Spatial light modulation femtosecond laser large-scale grating printing method

Abstract

The invention discloses a spatial light modulation femtosecond laser large-scale grating printing method which is characterized in that a spatial light modulator and femtosecond laser are combined, the characteristic that the spatial light modulator can be processed in parallel is utilized, a plurality of sub-pulses are formed firstly, then the distance between the sub-pulses is adjusted, and the femtosecond laser can be processed in parallel. The interference effect is generated through the sub-pulse superposition phase difference, and meanwhile, the large-area uniform grating structure can be machined on the surface of the material in combination with rapid movement of the displacement platform. According to the method, the grating preparation process is simplified, the large-area grating processing speed is increased, processing modes with different areas and different grating periods can be designed, and in addition, the submicron-scale grating with high robustness and excellent optical quality can be still prepared within a certain out-of-focus range through the sub-pulse superposition phase difference.

Description

Technical Field

[0001] The invention belongs to the technical field of nanostructure preparation, and in particular relates to a method for large-area scale grating printing by utilizing a spatial light modulator in combination with a femtosecond laser. Background Art

[0002] Large-area, high-resolution gratings have broad application prospects in many fields, such as spectral analysis, optical positioning, display technology, optical instruments, etc. However, they face many challenges in their manufacturing and application: first, they require high-precision processing equipment and process control; second, their processing and manufacturing costs are high. How to efficiently prepare large-area and high-precision gratings is still a technical barrier that the industry needs to break through.

[0003] Pulse laser direct writing grating uses a laser beam to write directly on the surface or inside of the material, and can produce gratings with specific periods and structures. Compared with other preparation processes such as electron beam exposure, ultraviolet lithography, nanoimprinting, etc., it has the characteristics of low cost, strong scalability, and no need for masks, and can be applied to the processing of various materials. In addition, by adjusting the frequency of the laser pulse and the transmission speed of the mobile platform, fast and continuous grating writing can be achieved. Further adjustment of laser parameters and processing conditions, such as laser power, pulse width, scanning speed, etc., can flexibly control parameters such as the period, length and shape of the grating. However, laser direct writing grating processing has high requirements for the focus of the laser on the surface or inside of the material. In addition, the single focus still has a major defect in processing gratings over a large area and with high precision. Summary of the invention

[0004] The purpose of the present invention is to provide a method for large-scale grating printing using spatial light modulation femtosecond laser, which combines a spatial light modulator with a femtosecond laser, and utilizes the characteristic of the spatial light modulator that can be processed in parallel, first forms multiple sub-pulses, and then adjusts the spacing of the sub-pulses, utilizes the superposition phase difference of the sub-pulses to produce an interference effect, and combines the rapid movement of the displacement platform to process a large-area uniform grating structure on the surface of the material. This method not only simplifies the process of grating preparation and improves the speed of large-area grating processing, but also can design processing modes of different areas and different grating periods. In addition, the superposition phase difference of the sub-pulses can still produce gratings with high robustness, excellent optical quality, and sub-micron level within a certain defocus range.

[0005] The specific technical solution for achieving the purpose of the present invention is: A method for spatial light modulation femtosecond laser scale grating printing, characterized in that the method comprises the following steps: The light beam output by the femtosecond pulse laser is expanded and then reflected to the spatial light modulator through a reflector, a polarization beam splitter, and a half-wave plate. After the phase distribution of the light beam is changed by loading multiple point phase holograms with equal spacing on the spatial light modulator, the light beam is converged to the sample after passing through a 4f system and a focusing objective lens to form multiple loaded sub-pulse phase holograms. The sample is fixed on a three-dimensional electric control displacement platform. By loading multiple point phase holograms with equal spacing on the spatial light modulator, a single light beam can be shaped into multiple sub-pulse beams, and then the phase difference of the sub-pulses is used to produce interference effect between the light beams. After focusing through the objective lens, the sample is displaced to the displacement platform after the femtosecond laser power exceeds the sample damage threshold. Sub-micron high-uniformity gratings can be etched on the sample surface. By controlling the translation range of the displacement platform and the spacing between the point phase holograms loaded by the spatial light modulation, gratings of different areas and different periods can be printed.

[0006] Furthermore, the spatial light modulator is loaded with multiple point phase holograms with equal spacing, and the number of points can be increased from 2 pixels to the maximum pixel range that can be accommodated by the spatial light modulator loaded with phase holograms; the spacing between points can be increased from 1 pixel to 10 pixels.

[0007] Furthermore, the sample is quartz, silicon, a metal film or an organic material film.

[0008] Furthermore, the focusing objective lens includes 20 times, 40 times, 50 times and 100 times objective lenses.

[0009] Furthermore, the period of the etched submicron high-uniformity grating depends on the spacing between points in a plurality of equally spaced point phase holograms loaded by a spatial light modulator. The grating period shows a trend of first decreasing and then increasing as the spacing between points increases. Therefore, the point spacing corresponding to the smallest period of the grating is 3 pixels.

[0010] Beneficial effects of the present invention: Compared with femtosecond laser induced metal surface plasma grating, the grating directly written and etched on the material surface by femtosecond laser combined with spatial light modulator has higher regularity and integrity, and also expands the range of etching materials.

[0011] The spatial light modulator can shape a single light beam into multiple light beams, so parallel processing is possible. Compared with etching the material surface after focusing a single focus through an objective lens, multi-focus parallel processing can greatly increase the processing speed. In addition, by adjusting the sub-pulse spacing and displacement platform settings loaded on the spatial light modulator, the period, length, shape and other parameters of the grating can be flexibly controlled, and any large-area sub-micron grating can be processed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a flow chart of an experimental device for implementing the present invention; Figure 2 It is a schematic diagram of the principle of printing a grating by loading a sub-pulse sequence and superimposing a phase difference on a spatial light modulator of the present invention to produce an interference effect; Figure 3 It is a schematic diagram of the large-scale grating printing on a 20-nanometer aluminum film-silicon wafer substrate sample of the present invention; Figure 4 These are polarization response reflection spectra of the prepared submicron grating structure and grating-free structure measured under different polarization states. DETAILED DESCRIPTION

[0013] Various embodiments of the present invention will be described below with reference to the accompanying drawings, but they are not intended to limit the present invention. In the present invention, a large-area submicron grating structure is printed by the method. Example

[0014] The present invention combines a spatial light modulator with a femtosecond laser, utilizes the characteristic of the spatial light modulator that can be processed in parallel, first forms a plurality of sub-pulses, then adjusts the spacing of the sub-pulses, utilizes the phase difference of the sub-pulses to produce an interference effect, and combines the rapid movement of the displacement platform to process a large-area uniform grating structure on the surface of the material. The method specifically includes the following steps: See also Figure 1 The light beam outputted by the femtosecond pulse laser 1 passes through the beam expander 2, the first reflector 3, the half-wave plate 4, and the polarization beam splitter prism 5, and then is reflected to the spatial light modulator 6. After the phase distribution of the light beam is changed by loading multiple point phase holograms with equal spacing on the spatial light modulator 6, it passes through the 4f system composed of lenses 8 and lenses 10, where the direction of the light path is determined by the second reflector 7 and the third reflector 9, and finally passes through the non-polarization beam splitter prism 11 and the non-polarization beam splitter prism 12, and converges to the sample placed on the processing platform 14 through the focusing objective lens 13, forming multiple loaded sub-pulse phase holograms. In order to facilitate the detection of the real-time formation process of the printed grating on the sample surface, a detection optical path composed of a white light source is also built. The white light source 15 passes through the non-polarizing beam splitter prism 11 and the non-polarizing beam splitter prism 12 and is focused onto the sample placed on the processing platform 14 through the objective lens 13. The detection light passes through the sample and returns to the non-polarizing beam splitter prism 12 and then passes through the fourth reflector 16, and then passes through the lens 17 and the long-wave pass 18 to present the image on the sample to the camera 19.

[0015] The sample is fixed on a three-dimensional electric control displacement processing platform. By loading multiple point phase holograms with equal spacing on the spatial light modulator, a single light beam can be shaped into multiple sub-pulse beams, which are focused by the objective lens. After the femtosecond laser power is greater than the sample damage threshold, a sub-micron high-uniformity grating can be etched on the sample surface by translating the displacement platform. By controlling the translation range of the displacement platform and the spacing between the point phase holograms loaded by the spatial light modulation, gratings of different areas and different periods can be printed. Example

[0016] The present invention is used to prepare a large-area sub-micron grating. In this embodiment, the spatial light modulator needs to generate an interference effect after loading a sub-pulse sequence and superimposing a phase difference.

[0017] See also Figure 2 , shows the principle schematic diagram of this embodiment. When the pulse laser is irradiated onto the spatial light modulator 6, a series of point phase sub-pulse sequences need to be loaded onto the spatial light modulator 6. By superimposing the phase difference, a double-spot interference effect is generated between the sub-pulses. At this time, the reflected laser carries the interference fringe array information and can be used as a source template to etch a periodic uniform grating on the sample surface in combination with the displacement platform 14. In addition, since the sample surface processing utilizes the interference effect after the sub-pulse sequence superimposes the phase difference, the focus can also be processed under a certain defocus condition, and the sample processing process has high robustness. Example

[0018] See also Figure 3 , Figure 3 The local SEM image of the submicron grating printed on the selected material 20 nanometer aluminum film-silicon wafer substrate is shown. By adjusting the spacing of a series of point phase sub-pulse sequences loaded on the spatial light modulator, grating arrays of different periods can be processed. The figure shows the minimum period grating corresponding to the point spacing of 3 pixels loaded on the spatial light modulator. At this time, the minimum period is limited by the laser diffraction limit, and the corresponding period formula is Λ=0.61λ / n•sinα. Example

[0019] See also Figure 4, the spectrum tested on the submicron grating processed in this embodiment, that is, the processed submicron grating is tested with a visible light spectrum, and the spatial light modulator combined with the femtosecond laser can obtain a grating structure with a period of about 500 nanometers through two overlays. When the period of the grating reaches the wavelength level or is smaller than the wavelength, its diffraction characteristics are related to the polarization and have polarization dependence. The tested spectrum is a reflection spectrum, and it is found in the test that the sample with the grating structure has an obvious response at different polarization angles compared with the sample without the grating structure. It can be seen from the experiment that the large-scale submicron grating sample prepared by the present invention has obvious reflection characteristic peaks at different polarization angles, and changes with the change of polarization, indicating that the prepared submicron grating can modulate light of different polarization states.

[0020] The above embodiments are only for further explanation of the present invention, and are not intended to limit the present invention. Any equivalent implementation of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for spatial light modulation femtosecond laser large-scale grating printing, characterized in that: The method comprises the following steps: The light beam output by the femtosecond pulse laser is expanded and then reflected to the spatial light modulator through a reflector, a polarization beam splitter, and a half-wave plate. After the phase distribution of the light beam is changed by loading multiple point phase holograms with equal spacing on the spatial light modulator, the light beam is converged to the sample after passing through a 4f system and a focusing objective lens to form multiple loaded sub-pulse phase holograms. The sample is fixed on a three-dimensional electric control displacement platform. By loading multiple point phase holograms with equal spacing on the spatial light modulator, a single light beam can be shaped into multiple sub-pulse beams, and then the phase difference of the sub-pulses is used to produce interference effect between the light beams. After focusing through the objective lens, the sample is displaced to the displacement platform after the femtosecond laser power exceeds the sample damage threshold. Sub-micron high-uniformity gratings can be etched on the sample surface. By controlling the translation range of the displacement platform and the spacing between the point phase holograms loaded by the spatial light modulation, gratings of different areas and different periods can be printed.

2. The method for spatial light modulation femtosecond laser large-scale grating printing according to claim 1, characterized in that: The spatial light modulator is loaded with multiple point phase holograms with equal spacing, and the number of points can be increased from 2 pixels to the maximum pixel range that can be accommodated by the spatial light modulator loaded with the phase hologram; the spacing between the points can be increased from 1 pixel to 10 pixels.

3. The method for spatial light modulation femtosecond laser large-scale grating printing according to claim 1, characterized in that: The sample is quartz, silicon, a metal film or an organic material film.

4. The method for spatial light modulation femtosecond laser large-scale grating printing according to claim 1, characterized in that: The focusing objective lenses include 20 times, 40 times, 50 times and 100 times objective lenses.

5. The method of spatial light modulation femtosecond laser large-scale grating printing according to claim 1, characterized in that: The period of the etched submicron high uniformity grating depends on the spacing between points in a plurality of equally spaced point phase holograms loaded by a spatial light modulator. The grating period shows a trend of first decreasing and then increasing as the spacing between points increases. Therefore, the point spacing corresponding to the smallest period of the grating is 3 pixels.

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