Liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging, preparation and application

Abstract

A liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging, its fabrication, and its application are disclosed. The liquid-filled hollow microsphere lens comprises a hollow microsphere with an opening on its surface and filled with liquid. By selecting the radius and thickness of the hollow microsphere shell, as well as the refractive index parameters of the surrounding environment and the liquid, and by adjusting the liquid injection height or type, the effective length, focal length, working distance, and half-width at half-maximum (HWHM) of the terahertz jet can be changed. In this invention, the sample to be imaged does not contact the microsphere lens, preventing sample contamination, reducing the complexity of experimental operations, improving imaging resolution, and possessing flexible tuning capabilities to meet the needs of different application fields for high-resolution terahertz imaging.

Description

Technical Field

[0001] This invention relates to the field of terahertz imaging technology, specifically to a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging, its preparation, and its application. Background Technology

[0002] Terahertz (THz) waves are electromagnetic waves in a specific frequency range, between 0.1 and 10 THz, falling between microwaves and infrared. This gives terahertz waves a significant penetration depth, allowing them to penetrate materials that traditional optical wavelengths cannot, such as plastics, ceramics, and insulating foams. Therefore, terahertz imaging technology shows great potential for applications in various fields, including biomedicine, security inspection, and aerospace. Compared to X-ray imaging, terahertz imaging is less damaging to biological tissues and is therefore widely used for non-destructive testing. However, the relatively long wavelength of terahertz waves limits the resolution of traditional far-field terahertz imaging techniques, typically constrained by the diffraction limit (0.61λ / NA, where λ is the wavelength of the incident light and NA is the numerical aperture of the objective lens), which cannot meet the demands of modern applications.

[0003] Various methods have been developed to improve the resolution of terahertz imaging. However, THz near-field imaging, THz confocal scanning imaging, THz image restoration processing, and metamaterials and metalenses have severely limited the application scope of high-resolution terahertz imaging technology due to problems such as complex equipment, large loss of energy and spectral bandwidth, and difficulty in information extraction.

[0004] In addition, existing structures used to generate the terahertz effect include single microspheres ([1] Yang Y, Liu H, Yang M, et al. Dielectric sphere-coupled THz super-resolution imaging[J]. Applied Physics Letters, 2018, 113(3)), hemispheres ([2] Minin IV, Minin OV, Kharitoshin NA. Localized high field enhancements from hemispherical 3D mesoscale dielectric particles in the refection mode[C] / / 2015 16th International Conference of Young Specialists on Micro / Nanotechnologies and ElectronDevices. IEEE, 2015: 331-333), and cubes ([3] Nguyen Pham HH, Hisatake S, Minin OV, et al. Enhancement of spatial resolution of terahertz imaging systems based on terajet generation by dielectric cube[J]. Apl Photonics, 2017, 2(5)), cones and frustums ([4] Cruz ALS, Cordeiro CMB, Franco MA R. Enhanced Terahertz transmission through 3D non-spherical terajets[C] / / 24th International Conference on Optical Fibre Sensors.SPIE, 2015, 9634:85-88), etc. The focal point of the terahertz jets they produce is usually close to the structure, which requires the sample to be in contact with these structures, increasing the risk of sample contamination. This requirement places high demands on the accuracy of experimental operations and equipment, limiting the practical application of the technology; the half-width at half-maximum of the terahertz jets produced by conventional structures is usually between 0.4λ and 0.Within the 5λ range, although the diffraction limit has been exceeded, higher imaging resolution is still required in practical applications, thus necessitating a smaller full width at half maximum (FWHM). Once existing structures are determined, the intensity, working distance, and FWHM of the jets they generate are difficult to adjust significantly, lacking flexible tuning capabilities and failing to meet the needs of different application scenarios. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging, its preparation and application. The sample to be imaged does not come into contact with the microsphere lens, so the sample will not be contaminated, reducing the complexity of experimental operation, improving imaging resolution, and having a flexible tuning function to meet the needs of different application fields for high-resolution terahertz imaging.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging includes a hollow microsphere with an opening on its surface and liquid filling the interior of the hollow microsphere.

[0008] The hollow microspheres have an outer shell shape that is sphere, ellipsoid, cube, cylinder or cone.

[0009] By selecting the hollow microsphere shell radius, shell thickness, and refractive index parameters of the surrounding environment and liquid, the effective length, focal length, working distance, and half-width at half-maximum characteristics required for the jet can be achieved.

[0010] The effective length, focal length, working distance, and half-width at half-maximum (HWHM) of the jet stream can be changed by adjusting the liquid injection height, thus achieving the zoom function; the effective length, focal length, working distance, and HWHM of the jet stream can also be changed by adjusting the liquid injection type.

[0011] By arranging multiple liquid-filled hollow microsphere lenses into an array, and by adjusting the lens array, a more complex optical system can be achieved, thereby improving imaging resolution and field of view.

[0012] When used in conjunction with other types of lenses and liquid-filled hollow microsphere lenses, the propagation and focusing of light can be further adjusted to achieve more precise zoom function and optimized imaging effect.

[0013] A method for fabricating a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging includes the following steps:

[0014] 1) Preparation of hollow microspheres;

[0015] 2) Openings are made on the surface of the hollow microspheres to obtain hollow microspheres with open holes;

[0016] 3) Then, liquid is injected into the hollow open-pore microspheres to obtain liquid-injected hollow microspheres.

[0017] A method for applying a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging includes the following steps:

[0018] Step 1: Select a terahertz light source, which includes a terahertz laser and a terahertz pulse generator;

[0019] Step 2: Set up a terahertz imaging system, which includes optical components, detectors, and data acquisition equipment;

[0020] Step 3: Prepare the sample to be imaged. The sample to be imaged can be a solid, liquid, or gaseous object of different types.

[0021] Step 4: Prepare hollow microsphere lenses with different injection heights and injection types;

[0022] Step 5: Place the liquid-filled hollow microspheres and generate the "terahertz jet" effect. Place the liquid-filled hollow microspheres in the propagation path of the terahertz wave and in front of the sample to be imaged to generate the "terahertz jet" effect, thereby modulating the subwavelength terahertz light field.

[0023] Step 6: Focus the terahertz beam. Focus the terahertz beam onto the surface of the sample to be imaged, and use optical elements to control the direction, focusing, and collection of the beam;

[0024] Step 7: Modify the optical properties of the liquid-filled hollow microspheres to control the properties of the jet stream and achieve zoom functionality, including the following three methods:

[0025] 7.1) Change the liquid height in the liquid-filled hollow microspheres to adjust the properties of the jet stream and achieve the zoom function;

[0026] 7.2) By changing the type of liquid in the liquid-filled hollow microspheres and altering the refractive index of the internal liquid, the properties of the jet can be adjusted to achieve the zoom function.

[0027] 7.3) By changing the radius and thickness of the hollow microsphere 1 shell, the properties of the jet stream can be adjusted to achieve the zoom function;

[0028] Step 8: Detect the terahertz signal. Use a detector (such as a terahertz detector) to detect the terahertz signal reflected or transmitted from the surface of the sample to be imaged; the detected terahertz signal includes information on amplitude and phase.

[0029] Step 9: Record and process terahertz signals. Record the detected terahertz signals through data acquisition equipment, and perform subsequent signal processing and image reconstruction to obtain reconstructed terahertz image information of the sample to be imaged.

[0030] Step 10: Display and analyze the reconstructed terahertz image information, and use image processing and analysis techniques to extract and interpret the features and structural information of the sample under test.

[0031] The size and material of the liquid-filled hollow microsphere lens are selected according to the specific application requirements.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. Improved ease of operation: Compared to the terahertz jet effect produced by traditional structures, the liquid-filled hollow microspheres used in this invention can generate a longer jet, allowing the sample to be imaged to be placed further away from the structure, reducing the probability of sample contamination and the difficulty of experimental operation. The application of liquid-filled hollow microspheres improves the practical convenience and applicability of using the terahertz jet effect to achieve terahertz high-resolution imaging.

[0034] 2. Improved resolution of terahertz imaging: The present invention uses liquid-filled hollow microspheres to generate a full width at half maximum (FWHM) of less than 0.3λ, further breaking through the diffraction limit of 0.61λ. This significantly improves the imaging resolution and enables clearer capture and analysis of sample details.

[0035] 3. Enhanced ability to control the properties of the laser jet: This invention provides a variety of injection-hollow microspheres for selection. By adjusting the injection height and injection type, the effective length, focal length, working distance, and half-width at half-maximum of the laser jet can be precisely controlled. It has the ability to zoom and adapt to different scenario requirements, thus broadening the application range.

[0036] 4. Optimized Optical Performance: The unique structure of the liquid-filled hollow microspheres facilitates the coupling of terahertz light fields and the focusing of terahertz energy, thereby optimizing optical performance and improving imaging quality. This means that the technical solution of this invention can achieve clearer and more accurate imaging results, improving imaging quality and reliability. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging according to the present invention.

[0038] Figure 2(a) is a schematic diagram of the three-dimensional structure of the hollow microspheres in the embodiment, and Figure 2(b) is a schematic diagram of the three-dimensional structure of the perforated hollow microspheres.

[0039] Figure 3 This is a schematic diagram of the experimental setup for terahertz high-resolution imaging using coupled liquid-filled hollow microspheres, as an example.

[0040] Figure 4 This is a schematic diagram of the jet stream generated by the liquid-injected hollow microspheres in the embodiment.

[0041] Figure 5 The numerical simulation results for the jetting effect generated by hollow microspheres with different injection heights are shown in the example. The injection height is uniformly increased from 0.375λ to 6.375λ, with an increment of 1.5λ.

[0042] Figure 6 The numerical simulation results for the jetting effect generated by hollow microspheres with different injection heights after changing the injection type are shown in the example. The injection height is uniformly increased from 0.375λ to 6.375λ, with an increment of 1.5λ. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] Reference Figure 1 A liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging includes a hollow microsphere 1, an opening 2 on the surface of the hollow microsphere 1, and a liquid 3 filled inside the hollow microsphere 1.

[0045] The hollow microsphere 1 has a spherical shell shape. By precisely selecting the shell radius, shell thickness, and refractive index parameters of the surrounding environment and liquid 3, the effective length, focal length, working distance, and half-width at half-maximum characteristics required for the jet are achieved.

[0046] By adjusting the injection height of liquid 3, the effective length, focal length, working distance, and half-width at half-maximum of the terahertz jet are changed, thus widening the depth of field of the terahertz imaging system, realizing zoom functionality, and providing more flexible and optimized imaging capabilities.

[0047] By adjusting the injection type of liquid 3, the effective length, focal length, working distance, and half-width at half-maximum of the jet can be changed, providing options suitable for more application scenarios.

[0048] To achieve higher resolution and a wider field of view in terahertz high-resolution imaging, an array of multiple liquid-filled hollow microsphere lenses can be considered. By rationally arranging and controlling these lenses, a more complex optical system can be realized, improving imaging resolution and field of view. This array structure can further expand the performance and applications of imaging systems.

[0049] To further optimize the performance of terahertz high-resolution zoom imaging, it can be combined with other types of lenses and liquid-filled hollow microsphere lenses. For example, by combining them with beam expanders or collimators in the imaging system, the propagation and focusing effects of light can be further adjusted, achieving more precise zoom functions and optimized imaging effects. This combination can improve the performance of the imaging system.

[0050] A method for fabricating a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging includes the following steps:

[0051] 1) Hollow microspheres 1 were prepared, and their three-dimensional structure is shown in Figure 2(a);

[0052] 2) Openings 2 are made on the surface of hollow microsphere 1 to obtain hollow microsphere with open holes. Its three-dimensional structure is shown in Figure 2(b).

[0053] 3) Then, liquid 3 is injected into the hollow microspheres to obtain liquid-injected hollow microspheres.

[0054] A method for applying a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging involves placing the liquid-filled hollow microsphere in the propagation path of the terahertz wave to generate a "terahertz jet" effect, thereby modulating the subwavelength terahertz light field, such as... Figure 3 As shown, it includes the following steps:

[0055] Step 1: Select a terahertz light source. Common terahertz light sources include terahertz lasers and terahertz pulse generators.

[0056] Step 2: Build a terahertz imaging system, which includes optical components (such as lenses, gratings, etc.), detectors (such as terahertz detectors, infrared detectors, etc.) and data acquisition equipment.

[0057] Step 3: Prepare the sample to be imaged. The sample can be a solid, liquid or gas, etc. The characteristics of the sample will determine the signal response observed during the imaging process.

[0058] Step 4: Prepare hollow microsphere lenses with different injection heights and injection types for coupling terahertz waves;

[0059] Step 5: Place the liquid-filled hollow microspheres and generate the "terahertz jet" effect. Place the liquid-filled hollow microspheres in the propagation path of the terahertz wave and in front of the sample to be imaged to generate the "terahertz jet" effect, thereby modulating the subwavelength terahertz light field and breaking through the diffraction limit on the spatial resolution of the system.

[0060] Step 6: Focus the terahertz beam. Focus the terahertz beam onto the surface of the sample to be imaged, and use optical elements to control the direction, focusing, and collection of the beam;

[0061] Step 7: Modify the optical properties of the liquid-filled hollow microspheres to control the properties of the jet stream and achieve zoom functionality, including the following three methods:

[0062] 7.1) Change the liquid height in the liquid-filled hollow microspheres to adjust the properties of the jet stream and achieve the zoom function;

[0063] 7.2) By changing the type of liquid in the liquid-filled hollow microspheres and altering the refractive index of the internal liquid, the properties of the jet can be adjusted to achieve the zoom function.

[0064] 7.3) By changing the radius and thickness of the hollow microsphere 1 shell, the properties of the jet stream can be adjusted to achieve the zoom function;

[0065] Step 8: Detect the terahertz signal. Use a detector (such as a terahertz detector) to detect the terahertz signal reflected or transmitted from the surface of the sample to be imaged; the detected terahertz signal includes information such as amplitude and phase.

[0066] Step 9: Record and process terahertz signals. Record the detected terahertz signals through data acquisition equipment, and perform subsequent signal processing and image reconstruction to obtain reconstructed terahertz image information of the sample to be imaged.

[0067] Step 10: Display and analyze the reconstructed terahertz image information, and use image processing and analysis techniques to extract and interpret the features and structural information of the sample under test.

[0068] This invention applies liquid-filled hollow microspheres to a terahertz high-resolution zoom imaging system. By introducing liquid-filled hollow microspheres, the properties of the terahertz jet can be precisely controlled, thereby broadening the application range and performance of the imaging system.

[0069] The jet stream generated by the liquid-injected hollow microspheres in this embodiment will be described and explained in detail below, such as... Figure 4 As shown, the jet stream generated by the liquid-injected hollow microspheres has the following characteristics:

[0070] (1) Focal length: Focal length represents the distance between the edge of the liquid-filled hollow microsphere and the position of the maximum intensity of the jet on the z-axis. The focal position depends on the refractive index of the selected material and allows the focal position to be adjusted as needed to meet the requirements of a specific application.

[0071] (2) Effective length: The effective length refers to the distance from the position of maximum light intensity of the focal spot to 1 / e of the distance from that value to the maximum value. 2 The distance between the two positions describes the spatial range of the jet and helps determine the focusing performance of the focal point.

[0072] (3) Half-width at half maximum (HWHM): HWHM refers to the full width at half maximum of the focal point. It represents the beam waist on the x-axis and is a key parameter for the lateral distribution of the beam. In imaging applications, it can determine the resolution that the system can achieve.

[0073] (4) Working distance: The working distance represents the distance from the edge of the structure to where the intensity value drops to 1 / e of the maximum light intensity. 2 The distance between two locations (e.g.) Figure 3The distance from the first dashed line to the third dashed line is shown in the figure; the working distance can be used to determine the propagation range of the jet and helps to understand the applicability of the jet.

[0074] The above-mentioned characteristics, such as effective length, focal length, working distance, and half-width at half-maximum, can be used to describe the properties of the jet.

[0075] The following details the ability of liquid-filled hollow microspheres to modulate these characteristics by changing the injection height and injection type.

[0076] To illustrate the effect of the liquid height in the liquid-filled hollow microspheres on the properties of the resulting jet, the liquid height was varied while keeping other structural parameters constant (i.e., the outer shell radius was set to 5λ, the shell thickness to 1.25λ, the refractive index of the shell material to 1.49, the refractive index of the surrounding environment to 1 (in air), and the refractive index of the liquid being injected to 1.46). The liquid height was uniformly increased from 0.375λ to 6.375λ, with an increment of 1.5λ. Figure 5 The optical field distribution of the solar jet generated by hollow microspheres with different injection heights is shown. Further analysis reveals that the maximum intensity of the solar jet can reach 6.58377 V as the injection height changes. 2 / m 2 Up to 79.2273V 2 / m 2 The focal length can vary within the range of 0-11.85λ, the effective length can be modulated within the range of 0.5λ to 22.72λ, and the working distance can vary within the range of 0.5λ to 34.573λ, significantly expanding the detection depth of terahertz waves and the imaging depth of the high-resolution imaging system. At the same time, this also means that the sample to be imaged can be placed at a greater distance from the liquid-filled hollow microsphere, reducing the difficulty of experimental operation and the probability of sample contamination. In addition, the half-width at half-maximum (HWHM) of the liquid-filled hollow microsphere can also reach a smaller range, with a minimum of 0.25λ, which greatly exceeds the diffraction limit of 0.61λ. This indicates that the liquid-filled hollow microsphere lens can significantly improve the resolution of the terahertz imaging system.

[0077] The following details the effect of changing the type of liquid injection on the properties of the resulting jet. With other structural parameters kept constant (i.e., the outer shell radius is set to 5λ, the shell thickness is 1.25λ, and the refractive index of the surrounding environment is 1 (in air)), the type of liquid injection is changed to another type, the refractive index becomes 1.62, and the injection height is still uniformly increased from 0.375λ to 6.375λ, with an increment of 1.5λ. Figure 6 This demonstrates the optical field distribution of jet streams generated by hollow microspheres with different injection heights, when the refractive index of the injected liquid is changed to 1.62. (Comparison) Figure 4It is evident that the distribution of the terahertz jet changed significantly after the injection type was altered, indicating that different injection types of hollow microspheres have varying abilities to modulate terahertz waves. Further analysis shows that when the refractive index of the injected liquid becomes 1.62, the maximum intensity of the terahertz jet can reach 10.3272 V with changes in injection height. 2 / m 2 Up to 115.874V 2 / m 2 The focal length can vary within the range of 0-5.05λ, the effective length can be modulated within the range of 4.15λ to 8.75λ, and the working distance can vary within the range of 6.11λ to 13.8λ. This also helps to form a larger terahertz detection depth and imaging depth of field of the high-resolution imaging system, increasing the operational space of the imaging process. In addition, the half-width at half-maximum (WHM) of the liquid-filled hollow microspheres can also reach a smaller range, with a minimum of 0.38λ, which can also be used to break the diffraction limit of 0.61λ. This indicates that this type of liquid-filled hollow microsphere lens can significantly improve the resolution of the terahertz imaging system.

[0078] As can be seen from the above, by changing the injection height and injection type of the liquid-filled hollow microspheres, the effective length, focal length, working distance, and half-width at half-maximum (HWHM) of the terahertz jet can be controlled within a wide range. In practical applications, it is necessary to select appropriate structural parameters and dielectric properties of the shell and liquid based on the specific application scenario and requirements. In conclusion, the simulation results above fully demonstrate the feasibility of the liquid-filled hollow microspheres proposed in this invention for realizing terahertz high-resolution zoom imaging.

Claims

1. A liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging, characterized in that: It includes hollow microspheres with openings on their surface and liquid filling the inside. By adjusting the liquid injection height, the effective length, focal length, working distance, and half-width at half-maximum of the jet can be changed, thus achieving a zoom function.

2. The liquid-filled hollow microsphere lens according to claim 1, characterized in that: The hollow microspheres have an outer shell shape that is sphere, ellipsoid, cube, cylinder or cone.

3. The liquid-filled hollow microsphere lens according to claim 1, characterized in that: By selecting the hollow microsphere shell radius, shell thickness, and refractive index parameters of the surrounding environment and liquid, the focal length, effective length, working distance, and half-width at half-maximum (HWHM) characteristics required for the laser jet can be achieved.

4. The liquid-filled hollow microsphere lens according to claim 1, characterized in that: The focal length, effective length, working distance, and half-width at half-maximum (HWHM) of the jet can be altered by adjusting the type of liquid injected.

5. The liquid-filled hollow microsphere lens according to claim 1, characterized in that: By arranging multiple liquid-filled hollow microsphere lenses into an array, and by adjusting the lens array, a more complex optical system can be achieved, thereby improving imaging resolution and field of view.

6. The liquid-filled hollow microsphere lens according to claim 1, characterized in that: The liquid-filled hollow microsphere lens, when used in conjunction with other types of lenses, further adjusts the propagation and focusing of light, achieving more precise zoom functionality and optimized imaging results.

7. A method for preparing a liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Preparation of hollow microspheres; 2) Openings are made on the surface of hollow microspheres to obtain hollow microspheres with open holes; 3) Then, liquid is injected into the hollow perforated microspheres to obtain liquid-injected hollow microspheres; 4) By adjusting the liquid injection height, the effective length, focal length, working distance, and half-width at half-maximum of the jet are changed, thus achieving the zoom function.

8. The application method of the liquid-filled hollow microsphere lens for terahertz high-resolution zoom imaging according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Select a terahertz light source, which includes a terahertz laser and a terahertz pulse generator; Step 2: Set up a terahertz imaging system, which includes optical components, detectors, and data acquisition equipment; Step 3: Prepare the sample to be imaged. The sample to be imaged can be a solid, liquid, or gaseous object of different types. Step 4: Prepare hollow microsphere lenses with different injection heights and injection types; Step 5: Place the liquid-filled hollow microspheres and generate the "terahertz jet" effect. Place the liquid-filled hollow microspheres in the propagation path of the terahertz wave and in front of the sample to be imaged to generate the "terahertz jet" effect, thereby modulating the subwavelength terahertz light field. Step 6: Focus the terahertz beam. Focus the terahertz beam onto the surface of the sample to be imaged, and use optical elements to control the direction, focusing, and collection of the beam; Step 7: Change the liquid height in the liquid-filled hollow microspheres to adjust the properties of the jet stream and achieve the zoom function; Step 8: Detect the terahertz signal. Use a detector to detect the terahertz signal reflected or transmitted from the surface of the sample to be imaged. Step 9: Record and process terahertz signals. Record the detected terahertz signals through data acquisition equipment, and perform subsequent signal processing and image reconstruction to obtain reconstructed terahertz image information of the sample to be imaged. Step 10: Display and analyze the reconstructed terahertz image information, and use image processing and analysis techniques to extract and interpret the features and structural information of the sample under test.

9. The application method according to claim 8, characterized in that: The size and material of the liquid-filled hollow microsphere lens are selected according to the specific application requirements.

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