Waveband splicing terahertz near-field imaging system and method based on frequency selective surface

Abstract

The application provides a wave band splicing terahertz near field imaging system and method based on a frequency selective surface, which comprises a terahertz spread spectrum module, a first combination module, a parabolic mirror and a near field probe.The terahertz spread spectrum module is used for generating a terahertz signal and receiving a reflection signal of a near field terahertz signal of a sample to be measured.The first combination module is used for combining the terahertz signal generated by the terahertz spread spectrum module and converging to the parabolic mirror.The parabolic mirror is used for collecting the terahertz signal incident on the frequency selective surface and converging to the tip of the near field probe.The near field probe is used for modulating the terahertz signal by exciting the terahertz signal in the vertical direction to obtain the near field terahertz signal and reflecting the near field terahertz signal to the terahertz spread spectrum module.The reflection signal of the near field terahertz signal is the same as the light path of the incident terahertz signal.The application can realize terahertz near field imaging test in a wide band range by using the multi-wave band splicing terahertz near field imaging test technology based on the frequency selective surface.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of terahertz near-field imaging, and particularly relates to a waveband splicing terahertz near-field imaging system and method based on a frequency selective surface. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Terahertz waves have the characteristics of strong penetration, good coherence, and low ionization energy, and have great application and development potential in many fields. Limited by the diffraction limit, the best spatial resolution of a terahertz far-field imaging system is about half of the incident wavelength, usually in the order of hundreds of microns, which cannot meet the needs of high-precision observation. This greatly limits the application of terahertz technology in micro-substance detection, micro-nano semiconductor device detection, etc.

[0004] At present, researchers have developed an electronic terahertz near-field imaging technology based on probe scattering, which realizes high-resolution imaging through nanometer probe scanning and near-field probe resonant coupling antenna principle. This technology uses the nanometer local enhancement of the electric field near the needle tip to realize the imaging of the fine structure of the substance by detecting the near-field evanescent wave containing the detailed information of the sample. Through two-dimensional grid scanning of the local terahertz electromagnetic wave in the near-field region of the sample, the terahertz scattering signal at each test point of the sample is collected, and the surface image of the sample is reconstructed after data processing. The image resolution obtained in this way is not limited by the wavelength, but mainly depends on the size of the scattering needle tip that generates the local terahertz wave, breaking through the traditional optical diffraction limit and improving the resolution to the nanometer level, thus making it possible to conduct super-resolution microscopic detection research on the measured substance.

[0005] However, most of the existing terahertz near-field imaging technologies are single-waveband near-field imaging technologies, which can only test within a limited bandwidth, limiting their application in wideband spectrum analysis of the measured substance. SUMMARY

[0006] In order to overcome the shortcomings of the prior art and realize terahertz near-field imaging within a wide frequency band, the present application provides a waveband splicing terahertz near-field imaging system and method based on a frequency selective surface. Different waveband terahertz waves are transmitted and reflected through the frequency selective surface, so as to realize wideband terahertz near-field imaging through multi-waveband splicing.

[0007] To achieve the above object, one or more embodiments of the present application provide the following technical solutions:

[0008] The first aspect of the present application provides a waveband splicing terahertz near-field imaging system based on a frequency selective surface, comprising:

[0009] A terahertz spread spectrum module is used to generate a terahertz signal and receive a reflection signal of a near-field terahertz signal of a sample to be measured.

[0010] A first combining module is used to combine the terahertz signals generated by the first terahertz spread spectrum module and the second terahertz spread spectrum module and converge to a parabolic mirror.

[0011] The parabolic mirror is used to collect the terahertz signals incident on the frequency selective surface and converge to the tip of the near-field probe.

[0012] The near-field probe is used to modulate the terahertz signal by making a vertical vibration excitation, obtain a near-field terahertz signal, and reflect the near-field terahertz signal to the terahertz spread spectrum module; wherein the reflection signal of the near-field terahertz signal has the same optical path as the incident terahertz signal.

[0013] The sample to be measured is arranged at the tip of the near-field probe.

[0014] A phase-locked amplification unit is used to process the reflection signal of the near-field terahertz signal received by the terahertz spread spectrum module to obtain local information of the sample to be measured at the position.

[0015] The second aspect of the present application provides a waveband splicing terahertz near-field imaging method based on a frequency selective surface, comprising: using a combining module to incident a plurality of terahertz waves of different wavebands to a parabolic mirror.

[0016] The parabolic mirror converges the incident terahertz waves to the tip of the near-field probe.

[0017] The near-field probe modulates the incident terahertz waves by making a vertical vibration excitation to obtain a near-field terahertz signal.

[0018] After the near-field terahertz signal is scattered by the near-field probe, it is collimated by an off-axis parabolic mirror, and then the reflection signal of the near-field terahertz signal is transmitted to the terahertz spread spectrum module by using the combining module.

[0019] The reflection signal of the near-field terahertz signal received by the terahertz spread spectrum module is processed by using a phase-locked amplification unit to obtain local information of the sample to be measured at the position.

[0020] The above one or more technical solutions have the following beneficial effects:

[0021] The multi-waveband splicing terahertz near-field imaging test system based on the frequency selective surface can realize terahertz near-field imaging test in a wideband range by using a low-pass frequency selective surface or a band-pass frequency selective surface to combine terahertz beams.

[0022] The advantages of the additional aspects of the present application will become apparent in the following description, become apparent from the following description, or be learned through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application, and are incorporated by reference herein. The embodiments depicted herein are provided by way of example only, and together with the specification serve to explain the application.

[0024] Figure 1 Structure diagram of waveband splicing terahertz near-field imaging system based on frequency selective surface of first embodiment;

[0025] Figure 2 (a) and Figure 2 (b) are respectively the front view and the back view of the band-pass frequency selective surface of the first embodiment;

[0026] Figure 3 The schematic diagram of the low-pass frequency selective surface of the first embodiment. DETAILED DESCRIPTION

[0027] Embodiment one

[0028] As Figure 1 shown, the embodiment discloses a waveband splicing terahertz near-field imaging system based on frequency selective surface, comprising: a terahertz spread spectrum module, a combining module, a parabolic mirror, a near-field probe, a sample to be measured, and a phase-locked amplification unit.

[0029] The terahertz spread spectrum module comprises: a first terahertz spread spectrum module, a second terahertz spread spectrum module, a third terahertz spread spectrum module, a fourth terahertz spread spectrum module, a fifth terahertz spread spectrum module, and a sixth terahertz spread spectrum module, which are respectively used to generate terahertz signals and receive the reflection signals of the near-field terahertz signals of the sample to be measured.

[0030] The combining module comprises: a first combining module, a second combining module, a third combining module, and a fourth combining module; the first combining module and the second combining module are symmetrically arranged, the second combining module and the third combining module are oppositely inclined, and the third combining module and the fourth combining module are symmetrically arranged.

[0031] The first combining module is used to combine the terahertz signals generated by the first terahertz spread spectrum module and the second terahertz spread spectrum module, and then converge to the parabolic mirror.

[0032] Specifically, the first combining module comprises a first frequency selective surface FSS1 and a mirror 1 arranged in parallel; the mirror 1 is configured to reflect the terahertz signal generated by the second terahertz spread spectrum module to the first frequency selective surface FSS1; the first frequency selective surface FSS1 is configured to combine the terahertz signal reflected by the mirror 1 and the terahertz signal generated by the first terahertz spread spectrum module, and then converge to the parabolic mirror;

[0033] The second combining module is configured to combine the terahertz signals generated by the third terahertz spread spectrum module and the fourth terahertz spread spectrum module, and then converge to the parabolic mirror;

[0034] Specifically, the second combining module comprises a second frequency selective surface FSS2 and a mirror 2 arranged in parallel; the mirror 2 is configured to reflect the terahertz signal generated by the third terahertz spread spectrum module to the second frequency selective surface FSS2; the third frequency selective surface FSS2 is configured to combine the terahertz signal generated by the fourth terahertz spread spectrum module and the terahertz signal reflected by the mirror 2, and then converge to the parabolic mirror;

[0035] The third combining module is configured to combine the terahertz signals generated by the first combining module and the fifth terahertz spread spectrum module, and then converge to the parabolic mirror;

[0036] Specifically, the third combining module comprises a third frequency selective surface FSS3 and a mirror 3 arranged in parallel; the mirror 3 is configured to reflect the terahertz signal generated by the fifth terahertz spread spectrum module to the third frequency selective surface FSS3; the third frequency selective surface FSS3 is configured to combine the terahertz signal incident from the first combining module and the terahertz signal reflected by the third mirror 3, and then converge to the parabolic mirror;

[0037] The fourth combining module is configured to combine the terahertz signals generated by the second combining module and the sixth terahertz spread spectrum module, and then converge to the parabolic mirror;

[0038] Specifically, the fourth combining module comprises a third frequency selective surface FSS4 and a mirror 4 arranged in parallel;

[0039] The mirror 4 is configured to reflect the terahertz signal generated by the sixth terahertz spread spectrum module to the fourth frequency selective surface FSS4; the fourth frequency selective surface FSS4 is configured to combine the terahertz signal incident from the second combining module and the terahertz signal reflected by the fourth mirror 4, and then converge to the parabolic mirror;

[0040] The parabolic mirror is configured to collect the terahertz signals incident from the combining module, and then converge to the near-field probe needle tip;

[0041] The near-field probe is used for modulating the terahertz signal by exciting vibration in the vertical direction, obtaining the near-field terahertz signal, and reflecting the near-field terahertz signal to the terahertz spread spectrum module; wherein the reflection signal of the near-field terahertz signal has the same optical path as the incident terahertz signal.

[0042] The to-be-measured sample is arranged at the tip of the near-field probe, and the distance between the near-field probe and the to-be-measured sample is arranged to be always kept within the range of several tip curvature radii.

[0043] The lock-in amplification unit is used for processing the reflection signal of the near-field terahertz signal received by the terahertz spread spectrum module, and obtaining the local information of the to-be-measured sample at the position.

[0044] Further, the first terahertz spread spectrum module comprises a terahertz spread spectrum device 1 and a lens 1, the lens 1 is used for collimating the terahertz signal generated by the terahertz spread spectrum device 1, and converging the reflection signal.

[0045] The second terahertz spread spectrum module comprises a terahertz spread spectrum device 2 and a lens 2, the lens 2 is used for collimating the terahertz signal generated by the terahertz spread spectrum device 2, and converging the reflection signal.

[0046] The third terahertz spread spectrum module comprises a terahertz spread spectrum device 3 and a lens 3, the lens 3 is used for collimating the terahertz signal generated by the terahertz spread spectrum device 3, and converging the reflection signal.

[0047] The fourth terahertz spread spectrum module comprises a terahertz spread spectrum device 4 and a lens 4, the lens 4 is used for collimating the terahertz signal generated by the terahertz spread spectrum device 4, and converging the reflection signal.

[0048] The fifth terahertz spread spectrum module comprises a terahertz spread spectrum device 5 and a lens 5, the lens 5 is used for collimating the terahertz signal generated by the terahertz spread spectrum device 5, and converging the reflection signal.

[0049] The sixth terahertz spread spectrum module comprises a terahertz spread spectrum device 6 and a lens 6, the lens 6 is used for collimating the terahertz signal generated by the terahertz spread spectrum device 6, and converging the reflection signal.

[0050] The working principle of the system of the present application is described in combination with a specific terahertz wave range:

[0051] The terahertz spread spectrum device 1 (110-170GHz) emits terahertz waves, which are collimated by the lens 1, pass through the band-pass frequency selective surface FSS1 with a passband of 110-170GHz or the low-pass frequency selective surface FSS1 with a cutoff frequency of 170GHz and the band-pass frequency selective surface FSS3 with a passband of 110-325GHz or the low-pass frequency selective surface FSS3 with a cutoff frequency of 325GHz, are focused by the off-axis parabolic mirror, converge at the tip of the near-field probe, are scattered by the near-field probe, are collimated by the off-axis parabolic mirror, then pass through the frequency selective surface FSS3 and the frequency selective surface FSS1, are converged by the lens 1, and are finally received by the terahertz spread spectrum device 1.

[0052] The terahertz spread spectrum device 2 (220-325GHz) emits terahertz waves, which are collimated by the lens 2, are reflected by the mirror, pass through the band-pass frequency selective surface FSS1 with a passband of 110-170GHz or the low-pass frequency selective surface FSS1 with a cutoff frequency of 170GHz, pass through the band-pass frequency selective surface FSS3 with a passband of 110-325GHz or the low-pass frequency selective surface FSS3 with a cutoff frequency of 325GHz, are focused by the off-axis parabolic mirror, converge at the tip of the near-field probe, are scattered by the near-field probe, are collimated by the off-axis parabolic mirror, then pass through the frequency selective surface FSS3, are reflected at the frequency selective surface FSS1, are converged by the lens 2, and are finally received by the terahertz spread spectrum device 2.

[0053] The terahertz spread spectrum device 5 (500-750GHz) emits terahertz waves, which are collimated by the lens, are reflected by the mirror, pass through the band-pass / low-pass frequency selective surface FSS3 with a passband of 110-325GHz, are focused by the off-axis parabolic mirror, converge at the tip of the near-field probe, are scattered by the near-field probe, are collimated by the off-axis parabolic mirror, then are reflected by the frequency selective surface FSS3, are converged by the lens 5, and are finally received by the terahertz spread spectrum device 5.

[0054] The terahertz spread spectrum device 3 (170-220GHz) emits terahertz waves, which are collimated by the lens 3, pass through the band-pass frequency selective surface FSS2 with a passband of 170-220GHz or the low-pass frequency selective surface FSS2 with a cutoff frequency of 220GHz and the band-pass frequency selective surface FSS4 with a passband of 170-500GHz or the low-pass frequency selective surface FSS4 with a cutoff frequency of 500GHz, are focused by the off-axis parabolic mirror, converge at the tip of the near-field probe, are scattered by the near-field probe, are collimated by the off-axis parabolic mirror, then pass through the frequency selective surface FSS4 and the frequency selective surface FSS2, are converged by the lens 3, and are finally received by the terahertz spread spectrum device 3.

[0055] The terahertz spread spectrum device 4 (325-500 GHz) emits terahertz waves, which are collimated by the lens 4 and irradiated onto the mirror to deflect the optical path direction, reflected by the band-pass frequency selection surface FSS2 with a passband of 170-220 GHz or the low-pass frequency selection surface FSS4 with a cutoff frequency of 220 GHz, focused by the off-axis parabolic mirror, and converged at the tip of the near-field probe. After scattering by the near-field probe, the terahertz waves are collimated by the off-axis parabolic mirror, transmitted through the frequency selection surface FSS4, reflected at the frequency selection surface FSS2, converged by the lens 4, and finally received by the terahertz spread spectrum device 4.

[0056] The terahertz spread spectrum device 6 (750-1100 GHz) emits terahertz waves, which are collimated by the lens 6 and irradiated onto the mirror to deflect the optical path direction, reflected by the band-pass frequency selection surface FSS4 with a passband of 170-500 GHz or the low-pass frequency selection surface FSS4 with a cutoff frequency of 500 GHz, focused by the off-axis parabolic mirror, and converged at the tip of the near-field probe. After scattering by the near-field probe, the terahertz waves are collimated by the off-axis parabolic mirror, reflected by the band-pass frequency selection surface FSS4 with a passband of 170-500 GHz or the low-pass frequency selection surface FSS4 with a cutoff frequency of 500 GHz, converged by the lens 6, and finally received by the terahertz spread spectrum device 6.

[0057] The distance between the near-field probe and the sample is set according to the curvature radius of the tip, and the distance is set to be between a few nanometers and a few microns; the terahertz near-field signal is modulated by vertical vibration excitation. After receiving the terahertz near-field scattering signal, the above-mentioned six waveband terahertz spread spectrum devices respectively downmix the signal to the intermediate frequency band, transmit the signal to the phase-locked amplification unit after intermediate frequency conditioning for weak signal extraction, and finally obtain the local information of the sample at the position after data acquisition and information processing. The near-field probe scans the sample point by point, and finally obtains the near-field microscopic image of the sample to be measured.

[0058] As shown in Figure 2 (a) and Figure 2 (b), for the band-pass frequency selection surface, a common grid and patch overlapping structure can be used. As shown in Figure 3 , for the low-pass frequency selection surface, a common sheet-like stacked structure is used.

[0059] Example Two

[0060] The embodiment discloses a waveband splicing near-field imaging method based on a frequency selection surface, comprising: using a combining module to make multiple terahertz waves of different wavebands incident to a parabolic mirror;

[0061] The parabolic mirror converges the incident terahertz waves to the tip of the near-field probe;

[0062] The near-field probe modulates the incident terahertz wave by doing vertical vibration excitation to obtain a near-field terahertz signal;

[0063] The near-field terahertz signal is scattered by the near-field probe and collimated by the off-axis parabolic mirror, and the reflected signal of the near-field terahertz signal is transmitted to the terahertz spread spectrum module by the combining module;

[0064] The reflected signal of the near-field terahertz signal received by the terahertz spread spectrum module is processed by the phase-locked amplification unit to obtain the local information of the sample to be measured at the position;

[0065] The combining module is used to make multiple terahertz waves of different wave bands incident on the parabolic mirror, comprising:

[0066] The terahertz signals generated by the first terahertz spread spectrum module and the second terahertz spread spectrum module are combined by the first combining module, and then converged to the parabolic mirror;

[0067] The terahertz signals generated by the third terahertz spread spectrum module and the fourth terahertz spread spectrum module are combined by the second combining module, and then converged to the parabolic mirror;

[0068] The terahertz signal generated by the fifth terahertz spread spectrum module and the terahertz signal incident on the first combining module are combined by the third combining module, and then converged to the parabolic mirror;

[0069] The terahertz signal generated by the sixth terahertz spread spectrum module and the terahertz signal incident on the second combining module are combined by the fourth combining module, and then converged to the parabolic mirror.

[0070] The above describes the specific embodiments of the present application in combination with the drawings, but is not a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A band-stitched terahertz near-field imaging system based on a frequency-selective surface, characterized in that, include: A terahertz spread spectrum module, which is used to generate terahertz signals and receive the reflected signals of the near-field terahertz signals of the sample under test; The first combining module is used to combine the terahertz signals generated by the first terahertz spread spectrum module and the second terahertz spread spectrum module and then converge them to the parabolic mirror. A parabolic mirror is used to collect terahertz signals incident through the frequency-selective surface and converge them to the tip of a near-field probe. A near-field probe is used to modulate a terahertz signal by vertical vibration excitation to obtain a near-field terahertz signal, and then reflects the near-field terahertz signal to a terahertz spread spectrum module; wherein the reflected signal of the near-field terahertz signal has the same optical path as the incident terahertz signal. The sample to be tested is placed at the tip of the near-field probe. A lock-in amplifier unit is used to process the reflected signal of the near-field terahertz signal received by the terahertz spread spectrum module to obtain local information of the sample under test at that location. The second combining module includes a second frequency selection surface and a second reflector arranged in parallel. The second reflector is used to reflect the terahertz signal generated by the fourth terahertz spread spectrum module to the second frequency selection surface; The third terahertz spread spectrum module, and the second frequency selection surface are used to combine the terahertz signal generated by the third terahertz spread spectrum module and the terahertz signal reflected by the second reflector, and then converge them to the parabolic mirror.

2. The band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 1, characterized in that, The first combining module includes a first frequency selection surface and a first reflector arranged in parallel. The first reflector is used to reflect the terahertz signal generated by the second terahertz spread spectrum module to the first frequency selection surface; The first frequency selection surface is used to combine the terahertz signal reflected by the first reflector and the terahertz signal generated by the first terahertz spread spectrum module and then converge them to the parabolic mirror.

3. The band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 1, characterized in that, The first combining module and the second combining module are arranged symmetrically.

4. The band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 1, characterized in that, It also includes a third combining module and a fifth terahertz spread spectrum module; The third combining module includes a third frequency selection surface and a third reflector arranged in parallel. The third reflector is used to reflect the terahertz signal generated by the fifth terahertz spread spectrum module to the third frequency selection surface; the third frequency selection surface is used to combine the terahertz signal collected by the first combining module and the terahertz signal reflected by the third reflector, and then converge them to the parabolic mirror.

5. The band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 4, characterized in that, It also includes a fourth combining module and a sixth terahertz spread spectrum module; The fourth combining module includes a fourth frequency selection surface and a fourth reflector arranged in parallel; the fourth reflector is used to reflect the terahertz signal generated by the sixth terahertz spread spectrum module to the fourth frequency selection surface; the fourth frequency selection surface is used to combine the terahertz signal incident from the second combining module and the terahertz signal reflected by the fourth reflector, and then converge them to the parabolic mirror. The fourth combining module is symmetrically arranged with the third combining module.

6. The band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 5, characterized in that, The first terahertz spread spectrum module, the second terahertz spread spectrum module, the third terahertz spread spectrum module, the fourth terahertz spread spectrum module, the fifth terahertz spread spectrum module, and the sixth terahertz spread spectrum module each include: a terahertz spread spectrum device and a lens. The lens is used to collimate the terahertz signal generated by the terahertz spread spectrum device and to converge the reflected signal.

7. The band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 2, characterized in that, The frequency selection surface can be either a bandpass frequency selection surface or a low-pass frequency selection surface.

8. A method for a band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in any one of claims 1-7, characterized in that, include: Multiple terahertz waves of different bands are incident onto a parabolic mirror using a combining module; The parabolic mirror focuses the incident terahertz waves to the tip of the near-field probe; The near-field probe modulates the incident terahertz wave by performing vertical vibration excitation to obtain a near-field terahertz signal. After being scattered by the near-field probe, the near-field terahertz signal is collimated by the off-axis parabolic mirror and then transmitted to the terahertz spread spectrum module using the combining module. The reflected signal of the near-field terahertz signal received by the terahertz spread spectrum module is processed by the lock-in amplifier unit to obtain local information of the sample under test at that location.

9. The method for a band-stitched terahertz near-field imaging system based on a frequency-selective surface as described in claim 8, characterized in that, The method of using a combining module to incident multiple terahertz waves of different bands onto a parabolic mirror includes: The terahertz signals generated by the first terahertz spread spectrum module and the second terahertz spread spectrum module are combined using the first combining module and then converged onto the parabolic mirror. The terahertz signals generated by the third and fourth terahertz spread spectrum modules are combined using the second combining module and then converged onto the parabolic mirror. The terahertz signal generated by the fifth terahertz spread spectrum module and the terahertz signal incident by the first combiner module are combined using the third combiner module and then focused onto the parabolic mirror. The terahertz signal generated by the sixth terahertz spread spectrum module and the terahertz signal incident by the second combiner module are combined by the fourth combiner module and then focused onto the parabolic mirror.

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