A co-simulation method for scattering-type near-field scanning imaging transceiver design.

Abstract

This invention discloses a two-dimensional and three-dimensional co-simulation method for the design of scattering near-field scanning imaging transceivers. The method includes: establishing a three-dimensional model based on the mirror dipole theory model, and establishing a two-dimensional model based on the cross-section; simulating the high-frequency periodic motion of the needle tip by changing the distance between the needle tip and the sample in both the two-dimensional and three-dimensional models, obtaining the near-field electric field intensity and scattering power intensity with and without a sample; when the needle tip curvature radius is greater than a set threshold, changing the side length of the three-dimensional model in the three-dimensional model to obtain the scattering power intensity under different spot sizes; changing the needle tip curvature radius in the two-dimensional model to obtain the near-field electric field intensity under different needle tip curvature radii; step s5) when the needle tip curvature radius is greater than the set threshold, establishing the relationship between the obtained scattering power intensity and near-field electric field intensity to obtain the scattering power intensity when the needle tip curvature radius is less than the threshold.

Description

Technical Field

[0001] This invention relates to the field of transceiver design for scattering near-field scanning imaging systems, and more specifically to a two-dimensional and three-dimensional co-simulation method for scattering near-field scanning imaging transceiver design. Background Technology

[0002] Terahertz (THz) waves refer to electromagnetic waves with frequencies ranging from 0.1 to 10 THz (wavelengths from 3000 to 30 μm). They overlap with millimeter waves in the long-wavelength range and with infrared light in the short-wavelength range. This region represents a transition from macroscopic classical theory to microscopic quantum theory, and also from electronics to photonics, and is known as the "terahertz gap" in the electromagnetic spectrum. Therefore, terahertz waves possess some characteristics of both millimeter and infrared waves, exhibiting strong penetrability, good coherence, low ionization energy, and high specificity. Currently, most THz spectroscopy research is based on far-field systems. However, the sample detection structure of far-field systems is highly susceptible to Rayleigh diffraction limits, resulting in optimal resolution no better than half the wavelength. The theoretical optimal resolution is only at the hundreds of micrometers level, and further expansion to the nanoscale requires further research.

[0003] THz super-resolution imaging is essential for various applications, including biological cell observation, semiconductor carrier concentration detection, advanced materials observation, and nanodevice imaging. Based on these needs, THz-SNOM (Torrent Scattering Scanning Near-Field Optical Microscopy) has achieved partial commercialization. It overcomes the optical diffraction limit, and its theoretical resolution is only related to the radius of curvature of the probe in the system, independent of the incident wavelength, making it the most promising near-field super-resolution microscope. THz-SNOM is based on the central concept of illuminating a sharp scanning probe tip and recording the scattered light as a function of the tip's position. It primarily achieves high-resolution imaging based on nanoprobe scanning and the principle of near-field THz nanoresonant coupling antennas. This technology utilizes the enhancement of the electric field near the tip in a nanometer-scale localized region, breaking through the traditional optical diffraction limit and improving resolution to the nanometer scale. The electric field strength and scattered signal power of the scattered field reflect the signal strength, originating from the dipole system formed by the tip and the sample. The dipole model can theoretically derive the near-field electric field values ​​for different materials and different tip-sample spacings. By modulating the probe vertically, the tip moves at a high frequency Ω in the vertical direction, and the scattered signal can be obtained to obtain the tip sample information. According to Poynting's theorem, energy exists wherever an electric field exists; energy can be stored in the electric field. The square of the electric field strength is proportional to the power intensity. However, at present, there are still some deficiencies in the model simulation method. Most simulation methods only use the electric field strength detected in the two-dimensional model to characterize the size of the near-field scattering signal, and cannot provide a reference for the design of the receiver of the near-field scattering scanning optical system in actual design. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and propose a joint simulation method for the transceiver design of a scattering near-field scanning imaging system.

[0005] In order to achieve the above purpose, the present invention proposes a two-dimensional and three-dimensional joint simulation method for the transceiver design of a scattering near-field scanning imaging, and the method includes: <000,0029>

[0006] Step s1) Based on the mirror dipole theory model, establish a three-dimensional solid model, and establish a two-dimensional model according to the cross-section of the three-dimensional model;

[0007] Step s2) In the two-dimensional model and the three-dimensional model respectively, simulate the high-frequency periodic movement of the tip by changing the distance between the tip and the sample, and obtain the near-field electric field strength and the scattering power intensity in the presence and absence of the sample;

[0008] Step s3) When the tip curvature radius is greater than the set threshold, in the three-dimensional model, change the side length of the three-dimensional model simulating the incident light spot, and obtain the scattering power intensity under different spot sizes;

[0009] Step s4) In the two-dimensional model, change the tip curvature radius, and obtain the near-field electric field strength under different tip curvature radii;

[0010] Step s5) When the tip curvature radius is greater than the set threshold, according to the scattering power intensity and the near-field electric field strength obtained in step s3) and step s4), establish the relationship between the two, and obtain the scattering power intensity when the tip curvature radius is less than the threshold.

[0011] As an improvement of the above method, the mirror dipole theory model in step s1) specifically includes:

[0012]

[0013] β two (ε

[0010] ,

[0009] , , s ,

[0008] , s , ,

[0007] , ,

[0012] ,

[0015] ,

[0011] , , t , ,

[0014] , eff-tip , ,

[0013] , s , , , , -1) / (ε s +1)

[0014]

[0015] Among them, α eff-tip is the effective polarizability of the coupling system, β is the reflection coefficient related to the sample, ε s represents the sample dielectric constant, α is the tip polarizability, ε tLet represent the dielectric constant of the needle tip, a be the radius of curvature of the needle tip, and r be the distance between the needle tip and the sample.

[0016] As an improvement to the above method, step s2) specifically includes:

[0017] By varying the distance r between the needle tip and the sample, N points are selected in [-A, A] to simulate the high-frequency periodic motion of the needle tip, thus simulating a real scattering-type near-field optical scanning system. The high-frequency periodic motion satisfies the following equation:

[0018] r=Acos(2πΩt+φ)+z+a

[0019] Where Ω is the needle tip vibration frequency, A is the needle tip vibration amplitude, z is the initial distance between the needle tip and the sample, and a is the needle tip radius of curvature;

[0020] The near-field electric field intensity at the corresponding point in the two-dimensional model and the scattering power intensity of the corresponding scattering surface in the three-dimensional model were recorded when the distance r between the needle tip and the sample was different, with and without a sample.

[0021] As an improvement to the above method, step s3) specifically includes:

[0022] When the radius of curvature a of the needle tip is greater than a set threshold, the area of ​​the incident surface is changed by changing the side length of the three-dimensional model, thereby obtaining different spot sizes, and the scattering power intensity of the corresponding different scattering surfaces is recorded; where the incident surface and the scattering surface are the same surface.

[0023] As an improvement to the above method, step s4) specifically includes:

[0024] When the tip curvature radius 'a' is less than a set threshold, the near-field electric field intensity under different tip curvature radii can be obtained in the two-dimensional model by changing the tip curvature radius 'a'.

[0025] As an improvement to the above method, step s5) specifically includes:

[0026] When the radius of curvature of the needle tip is greater than a set threshold, based on the scattered power intensity and near-field electric field intensity obtained in steps s3) and s4), Poynting's theorem states that the square of the near-field electric field intensity is proportional to the power intensity, satisfying the following equation:

[0027]

[0028] Among them, P 有样品 and P 无样品 E represents the power intensity with and without the sample, respectively. 有样品 and E 无样品 represents the near-field electric field intensity with and without the sample, respectively, and k represents the coefficient;

[0029] When the radius of curvature of the needle tip is less than a set threshold, the near-field electric field intensity obtained by the two-dimensional model is used to estimate the scattering power intensity of the three-dimensional model based on the above proportional relationship.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] This invention simulates the vibration effect of the needle tip during imaging by simulating different needle tip sample distances, establishing two-dimensional and three-dimensional models. Unlike existing technologies that only use the electric field intensity detected by the two-dimensional model built from the three-dimensional model cross-section as the basis for evaluating near-field signal strength, this invention uses the combined electric field intensity detected by the two-dimensional model and the signal power intensity detected by the three-dimensional model as the basis for evaluating near-field signal strength. It also demonstrates that the square of the electric field intensity is proportional to and correlated with the signal power intensity. Different simulation methods are selected under different simulation conditions to analyze the near-field signal. When calculating the return power of the receiving surface on a large scale, the two-dimensional model is only a cross-sectional simulation, with the receiving surface being a straight line, which cannot quantitatively simulate the actual system. The received power is simulated using a three-dimensional model. The model size is based on the simulated incident light spot size, and the return power value within this range is simulated, which can provide guidance for the actual system design. When simulating a small tip curvature radius, a very small mesh is required, which leads to a sharp increase in the number of meshes. The three-dimensional model cannot handle such a large amount of computation. Therefore, a two-dimensional model is used to calculate the electric field intensity of the near-field scattered signal and correlate it with the signal power intensity. This reflects the power intensity of the tip scattered signal under a small tip curvature radius, thus providing guidance for system design. The joint simulation of the two models plays a complementary role, providing a reference for the design of terahertz near-field scattering scanning optical systems and promoting the development of terahertz near-field optical super-resolution imaging. Attached Figure Description

[0032] Figure 1 This is a flowchart of the two-dimensional and three-dimensional co-simulation method for the design of scattering near-field scanning imaging transceiver according to the present invention;

[0033] Figure 2 This is a design diagram for a scattering-type near-field scanning imaging transceiver;

[0034] Figure 3 This is a diagram of a dipole model;

[0035] Figure 4 It is a 3D model diagram;

[0036] Figure 5 It is a two-dimensional model diagram;

[0037] Figure 6 It is a three-dimensional probe scattering power diagram;

[0038] Figure 7 It is a two-dimensional near-field electric field diagram;

[0039] Figure 8 (a) is a light spot distribution diagram. Figure 8 (b) is a cross-sectional beam power distribution diagram;

[0040] Figure 9 This is a normalized plot of the near-field electric field intensity under the condition of a large needle tip radius of curvature.

[0041] Figure 10 This is a normalized graph of the near-field electric field intensity under the condition of a small needle tip radius of curvature. Detailed Implementation

[0042] This invention establishes a three-dimensional model based on the dipole model, and simplifies it into a two-dimensional model based on the cross-section of the three-dimensional model. By changing the distance between the tip and the sample, it simulates the high-frequency periodic motion of the tip, thus simulating the working principle of a scattering-type near-field optical imaging system. The scattered signal power intensity is calculated using the three-dimensional model, and the scattered signal electric field intensity is calculated using the two-dimensional model. The relationship between the two is established. The three-dimensional model can simulate the transceiver surface in the scattering-type near-field optical imaging transceiver system and calculate the scattered power of that surface. However, the three-dimensional model has a large computational load and cannot simulate the scattered signal power intensity when the actual tip curvature radius is relatively thin. Therefore, the two-dimensional model is used to simulate the scattered signal electric field intensity when the tip is relatively thin. By using the relationship between power and electric field, the scattered signal power intensity at this time is estimated.

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

[0044] Example

[0045] like Figure 1 As shown, embodiments of the present invention propose a two-dimensional and three-dimensional co-simulation method for the design of scattering near-field scanning imaging transceivers, specifically including the following steps:

[0046] Step s1) Based on the dipole model, establish a three-dimensional solid model, and establish a two-dimensional model based on the cross-section of the three-dimensional model;

[0047] Step s2) In the two-dimensional and three-dimensional models, the high-frequency periodic motion of the needle tip is simulated by changing the distance between the needle tip and the sample. The near-field electric field intensity and the scattered power intensity are obtained with and without the sample.

[0048] Step s3) In the three-dimensional model, when the radius of curvature of the needle tip is large, change the side length of the simulated incident light spot to obtain the scattering power intensity under the light spot size;

[0049] Step s4) In the two-dimensional model, change the radius of curvature of the needle tip to obtain the near-field electric field intensity under different radii;

[0050] Step s5) Establish the relationship between the near-field electric field intensity and the scattering power intensity, and estimate the scattering power intensity in the case of a small tip curvature radius.

[0051] The block diagram of the transceiver system of the scattering-type near-field optical scanning system is as Figure 2 shown. The transmitted signal is transmitted through a horn antenna, and the scattered signal is received through a horn signal. The generation of the scattered signal is through the dipole effect formed by the tip-sample. The dipole mathematical model is as Figure 3 shown.

[0052]

[0053] β = (ε s - 1) / (ε s + 1)

[0054]

[0055] where α eff-tip is the effective polarizability of the coupling system, β is the reflection coefficient related to the sample, ε s represents the sample dielectric constant, α is the tip polarizability, ε t represents the tip dielectric constant, a is the tip curvature radius, and r is the distance between the tip and the sample.

[0056] Establish a three-dimensional model as Figure 4 shown, and simplify it to a two-dimensional model as Figure 5 shown. By changing the distance between the tip and the sample, simulate the high-frequency periodic motion of the tip to simulate the actual scattering-type near-field optical scanning system.

[0057] r = A cos(2πΩt + φ) + z + a

[0058] where r is the distance between the tip and the sample, Ω is the tip vibration frequency, and A is the tip vibration amplitude.

[0059] The three-dimensional model can obtain the tip scattering power, as Figure 6 shown, and the two-dimensional model can obtain the near-field electric field intensity, as Figure 7 shown.

[0060] Spot power distribution Figure 8 shown, where Figure 8 (a) is the spot distribution diagram, Figure 8 (b) is the cross-sectional spot power distribution diagram;

[0061] As can be seen from the figure, the power intensity under the tip accounts for a relatively small ratio of the entire spot power intensity. After being enhanced through the dipole effect, it is scattered to the receiving surface to obtain the scattering power. In the case of a large tip curvature, calculate the scattering power and the electric field intensity with and without a sample. The normalizing curve diagram of the electric field intensity is as Figure 9 As shown. Simultaneously, the relationship between power and electric field is established: P∝E 2 Furthermore:

[0062]

[0063] Where k represents a coefficient. This connection allows us to compensate for the limitation of three-dimensional models in calculating scattered power when the tip curvature radius is small, due to the high computational cost. Conversely, a two-dimensional model can be used to calculate the electric field intensity when the tip curvature radius is small, such as... Figure 10 As shown, the scattering power can be estimated by the relationship between the two.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A two-dimensional and three-dimensional co-simulation method for the design of scattering-type near-field scanning imaging transceivers, the method comprising: Step s1) Based on the mirror dipole theory model, establish a three-dimensional model, and establish a two-dimensional model based on the cross-section of the three-dimensional model; Step s2) In the two-dimensional model and the three-dimensional model, the high-frequency periodic motion of the needle tip is simulated by changing the distance between the needle tip and the sample. The near-field electric field intensity and the scattered power intensity are obtained with and without the sample. Step s3) When the radius of curvature of the needle tip is greater than the set threshold, in the three-dimensional model, change the side length of the three-dimensional model of the simulated incident light spot to obtain the scattering power intensity under different light spot sizes. Step s4) In the two-dimensional model, change the tip curvature radius to obtain the near-field electric field intensity under different tip curvature radii; Step s5) When the tip curvature radius is greater than the set threshold, establish the relationship between the scattered power intensity and the near-field electric field intensity obtained in steps s3) and s4) to obtain the scattered power intensity when the tip curvature radius is less than the threshold. Step s2) specifically includes: By varying the distance r between the needle tip and the sample, N points are selected in [-A, A] to simulate the high-frequency periodic motion of the needle tip, thus simulating a real scattering-type near-field optical scanning system. The high-frequency periodic motion satisfies the following equation: r=Acos(2πΩt+φ)+z+a Where Ω is the needle tip vibration frequency, A is the needle tip vibration amplitude, z is the initial distance between the needle tip and the sample, and a is the needle tip radius of curvature; The near-field electric field intensity at the corresponding point in the two-dimensional model and the scattering power intensity of the corresponding scattering surface in the three-dimensional model were recorded when the distance r between the needle tip and the sample was different, with and without the sample. Step s5) specifically includes: When the radius of curvature of the needle tip is greater than a set threshold, based on the scattered power intensity and near-field electric field intensity obtained in steps s3) and s4), Poynting's theorem states that the square of the near-field electric field intensity is proportional to the power intensity, satisfying the following equation: Among them, P 有样品 and P 无样品 E represents the power intensity with and without the sample, respectively. 有样品 and E 无样品 represents the near-field electric field intensity with and without the sample, respectively, and k represents the coefficient; When the radius of curvature of the needle tip is less than a set threshold, the near-field electric field intensity obtained by the two-dimensional model is used to estimate the scattering power intensity of the three-dimensional model based on the above proportional relationship.

2. The two-dimensional and three-dimensional co-simulation method for scattering-type near-field scanning imaging transceiver design according to claim 1, characterized in that, The mirror dipole theory model in step s1) specifically includes: β=(ε s -1) / (e s +1) Where, α eff-tip ε is the effective polarizability of the coupled system, β is the sample-related reflection coefficient, and ε s The dielectric constant of the sample is represented by α, the tip polarizability is represented by ε. t Let represent the dielectric constant of the needle tip, a be the radius of curvature of the needle tip, and r be the distance between the needle tip and the sample.

3. The two-dimensional and three-dimensional co-simulation method for scattering-type near-field scanning imaging transceiver design according to claim 1, characterized in that, Step s3) specifically includes: When the radius of curvature a of the needle tip is greater than a set threshold, the area of ​​the incident surface is changed by changing the side length of the three-dimensional model, thereby obtaining different spot sizes, and the scattering power intensity of the corresponding different scattering surfaces is recorded; where the incident surface and the scattering surface are the same surface.

4. The two-dimensional and three-dimensional co-simulation method for scattering-type near-field scanning imaging transceiver design according to claim 1, characterized in that, Step s4) specifically includes: In the two-dimensional model, the near-field electric field intensity under different needle tip curvature radii is obtained by changing the needle tip curvature radius 'a'.

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