Method for generating miniature dispersion structure in thermoplastic medium

Abstract

The invention discloses a method for generating a miniature dispersion structure in a thermoplastic medium. According to the invention, local stress concentration is introduced into a thermoplastic medium by using micro explosion and shock waves induced by ultrafast laser, highly complicated dispersion signals can be generated on a microscale through a photoelastic effect, and rich and diversified spectral responses are provided. Complex color distribution of a stress concentration area can be observed in a color polarization mode. The dispersion structure has an ultra-wide working wave band (400-1400 nm) and an ultra-compact occupied area (50 * 50 [mu] m < 2 >), is compatible with transmission and reflection modes, is suitable for various materials, and has robustness to various harsh conditions. The method provides a new path for implanting a micro-scale and broadband optical dispersion function into a transparent substrate, paves a way for a multifunctional, low-cost and flexible integrated spectrum system, and has huge potential in applications such as on-chip integrated spectrometers and spectral imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafast laser micro-nano processing, and particularly relates to a method for generating a micro-dispersion structure inside a thermoplastic medium. Background Art

[0002] Optical dispersion, as a fundamental physical phenomenon, is widely applied in various optical measurement, sensing, and communication devices. With the rapid growth in the demand for portable, wearable, and implantable optoelectronic devices, the miniaturization of optical devices and systems has become a key goal. Therefore, it is crucial to reduce the size of the dispersion structure to the micrometer scale. However, the dependence of light diffraction and refraction on spatial dimensions significantly limits the further miniaturization of traditional optical dispersion structures, which can typically only be reduced to the millimeter scale, not meeting the design requirements of future ultra-small and portable devices.

[0003] Transparent thermoplastic materials have characteristics such as high plasticity, low cost, a wide light transmission window, and strong chemical stability. In theory, integrating miniaturized spectral response elements into thermoplastic materials can fully utilize the excellent properties of the substrate to achieve high-performance microscale optical dispersion. However, the inherent processing deformation characteristics of thermoplastic materials make it difficult to use them in the fabrication of fine micro-nano photon components. Therefore, how to process micro-dispersion structures in thermoplastic materials has become a challenge. Summary of the Invention

[0004] To achieve the writing of a micro-optical dispersion structure inside a transparent thermoplastic medium, the present invention proposes a method for generating a micro-dispersion structure in a thermoplastic medium. The present invention efficiently generates a micro-dispersion structure in a thermoplastic medium by utilizing the mechanism of the interaction between an ultrafast laser and the thermoplastic medium. This structure not only has excellent optical properties but also good repeatability, and the morphology of the dispersion structure can be flexibly regulated by designing the laser processing strategy. In addition, this dispersion structure has an ultra-wide working wavelength range (400 - 1400 nm), an ultra-compact footprint (50×50 μm 2 ), is compatible with both transmission and reflection modes, is applicable to a variety of materials, and has robustness against various harsh conditions. This structure can provide a rich spectral response within a small size, providing new ideas for the development of on-chip spectrometers.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] 1. A method for generating a micro-dispersion structure inside a thermoplastic medium

[0007] Step 1: Mount a sheet-shaped thermoplastic medium on the displacement stage of a laser processing system, and then determine the laser processing parameters according to the thickness of the thermoplastic medium sheet and the characteristics of the thermoplastic medium;

[0008] Step 2: The laser processing system generates the first single-point structure within the thermoplastic medium sheet according to the determined laser processing parameters; the single-point structure includes a black cavity at the center and an annular region surrounding the cavity, and there is a distinct demarcation line between the annular region and the surrounding matrix.

[0009] Step 3: Move the displacement stage of the laser processing system to the specified position, and then generate the second single-point structure around the first single-point structure. The second single-point structure interacts with the first single-point structure during generation and forms a micro-dispersion vortex structure in the first single-point structure. The width of the generated micro-dispersion vortex structure is between 8.5 - 60 μm.

[0010] In the said Step 1, the laser processing parameters include processing depth, laser repetition frequency, single-pulse energy of the laser, laser pulse width, and number of pulses.

[0011] The higher the laser repetition frequency, the larger the size of the single-point structure; the higher the single-pulse energy of the laser, the larger the size of the single-point structure; the more the number of laser pulses, the larger the size of the single-point structure. The laser pulse width is in the range of 226 fs to 6 ps, which has little effect on the size of the single-point structure and the formation of the vortex.

[0012] The processing position of the thermoplastic medium sheet is at least 200 μm away from its upper and lower surfaces. If the current laser parameters cause the surface to be penetrated and the vortex cannot be formed at the current processing depth, it is necessary to adjust the processing depth, or appropriately reduce the single-pulse energy of the laser, lower the laser repetition frequency, and reduce the number of laser pulses.

[0013] In the said Step 3, the distance that the displacement stage moves is greater than 1.5 times and less than 2 times the radius of the single-point structure.

[0014] In the said Step 3, the distance that the displacement stage moves is 1.8 times the radius of the single-point structure.

[0015] II. A method for generating a dispersion vortex array inside a thermoplastic medium

[0016] Step 1: Install the sheet-shaped thermoplastic medium on the displacement stage of the laser processing system, and then determine the laser processing parameters according to the thickness of the thermoplastic medium sheet and the characteristics of the thermoplastic medium;

[0017] Step 2: The laser processing system generates the first single-point structure within the thermoplastic medium sheet according to the determined laser processing parameters; the single-point structure includes a black cavity at the center and an annular region surrounding the cavity, and there is a distinct demarcation line between the annular region and the surrounding matrix.

[0018] Step 3: Move the displacement stage of the laser processing system to the specified position and generate the next single-point structure. During the generation of the next single-point structure, it interacts with the single-point structures already generated in the thermoplastic medium sheet and forms a micro-dispersion vortex structure in the interacting single-point structures. Generate the micro-dispersion vortex structures step by step according to the order of the target dispersion vortex array until the target dispersion vortex array is generated.

[0019] The micro-dispersion vortex structure appears in the annular region around the central cavity of the previous single-point structure, and the axis direction of the micro-dispersion vortex structure is along the direction from the irradiation center of the next single-point structure to the irradiation center of the previous single-point structure. The irradiation center is the center of the cavity of each single-point structure. Denote the irradiation center of the next single-point structure as the secondary irradiation center and the irradiation center of the previous single-point structure as the primary irradiation center.

[0020] During the generation of the next single-point structure, it interacts with at least one single-point structure already generated in the thermoplastic medium sheet.

[0021] In Step 1, the laser processing parameters include processing depth, laser repetition frequency, single-pulse energy of the laser, laser pulse width, and number of pulses.

[0022] The higher the laser repetition frequency, the larger the size of the single-point structure; the higher the single-pulse energy of the laser, the larger the size of the single-point structure; the more the number of laser pulses, the larger the size of the single-point structure. The laser pulse width is in the range of 226 fs to 6 ps, which has little effect on the size of the single-point structure and the formation of the vortex.

[0023] The processing position of the thermoplastic medium sheet is at least 200 μm away from its upper and lower surfaces. If the current laser parameters cause the surface to be penetrated and the vortex cannot be formed at the current processing depth, it is necessary to adjust the processing depth, or appropriately reduce the single-pulse energy of the laser, lower the laser repetition frequency, and reduce the number of laser pulses.

[0024] Irradiate the micro-dispersion vortex structure with incident light of different spectral distributions, and the gray-scale images obtained in the microscope polarization light mode show different light and dark distributions, that is, different positions of the vortex structure have different responses to the spectrum.

[0025] The generated micro-dispersion vortex structure can show a complex color distribution in the microscope polarization light mode, and the generated color distribution is independent of the incident angle of the incident light. Changing the angle of the transmission axis of the first polarizer will cause the color distribution to change periodically; changing the angle of the transmission axis of the second polarizer will also cause the color distribution to change periodically.

[0026] The method proposed by the present invention can generate good broadband microscale optical dispersion signals. By utilizing the mechanism of ultrafast laser-induced microexplosion and material density modulation, unprecedented microvortex structures can be prepared on a large scale in thermoplastic media. The formation of microvortices is accompanied by complex stress concentration and significant optical anisotropy. Combining with the photoelastic effect, it can make light form a gradually changing, frequency-dependent microscale optical dispersion signal when propagating in the substrate. This method can be applied to a variety of thermoplastic materials, such as polycarbonate (PC), polysulfone (PSU), etc. The generated structure is not affected by the incident angle of the incident light and can work in both transmission and reflection modes, thus facilitating integration into various plastic optical components or chip-type sensors, with the advantages of flexibility, stability, high cost-effectiveness, etc.

[0027] The present invention has the following beneficial effects:

[0028] The generation of microscale optical dispersion inside the thermoplastic substrate in the present invention well combines the characteristics of thermoplastic materials such as high plasticity, low cost, wide light transmission window, and strong chemical stability, which is very suitable for the development needs of portable, wearable, and implantable optoelectronic devices.

[0029] The method proposed by the present invention for generating microscale dispersion structures in thermoplastic media, the size of the generated microscale dispersion vortex structure is affected by the substrate material, laser processing parameters, and point spacing. Just generating a second single-point structure near the first single-point structure can self-organize to form a microvortex structure without additional operations, and the process is efficient and convenient. In addition, by repeatedly generating single points near the previously generated single-point structure, a large-scale microscale dispersion vortex array can be manufactured in a short time. It should be noted that the generation of vortex structures follows two laws: sequential dependence and direction dependence. Therefore, by designing the position and sequence of laser-induced single-point structures, the vortex structures can be finely controlled, greatly enhancing the controllability of the dispersion structure, making the generated dispersion scheme more flexible and variable, so as to better meet the actual application requirements.

[0030] The method proposed by the present invention for generating microscale dispersion structures in thermoplastic media can control the size of the dispersion within an extremely small range (50×50μm), and in the limit case, it can reach 10×10μm, which well meets the goal of reducing the size of the dispersion structure. In the chromatic polarization mode, this dispersion structure can achieve gradually changing frequency-dependent optical modulation, and the spectral responses at different positions are different, with rich differences between each other, providing good conditions for manufacturing an integrated on-chip spectrometer with high spectral resolution.

[0031] The present invention can be applied to a variety of thermoplastic materials, such as PC, PETG (polyethylene terephthalate), PES (polyethersulfone), and PSU (polysulfone), etc., which contain benzene ring structures and have wide applicability. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the method flow of the present invention.

[0033] Figure 2 It is a schematic diagram of the micro-vortex generation principle.

[0034] Figure 3 It is a photo of the micro-vortex array and an example diagram of complex topography regulation.

[0035] Figure 4 It is the partial spectral response of the micro-dispersion vortex. Detailed implementation manners

[0036] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0037] The overall design concept of the present invention is as follows:

[0038] As Figure 1 shown, the present invention includes the following steps:

[0039] Step 1: Install a thermoplastic medium sheet with a benzene ring structure and a thickness greater than 600 μm on the displacement stage of the laser processing system, and determine the corresponding laser processing parameters according to the thickness of the sheet and the characteristics of the thermoplastic medium. The laser processing parameters include processing depth, laser repetition frequency, single-pulse laser energy, laser pulse width, and number of pulses. It should be particularly noted that, with other parameters remaining unchanged: the higher the laser repetition frequency, the larger the size of the single-point structure; the higher the single-pulse laser energy, the larger the size of the single-point structure; the more the number of laser pulses, the larger the size of the single-point structure. The laser pulse width is in the range of 226 fs to 6 ps, and has little effect on the size of the single-point structure and the formation of vortices. The processing position is at least 200 μm away from the upper and lower surfaces. If the current laser parameters cause the surface to be penetrated and vortices cannot be formed at the current processing depth, it is necessary to adjust the processing depth, or appropriately reduce the single-pulse laser energy, lower the laser repetition frequency, and reduce the number of laser pulses.

[0040] Step 2: The laser processing system generates the first single-point structure in the thermoplastic medium according to the determined laser processing parameters. The single-point structure includes a black cavity at the center and an annular region surrounding the cavity, and there is an obvious demarcation line between the annular region and the surrounding matrix. In the thermoplastic matrix, ultrafast laser irradiation will produce microvoid structures and cause significant material deformation.

[0041] Step 3: Move the displacement stage to the specified position and generate a second single-point structure around the first single-point structure. During the generation process, the second single-point structure interacts with the first single-point structure and forms a micro-dispersion vortex structure in the first single-point structure. The width of the generated micro-dispersion vortex structure is between 8.5 - 50 μm. The vortex always appears in the annular region around the central cavity of the previous structure and along the axis direction from the secondary irradiation center to the primary irradiation center. When irradiating the micro-dispersion vortex structure with incident light of different spectral distributions, the gray-scale images obtained in the polarized light mode show different light and dark distributions, that is, different positions of the vortex structure have different responses to the spectrum. The generated micro-dispersion vortex structure can show a complex color distribution in the microscope polarized light mode, and the generated color distribution is independent of the incident angle of the incident light. Changing the angle of the transmission axis of the first polarizer will cause a periodic change in the color distribution; changing the angle of the transmission axis of the second polarizer will also cause a periodic change in the color distribution.

[0042] Figure 2 (a) in it is a schematic diagram of the micro-vortex generation principle. The first single-point structure 1 induced by the laser 4 inside the thermoplastic medium 3, Figure 2 A in (b) of it. The second single-point structure 2 induced by the laser 4 inside the thermoplastic medium 3, Figure 2 B in (b) of it. Generally, when an ultrafast laser is focused inside a thermoplastic material, the instantaneous energy deposition at an extremely high peak power causes the temperature of the material in the focal region to rise sharply within an extremely short time, far exceeding the evaporation point of the material. The instantaneous material evaporation leads to micro-explosions and shock waves, pushing the surrounding material to spread outward and form a cavity structure. After irradiation, the material in the focal region quickly cools and solidifies, forming a density modulation region, and the inside of the annular region should be lower than the matrix density.

[0043] In nature, the velocity differences caused by external perturbations usually lead to the generation of vortices in fluids. Theoretically, microscale velocity differences can be artificially created to generate micro-vortices. The density modulation region around the cavity induced by an ultrafast laser provides an excellent tool for constructing velocity differences. By using the annular low-density region created around the first single-point structure void through ultrafast laser irradiation, secondary irradiation is carried out at a certain distance from the first void to induce a micro-explosion, which drives the material in the focal volume to diffuse into the annular low-density region. Since the shock wave propagates faster in the low-density medium, once it crosses the circular boundary of the low-density region, the material diffusion velocity changes in different directions. Specifically, the material diffusion velocity is the fastest along the direction towards the center of the first irradiation, and the material diffusion velocity gradually decreases as it deviates from this direction and is symmetrically distributed on both sides of the fastest path, which is similar to the conditions for vortex formation in nature. This velocity modulation can generate a pair of symmetric vortices, and the optimal distance between the two irradiation centers is approximately 1.8 times the radius of the density modulation region.

[0044] Figure 3 Figure 4 shows a photo of a micro-vortex array and examples of complex morphology regulation. In this embodiment, a 3-mm-thick polycarbonate (PC) material is used as the substrate, and the laser processing parameters are as follows: 1. Laser repetition rate: 50 kHz; 2. Single-pulse energy of the laser: 3.25 μJ; 3. Number of laser pulses: 40,000; 4. Laser pulse width: 226 fs. By repeatedly generating single points near the previously generated single-point structure, a large-scale micro-dispersion vortex array can be fabricated in a short time. In addition, by taking advantage of the fact that vortices always appear in the sparse regions around the previously induced voids, complex vortex structure regulation can be achieved by adjusting the laser focusing position and changing the generation order of the single-point structures. Morphology 1 is an oblique 2×2 array, morphology 2 shows that three vortices can be successfully formed within a single-point structure, and morphology 3 shows that a more complex vortex distribution can be induced within the single-point structure to form a hexagonal pattern, highlighting the excellent controllability of the present invention.

[0045] The present invention also proposes a method for generating a dispersion vortex array inside a thermoplastic medium, which specifically includes the following steps:

[0046] Step 1: Mount the thermoplastic medium sheet on the displacement stage of the laser processing system, and then determine the laser processing parameters according to the thickness of the thermoplastic medium sheet and the properties of the thermoplastic medium.

[0047] Step 2: The laser processing system generates the first single-point structure inside the thermoplastic medium sheet according to the determined laser processing parameters; the single-point structure includes a black cavity at the center and an annular region surrounding the cavity, and there is an obvious boundary between the annular region and the surrounding matrix.

[0048] Step 3: Move the displacement stage of the laser processing system to the specified position and generate the next single-point structure. During the generation of the next single-point structure, it interacts with the already generated single-point structures in the thermoplastic medium sheet and forms a micro-dispersion vortex structure in the interacting single-point structures. Generate the micro-dispersion vortex structures step by step according to the order of the target dispersion vortex array until the target dispersion vortex array is generated.

[0049] Figure 4 It is the partial spectral response of the micro-dispersion vortex. In this example, polycarbonate (PC) material is used as the substrate. The front and back of the substrate material with the written dispersion micro-vortices are respectively pasted with polarization films. At this time, complex optical dispersion signals can be generated at the micro-vortices and directly captured as grayscale images by an image sensor. By processing and analyzing the grayscale images when monochromatic light of different wavelengths is incident, the spectral response curves at different positions of the dispersion micro-vortices can be obtained. The specific operation steps are as follows:

[0050] Step 1: Irradiate the vortex structure with monochromatic light with wavelengths of 400 - 720 nm and a wavelength interval of 1 nm in sequence to obtain 321 grayscale images. Each grayscale image represents the response of the vortex to a monochromatic light when a monochromatic light of a different wavelength is incident.

[0051] Step 2: Perform an average pooling operation with a size of 8×8 and a step size of 8 on the obtained 321 grayscale images. Average pooling helps to remove a part of the random oscillation noise, reduce the data volume, and improve the data processing speed.

[0052] Step 3: For the pixel points at different positions of the image after average pooling, a spectral response curve with the wavelength as the abscissa and the pixel point intensity value as the ordinate can be fitted. In this example, the spectral response curves of four pixel points are shown.

[0053] It can be seen from the results that the spectral response curves of different pixel points are different. By using the difference in spectral response, the spectrum of the unknown incident light can be analyzed, thus providing new ideas for the development of on-chip integrated micro-spectrometers.

[0054] Finally, it should be noted that the above embodiments and descriptions are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Without departing from the spirit and scope of the disclosure of the technical solutions of the present invention, they should all be covered within the protection scope of the claims of the present invention.

Claims

1. A method for generating a micro-dispersive structure in a thermoplastic medium, characterized in that: The following steps are involved: Step 1: Mount the sheet of thermoplastic medium on the displacement stage of the laser processing system, and then determine the laser processing parameters according to the thickness of the thermoplastic medium sheet and the characteristics of the thermoplastic medium; Step 2: The laser processing system generates the first single point structure in the thermoplastic medium sheet according to the determined laser processing parameters; Step 3: Move the translation stage of the laser processing system, and then generate a second single-point structure around the first single-point structure. During the generation process, the second single-point structure interacts with the first single-point structure and forms a micro-dispersion vortex structure in the first single-point structure.

2. A method for generating micro-dispersive structures in a thermoplastic medium according to claim 1, characterized in that: In step 1, the laser processing parameters include processing depth, laser repetition frequency, laser single pulse energy, laser pulse width and pulse number.

3. A method for generating a micro-dispersion structure in a thermoplastic medium according to claim 1, characterized in that: The higher the laser repetition frequency, the larger the size of the single-point structure; the higher the laser single pulse energy, the larger the size of the single-point structure; the more the laser pulses, the larger the size of the single-point structure.

4. A method for generating micro-dispersive structures in a thermoplastic medium according to claim 1, characterized in that: The processing position of the thermoplastic medium sheet is at least 200 μm away from the upper and lower surfaces thereof.

5. A method for generating micro-dispersive structures in a thermoplastic medium according to claim 1, characterized in that: In step 3, the distance moved by the translation stage is greater than 1.5 times and less than 2 times the radius of the single-point structure.

6. A method for generating micro-dispersive structures in a thermoplastic medium according to claim 1, characterized in that: In step 3, the distance moved by the translation stage is 1.8 times the radius of the single-point structure.

7. A method for generating a dispersive vortex array in a thermoplastic medium, characterized in that: The following steps are involved: Step 1: Mount the sheet of thermoplastic medium on the displacement stage of the laser processing system, and then determine the laser processing parameters according to the thickness of the thermoplastic medium sheet and the characteristics of the thermoplastic medium; Step 2: The laser processing system generates the first single point structure in the thermoplastic medium sheet according to the determined laser processing parameters; Step 3: Move the translation stage of the laser processing system and generate the next single-point structure, wherein the next single-point structure interacts with the single-point structure already generated in the thermoplastic medium sheet during the generation process and forms a micro-dispersion vortex structure in the interacting single-point structure, and the micro-dispersion vortex structure is gradually processed and generated in the order of the target dispersion vortex array until the target dispersion vortex array is generated.

8. A method for generating a dispersive vortex array in a thermoplastic medium according to claim 7, characterized in that: The micro-dispersive vortex structure appears in the annular area around the central cavity of the previous single-point structure, and the axial direction of the micro-dispersive vortex structure is from the irradiation center of the next single-point structure to the irradiation center of the previous single-point structure.

9. A method for generating a dispersive vortex array in a thermoplastic medium according to claim 7, characterized in that: The next single-point structure interacts with at least one single-point structure that has been generated in the thermoplastic medium sheet during the generation process.

10. A method for generating a dispersive eddy current array in a thermoplastic medium according to claim 7, characterized in that: The processing position of the thermoplastic medium sheet is at least 200 μm away from the upper and lower surfaces thereof.

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