Femtosecond laser plasma micro lens based on interference technology and preparation method

Abstract

The invention discloses a femtosecond laser plasma microlens based on an interference technology and a preparation method thereof, and the femtosecond laser plasma microlens comprises a femtosecond laser which is used for generating a femtosecond laser beam; the concentric circular ring beam generation and control system is used for dividing the femtosecond laser beam into two beams and generating a concentric circular ring interference pattern; and the plasma lens positioning and size control system is used for focusing the concentric circular ring interference pattern into a micron-sized plasma lens. Therefore, the invention is suitable for the fields of laser processing, laser medical treatment and the like, has wide application prospect and practical value, and provides an effective solution for high-intensity laser focusing.

Description

Technical Field

[0001] The present invention relates to a femtosecond laser plasma microlens based on interference technology and a preparation method thereof, and belongs to the field of laser technology. Background Art

[0002] With the development of laser technology, the application of femtosecond lasers has become increasingly in-depth in scientific research, medical treatment, industry and other fields. Femtosecond lasers have high peak power and extremely short pulse widths (usually between a few femtoseconds and several hundred femtoseconds). After focusing, they can perform fine processing on target substances at the micron or even nanometer level without damaging or minimally damaging the surrounding materials. Femtosecond lasers have extremely high precision and controllability in material processing, cell surgery, spectral analysis, etc. However, when focusing high-intensity femtosecond lasers, traditional lenses have problems such as low damage thresholds and easy damage, and there is an urgent need to explore alternative focusing technologies with high thresholds.

[0003] As an innovative solution, the basic principle of plasma lenses is to use the refractive index characteristics of plasma to control the propagation of laser beams. The advantages of plasma lenses are their high damage thresholds, which can withstand higher laser powers than traditional lenses. At the same time, the focal length of plasma lenses can be adjusted by changing the density and distribution of plasma, which gives them great flexibility in adapting to different application scenarios. However, existing plasma lenses have problems such as complex preparation and cumbersome adjustment processes, which limit their applications. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, in view of the above problems, the object of the present invention is to provide a femtosecond laser plasma microlens based on interference technology and a preparation method thereof that can achieve high-intensity laser focusing.

[0005] To achieve the above invention object, the technical solution adopted by the present invention is as follows: In a first aspect, the femtosecond laser plasma microlens based on interference technology provided by the present invention includes: A femtosecond laser for generating a femtosecond laser beam; A concentric ring beam generation and control system for splitting the femtosecond laser beam into two beams and generating a concentric ring interference pattern; A plasma lens positioning and size control system for focusing the concentric ring interference pattern into a micron-scale plasma lens.

[0006] Further, it further includes a collimation system arranged at the light output of the femtosecond laser for collimating the femtosecond laser beam.

[0007] Furthermore, the concentric circular ring beam generation and control system is implemented using the dual-beam Mach-Zehnder interference principle. It divides the femtosecond laser into two beams, one as the reference beam and the other as the signal beam. Among them, a focusing lens is arranged in the optical path of the signal beam, and a delay line displacement stage is arranged in the optical path of the reference beam. By controlling the delay line displacement stage, spatio-temporal interference occurs between the two pulses of the reference beam and the signal beam, generating a concentric circular ring interference pattern.

[0008] Furthermore, the concentric circular ring beam generation and control system includes a first beam splitter, a first total reflector, a second total reflector, a third total reflector, a fourth total reflector, a fifth total reflector, a sixth total reflector, and a second beam splitter, where: The collimated femtosecond laser beam is split into two beams by the first beam splitter. One of the beams is emitted to the first total reflector, and the femtosecond laser reflected by the first total reflector is emitted to the focusing lens. The femtosecond laser focused by the focusing lens is emitted to the second total reflector; The other beam is successively reflected by the third total reflector, the fourth total reflector, the fifth total reflector, and the sixth total reflector. Among them, the fourth total reflector and the fifth total reflector are installed on the delay line displacement stage. The two laser beams emitted from the second total reflector and the sixth total reflector meet and undergo coaxial interference at the second beam splitter. Among them, by changing the focal length of the focusing lens, the density of the interference pattern can be adjusted, thereby affecting the focal length of the subsequent generated plasma lens.

[0009] Furthermore, the plasma lens positioning and size control system includes a scanning galvanometer and an objective lens; The scanning galvanometer is used to determine the position of the plasma lens; The objective lens is used to focus the concentric circular ring interference pattern and can adjust the size of the plasma lens.

[0010] Furthermore, the focus after the objective lens focuses the concentric circular ring interference pattern is an ellipse with two diameters. One is the diameter perpendicular to the light beam , and the other is the diameter along the laser beam : , ; Among them, a is the original beam width, r is the focal length of the objective lens, λ is the wavelength. When r < a / 2, that is, the focal length of the objective lens is preferably less than 1 / 2 of the original spot diameter, and the concentric circular ring interference pattern can be focused into a micron-scale plasma lens, that is, a plasma lens with a focusing effect.

[0011] Furthermore, the plasma lens is concentric circular ring-shaped.

[0012] In a second aspect, the present invention also provides a method for preparing a femtosecond laser plasma microlens based on interference technology, including: The femtosecond laser emits femtosecond laser after being collimated and then exits; The concentric ring beam generation and control system adopts the principle of double-beam Mach-Zehnder interference, divides the femtosecond laser into two beams, one beam is used as the reference light, and the other beam is used as the signal light. A focusing lens is arranged in the optical path of the signal light, and a delay line displacement stage is arranged in the optical path of the reference light. By controlling the delay line displacement stage, the two pulses of the reference light and the signal light undergo spatio-temporal interference to generate a concentric ring-shaped interference pattern; The position of the plasma lens is determined by a scanning galvanometer, and the concentric ring-shaped interference pattern is focused by an objective lens to generate a concentric circular ring-shaped plasma lens at the focal point, wherein the plasma lens is used to focus the ultrafast laser beam.

[0013] Furthermore, the focal length of the plasma lens is changed by changing the focal length of the focusing lens.

[0014] Furthermore, the size of the plasma lens can be adjusted by changing the magnification of the objective lens.

[0015] Due to the above technical solutions adopted by the present invention, it has the following characteristics: 1. High damage threshold: The present invention has a high damage threshold because the plasma itself can withstand a higher laser power density and is not prone to thermal decomposition, evaporation, or optical breakdown like traditional lens materials. Therefore, the present invention can effectively focus high-intensity femtosecond lasers and is applicable to application scenarios requiring high-power laser processing.

[0016] 2. Focal length tunability: The present invention can precisely control the relative phase of the two laser beams by changing the position of the delay line displacement stage and the focal length of the focusing lens in the interference optical path, thereby realizing the adjustment of the radius of the concentric ring interference pattern. This adjustment mechanism enables the tunability of the focal length and meets the scenarios with different working distances and focusing requirements.

[0017] 3. Flexibility and adaptability: The plasma lens positioning and size control system of the present invention can achieve precise positioning and size control of the plasma lens through the combination of a scanning galvanometer and an objective lens. This design enables the microlens to quickly adapt to different processing requirements and improves the flexibility and adaptability of the equipment.

[0018] 4. Easy to control: Compared with the traditional method for preparing a plasma lens, the interference optical path structure of the present invention is relatively simple, easy to set up and maintain. By precisely controlling each optical element in the interference optical path, a desired concentric ring interference pattern can be conveniently generated, and then a plasma lens with an expected focusing effect can be produced.

[0019] In summary, the present invention is applicable to fields such as laser processing and laser medicine, has broad application prospects and practical value, and provides an effective solution for high-intensity laser focusing. Description of the Drawings

[0020] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings: Figure 1 is the schematic diagram of the plasma lens structure according to the embodiment of the present invention; Figure 2 is the internal optical path diagram of the concentric ring beam generation and control system according to the embodiment of the present invention; Figure 3 is the interference pattern and focusing effect according to the embodiment of the present invention, where (a) is the concentric ring-shaped interference pattern formed after interference; (b) is the focused wavefront reconstructed based on this pattern. Detailed Embodiments

[0021] It should be understood that the terms used herein are only for the purpose of describing specific exemplary embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" as used herein may also include the plural forms. The terms "comprising", "including", "containing", and "having" are inclusive and thus specify the presence of the stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or their combinations. The method steps, processes, and operations described herein are not to be construed as necessarily requiring them to be performed in the particular order described or illustrated, unless the order of performance is explicitly stated. It should also be understood that additional or alternative steps may be used.

[0022] Although terms such as first, second, third, etc. may be used in the text to describe multiple elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Unless the context clearly indicates otherwise, terms such as "first", "second", and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer, or section discussed below may be referred to as the second element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0023] For ease of description, spatial relative relationship terms may be used in the text to describe the relationship of one element or feature shown in the figure relative to another element or feature. These relative relationship terms such as "inner", "outer", "inside", "outside", "below", "above", etc. This spatial relative relationship term is intended to include different orientations of the device in use or operation other than the orientation depicted in the figure.

[0024] After being focused, the femtosecond laser can generate a high concentration of plasma, and the shape of the generated plasma is mainly affected by the laser wavefront. Therefore, only by modulating the laser wavefront can the shape and distribution of the plasma be controlled. Therefore, through femtosecond laser wavefront control technologies such as holographic interference, it is expected to make the femtosecond laser plasma microlens with a simple adjustment process and fast dynamic response possible. The femtosecond laser plasma microlens and preparation method based on the interference technology provided by the present invention include: a femtosecond laser for generating a femtosecond laser beam; a concentric ring beam generation and control system for splitting the femtosecond laser beam into two beams and generating a concentric ring interference pattern; a plasma lens positioning and size control system for focusing the concentric ring interference pattern into a micron-scale plasma lens, thereby realizing the focusing of high-intensity laser. Therefore, the present invention has the characteristics of high damage threshold, adjustable focal length, simple structure, and easy control.

[0025] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be fully conveyed to those skilled in the art.

[0026] As Figure 1 shown, the femtosecond laser plasma microlens based on the interference technology provided by the present invention includes a femtosecond laser and a laser collimation system 1, a concentric ring beam generation and control system 2, and a plasma lens positioning and size control system 3, wherein: A femtosecond laser and a laser collimation system 1 are used to generate and collimate a femtosecond laser beam; A concentric ring beam generation and control system 2 is used to split the femtosecond laser beam into two beams and generate a concentric ring interference pattern; A plasma lens positioning and sizing control system 3 is used to focus the concentric ring interference pattern into a micron-level concentric circular plasma lens.

[0027] In a preferred embodiment, the femtosecond laser and the laser collimation system 1 include a femtosecond laser and a laser collimation system. The femtosecond laser emits the generated femtosecond laser pulses to the laser collimation system, and the laser collimation system is used to collimate the femtosecond laser beam.

[0028] Further, the focused laser power of the femtosecond laser pulse is greater than 10 10 W / cm 2 .

[0029] In a preferred embodiment, the concentric ring beam generation and control system 2 is implemented using the dual-beam Mach-Zehnder interference principle. It splits the femtosecond laser into two beams, one as the reference beam and the other as the signal beam. Among them, a focusing lens is provided in the optical path of the signal beam, and a delay line displacement stage is provided in the optical path of the reference beam. By controlling the delay line displacement stage, spatio-temporal interference occurs between the two pulses of the reference beam and the signal beam, generating a concentric ring interference pattern.

[0030] Further, as Figure 2 shown, the concentric ring beam generation and control system 2 includes a first beam splitter 4, a first total reflector 5, a focusing lens 6, a second total reflector 7, a third total reflector 8, a fourth total reflector 9, a fifth total reflector 10, a sixth total reflector 11, a delay line displacement stage 12, and a second beam splitter 13, where: The collimated femtosecond laser beam is split into two beams by the first beam splitter 4. One of the beams is emitted to the first total reflector 5, and the femtosecond laser reflected by the first total reflector 5 is emitted to the focusing lens 6. Micro-focusing is achieved through the focusing lens 6 with an optional focal length, and the femtosecond laser focused by the focusing lens 6 is emitted to the second total reflector 7. The other beam is reflected successively by the third total reflector 8, the fourth total reflector 9, the fifth total reflector 10, and the sixth total reflector 11. Among them, the fourth total reflector 9 and the fifth total reflector 10 are mounted on the delay line displacement stage 12. The two beams of laser emerging from the second total reflector 7 and the sixth total reflector 11 meet at the second beam splitter 13 and undergo coaxial interference. Since one of the beams is a focused beam, the interference pattern is a concentric ring. Among them, by changing the focal length of the focusing lens 6, the density of the interference pattern can be adjusted, thereby affecting the focal length of the subsequent generated plasma lens.

[0031] Furthermore, by adjusting the position of the delay line stage 12, a concentric ring interference pattern can be obtained within a certain optical path. Specifically, the use of the delay line stage 12 is mainly to fix the optical element that needs to be moved slightly on the delay line stage 12. The software supporting the delay stage 13 can set relevant parameters such as the moving step and time, so as to perform position control of the optical element thereon with micron-level precision. The two femtosecond laser beams split by the beam splitter 4 are both pulsed lasers. Therefore, in order for the two lights to interfere, they must not only overlap in space but also in time. By controlling the position of the delay line stage 12 by software, the optical path difference of the two laser beams split by the beam splitter 4 can be changed, so that the time domain pulse positions of the two beams of light coincide exactly, thereby generating an interference pattern.

[0032] In a preferred embodiment, the plasma lens positioning and size control system 3 includes a scanning galvanometer and an objective lens. The parameters of the scanning galvanometer are adjustable and are used to determine the position of the plasma lens. The magnification of the objective lens is adjustable and is used to focus the concentric ring interference pattern and adjust the size of the plasma lens. The principle of determining the position of the scanning galvanometer and the objective lens is as follows: after determining the position of the plasma lens in a plane perpendicular to the direction of light propagation, the position of the concentric ring light spot is controlled to this position through the scanning galvanometer, and then the objective lens is placed behind the light spot to focus the light spot.

[0033] Furthermore, the focal point of the objective lens after focusing is usually an ellipse with two diameters. One is the diameter perpendicular to the laser beam. , which is the diffraction limit, is given by the original beam width a ,focal length r and wavelength λ; the other is the diameter along the laser beam : , ; Since the present invention utilizes the concentric ring characteristics of the focused plasma, As small as possible, at most About the same size. Calculated according to the above two formulas r < a / 2, that is, the focal length of the objective lens is preferably smaller than 1 / 2 of the original spot diameter, which is used to focus the concentric ring interference pattern into a micron-scale concentric ring-shaped plasma lens, that is, a plasma lens with a focusing effect, which can make the focused plasma ignore the filamentation effect in the laser propagation direction.

[0034] The present invention also provides a method for preparing a femtosecond laser plasma microlens based on interference technology, and the specific process is as follows: S1. The femtosecond laser emits femtosecond laser, which is collimated by the laser collimation system and then exits. Among them, the wavelength of the femtosecond laser is 800 nm, the pulse width is 35 fs, and the repetition frequency is 1 kHz.

[0035] S2. The concentric ring beam generation and control system 2 uses a dual-beam Mach-Zehnder interferometer to divide the femtosecond laser into two beams. One beam is used as the reference light, and the other beam is used as the signal light. A convex lens with a focal length of 300 mm is set as the focusing lens 6 in the optical path of the signal light, and a delay line displacement stage 12 is set in the optical path of the reference light. By scanning the delay line displacement stage 12, the two pulses of the reference light and the signal light generate spatio-temporal interference, generating a concentric ring-shaped interference pattern.

[0036] S3. Determine the position of the plasma lens through the scanning galvanometer, focus the interference pattern through the objective lens, generate a concentric circular plasma lens at the focal point, and use the above plasma lens to focus the ultrafast laser beam.

[0037] In this embodiment, Figure 3 (a) in it is the CCD image of the concentric circle interference pattern, and (b) is the laser focusing effect reconstructed based on this phase distribution. Thus, it can be seen that the beam can produce a focusing effect by passing through the concentric circular plasma microlens.

[0038] Furthermore, changing the focal length of the focusing lens 6 in step S2 can change the focal length of the plasma lens. The specific principle is as follows: The concentric circular interference pattern that has not been focused by the objective lens is equivalent to the reproduced pattern of the hologram, and the phase information of the focusing lens 6 is recorded in it. Therefore, it is equivalent to a Fresnel zone plate with the same focal length as the focusing lens 6. And the focusing effect of the objective lens will compress the spatial distribution of the interference pattern. For example, after the objective lens focuses, the spot is smaller and the plasma ring spacing is denser, resulting in a shorter focal length of the plasma lens. The derived formula is as follows: f 等离子体 = (f 物镜 ) 2 / f 聚焦透镜 ; Among them, f 等离子体 is the focal length of the plasma lens, f 物镜 is the focal length of the objective lens, f 聚焦透镜 is the focal length of the focusing lens. This formula only serves as a theoretical guidance. Of course, the actual focal length of the plasma lens may also be affected by the nonlinear effect in the air. Therefore, it needs to be debugged during the experiment. This embodiment uses a variable-focus objective lens to avoid the cumbersome process of objective lens replacement.

[0039] Furthermore, by changing the magnification of the objective lens in the plasma lens positioning and size control system 3, the size of the plasma lens can be adjusted.

[0040] Furthermore, set the parameters of the scanning galvanometer to determine the position of the plasma lens. The specific process is as follows: According to the instructions of the control software supporting the scanning galvanometer, control the inclination of the mirrors responsible for the X-axis and Y-axis inside the scanning galvanometer, so as to scan the incoming light beam to the desired position, that is, input the x and y coordinates in the control software, and the light beam will move to the corresponding position, which is the position of the plasma lens.

[0041] In summary, the present invention has the advantages of simple structure, convenient adjustment, high damage threshold, adjustable focal length, etc., and has high practical value and market prospects.

[0042] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the differences between each embodiment and other embodiments are emphasized. In the description of this specification, the descriptions referring to terms such as "a preferred embodiment", "furthermore", "specifically", "in this embodiment", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A femtosecond laser plasma microlens based on interference technology, characterized in that, Comprising: A femtosecond laser for generating a femtosecond laser beam; A concentric ring beam generation and control system for splitting the femtosecond laser beam into two beams and generating a concentric ring interference pattern; A plasma lens positioning and sizing control system for focusing the concentric ring interference pattern into a micrometer-scale plasma lens.

2. The femtosecond laser plasma microlens based on the interference technique according to claim 1, characterized in that, It further includes a collimation system disposed at the light output of the femtosecond laser for collimating the femtosecond laser beam.

3. The femtosecond laser plasma microlens based on the interference technique according to claim 1, characterized in that, The concentric ring beam generation and control system is implemented using the dual-beam Mach-Zehnder interference principle. It splits the femtosecond laser into two beams, one as the reference light and the other as the signal light. Among them, a focusing lens is disposed in the optical path of the signal light, and a delay line displacement stage is disposed in the optical path of the reference light. By controlling the delay line displacement stage, the reference light and the signal light undergo spatio-temporal interference to generate a concentric ring interference pattern.

4. The femtosecond laser plasma microlens based on the interference technique according to claim 3, characterized in that, The concentric ring beam generation and control system includes a first beam splitter, a first total reflector, a second total reflector, a third total reflector, a fourth total reflector, a fifth total reflector, a sixth total reflector, and a second beam splitter, where: The collimated femtosecond laser beam is split into two beams by the first beam splitter. One beam is emitted to the first total reflector, and the femtosecond laser reflected by the first total reflector is emitted to the focusing lens. The femtosecond laser focused by the focusing lens is emitted to the second total reflector; The other beam is successively reflected by the third total reflector, the fourth total reflector, the fifth total reflector, and the sixth total reflector. Among them, the fourth total reflector and the fifth total reflector are mounted on the delay line displacement stage. The two laser beams emitted from the second total reflector and the sixth total reflector meet at the second beam splitter and undergo coaxial interference. Among them, by changing the focal length of the focusing lens, the density of the concentric ring interference pattern can be adjusted, thereby affecting the focal length of the subsequent generated plasma lens.

5. The femtosecond laser plasma microlens based on the interference technique according to claim 1, characterized in that, The plasma lens positioning and sizing control system includes a scanning galvanometer and an objective lens; The scanning galvanometer is used to determine the position of the plasma lens; The objective lens is used to focus the concentric ring interference pattern and can adjust the size of the plasma lens.

6. The femtosecond laser plasma microlens based on the interference technique according to claim 5, characterized in that, The focus after the objective lens focuses the concentric ring interference pattern is an ellipse with two diameters, one perpendicular to the light beam , and the other along the diameter of the laser beam : ， ； Among them, a is the original beam width, r is the focal length of the objective lens, λ is the wavelength. When r < a / 2, that is, the focal length of the objective lens is preferably less than 1 / 2 of the original spot diameter, and it can focus the concentric circular interference pattern into a micron-level plasma lens, that is, a plasma lens with a focusing effect.

7. The femtosecond laser plasma microlens based on the interference technique according to claim 5, characterized in that, The plasma lens is concentric circular ring-shaped.

8. A preparation method of a femtosecond laser plasma microlens based on an interference technique according to any one of claims 1 to 7, characterized in that, Comprising: The femtosecond laser emits the femtosecond laser after collimation; The concentric ring beam generation and control system uses the dual-beam Mach-Zehnder interference principle to split the femtosecond laser into two beams, one as the reference light and the other as the signal light. A focusing lens is disposed in the optical path of the signal light, and a delay line displacement stage is disposed in the optical path of the reference light. By controlling the delay line displacement stage, the reference light and the signal light undergo spatio-temporal interference to generate a concentric ring-shaped interference pattern; The position of the plasma lens is determined by the scanning galvanometer, and the concentric ring-shaped interference pattern is focused using the objective lens to generate a concentric circular ring-shaped plasma lens at the focal point, where the plasma lens is used to focus the ultrafast laser beam.

9. The preparation method according to claim 8, characterized in that, The focal length of the plasma lens is changed by changing the focal length of the focusing lens.

10. The preparation method according to claim 8, characterized in that, The size of the plasma lens can be adjusted by changing the magnification of the objective lens.

Images