. The switching of the laser pulses and chirp signals is synchronized, achieving stable multifocal focusing.

[0088] The chirp signal forms an acoustic control sub-grating in the acousto-optic crystal that matches each corresponding split beam, so that each corresponding split beam is located at the center of the acoustic control sub-grating formed by the chirp signal. One split beam corresponds to one acoustic control sub-grating formed by the chirp signal and one focal length.

[0089] Optionally, the second acousto-optic driving source is further used to adjust the frequency interval in the superimposed frequency signal, and the first acousto-optic driving source sequentially generates chirp signals of different lengths to control multi-focal focusing with unequal intervals.

[0090] Optionally, the second acousto-optic driving source is used to adjust the number of frequency superpositions in the superposition frequency signal, thereby controlling the number of laser beam splittings.

[0091] In another embodiment, if Figure 5 As shown, in order to achieve multi-focal length focusing with unequal intervals, the driving frequency of the laser beam splitting unit 1 can be set to unequal frequency intervals, and chirp signals of different lengths are set to be loaded in sequence. The superimposed frequency signal generated by the laser beam splitting unit 1 is synchronized with the chirp signal generated by the laser multi-focal length focusing unit 3, so that multi-focal length focusing is just achieved when the split laser reaches the laser multi-focal length focusing unit 3.

[0092] In another embodiment, if Figure 6 As shown, in order to achieve multi-focal length focusing of any number of beams, the laser beam splitting unit 1 can be set to superimpose multiple frequencies to form any number of split beams, and at the same time set a corresponding number of chirp signals to be loaded in sequence and synchronized with the timing. When the multiple split beams reach the laser multi-focal length focusing system 3, the multiple chirp signals respectively reach the incident position of the split beams to achieve multi-focal length focusing of multiple beams.

[0093] In the above embodiment, the first acousto-optic interaction medium and the second acousto-optic interaction medium are any one of fused quartz, quartz crystal, tellurium oxide or lead molybdate.

[0094] In another alternative embodiment, Figure 6 As shown, the laser beam splitting unit is a diffraction optical element DOE;

[0095] The diffractive optical element DOE is used to split an incident laser beam into multiple beams.

[0096] DOE usually uses micro-nano etching technology to form diffraction units. The laser diffracts after passing through each diffraction unit and generates interference at a certain distance to form a specific light intensity distribution. It can also realize multi-beam splitting of the incident laser beam, such as Figure 7 shown.

[0097] Exemplarily, taking the use of an acousto-optic device as a laser beam splitting unit to form three equally spaced laser beams with unequal focal lengths as an example, the implementation process of the multi-focal length laser focusing system and the multi-focal length laser focusing method of the present invention is demonstrated.

[0098] First, the incident laser is split into three beams by the laser beam splitting unit 1. Assume that the angle Δθ between each beam and the adjacent beam is 2 mrad, the incident laser wavelength λ is 1064 nm, the acoustic field velocity of the tellurium oxide acousto-optic crystal is 670 m / s, and the center frequency f0 is 70 MHz. The formula is:

[0099]

[0100] The calculated frequency interval Δf≈1.26MHz, the three different input frequencies f are:

[0101]

[0102] The incident beam is split into three equally spaced split beams according to the input driving frequency.

[0103] After the split light beam passes through the collimator lens and the cylindrical lens in sequence, the outgoing light path is collimated and stretched, and then enters the laser multi-focal length focusing unit.

[0104] For example, the focusing of three split beam spots is 120mm, 90mm, and 150mm from top to bottom, the incident laser wavelength λ is 1064nm, and the acoustic field velocity of the tellurium oxide acousto-optic crystal is 670m / s. According to the formula:

[0105]

[0106] The chirp rates of the three chirp signals are calculated to be With the center frequency fc =70MHz as an example, the driving waveform signals of the acousto-optic device are sequentially introduced as follows:

[0107]

[0108] A first signal generator generates the chirp drive signal, which, after passing through a first radio frequency power amplifier, acts on the piezoelectric transducer of the first acousto-optic device. The laser pulse frequency is synchronized with the chirp signal generation frequency, ensuring that when each split laser pulse reaches the laser multifocal focusing unit, the corresponding chirp signal is precisely transmitted to the corresponding position of the acousto-optic device. Each split beam sequentially passes through the acoustic grating formed by the corresponding chirp signal, thereby focusing at the focal length corresponding to the chirp rate.

[0109] In an embodiment of the present invention, a laser beam splitting unit controls the number, deflection angle, and intensity of the split laser beams. A laser multi-focal length focusing unit adjusts the focal length of the beam by adjusting the chirp rate of the chirp signal, controlling the focal length and position of the split laser beams. This facilitates optical path modulation, enabling focusing at different multi-focal lengths. Furthermore, multi-focal length focusing can be achieved without the need for multiple sets of focusing lenses. This solves the technical problem of existing laser focusing devices, which have a single focal length and cannot achieve simultaneous focusing at multiple focal lengths, by achieving multi-beam, multi-focal length focusing while reducing the device's size. Furthermore, the optical path is easily adjustable, making operation simple.

[0110] Example 2

[0111] In a second aspect, the present invention further provides a multi-focal length laser focusing method, which is applied to the multi-focal length laser focusing system as described in any one of the first aspects, comprising:

[0112] S1. Setting parameters of the laser beam splitting unit based on the target deflection angle and target spot intensity of the split laser beam;

[0113] S2. Based on the target number of output split laser beams and the target focal length of the focus, determine the number and chirp rate of chirp signals generated by the laser multifocal focusing unit, and set parameters for the laser multifocal focusing unit;

[0114] S3. The incident laser beam is incident on the multi-focal length laser focusing system, and light spots having the target number and respectively focused at the target focal length are output.

[0115] Optionally, also include:

[0116] By adjusting the angles between the split laser beams and the corresponding chirp signals of different lengths, multi-focal length focusing with unequal intervals is generated.

[0117] In one specific embodiment, when the laser beam splitting unit in a multi-focal laser focusing system utilizes a second acousto-optic drive source and a second acousto-optic device, the drive power and drive frequency of the laser beam splitting unit are determined based on the target deflection angle and target spot intensity of the split laser beams. By controlling the parameters of the laser beam splitting unit (parameters of the superimposed frequency signal), the number, intensity, and deflection angle of the split laser beams are controlled. By controlling the chirp rate of the chirp signal in the laser multi-focal focusing unit, the focal length of the beam can be adjusted, facilitating optical path modulation and achieving different multi-focal focusing distances.

[0118] In another alternative embodiment, when the laser beam splitting unit in the multi-focal length laser focusing system adopts a diffraction optical element DOE, if the amount of beam splitting and focusing needs to be adjusted, other diffraction optical elements DOE need to be replaced, and the chirp signal of the multi-focal length focusing unit will be changed accordingly.

[0119] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-focal length laser focusing system, characterized in that: include: Laser beam splitting unit, optical path conversion unit and laser multi-focal length focusing unit; The laser beam splitting unit is used to split the incident laser beam; The optical path transformation unit includes a collimator and a cylindrical mirror; the collimator is used to collimate multiple split laser beams; the cylindrical mirror is used to stretch the collimated laser beam; The laser multi-focal length focusing unit includes a first acousto-optic driving source and a first acousto-optic device, wherein the first acousto-optic driving source is used to sequentially generate a plurality of chirp signals with adjustable energy, and the first acousto-optic device is used to form a corresponding acoustic sub-grating according to each chirp signal, so as to focus each split laser beam output by the optical path conversion unit at a different focal length. The laser beam splitting unit is further used to adjust the angle and intensity of the split laser beam; the first acousto-optic driving source is further used to adjust the number and chirp rate of the chirp signal, thereby controlling the number of focused split laser beams and the focused focal length.

2. The multi-focal length laser focusing system according to claim 1, wherein: The laser beam splitting unit includes a second acousto-optic driving source and a second acousto-optic device having a Bragg diffraction effect; The second acousto-optic driving source is used to generate signals of different frequencies and superimpose them to obtain a superimposed frequency signal; The second acousto-optic device forms an acoustic grating with adjustable split beam intensity under the action of the superimposed frequency signal, which is used to cause the incident laser beam to undergo Bragg diffraction at different diffraction angles to obtain a one-dimensional laser beam splitting array.

3. The multi-focal length laser focusing system according to claim 2, wherein: The second acousto-optic driving source includes a second signal generator and a second radio frequency power amplifier; the second signal generator is used to generate signals of different frequencies and superimpose them to obtain a superimposed frequency signal; the superimposed frequency signal is represented by a superposition of a series of cosine functions with different frequencies; the second radio frequency power amplifier is used to amplify the superimposed frequency signal; The second acousto-optic device includes a second piezoelectric transducer and a second acousto-optic interaction medium; the second piezoelectric transducer is a piezoelectric crystal sheet attached to the second acousto-optic interaction medium, and is used to generate mechanical vibration under the drive of the superimposed frequency signal generated by the second acousto-optic driving source, acting on the second acousto-optic interaction medium to form an acoustic grating with adjustable splitting beam intensity; the second acousto-optic interaction medium is used to cause the incident laser beam to undergo Bragg diffraction at different diffraction angles, thereby obtaining a one-dimensional laser beam splitting array.

4. The multi-focal length laser focusing system according to claim 2, wherein: The second acousto-optic driving source is used to adjust the number of frequency superpositions in the superposition frequency signal, thereby controlling the number of laser beam splittings.

5. The multi-focal length laser focusing system according to claim 3, wherein: The second acousto-optic interaction medium is any one of fused quartz, quartz crystal, tellurium oxide or lead molybdate.

6. The multi-focal length laser focusing system according to claim 1, wherein: The laser beam splitting unit is a diffraction optical element DOE; The diffractive optical element DOE is used to split an incident laser beam into multiple beams.

7. The multi-focal length laser focusing system according to claim 2, wherein: The acoustic modulator sub-grating formed by the chirp signal in the acousto-optic crystal matches each corresponding split beam, so that each corresponding split beam is located at the center of the acoustic modulator sub-grating formed by the chirp signal.

8. The multi-focal length laser focusing system according to claim 2, wherein: The superposition frequency signal generated by the laser beam splitting unit is the same as the switching frequency of the multiple chirp signals generated by the laser multi-focal length focusing unit; the laser pulses generated by the laser beam splitting unit are synchronized with the switching of the chirp signals; The superimposed frequency signal generated by the laser beam splitting unit is synchronized with the chirp signal generated by the laser multi-focal length focusing unit.

9. A multi-focal length laser focusing method, characterized in that: The multi-focal length laser focusing system according to any one of claims 1 to 8 comprises: S1. Setting parameters of the laser beam splitting unit based on the target deflection angle and target spot intensity of the split laser beam; S2. Based on the target number of output split laser beams and the target focal length of the focus, determine the number and chirp rate of chirp signals generated by the laser multifocal focusing unit, and set parameters for the laser multifocal focusing unit; S3. The incident laser beam is incident on the multi-focal length laser focusing system, and light spots having the target number and respectively focused at the target focal length are output.

10. The multi-focal length laser focusing method according to claim 9, wherein: Also includes: By adjusting the angles between the split laser beams and the corresponding chirp signals of different lengths, multi-focal length focusing with unequal intervals is generated.

Images