Terahertz light field visualization analyzer and preparation method, test method and analysis method thereof

Abstract

The present invention provides a terahertz light field visualization analyzer and a preparation method, a test method, and an analysis method thereof. The terahertz light field visualization analyzer includes a terahertz source, a lens, an adjustable sample stage, a core device placed at an adjustable position on the adjustable sample stage, and a microscope. The terahertz source is focused on the core device through the lens. The present invention proposes a novel THz light field visualization analyzer based on the one-step preparation of carbon-based terahertz metamaterial devices by a laser induction method, the absorption characteristics of carbon-based metamaterials to THz waves, the thermochromic effect of cholesteric liquid crystal capsules, etc., and quantifies THz intensity, frequency, polarization and other properties through simple image analysis. This THz visualization analyzer is simple to prepare and low in cost, and meets the practical application requirements of portability and easy operation at room temperature, and has certain potential in the future development and application of THz systems.

Description

Technical Field

[0001] The invention relates to the terahertz field, and in particular to a terahertz light field visualization analyzer. Background Art

[0002] Terahertz (THz) waves usually refer to electromagnetic waves with a frequency range of 0.1-10 THz, which is between microwaves and infrared. Due to the unique properties of THz waves, THz technology has great scientific value and broad application prospects in the fields of object imaging, environmental monitoring, biomedicine, high-speed space communications and national security. As the key to the application in this field, THz optical field analyzers have very important research significance. Most traditional THz analyzers can only analyze one of the THz optical parameters separately, without achieving integration, and the equipment is complex to manufacture, bulky and costly. Therefore, THz analyzers still face practical challenges of high efficiency and low cost. Metamaterials, including metasurfaces, are sub-wavelength artificial microstructure materials, and electromagnetic parameters (dielectric constant ε, magnetic permeability μ) can be arbitrarily designed in theory. Especially in the THz band, there is no particularly effective material in nature to manipulate THz waves, making metamaterials an ideal platform for manipulating THz waves. On the one hand, metamaterials can realize the control of THz intensity, frequency, polarization, etc. during transmission; on the other hand, metamaterials can control near-field THz surface plasmons. In addition, metamaterial devices have the advantages of small size, light weight, high efficiency, etc., which can expand the functions of traditional THz devices and have become a research hotspot for the integration and miniaturization of THz systems. Based on these advantages of metamaterials, it becomes an ideal device for analyzing THz light fields.

[0003] Carbon is a basic element that constitutes various organic substances and even living things. Carbon-based materials, such as graphite, graphene, and carbon nanotubes, have a wide range of applications in physics, chemistry, and materials science due to their excellent properties, including high surface area, high carrier mobility, and high thermal conductivity. In recent years, some THz metamaterial devices based on carbon-based materials such as graphite / graphene have been proposed one after another. However, the performance of these devices depends on the production of complex structured graphene. In 2014, Tour et al. used a carbon dioxide infrared laser system to directly laser ablate polyimide (PI) and successfully prepared porous graphene. The product of this preparation method is called laser-induced graphene (LIG). The porous graphene produced by this method has a high surface area, high thermal stability, and excellent conductivity. The entire processing process can be carried out in ambient air, without any solvent, and at a low cost. This method of laser ablation of PI avoids complex wet chemical methods and can directly prepare patterned structures, creating a good foundation for the wider application of carbon-based metamaterial devices.

[0004] Cholesteric liquid crystal (CLC) is sensitive to temperature. Temperature changes can change the pitch p of the molecular structure. Different pitches reflect light of different wavelengths, making CLC present different colors. Cholesteric liquid crystal capsules (CLCM) can not only protect the core liquid crystal, broaden the scope of use of liquid crystal materials, but also give full play to the performance of liquid crystal materials. THz light field radiation causes the temperature of CLCM to rise, and temperature changes will cause the color of CLCM to change. The image feature information such as the color of CLCM under different THz light fields can be obtained by using a microscopic storage device. The parameters of the THz light field are matched one by one with the image feature information obtained based on the conventional optical microscopic imaging system, and the THz light field parameters are converted into visible light. The changes in the THz light field parameters can be directly observed by the eyes, which is convenient and practical, does not require electro-optical conversion, and is low in cost. Summary of the invention

[0005] The purpose of the present invention is to provide a terahertz light field visualization analyzer capable of detecting high-intensity THz intensity, frequency and polarization characteristics, and a preparation method, a testing method and an analysis method thereof. The device is stable and practical and does not require any additional components.

[0006] To achieve the above objectives, the present invention provides a terahertz light field visualization analyzer, comprising a terahertz source, a lens, an adjustable sample stage, a core device placed at an adjustable position on the adjustable sample stage, and a microscope, wherein the terahertz source is focused on the core device through the lens.

[0007] A further improvement of the present invention is that the core device is composed of a metal substrate layer, a carbon-based metamaterial layer, and cholesteric liquid crystal capsules; the cholesteric liquid crystal capsules are added to the carbon-based metamaterial structure layer by micro-nano operation with the help of capillaries.

[0008] A further improvement of the present invention is that the microscope device is composed of an optical microscope equipped with an industrial camera and an imaging lens and a display, and the color change of the cholesteric liquid crystal capsule is detected by the optical microscope and presented through the display.

[0009] A further improvement of the present invention is that the selected cholesteric liquid crystal capsule is a micron-sized liquid crystal capsule with temperature-sensitive characteristics.

[0010] A further improvement of the present invention is that the carbon-based metamaterial structure is designed by using simulation software, and the THz light field parameters are distinguished by setting various parameters of the metamaterial structure; the carbon-based metamaterial layer is prepared by directly writing the metamaterial structure on the polyimide film using a carbon dioxide laser with a wavelength of 10.6μm; and the performance of the carbon-based metamaterial is adjusted by controlling various parameters of the laser.

[0011] A further improvement of the present invention is that the core device is prepared by the following steps: mixing cholesteric liquid crystal capsule powder with methyl silicone oil to form a matching liquid; using an optical microscope and a capillary, adding the cholesteric liquid crystal capsules to the carbon-based metamaterial structure layer by micro-nano operation under the field of view of the optical microscope, and finally placing it on a metal substrate.

[0012] A further improvement of the present invention is that the color change of the cholesteric liquid crystal capsule can be detected more accurately by comparing the results obtained by the transmission type and the reflection type detection methods.

[0013] The present invention also provides a method for preparing a terahertz light field visualization analyzer, comprising the following steps:

[0014] Provide terahertz sources, lenses, adjustable sample stages, and microscopic devices;

[0015] A core device is provided, which is composed of a metal substrate layer, a carbon-based metamaterial layer, and a cholesteric liquid crystal capsule; the cholesteric liquid crystal capsule is added to the carbon-based metamaterial structure layer by micro-nano operation with the help of a capillary; wherein the carbon-based metamaterial layer is obtained in one step by directly writing the metamaterial structure on a polyimide film using a carbon dioxide laser.

[0016] The present invention also provides a method for testing a terahertz light field visualization analyzer, comprising the following steps:

[0017] S1: placing the core device embedded with cholesteric liquid crystal capsules at the focus of THz radiation;

[0018] S2: Using THz wire grid to control THz intensity; in order to ensure that the cholesteric liquid crystal capsule reaches a stable thermal equilibrium state, the THz wire grid is rotated at a time interval of 10s;

[0019] S3: Using a microscope to take images of samples under different THz radiation; the microscope itself has display and image storage functions, through which image information of the tested sample is obtained and saved to an external storage device display for processing.

[0020] The present invention also provides an analysis method using a terahertz light field visualization analyzer to determine the corresponding relationship between various parameters of the THz light field and image feature information obtained based on a conventional optical microscopic imaging system; image feature information of cholesteric liquid crystal capsules under different THz light fields obtained from a microscope is processed using image software; under different THz light field conditions, the cholesteric liquid crystal capsules will present changes in image information such as different colors; changes in THz intensity correspond to changes in image information such as the color of the cholesteric liquid crystal capsules at the same unit and position of the carbon-based metamaterial structure, and the THz light field intensity is detected by the changes in the image information of the cholesteric liquid crystal capsules; changes in THz frequency correspond to changes in image information such as the color of the cholesteric liquid crystal capsules at different positions of the same unit of the carbon-based metamaterial structure, and the THz light field frequency is distinguished by the changes in the image information of the cholesteric liquid crystal capsules; changes in THz polarization correspond to changes in image information such as the color of the cholesteric liquid crystal capsules at different positions of the same frequency in the carbon-based metamaterial structure, and the THz light field polarization is distinguished by the changes in the image information of the cholesteric liquid crystal capsules.

[0021] The beneficial effects of the present invention are as follows: Based on the thermochromic effect of CLCM and the absorption characteristics of carbon-based metamaterials to THz waves, the present invention proposes a new type of THz light field visualization analyzer, which quantifies THz intensity, frequency, polarization and other properties through simple image analysis. This THz visualization analyzer is simple to prepare and low in cost, and meets the practical application requirements of portability and easy operation at room temperature, and has certain potential in the future development and application of THz systems. In addition, the method of the present invention using a laser-induced method to prepare a carbon-based terahertz metamaterial device in one step provides convenience for the preparation of a visualization analyzer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the terahertz light field visualization analyzer of the present invention

[0023] Figure 2 Schematic diagram of laser-induced preparation of carbon-based metamaterials in the present invention.

[0024] Figure 3 The surface morphology and Raman spectrum of the carbon-based metamaterial prepared in the present invention are shown under an electron microscope.

[0025] Figure 4 This is a frequency simulation experiment diagram of the carbon-based metamaterial structure designed in the present invention.

[0026] Figure 5 This is a diagram of the polarization simulation experiment of the carbon-based metamaterial structure designed in the present invention.

[0027] Figure 6 This is a diagram of experimental results of a terahertz light field visualization analyzer designed in the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should be emphasized that in the process of describing the present invention, various formulas and constraints are distinguished by consistent labels, but the use of different labels to mark the same formula and / or constraints is not excluded. The purpose of this setting is to more clearly illustrate the characteristics of the present invention.

[0030] The invention discloses a terahertz light field visualization analyzer, comprising a carbon-based metamaterial structure prepared by laser induction and a cholesteric liquid crystal capsule which produces microscopically visible color changes as the THz light field changes.

[0031] like Figure 1 As shown, the terahertz light field visualization analyzer device of the present invention comprises a terahertz source 1, a lens 2, an adjustable sample stage 3 and a sample 4. The terahertz source 1 is focused on the sample 4 through the lens 2; the sample 4 is composed of a metal substrate layer 5, a polyimide film layer 6, a cholesteric liquid crystal capsule layer 7, an optical microscope 8 and a display 9.

[0032] Schematic diagram of laser-induced preparation of carbon-based metamaterials Figure 2 As shown in the figure, a CO2 laser with a wavelength of 10.6 μm is used to irradiate the designed metamaterial structure directly onto the polyimide film through computer control software for preparation. Figure 3 The carbon-based metamaterial structure generated under an electron microscope and its Raman spectrum at room temperature are displayed. The generated carbon-based material exhibits a porous structure. Figure 3The carbon-based materials prepared by laser induction have three typical characteristic peaks: D, G and 2D peaks; the D peak (~1350cm-1) represents the defect peak, reflecting structural defects or edges, the G peak (~1580cm-1) reflects its symmetry and degree of crystallinity, and the 2D peak (~2700cm-1) represents the vibration mode of two photonic lattices and is the frequency doubling peak of the D peak.

[0033] Embodiment 1:

[0034] This embodiment is the simulation experiment result of the designed carbon-based metamaterial structure under simulation software. Figure 4 The left picture shows Figure 1 The electric field energy diagram of a unit of the designed carbon-based metamaterial structure at 1.75 THz. It can be seen from the electric field energy diagram that the energy received by different positions of the same unit of the carbon-based metamaterial structure is different. Figure 4 The middle right figure shows the results of the simulated absorption experiment. There are three obvious absorption peaks at 1.75, 2.0 and 2.5 THz. Figure 4 In the electric field energy diagram shown, the frequency f1 at 1.75THz corresponds to the right structure of the metamaterial unit. Similarly, the frequencies 2.0THz and 2.5THz correspond to the other two structures of the metamaterial unit. In this way, the frequency of THz light field can be detected. Figure 5 The left figure shows Figure 1 The carbon-based metamaterial structure designed in the paper has different absorption characteristics under TE and TM polarization modes. Figure 5 The middle figure and the right figure in the figure respectively show the surface electric field energy distribution of the designed carbon-based metamaterial structure at a frequency of 2.5THz under different polarization modes. Since the designed metamaterial structure has polarization correlation, different energy distributions will appear at different positions at the same frequency; thus, the polarization of the THz light field can be distinguished and detected.

[0035] Embodiment 2:

[0036] This embodiment shows the relationship between the THz light field intensity and the changes in image information such as the color of the CLCM in a steady state. In order to show the relationship between different THz intensities and the color changes of the CLCM, this experiment uses the rotation of the THz wire grid to control the THz wave radiation intensity. CLCM has a good temperature sensitivity of about 0.1°C, and the thermochromic time is in milliseconds. In order to ensure that the CLCM reaches a stable thermal equilibrium state, the THz wire grid is rotated at time intervals of 10s. The initial power is 0, and there is no THz transmission. After 10s, the wire grid is rotated with a sampling interval of 0.1mW and the CLCM image data at this time is saved. Thereafter, continue to rotate according to the specified time intervals and sampling intervals until the power is 0.6mW, and the THz wave is completely transmitted. Figure 6Figure (a) is a CLCM image of the same unit and position of the carbon-based metamaterial structure observed and photographed under a microscope at different THz intensities: It shows the color change of CLCM at different THz intensities under thermal equilibrium. When the THz intensity increases, the temperature of CLCM increases, its reflected wave moves from long wavelength to short wavelength, and the color gradually changes from red to green. To facilitate image analysis, the CLCM image based on color tone is processed using image processing software. Figure 6 Figure (b) shows the relationship between the average hue value and THz intensity after the color change image is digitized under thermal equilibrium. The ordinate is the average hue value at the same position of the CLCM image under different THz intensities collected by taking the average value of 5×5 pixels outward from the center of the CLCM using the pipette tool, and the data is fitted by a second-order polynomial. Figure 6 (b) The fitting curve shown in the figure, the horizontal axis represents the THz power. The fitting result report and fitting function are as follows Figure 6 As shown, the corrected fit R 2 The factor reaches 0.96802. The intensity of the THz light field is detected by the change of CLCM color and other image information.

[0037] The device and test method of the present invention are both relatively simple and efficient, and can especially detect high-intensity THz intensity, frequency and polarization characteristics, and utilize the carbon-based metamaterial structure to absorb THz and the thermochromic effect of CLCM to quantify the color change caused by the THz light field. The device of the present invention is stable and practical, and does not require any additional components for measurement.

[0038] In summary, this technical solution proposes a new type of THz light field visualization analyzer based on the thermochromic effect of CLCM and the absorption characteristics of carbon-based metamaterials to THz waves; through simple image analysis, the THz intensity, frequency, polarization and other properties are quantified. This THz visualization analyzer is simple to prepare and low-cost, and meets the practical application requirements of portability and easy operation at room temperature. It has certain potential in the future development and application of THz systems.

[0039] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A terahertz light field visualization analyzer, characterized in that: The invention comprises a terahertz source (1), a lens (2), an adjustable sample stage (3), a core device (4) placed at an adjustable position on the adjustable sample stage (3), and a microscope device. The terahertz source (1) is focused on the core device (4) through the lens (2); the core device (4) is composed of a metal substrate layer (5), a carbon-based metamaterial layer (6), and a cholesteric liquid crystal capsule (7); the cholesteric liquid crystal capsule (7) is added to the carbon-based metamaterial structure layer by means of a capillary through micro-nano operation; the carbon-based metamaterial layer (6) is prepared by using a 10.6 A carbon dioxide laser is used to directly write metamaterial structures on polyimide films.

2. The terahertz light field visualization analyzer according to claim 1, characterized in that: The microscopic device is composed of an optical microscope (8) equipped with an industrial camera and an imaging lens, and a display (9); the color change of the cholesteric liquid crystal capsule is detected by the optical microscope (8) and presented through the display (9).

3. The terahertz light field visualization analyzer according to claim 1, characterized in that: The selected cholesteric liquid crystal capsule is a micron-sized liquid crystal capsule with temperature-sensitive characteristics.

4. The terahertz light field visualization analyzer according to claim 1, characterized in that: The carbon-based metamaterial structure is designed using simulation software, and the THz light field parameters are differentiated by setting the various parameters of the metamaterial structure; the performance of the carbon-based metamaterial is adjusted by controlling the various parameters of the laser.

5. The terahertz light field visualization analyzer according to claim 4, characterized in that: The core device is prepared by the following steps: mixing cholesteric liquid crystal capsule powder with methyl silicone oil to form a matching liquid; using an optical microscope and a capillary, adding the cholesteric liquid crystal capsule to the carbon-based metamaterial structure layer by micro-nano operation under the field of view of the optical microscope, and finally placing it on a metal substrate.

6. The terahertz light field visualization analyzer according to claim 1, characterized in that: The results obtained by comparing the transmission and reflection detection methods can be used to more accurately detect the color change of the cholesteric liquid crystal capsule.

7. The method for preparing the terahertz light field visualization analyzer according to any one of claims 1 to 6, characterized in that: The steps include: Providing a terahertz source (1), a lens (2), an adjustable sample stage (3) and a microscope device; A core device (4) is provided, wherein the core device (4) is composed of a metal substrate layer (5), a carbon-based metamaterial layer (6), and a cholesteric liquid crystal capsule (7); the cholesteric liquid crystal capsule (7) is added to the carbon-based metamaterial structure layer by means of a capillary through micro-nano operation; wherein the carbon-based metamaterial layer (6) is obtained in one step by directly writing a metamaterial structure on a polyimide film using a carbon dioxide laser.

8. A testing method using the terahertz light field visualization analyzer according to any one of claims 1 to 6, characterized in that: The steps include: S1: placing the core device embedded with cholesteric liquid crystal capsules at the focus of THz radiation; S2: Use THz wire grid to control THz intensity; in order to ensure that the cholesteric liquid crystal capsule reaches a stable thermal equilibrium state, the THz wire grid is rotated at intervals of 10 s; S3: Using a microscope to take images of samples under different THz radiation; the microscope itself has display and image storage functions, through which image information of the tested sample is obtained and saved to an external storage device display for processing.

9. An analysis method using the terahertz light field visualization analyzer according to any one of claims 1 to 6, characterized in that: Determine the correspondence between various parameters of the THz light field and the image feature information obtained based on a conventional optical microscopy imaging system; use image software to process the image feature information of the cholesteric liquid crystal capsule under different THz light fields obtained from the microscope; under different THz light field conditions, the cholesteric liquid crystal capsule will present changes in different color image information; the change in THz intensity corresponds to the change in the color image information of the cholesteric liquid crystal capsule at the same unit and position of the carbon-based metamaterial structure, and the detection of the THz light field intensity is achieved through the change in the image information of the cholesteric liquid crystal capsule; the change in THz frequency corresponds to the change in the color image information of the cholesteric liquid crystal capsule at different positions of the same unit of the carbon-based metamaterial structure, and the distinction of the THz light field frequency is achieved through the change in the image information of the cholesteric liquid crystal capsule; the change in THz polarization corresponds to the change in the color image information of the cholesteric liquid crystal capsule at different positions of the same frequency of the carbon-based metamaterial structure, and the distinction of the polarization of the THz light field is achieved through the change in the image information of the cholesteric liquid crystal capsule.

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