阅读说明：本技术 一种基于多焦点可控的动态激光并行加工的方法 (Dynamic laser parallel processing method based on multi-focus controllable ) 是由 朱林伟 周立强 史强 于 2021-07-07 设计创作，主要内容包括：本发明公开了一种基于多焦点可控的动态激光并行加工的方法,使用复振幅编码的方法生成多幅多焦点相位图,使用空间光调制器动态加载计算出的多幅相位图,实现多焦点可控的动态移动；利用飞秒激光微纳加工系统结合空间光调制器进行多焦点可控的动态激光并行加工。本发明这种多焦点动态并行微纳加工方法只需SLM动态加载相位图进行加工,无需使用位移台和振镜等精密仪器,可以省去大量繁琐步骤,并且可以同时加工不同结构,大大提高了加工的灵活性和加工效率；提高多焦点微纳加工的精确度。(The invention discloses a multi-focus controllable dynamic laser parallel processing method, which comprises the steps of generating a plurality of multi-focus phase diagrams by using a complex amplitude coding method, and dynamically loading the plurality of calculated phase diagrams by using a spatial light modulator to realize multi-focus controllable dynamic movement; and performing multi-focus controllable dynamic laser parallel processing by utilizing the femtosecond laser micro-nano processing system and combining the spatial light modulator. According to the multi-focus dynamic parallel micro-nano processing method, only the phase diagram is dynamically loaded by the SLM for processing, precision instruments such as a displacement table and a galvanometer are not needed, a large number of complicated steps can be omitted, different structures can be processed simultaneously, and the processing flexibility and the processing efficiency are greatly improved; and the accuracy of multi-focus micro-nano processing is improved.)

1. A dynamic laser parallel processing method based on multi-focus controllable is characterized in that: generating a plurality of multifocal phase images by using a complex amplitude coding method, and dynamically loading the calculated plurality of phase images by using a spatial light modulator to realize multifocal controllable dynamic movement; performing multi-focus controllable dynamic laser parallel processing by utilizing a femtosecond laser micro-nano processing system and combining a spatial light modulator;

the method comprises the following specific steps:

step 1: determining the number N of focal points, and designing the position delta x of each focal point₁,Δy₁；…；Δx_N，Δy_N；

Step 2: separately calculating the pure phase distribution psi of each focal point₁，…,ψ_N；

And step 3: calculating the complex amplitude distribution of the designed incident field, representing the complex amplitude as two phase distributions, phase1 and phase2, and then encoding by two complementary checkerboard functions to obtain a phase diagram;

and 4, step 4: respectively designing the motion trail of each focus based on the steps 1, 2 and 3, and equally dividing each motion trail into a plurality of points to generate a group of holographic phase diagrams;

and 5: realizing multi-focus dynamic movement by dynamic loading of a spatial light modulator;

step 6: and (5) applying the step 5 to a femtosecond laser micro-nano processing system to realize multi-focus controllable laser parallel processing.

2. The method of claim 1, wherein the method comprises the following steps: the calculation formula of the pure phase distribution of each focus in the step 2 is as follows:

wherein, λ: is the wavelength; r: is the aperture radius; n is_t: is the refractive index of the objective lens immersion medium; x is the number of₀,y₀: is the position coordinate of the back focal plane of the objective lens; Δ x, Δ y: is the relative displacement component in the x, y direction of the focal plane compared to the original focal spot of the objective without phase modulation.

3. The method of claim 1, wherein the method comprises the following steps: the formula for calculating the complex amplitude distribution of the incident field in the step 3 is as follows:

wherein, n: taking an integer as the sequential number of the focus; n: taking an integer for the controllable focus quantity; i: is an imaginary unit; m: let m be 0 here for the number of topological charges;

the above formula can be rewritten as a superposition of two equal-amplitude pure phase functions, i.e.

Wherein B ═ A_maxA constant number,/2_maxIs the maximum of the amplitude A (x, y) versus the spatially distributed phase function, the amplitude and phase relationship beingAnd

4. the method of claim 1, wherein the method comprises the following steps: in the step 3, two complementary checkerboard functions are used for coding, and the transmissivity function of the complementary two-dimensional binary grating is kept unchanged under the Nyquist limit;

the two-dimensional checkerboard pattern is described by the following expression:

in the formula, sinc (xi) ≡ sin (pi xi)/(pi xi) represents a sinc function of argument xi, p is the period of the two-dimensional binary grating, and m is₁And m₂Indicating the diffraction order.

5. The method of claim 1, wherein the method comprises the following steps: and 6, dynamically loading a plurality of phase diagrams by using a spatial light modulator in the femtosecond laser micro-nano processing system, and modulating incident light into controllable dynamic multi-focus to realize multi-focus dynamic micro-nano processing.

Technical Field

The invention belongs to the technical field of multifocal controllable dynamic laser parallel processing, and particularly relates to a multifocal controllable dynamic laser parallel processing method.

Background

The femtosecond laser has the advantages of high energy density, high coherence, good directivity and the like. Therefore, the femtosecond laser has wide application in the fields of micro-nano processing, medicine, scientific research and the like. With the development of the femtosecond laser technology, the femtosecond laser direct writing technology becomes one of the popular research technologies in the field of micro-nano processing more and more. Compared with the traditional micro-nano processing technologies such as mask lithography, electron beam etching and the like, the femtosecond laser direct writing technology has the advantages of no mask, no contact, flexibility, rapidness and high-precision three-dimensional processing capability.

However, the femtosecond laser direct writing technology often adopts a single beam processing method in practical application, and the low throughput and low efficiency of the method limit the practical batch application thereof. In order to improve the processing efficiency, an optical element is usually used to generate a spot array for parallel processing, for example, a microlens array is used to split laser beams for processing, or a diffraction element such as a grating is used to split a beam into multiple beams for multi-focus parallel processing. The micro lens array can focus the incident light into a plurality of light spots, the grating can diffract the incident light into a plurality of orders of light spots, and the intensity of array light spots generated by the micro lens array and the grating is not uniform.

And regulating an incident light field by using a spatial light modulator to perform micro-nano processing. The spatial light modulator is loaded with the computer-generated holographic phase diagram, so that an incident light field can be modulated, femtosecond laser can be focused to a plurality of focuses, and any multi-focus array and pattern can be processed, so that the processing speed, the processing efficiency and the processing flexibility are greatly improved. The corresponding holographic phase map can be obtained by using a two-dimensional Fourier transform iterative algorithm, such as Gerchberg-Saxton (GS) algorithm, Weiighted Gerchberg-Saxton (WGS) algorithm, and the like. The iterative algorithms need repeated iteration for long-time calculation, even a unique solution cannot be obtained in the calculation process, the uniformity is not high under the actual high numerical aperture focusing, and the accurate regulation and control of a focusing field cannot be realized.

Disclosure of Invention

In order to overcome the problems, the invention provides a method based on multi-focus controllable dynamic laser parallel processing.

The technical scheme adopted by the invention is as follows:

a method based on multi-focus controllable dynamic laser parallel processing uses a complex amplitude coding method to generate a plurality of multi-focus phase images, and uses a spatial light modulator to dynamically load the calculated plurality of phase images to realize multi-focus controllable dynamic movement; performing multi-focus controllable dynamic laser parallel processing by utilizing a femtosecond laser micro-nano processing system and combining a spatial light modulator;

the method comprises the following specific steps:

step 1: determining the number N of focal points, and designing the position delta x of each focal point₁,Δy₁；…；Δx_N，Δy_N；

Step 2: separately calculating the pure phase distribution psi of each focal point₁，…,ψ_N；

And step 3: calculating the complex amplitude distribution of the designed incident field, representing the complex amplitude as two phase distributions, phase1 and phase2, and then encoding by two complementary checkerboard functions to obtain a phase diagram;

and 4, step 4: based on the steps 1, 2 and 3, motion tracks of each focus can be designed respectively, and each motion track is divided into a plurality of points equally, so that a group of holographic phase diagrams can be generated;

and 5: dynamically loading by using a spatial light modulator so as to realize multi-focus dynamic movement;

step 6: and (5) applying the step 5 to a femtosecond laser micro-nano processing system to realize multi-focus controllable laser parallel processing.

Further: the calculation formula of the pure phase distribution of each focus in the step 2 is as follows:

wherein, λ: is the wavelength; r: is the aperture radius; n is_t: is the refractive index of the objective lens immersion medium; x is the number of₀,y₀: is the position coordinate of the back focal plane of the objective lens; Δ x, Δ y: is the relative displacement component in the x, y direction of the focal plane compared to the original focal spot of the objective without phase modulation.

Further: the formula for calculating the complex amplitude distribution of the incident field in the step 3 is as follows:

wherein, n: taking an integer as the sequential number of the focus; n: taking an integer for the controllable focus quantity; i: is an imaginary unit; m: let m be 0 here for the number of topological charges;

the above formula can be rewritten as a superposition of two equal-amplitude pure phase functions, i.e.

Wherein B ═ A_maxA constant number,/2_maxIs the maximum of the amplitude A (x, y) versus the spatially distributed phase function, the amplitude and phase relationship beingAnd

further: in the step 3, two complementary checkerboard functions are used for coding, and the transmittance function of the complementary two-dimensional binary grating (checkerboard graph) is kept unchanged under the Nyquist limit;

the two-dimensional checkerboard pattern may be described by the following expression:

in the formula, sinc (xi) ≡ sin (pi xi)/(pi xi) represents a sinc function of argument xi, p is the period of the two-dimensional binary grating, and m is₁And m₂Indicating the diffraction order.

Further: and 6, dynamically loading a plurality of phase diagrams by using a spatial light modulator in the femtosecond laser micro-nano processing system, and modulating incident light into controllable dynamic multi-focus to realize multi-focus dynamic micro-nano processing.

The invention has the following advantages:

1. the multi-focus dynamic parallel micro-nano processing method only needs SLM dynamic loading phase diagram for processing, does not need to use precision instruments such as a displacement table, a galvanometer and the like, can save a large number of complicated steps, can process different structures simultaneously, and greatly improves the processing flexibility and the processing efficiency;

2. and the accuracy of multi-focus micro-nano processing is improved.

Drawings

FIG. 1 is a flow chart of a method for dynamic laser parallel processing based on multi-focus controllable according to the present invention;

fig. 2 is a multifocal phase diagram and corresponding CCD images ((a) - (d) phase diagrams, (e) - (h) CCD images (dotted line indicates motion track, arrow indicates motion direction)) of a method for multifocal controllable dynamic laser parallel processing according to the present invention;

fig. 3 is an SEM result chart of dynamic processing based on the multi-focus controllable dynamic laser parallel processing method according to the present invention (a) an SEM result chart of four-focus dynamic processing, and (b) an SEM result chart of a triangle structure).

Detailed Description

The present invention will be further described below, but the present invention is not limited to these.

Examples

As shown in fig. 1, the present invention provides a method for dynamic laser parallel processing based on multi-focus controllable, which comprises the following specific steps:

step 1: determining the number N of focal points, and designing the position delta x of each focal point₁,Δy₁；…；Δx_N,Δy_N；

Step 2: separately calculating the pure phase distribution psi of each focal point₁，…,ψ_N；

And step 3: calculating the complex amplitude distribution of the designed incident field, representing the complex amplitude as two phase distributions, phase1 and phase2, and then encoding by two complementary checkerboard functions to obtain a phase diagram;

and 4, step 4: based on the steps, the motion trail of each focus can be respectively designed, and each motion trail is divided into a plurality of points, so that a group of holographic phase diagrams can be generated;

and 5: dynamically loading by using a spatial light modulator so as to realize multi-focus dynamic movement;

step 6: and (5) applying the step 5 to laser micro-nano processing to realize multi-focus controllable laser parallel processing.

4 points are designed to move along different tracks respectively, and 400 phase maps are generated quickly. The 400 phase maps calculated by dynamically loading the maps at a frequency of 10Hz with a program of spatial light modulators, take 40s to complete a cycle. Fig. 2(e) - (h) show spot images in the CCD at times t-0 s, 10s, 20s, and 30s (t-0 s for loading the first phase map, t-10 s for loading the 101 th phase map, t-20 s for loading the 201 st phase map, and t-30 s for loading the 301 th phase map), respectively. Fig. 2(a) - (d) are phase diagrams corresponding to fig. 2(e) - (h). It can be clearly seen from fig. 2 that the phase diagrams are calculated by the above formula, and the four focal points can move along different tracks by dynamically loading the phase diagrams by using the spatial light modulator.

Scanning electron microscopy results of the dynamically loaded different path holographic phase patterned structure are shown in figure 3. Fig. 3(a) is a SEM image of different shapes of four focus dynamic processing. When the phase diagram is calculated, the side length of the square, the diameter of the circle and the side length of the triangle are 8 um. During processing, the phase diagram is dynamically loaded by the SLM at a frequency of 20Hz for processing. The processed size is basically consistent with the designed size and accords with the expectation.

It is noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.