Terahertz near-field imaging light path calibration device and method

Abstract

The invention relates to a terahertz near-field imaging light path calibration device and a terahertz near-field imaging light path calibration method. The device comprises a first visible light source, a second visible light source, a first collimation visible light source, a second collimation visible light source, a first light path collimation system, a second light path collimation system, a light path adjusting system, a circular reflector, a terahertz quantum cascade laser, a thermal detection array, a terahertz quantum well detector and an atomic force microscope platform. The THz laser source and the detector are simulated through the divergent visible light source, the lifting position point of the light path is calculated, light beams can be accurately coupled to the position of the needle point after being focused, errors caused by improper light path adjustment are reduced, meanwhile, the overlapping effect of light spots at the needle point is calibrated through the circular reflector and the thermal detection array, and the detection accuracy is improved. And the thermal detection array is used for observing the convergence effect of THz reflection light spots at the position of the detector, so that the effective focusing and coupling efficiency of THz waves in a near-field region of a probe sample can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz detection imaging, and in particular to a terahertz near-field imaging optical path calibration device and method. Background Art

[0002] Researchers' exploration and study of materials and biomolecules have penetrated deep into the nanoscale. The need to study the interaction between light and matter at the nanoscale has promoted the continuous development of refined characterization technology. The use of local near-field detection can achieve nanoscale optical characterization and mapping of material properties. Scattering scanning near-field optical microscopy (s-SNOM) uses the sharp metal tip of the atomic force microscope (AFM) probe to limit the far-field incident light source and enhance the local field below the tip. The evanescent wave carrying the fine structural information of the sample surface is excited by the probe and can be converted into a propagating field. The near-field interaction between the probe tip and the sample surface causes the phase and amplitude of the scattered field to change. The scattered light from the tip is received by the far-field detector. Through sinusoidal modulation of the probe and phase-locked high-order demodulation, efficient collection of the near-field scattered signal is achieved. The use of near-field scanning imaging can break through the diffraction limit and achieve a spatial resolution that is only related to the tip curvature radius and is independent of the incident wavelength.

[0003] Terahertz (THz) waves have excellent penetration into non-polar substances and excellent detection sensitivity in the low carrier concentration range. The vibrational and rotational frequencies of most biomolecules fall within this frequency band, so the THz frequency band can form a fingerprint spectrum for material composition identification. Using THz s-SNOM, non-destructive testing of samples and acquisition of high-resolution near-field signals from the sample surface are possible. It has been widely used in research on semiconductor micro-nanomaterials and structure analysis, localized carrier dynamics, biomedical imaging, and nanoscale quantum phenomena.

[0004] The THz s-SNOM device can detect high-order near-field signals. The key to achieving nanoscale spatial resolution lies in focusing the incident THz wave onto the probe tip to excite the evanescent field and reduce the far-field background noise caused by reflections from the tip axis and the sample surface. Therefore, the alignment and correction of the optical path are particularly important, and the center of the converging spot of the THz wave should be made to illuminate the vicinity of the tip as much as possible. However, since THz waves are invisible, it is impossible to use a simple visible light microscope lens to visually confirm whether they are focused near the tip. Therefore, obtaining THz near-field signals is relatively difficult. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a terahertz near-field imaging optical path calibration device and method, which can reduce the error caused by improper optical path adjustment and improve the effective focusing and coupling efficiency of THz waves in the near-field area of ​​the probe sample.

[0006] The technical solution adopted by the present invention to solve the technical problem is: to provide a terahertz near-field imaging optical path calibration device, comprising:

[0007] a first visible light source, used to simulate a terahertz quantum cascade laser and generate a first visible light divergent beam;

[0008] a second visible light source, used to simulate a terahertz quantum well detector and generate a second visible light divergent beam;

[0009] a first collimated visible light source, configured to generate a first visible guide light beam;

[0010] a second collimated visible light source, for generating a second visible guide light beam;

[0011] a first optical path collimation system, configured to collimate the first divergent visible light beam and enable the first divergent visible light beam and the first visible light guiding beam to propagate coaxially;

[0012] a second optical path collimation system, configured to collimate the second divergent visible light beam and enable the second divergent visible light beam and the second visible light guiding beam to propagate coaxially;

[0013] an optical path adjustment system, configured to adjust the optical paths of the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially, so as to focus them on the needle tip;

[0014] a circular reflector, used to calibrate focusing effects of the first visible light diverging beam, the first visible light guiding beam, the second visible light diverging beam, and the second visible light guiding beam at the needle tip;

[0015] a terahertz quantum cascade laser, configured to replace the first visible light source and emit terahertz light after the optical paths of the first visible light diverging beam, the first visible guide beam, the second visible light emitting beam, and the second visible guide beam are adjusted;

[0016] a thermal detection array, configured to replace the second visible light source and calibrate the intensity of the terahertz light spot after the optical paths of the first visible light diverging beam, the first visible light guiding beam, the second visible light emitting beam, and the second visible light guiding beam are adjusted; and to replace the circular reflector and calibrate the relative positions of the visible light spot and the terahertz light spot formed by the first visible light guiding beam and the second visible light guiding beam after the intensity of the terahertz light spot is calibrated;

[0017] A terahertz quantum well detector, used to replace the thermal detection array and detect terahertz light after the thermal detection array has completed calibrating the terahertz light spot intensity;

[0018] The atomic force microscope platform is used to replace the thermal detection array after the thermal detection array completes calibration of the position of the light spot formed by the first visible light guide beam and the second visible light guide beam, and provide a tapping mode probe, an advance and retract needle, and a scanning imaging platform.

[0019] The first optical path collimation system comprises:

[0020] a first off-axis parabolic mirror, configured to collimate the first divergent visible light beam;

[0021] The first ITO conductive glass is used to reflect the collimated first visible light diverging beam and transmit the first visible light guiding beam, so that the first visible light diverging beam and the first visible light guiding beam propagate coaxially.

[0022] The second optical path collimation system comprises:

[0023] a second off-axis parabolic mirror, configured to collimate the second divergent visible light beam;

[0024] The second ITO conductive glass is used to reflect the collimated second visible light diverging beam and transmit the second visible light guiding beam, so that the second visible light diverging beam and the second visible light guiding beam propagate coaxially.

[0025] The optical path adjustment system includes:

[0026] a right-angle reflector, configured to reflect the first divergent visible light beam and the first visible light guiding beam propagating coaxially, and the second divergent visible light beam and the second visible light guiding beam propagating coaxially;

[0027] a plane oblique reflecting mirror, configured to elevate the incident optical paths of the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially;

[0028] The confocal off-axis parabolic mirror is used to focus the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially to the needle tip.

[0029] The emitting ends of the first visible light source and the second visible light source are both provided with apertures, and the apertures are used to adjust the divergence angles of the first visible light divergence beam and the second visible light divergence beam.

[0030] The technical solution adopted by the present invention to solve the technical problem is: to provide a terahertz near-field imaging optical path calibration method, using the above-mentioned terahertz near-field imaging optical path calibration device, including the following steps:

[0031] Turning on the first collimated visible light source and the second collimated visible light source, calculating the theoretical position of the visible light spot on the plane oblique reflector in the optical path adjustment system based on the reflection angle, focal length, and needle tip height of the confocal off-axis parabolic mirror in the optical path adjustment system, adjusting the right-angle reflector and the plane oblique reflector in the optical path adjustment system, observing from the image captured by the industrial camera above the circular reflector until the focal points of the first visible guide beam and the second visible guide beam coincide on the mirror surface of the circular reflector, and confirming that the optical paths of the first visible guide beam and the second visible guide beam are adjusted;

[0032] Turning on the first visible light source and the second visible light source, fine-tuning the optical path, and observing through the image captured by the industrial camera above the circular reflector, so that the light spots of the first visible light diverging beam and the second visible light diverging beam, as well as the first visible guiding beam and the second visible guiding beam falling on the circular reflector converge and achieve four-point coincidence;

[0033] Recording the front face positions of the first visible light source and the second visible light source, replacing the first visible light source with the terahertz quantum cascade laser, replacing the second visible light source with the thermal detection array, turning on the terahertz quantum cascade laser and fine-tuning its position so that the intensity of the terahertz convergent light detected in the thermal detection array reaches a maximum, then replacing the thermal detection array with the terahertz quantum well detector, inputting the trigger signal and drive signal of the pulse source and the light response signal output by the pre-current amplifier of the terahertz quantum well detector into an oscilloscope, and fine-tuning the positions of the terahertz quantum cascade laser and the terahertz quantum well detector so that the value of the synchronous light response signal collected by the oscilloscope reaches a maximum;

[0034] The circular reflector is replaced by the thermal detection array, and the position of the thermal detection array is moved so that the thermal detection array detects the visible light spot and the terahertz light spot, and then the position of the thermal detection array is fine-tuned so that the convergence point of the visible light spot is located at the center of the convergence point of the terahertz light spot;

[0035] The thermal detection array is replaced with an atomic force microscope platform, and the needle tip is set to work in tapping mode to obtain the morphological height information of all pixel points in the scanned area of ​​the measured sample and a high spatial resolution terahertz near-field microscopic image.

[0036] When confirming that the optical paths of the first visible guide light beam and the second visible guide light beam are adjusted, the following method is used:

[0037] determining whether the first visible guide beam can fall on the exit end surface of the second collimated visible light source after being reflected by the circular reflector, and if so, adjusting the optical paths of the first visible guide beam and the second visible guide beam is completed;

[0038] Alternatively, it is determined whether the second visible guide beam can fall on the exit end face of the first collimated visible light source after being reflected by the circular reflector. If so, the optical paths of the first visible guide beam and the second visible guide beam are adjusted.

[0039] Beneficial effects

[0040] Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention uses a divergent visible light source to simulate a THz laser source and a detector, calculates the position point of the optical path elevation, so that the light beam can be more accurately coupled to the needle tip position after focusing, reducing the error caused by improper optical path adjustment. At the same time, a circular reflector and a thermal detection array are used to calibrate the overlap effect of the light spot at the needle tip, and a thermal detection array is used to observe the convergence effect of the THz reflected light spot at the detector position, which can improve the effective focusing and coupling efficiency of the THz wave in the near-field area of ​​the probe sample, thereby generating a near-field scattering signal with a high signal-to-noise ratio, and promoting the development and wide application of THz near-field microscopy instruments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic diagram of a terahertz near-field imaging optical path calibration device according to an embodiment of the present invention;

[0042] Figure 2 is a spot diagram of four overlapping focused light spots observed from a visible light microscope in an embodiment of the present invention;

[0043] Figure 3 It is the terahertz light focusing spot observed by the thermal detection array during the initial debugging in the embodiment of the present invention;

[0044] Figure 4 This is the terahertz light focusing spot observed by placing a thermal detection array at the AFM position in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0046] The embodiment of the present invention relates to a terahertz near-field imaging optical path calibration device, such as Figure 1 Shown, including:

[0047] A first visible light source 2, used to simulate a terahertz quantum cascade laser to generate a first visible light divergent beam;

[0048] A second visible light source 11 is used to simulate a terahertz quantum well detector and generate a second visible light divergent beam;

[0049] A first collimated visible light source 1, for generating a first visible guiding light beam;

[0050] A second collimated visible light source 12, for generating a second visible guide beam;

[0051] A first optical path collimation system is configured to collimate the first visible light diverging beam and enable the first visible light diverging beam and the first visible light guiding beam to propagate coaxially; the first optical path collimation system comprises:

[0052] a first off-axis parabolic mirror 4, for collimating the first divergent visible light beam;

[0053] The first ITO conductive glass 3 is used to reflect the collimated first visible light diverging beam and transmit the first visible light guiding beam, so that the first visible light diverging beam and the first visible light guiding beam propagate coaxially.

[0054] A second optical path collimation system is configured to collimate the second divergent visible light beam and enable the second divergent visible light beam and the second visible light guiding beam to propagate coaxially; the second optical path collimation system comprises:

[0055] a second off-axis parabolic mirror 10, for collimating the second divergent visible light beam;

[0056] The second ITO conductive glass 9 is used to reflect the collimated second visible light diverging beam and transmit the second visible light guiding beam, so that the second visible light diverging beam and the second visible light guiding beam propagate coaxially;

[0057] An optical path adjustment system is used to adjust the optical paths of the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially, so that they are focused on the needle tip; the optical path adjustment system includes:

[0058] a right-angle reflector 5, configured to reflect the first divergent visible light beam and the first visible light guiding beam propagating coaxially, and the second divergent visible light beam and the second visible light guiding beam propagating coaxially;

[0059] a plane oblique reflecting mirror 6, configured to elevate the incident optical paths of the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially;

[0060] The confocal off-axis parabolic mirror 7 is used to focus the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially to the needle tip.

[0061] a circular reflector 8, used for calibrating the focusing effects of the first visible light diverging beam, the first visible light guiding beam, the second visible light diverging beam, and the second visible light guiding beam at the needle tip;

[0062] a terahertz quantum cascade laser 2', configured to replace the first visible light source 2 and emit terahertz light after the optical paths of the first visible light diverging beam, the first visible guide beam, the second visible light emitting beam, and the second visible guide beam are adjusted;

[0063] a thermal detection array 11', configured to replace the second visible light source 11 and calibrate the intensity of the terahertz light spot after the optical paths of the first visible light diverging beam, the first visible light guiding beam, the second visible light emitting beam, and the second visible light guiding beam are adjusted; and to replace the circular reflector 8 and calibrate the relative positions of the visible light spot and the terahertz light spot formed by the first visible light guiding beam and the second visible light guiding beam after the terahertz light spot intensity is calibrated;

[0064] The terahertz quantum well detector 11' is used to replace the thermal detection array 11' to detect terahertz light after the thermal detection array has completed calibrating the terahertz light spot intensity;

[0065] The atomic force microscope platform 8' is used to replace the thermal detection array 11' after the thermal detection array calibrates the position of the light spot formed by the first visible light guide beam and the second visible light guide beam, and provides a tapping mode probe, an advance and retract needle, and a scanning imaging platform.

[0066] In this embodiment, the first visible light source 2, the second visible light source 11, the first collimated visible light source 1, and the second collimated visible light source 12 all emit green light. Apertures are provided at the emission ends of the first visible light source 2 and the second visible light source 11, and the divergence angles of the first and second green divergent light beams are adjusted by adjusting the apertures of the apertures. The aperture size of the aperture is adjusted to an appropriate position so that the range of the first green light divergent beam just covers the receiving surface of the first off-axis parabolic mirror 4, and the range of the second green light divergent beam just covers the receiving surface of the second off-axis parabolic mirror 10. The two divergent beams are turned and parallel by the first off-axis parabolic mirror 4 and the second off-axis parabolic mirror 10. After being reflected by the first ITO conductive glass 3 and the second ITO conductive glass 9, the two divergent beams are respectively transmitted coaxially and collinearly with the transmitted first green light guide beam and the second green light guide beam. After passing through the right-angle reflector 5 and the plane oblique reflector 6 to achieve beam deflection and lifting, the confocal off-axis parabolic mirror 7 finally focuses the incident beams symmetrically on both sides onto the circular reflector 8 and adjusts the focus spots to overlap.

[0067] After calibration, the first visible light source 2 and the second visible light source 11 are replaced with a THz QCL module 2' and a THz QWP module 11", respectively. After the module dewar device is cooled with liquid helium, a DC power supply is applied to the THz QCL module 2'. Under the action of electric pumping, continuous photon output is generated in the form of inter-subband electron radiation transition. After passing through the reflection light path, it is focused by the confocal off-axis parabolic mirror 7 to the near-field region at the probe tip. The tip focuses, couples, confines and enhances the local field of the incident light, and can convert the excited weak evanescent wave into a propagation field. The tapping motion of the AFM probe causes the tip-sample distance to vary sinusoidally, and the scattered light carrying the fine structure information of the sample is sinusoidally modulated. The tip scattered light is detected by the THz QWP module 11" in the far-field region. After absorbing the energy of the incident photon, the electrons in the quantum well transition to a quasi-continuous state. Under the action of an external bias, photogenerated carriers with a picosecond response time form a photocurrent. After IV conversion is achieved through a preamplifier, it is connected to the input of a phase-locked amplifier, and the scattered light is demodulated at the second-order frequency of the needle tip tapping oscillation to obtain a high signal-to-noise ratio near-field THz scattering signal without far-field background.

[0068] It should be noted that the confocal off-axis parabolic mirror 7 has different refractive indices and focal lengths for THz light and green light. After the initial alignment of the guiding optical path, the positions of the THz QCL module 2' and the confocal off-axis parabolic mirror 7 still need to be fine-tuned during the THz optical path calibration, based on the locking results of the phase-locked amplifier and the demodulation results of the second-order scattered signal.

[0069] At the same time, this embodiment also proposes a terahertz near-field imaging optical path calibration method for the above device, and the specific implementation steps are as follows:

[0070] S1. First, turn on the first collimated visible light source 1 and the second collimated visible light source 12 placed opposite each other to generate a first green light guiding beam and a second green light guiding beam. The two guiding beams are respectively reflected by the first ITO conductive glass 3 and the second ITO conductive glass 9, the right-angle mirror 5, and the plane oblique reflecting mirror 6, and then the two visible light beams are converged by the confocal off-axis parabolic mirror 7.

[0071] S2. Calculate the theoretical position of the visible light spot on the plane oblique reflector 6 based on the reflection angle, focal length and needle tip height of the confocal off-axis parabolic mirror 7, adjust the reflector group, and observe the image captured by the industrial camera above the circular reflector 8 until the focal points of the two green light beams coincide on the mirror surface, and confirm that the optical path adjustment of the first green light guide beam and the second green light guide beam is completed.

[0072] When it is confirmed that the optical paths of the first green light guide beam and the second green light guide beam are adjusted, if the convergence point of one of the green light beams can fall on the exit end face of the other collimated visible light source after being reflected by the circular reflector 8, the optical path adjustment of the guide beams is completed, that is:

[0073] Determine whether the first green guide beam can fall on the exit end face of the second collimated visible light source 12 after being reflected by the circular reflector 8. If so, the optical paths of the first green guide beam and the second green guide beam are adjusted.

[0074] Alternatively, it is determined whether the second green guiding beam can fall on the exit end face of the first collimated visible light source 1 after being reflected by the circular reflector 8. If so, the optical paths of the first green guiding beam and the second green guiding beam are adjusted.

[0075] It can be seen that the present invention uses a divergent visible light source to simulate the THz laser source and detector, calculates the position point of the optical path elevation, and enables the light beam to be more accurately coupled to the needle tip position after focusing, reducing the error caused by improper optical path adjustment.

[0076] S3, turn on the first visible light source 2 and the second visible light source 11, obtain the first green light divergent beam and the second green light divergent beam, the two divergent beams are respectively adjusted to be collimated and parallel by the first off-axis parabolic mirror 4 and the second off-axis parabolic mirror 10, and then respectively reflected by the conductive surfaces of the first ITO conductive glass 3 and the second ITO conductive glass 9, and then passed through the right-angle mirror 5 and the plane oblique reflector 6, and converged by the confocal off-axis parabolic mirror 7 to simulate the focusing effect of THz light, fine-tune the optical path, and observe through the industrial camera so that the first green light divergent beam, the second green light divergent beam, the first green light guide beam and the second green light guide beam pass through the optical path system and fall on the circular reflector 8. The light spots converge to achieve four-point coincidence (see Figure 2 ), and the reflected light spots can be observed on the front faces of the four light sources;

[0077] S4. Record the front face positions of the divergent first visible light source 2 and the second visible light source 11, replace them with the THz QCL module 2' and the thermal detection array 11' respectively, turn on the THz QCL module 2' and fine-tune its position so that the intensity of the THz convergent light detected in the thermal detection array 11' reaches the maximum (see Figure 3 ), then replace the thermal detection array 11' with a THz QWP module 11", use a pulse source to power the THz QCL module 2', input the trigger signal and drive signal of the pulse source and the optical response signal output by the pre-current amplifier of the THz QWP module 11" into an oscilloscope, and fine-tune the positions of the THz QCL module 2' and the THz QWP module 11" so that the value of the synchronous optical response signal collected by the oscilloscope reaches the maximum;

[0078] S5. Replace the circular reflector 8 with the thermal detection array 11' and move its position so that it detects the green light spot and the THz light spot, and then fine-tune its position so that the convergence point of the green light spot is located at the center of the THz convergence point (see Figure 4 ), simulating the converging effect at the needle tip;

[0079] It is not difficult to find that the present invention uses a circular reflector and a thermal detection array to calibrate the overlap effect of the light spot at the needle tip, and uses the thermal detection array to observe the convergence effect of the THz reflected light spot at the detector position, which can improve the effective focusing and coupling efficiency of the THz wave in the near-field area of ​​the probe sample, thereby generating a near-field scattering signal with a high signal-to-noise ratio, and promoting the development and widespread application of THz near-field microscopy instruments.

[0080] S6. Replace the thermal detection array 11' with the AFM platform 8', set the tip to operate in tapping mode, apply DC power to the THzQCL module 2' to operate in continuous wave mode, and focus the near-field signal at the probe sample through the above-mentioned optical path system to excite the near-field signal. After the scattered signal is sinusoidally modulated by the probe, the THz QWP module 11" detects and collects the tip near-field scattered light. The output signal of the pre-current amplifier is used as the input signal of the lock-in amplifier, and the probe tapping drive signal is used as the reference signal of the lock-in amplifier. The scattered signal is demodulated at the second harmonic, and the output of the lock-in amplifier is connected to the analog input channel of the AFM controller to obtain the THz second-order near-field response signal at the sample point under the probe. By scanning mobile imaging, the morphological height information of all pixel points in the scanned area of ​​the sample under test and a high-spatial-resolution THz near-field microscopic image can be obtained.

[0081] By implementing this embodiment, a simulated divergent visible light source and collimated visible light guidance are used to perform preliminary calibration of the near-field imaging system, and a thermal detection array is used to perform fine correction of the THz optical path. This can reduce the difficulty of debugging the THz near-field imaging system to a certain extent, increase the possibility of extracting high-order near-field scattering signals with a high signal-to-noise ratio, and provide important technical support for the development of THz near-field microscopic imaging instruments.

Claims

1. A terahertz near-field imaging optical path calibration device, characterized in that: include: a first visible light source, used to simulate a terahertz quantum cascade laser and generate a first visible light divergent beam; a second visible light source, used to simulate a terahertz quantum well detector and generate a second visible light divergent beam; a first collimated visible light source, configured to generate a first visible guide light beam; a second collimated visible light source, for generating a second visible guide light beam; a first optical path collimation system, configured to collimate the first divergent visible light beam and enable the first divergent visible light beam and the first visible light guiding beam to propagate coaxially; a second optical path collimation system, configured to collimate the second divergent visible light beam and enable the second divergent visible light beam and the second visible light guiding beam to propagate coaxially; an optical path adjustment system, configured to adjust the optical paths of the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially, so as to focus them on the needle tip; a circular reflector, used to calibrate focusing effects of the first visible light diverging beam, the first visible light guiding beam, the second visible light diverging beam, and the second visible light guiding beam at the needle tip; a terahertz quantum cascade laser, configured to replace the first visible light source and emit terahertz light after the optical paths of the first visible light diverging beam, the first visible guide beam, the second visible light emitting beam, and the second visible guide beam are adjusted; a thermal detection array, configured to replace the second visible light source and calibrate the intensity of the terahertz light spot after the optical paths of the first visible light diverging beam, the first visible light guiding beam, the second visible light emitting beam, and the second visible light guiding beam are adjusted; and to replace the circular reflector and calibrate the relative positions of the visible light spot and the terahertz light spot formed by the first visible light guiding beam and the second visible light guiding beam after the intensity of the terahertz light spot is calibrated; A terahertz quantum well detector, used to replace the thermal detection array and detect terahertz light after the thermal detection array has completed calibrating the terahertz light spot intensity; The atomic force microscope platform is used to replace the thermal detection array after the thermal detection array completes calibration of the position of the light spot formed by the first visible light guide beam and the second visible light guide beam, and provide a tapping mode probe, an advance and retract needle, and a scanning imaging platform.

2. The terahertz near-field imaging optical path calibration device according to claim 1, characterized in that: The first optical path collimation system comprises: a first off-axis parabolic mirror, configured to collimate the first divergent visible light beam; The first ITO conductive glass is used to reflect the collimated first visible light diverging beam and transmit the first visible light guiding beam, so that the first visible light diverging beam and the first visible light guiding beam propagate coaxially.

3. The terahertz near-field imaging optical path calibration device according to claim 1, characterized in that: The second optical path collimation system comprises: a second off-axis parabolic mirror, configured to collimate the second divergent visible light beam; The second ITO conductive glass is used to reflect the collimated second visible light diverging beam and transmit the second visible light guiding beam, so that the second visible light diverging beam and the second visible light guiding beam propagate coaxially.

4. The terahertz near-field imaging optical path calibration device according to claim 1, characterized in that: The optical path adjustment system includes: a right-angle reflector, configured to reflect the first divergent visible light beam and the first visible light guiding beam propagating coaxially, and the second divergent visible light beam and the second visible light guiding beam propagating coaxially; a plane oblique reflecting mirror, configured to elevate the incident optical paths of the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially; The confocal off-axis parabolic mirror is used to focus the first visible light diverging beam and the first visible light guiding beam propagating coaxially, and the second visible light diverging beam and the second visible light guiding beam propagating coaxially to the needle tip.

5. The terahertz near-field imaging optical path calibration device according to claim 1, characterized in that: The emitting ends of the first visible light source and the second visible light source are both provided with apertures, and the apertures are used to adjust the divergence angles of the first visible light divergence beam and the second visible light divergence beam.

6. A terahertz near-field imaging optical path calibration method, characterized in that: The terahertz near-field imaging optical path calibration device according to any one of claims 1 to 5 comprises the following steps: Turning on the first collimated visible light source and the second collimated visible light source, calculating the theoretical position of the visible light spot on the plane oblique reflector in the optical path adjustment system based on the reflection angle, focal length, and needle tip height of the confocal off-axis parabolic mirror in the optical path adjustment system, adjusting the right-angle reflector and the plane oblique reflector in the optical path adjustment system, observing from the image captured by the industrial camera above the circular reflector until the focal points of the first visible guide beam and the second visible guide beam coincide on the mirror surface of the circular reflector, and confirming that the optical paths of the first visible guide beam and the second visible guide beam are adjusted; Turning on the first visible light source and the second visible light source, fine-tuning the optical path, and observing through the image captured by the industrial camera above the circular reflector, so that the light spots of the first visible light diverging beam and the second visible light diverging beam, as well as the first visible guiding beam and the second visible guiding beam falling on the circular reflector converge and achieve four-point coincidence; Recording the front face positions of the first visible light source and the second visible light source, replacing the first visible light source with the terahertz quantum cascade laser, replacing the second visible light source with the thermal detection array, turning on the terahertz quantum cascade laser and fine-tuning its position so that the intensity of the terahertz converged light detected in the thermal detection array reaches a maximum, then replacing the thermal detection array with the terahertz quantum well detector, inputting the trigger signal and drive signal of the pulse source and the light response signal output by the pre-current amplifier of the terahertz quantum well detector into an oscilloscope, and fine-tuning the positions of the terahertz quantum cascade laser and the terahertz quantum well detector so that the value of the synchronous light response signal collected by the oscilloscope reaches a maximum; The circular reflector is replaced by the thermal detection array, and the position of the thermal detection array is moved so that the thermal detection array detects the visible light spot and the terahertz light spot, and then the position of the thermal detection array is fine-tuned so that the convergence point of the visible light spot is located at the center of the convergence point of the terahertz light spot; The thermal detection array is replaced with an atomic force microscope platform, and the needle tip is set to work in tapping mode to obtain the morphological height information of all pixel points in the scanned area of ​​the measured sample and a high spatial resolution terahertz near-field microscopic image.

7. The terahertz near-field imaging optical path calibration method according to claim 6, characterized in that: When confirming that the optical paths of the first visible guide light beam and the second visible guide light beam are adjusted, the following method is used: determining whether the first visible guide beam can fall on the exit end surface of the second collimated visible light source after being reflected by the circular reflector, and if so, adjusting the optical paths of the first visible guide beam and the second visible guide beam is completed; Alternatively, it is determined whether the second visible guide beam can fall on the exit end face of the first collimated visible light source after being reflected by the circular reflector. If so, the optical paths of the first visible guide beam and the second visible guide beam are adjusted.

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