Terahertz near-field spectral signal measuring system and measuring method

Abstract

The invention provides a terahertz near-field spectral signal measurement system and a measurement method. The invention relates to the technical field of terahertz spectrum detection and imaging, and in particular relates to a terahertz near-field spectral signal measurement system which comprises a sample bearing plate, the sample bearing plate is provided with a through hole and a cooling channel, a sample to be detected is arranged in the through hole, and a cooling medium flows through the cooling channel; the emission source module is used for emitting detection light pulses and terahertz waves and guiding the terahertz waves to penetrate through the sample to be detected through the through hole; the light guide microprobe module is configured to be arranged in a near-field area of a sample to be detected; wherein under the condition that the cooling medium flows through the cooling channel to enable the temperature of the near-field region to be lower than the preset temperature, the light guide microprobe module is configured to receive the terahertz wave penetrating through the sample to be detected under the action of the detection light pulse, and a terahertz spectrum signal of the sample to be detected is obtained.

Description

Technical Field

[0001] This disclosure relates to the field of terahertz spectral detection and imaging technology, and more specifically, to a terahertz near-field spectral signal measurement system and measurement method. Background Technology

[0002] One of the important development directions in terahertz science research is high-resolution spectral detection and imaging technology. As the technology matures, terahertz time-domain spectroscopy can obtain multi-dimensional information about samples, while terahertz near-field detection technology detects signals in the near-field range of the sample surface.

[0003] In realizing the present invention, the inventors discovered that when performing terahertz measurements on matter in related technologies, it is necessary to set relatively stringent measurement conditions, which leads to inconvenient measurement operations and low measurement efficiency. Summary of the Invention

[0004] In view of this, this disclosure provides a terahertz near-field spectral signal measurement system and method.

[0005] One aspect of this disclosure provides a terahertz near-field spectral signal measurement system, comprising: a sample carrier plate having a through hole and a cooling channel, wherein a sample to be tested is disposed in the through hole and the cooling channel is for through which a cooling medium flows; an emission source module for emitting a probe light pulse and a terahertz wave, and guiding the terahertz wave through the through hole and through the sample to be tested; and a photoconductive microprobe module configured to be disposed in the near-field region of the sample to be tested; wherein, when the cooling medium flows through the cooling channel to make the temperature of the near-field region lower than a preset temperature, the photoconductive microprobe module is configured to receive the terahertz wave passing through the sample to be tested under the action of the probe light pulse, thereby obtaining the terahertz spectral signal of the sample to be tested.

[0006] According to embodiments of this disclosure, a cooling unit is also included; the cooling unit is connected to ports at both ends of the cooling channel; the cooling unit is configured to transfer cooling medium from a port at one end of the cooling channel to a port at the other end of the cooling channel.

[0007] According to an embodiment of this disclosure, the cooling medium includes nitrogen; the cooling unit includes a liquid nitrogen storage device and an air extraction device, wherein the outlet of the liquid nitrogen storage device is connected to one end port of the cooling channel, and the inlet of the air extraction device is connected to the other end port of the cooling channel; the air extraction device is configured to allow the vaporized liquid nitrogen to flow through the cooling channel to reduce the temperature in the near-field region.

[0008] According to embodiments of this disclosure, it further includes: a temperature sensor, mounted on a sample carrier plate, for detecting the temperature of the near-field region, so as to activate the emission source module and the photoguide microprobe module when the temperature of the near-field region is lower than a preset temperature.

[0009] According to an embodiment of this disclosure, the emission source module includes: a laser source unit for generating pump light pulses and probe light pulses; and a terahertz emission unit for being excited by the pump light pulses to generate terahertz waves and guiding the terahertz waves through a through-hole to pass through the sample to be tested.

[0010] According to embodiments of this disclosure, the laser source unit includes a fiber femtosecond laser and a beam splitter, wherein the beam splitter is used to split the pulsed laser emitted by the fiber femtosecond laser into pump light pulses and probe light pulses.

[0011] According to an embodiment of this disclosure, the terahertz transmitting unit includes: a terahertz transmitting antenna, a voltage source, and a terahertz lens, wherein a pump light pulse irradiates an irradiated area in the terahertz transmitting antenna to generate a first photogenerated carrier, and the first photogenerated carrier radiates a terahertz wave under the action of a bias voltage of the voltage source; the terahertz lens is used to collimate the terahertz wave radiated by the terahertz transmitting antenna and guide the terahertz wave through a through-hole to pass through the sample under test.

[0012] According to embodiments of this disclosure, the terahertz transmitting unit further includes an optical fiber delay line, which is used to delay the pump light pulse to change the optical path length of the pump light pulse relative to the probe light pulse.

[0013] According to embodiments of this disclosure, the device further includes a host computer; the photoconductive microprobe module includes: a microprobe and a current amplifier; a probe light pulse irradiates the irradiated area in the microprobe to generate a second photogenerated carrier; a terahertz wave passing through the sample under test causes the second photogenerated carrier to move directionally, generating a target photocurrent signal; the current amplifier converts the target photocurrent signal into a voltage signal and amplifies it to obtain a target voltage signal; the host computer is configured to obtain the terahertz spectral signal of the sample under test based on the target voltage signal.

[0014] Another aspect of this disclosure provides a method for measuring terahertz near-field spectral signals, comprising: using a sample carrier plate to carry a sample to be tested and reducing the temperature of the near-field region of the sample to be tested to below a preset temperature; using an emission source module to emit a probe light pulse and a terahertz wave, and guiding the terahertz wave through the sample to be tested; and using a photoconductive microprobe module in the near-field region of the sample to be tested, receiving the terahertz wave passing through the sample to be tested under the action of the probe light pulse, thereby obtaining the terahertz spectral signal of the sample to be tested.

[0015] According to embodiments of this disclosure, the sample support plate constructs an open low-temperature environment for the sample under test through its through holes and cooling channels. This makes the sample insensitive to environmental changes. Since there is no need for a sealed cavity or vacuum vent, localized low-temperature control of the sample and obtaining a stable signal can be achieved under open, dry, low-temperature gas conditions. This reduces the complexity of the measurement system setup and maintenance, and improves measurement efficiency. Furthermore, this disclosure uses an optically guided microprobe as the detection device. By placing the optically guided microprobe in the near-field region of the sample under test and utilizing the near-field coupling effect of the probe tip and the optical guiding principle, the diffraction limit is overcome, and the spatial resolution of the measurement results can reach [value missing]. It has broad application prospects. Attached Figure Description

[0016] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic diagram of a measurement system structure according to an embodiment of the present disclosure is shown.

[0018] Figure 2 A schematic diagram of the structure of a sample carrier plate according to an embodiment of the present disclosure is shown.

[0019] Figure 3 A schematic diagram illustrating the connection structure of the terahertz emitting unit and the optical guide microprobe module according to an embodiment of the present disclosure is shown.

[0020] Figure 4 A flowchart illustrating a terahertz near-field spectral signal measurement method according to an embodiment of the present disclosure is shown schematically.

[0021] Explanation of reference numerals in the attached figures:

[0022] 1: Laser source unit; 2: Polarization controller; 3: Terahertz emission unit; 4: Optical guide microprobe module; 5: Host computer; 6: Sample carrier plate; 301: Fiber optic delay line; 302: Terahertz transmitting antenna; 303: Terahertz lens; 304: Voltage source; 305: Antenna bracket; 401: Fiber optic collimator; 402: Lens group; 403: Reflector; 404: Microprobe; 405: Vertical plate; 406: Support rod; 407: Motorized three-dimensional translation stage; 408: High-speed current amplifier; 409: Lock-in amplifier; 601: Liquid nitrogen storage device; 602: Plate; 603: Cooling channel; 604: Compression fitting; 605: Cold nitrogen inlet pipe; 606: Cold nitrogen outlet pipe; 607: Vacuuming device; 608: Temperature sensor. Detailed Implementation

[0023] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0025] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0026] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0027] In related technologies, terahertz waves refer to waves with frequencies between [frequency range missing]. Electromagnetic waves, corresponding to wavelengths of arrive With a spectrum between infrared and microwave radiation, it has good penetrability, non-ionization and fingerprint spectral characteristics, and is therefore widely used in materials testing, biomedicine, micro-nano structure characterization and other fields.

[0028] Existing terahertz measurement systems for matter theoretically fall into two main categories: scattering-type terahertz scanning near-field optical microscopy systems and terahertz near-field spectroscopy systems based on optically guided microprobes. While the former can achieve nanometer-level resolution, it is complex, costly, and requires extremely high vibration and environmental stability. Furthermore, it suffers from low signal-to-noise ratio, slow measurement speed, and poor repeatability. For the latter, to avoid the influence of air disturbances, temperature fluctuations, and water background on the signal and to obtain a higher signal-to-noise ratio, existing terahertz spectroscopy measurement systems must operate in a low-temperature vacuum-dry environment or on a closed, vibration-proof platform. This requires precise optical paths, complex systems, and inconvenient operation. Some measurement systems utilize freezing methods to suppress water absorption in the terahertz band, and the temperature control of the sample depends on a liquid sample cell or an overall environmental temperature control chamber, which introduces many inconveniences to achieving controllable low-temperature adjustment of the sample. For experiments requiring the study of material vibrations, phase transitions, superconductivity, or carrier dynamics at low temperatures, existing low-temperature terahertz time-domain spectroscopy systems using optically guided microprobes have the following drawbacks:

[0029] (1) The lack of efficient and compact low-temperature environment creation modules makes it difficult to achieve temperature control and real-time monitoring of local areas of the material or micro / nano structure under test.

[0030] (2) The entire measurement system usually relies on a sealed or vacuum-sealed cavity for heat insulation, which is complex to design, inconvenient to operate and difficult to maintain.

[0031] In view of this, embodiments of the present disclosure provide a terahertz near-field spectral signal measurement system, comprising: a sample carrier plate having a through hole and a cooling channel, wherein a sample to be tested is disposed in the through hole and the cooling channel is used for the flow of a cooling medium; an emission source module for emitting a probe light pulse and a terahertz wave, and guiding the terahertz wave through the through hole and through the sample to be tested; and a photoconductive microprobe module configured to be disposed in the near-field region of the sample to be tested; wherein, when the cooling medium flows through the cooling channel to make the temperature of the near-field region lower than a preset temperature, the photoconductive microprobe module is configured to receive the terahertz wave passing through the sample to be tested under the action of the probe light pulse, thereby obtaining the terahertz spectral signal of the sample to be tested.

[0032] Figure 1 A schematic diagram of a measurement system structure according to an embodiment of the present disclosure is shown.

[0033] According to embodiments of this disclosure, reference is made to Figure 1The sample carrier plate 6 described above is provided with through holes and cooling channels. The sample to be tested is placed in the through holes, and the cooling channels are used for the flow of cooling medium. If the sample to be tested is small, it can be placed on a silicon wafer or thin film and then placed on the sample carrier plate 6; if the sample is large, it can be placed directly above the through holes. Then, the position of the sample to be tested can be adjusted so that terahertz waves can pass through it. Multiple cooling channels in the sample carrier plate 6 can be interconnected. When the cooling medium flows through the cooling channels, the temperature of the sample carrier plate 6 can be gradually reduced. When the temperature of the near-field region of the sample to be tested is lower than the preset temperature by the cooling of the sample carrier plate 6, the acquisition of terahertz waves passing through the sample to be tested can begin.

[0034] Based on embodiments of this disclosure, continued reference is made to... Figure 1 The aforementioned emission source module includes a laser source unit 1, a polarization controller 2, and a terahertz emission unit 3. The laser source unit splits the pulsed laser light it generates into two beams via a beam splitter. One beam is guided by an optical fiber to the optical guide microprobe module 4, while the other beam is guided by an optical fiber through the polarization controller 2 and then to the terahertz emission unit 3 to generate a terahertz wave. The optical guide microprobe module 4 is located above the sample support plate 6, and its probe portion can penetrate deep into the near-field region of the sample under test. Furthermore, since the terahertz emission unit 3 is located below the sample support plate 6, the terahertz wave can pass through the sample under test from below, generating a terahertz wave that passes through the sample and is received by the optical guide microprobe module 4.

[0035] exist Figure 1 The host computer 5 is also shown. On the one hand, the host computer 5 can control the terahertz emitting unit 3 to convert the pulsed light signal into an electromagnetic wave signal. On the other hand, it can receive the terahertz wave signal collected by the photoconductive microprobe module 4 and perform Fourier transform on the terahertz wave signal collected by the photoconductive microprobe module 4 to convert it into the terahertz spectral signal of the sample to be tested, thereby completing the measurement of the terahertz near-field spectral signal of the sample to be tested.

[0036] According to embodiments of this disclosure, the sample support plate constructs an open low-temperature environment for the sample under test through its through holes and cooling channels. This makes the sample insensitive to environmental changes, eliminating the need for a drying environment during the experiment. Localized low-temperature control of the sample and obtaining a stable signal can be achieved under open, dry, low-temperature gas conditions, thus reducing the complexity of the measurement system setup and maintenance and improving measurement efficiency. Furthermore, this disclosure uses an optically guided microprobe as the detection device. By placing the optically guided microprobe in the near-field region of the sample under test and utilizing the near-field coupling effect of the probe tip and the optical guiding principle, the diffraction limit is overcome, and the spatial resolution of the measurement results can reach [value missing]. It has broad application prospects.

[0037] According to embodiments of this disclosure, the terahertz near-field spectral signal measurement system further includes a cooling unit; the cooling unit is connected to ports at both ends of a cooling channel; the cooling unit is configured to transfer cooling medium from a port at one end of the cooling channel to a port at the other end of the cooling channel.

[0038] According to embodiments of this disclosure, the cooling channel can adopt a straight-through structure with openings at both ends. The cooling channel can be arranged in a serpentine shape inside the sample support plate, with its first and second ports located at opposite ends. A closed-loop circuit is formed between the cooling unit and the cooling channel via pipelines: the outlet of the cooling unit is sealed to the first port of the cooling channel via a first pipe section, and the return port of the cooling unit is sealed to the second port of the cooling channel via a second pipe section. The cooling unit can integrate a pumping device and a heat exchange device. During operation, the pumping device drives the cooling medium to flow from the first port of the cooling channel, along the channel's axial direction to the second port. The cooling medium then returns to the cooling unit and releases heat at the heat exchange device, completing the cycle. This flow direction remains unidirectional and constant, allowing the cooling medium to flow sequentially through the entire cooling channel, achieving continuous heat removal from the area to be cooled. The aforementioned cooling medium can be isobutane, propane, propylene, nitrogen, or carbon dioxide, etc.

[0039] According to an embodiment of this disclosure, the cooling medium includes nitrogen; the cooling unit includes a liquid nitrogen storage device and an air extraction device, wherein the outlet of the liquid nitrogen storage device is connected to one end port of the cooling channel, and the inlet of the air extraction device is connected to the other end port of the cooling channel; the air extraction device is configured to allow the vaporized liquid nitrogen to flow through the cooling channel to reduce the temperature in the near-field region.

[0040] According to the embodiments of this disclosure, the cooling medium can be in the form of the cold source described above, or it can be a nitrogen gas flow cooling method, i.e. nitrogen forced convection cooling; a liquid nitrogen tank is set at one end of the cooling channel, and an air extraction device is set at the other end of the cooling channel. After the air extraction device is started, the nitrogen in the liquid nitrogen tank after forced vaporization flows through the cooling channel, thereby cooling the entire sample support plate.

[0041] Figure 2 A schematic diagram of the structure of a sample carrier plate according to an embodiment of the present disclosure is shown.

[0042] According to embodiments of this disclosure, such as Figure 2 As shown, the cooling unit may include a liquid nitrogen storage device 601, a compression fitting 604, a cold nitrogen inlet pipe 605, a cold nitrogen outlet pipe 606, and a vacuum device 607; the figure also shows the sample support plate 602 and the cooling channel 603.

[0043] The 602 board can be made of high thermal conductivity copper or aluminum alloy, with a thickness of up to 12mm. A central recessed area can be provided on the upper surface of the board, with a depth of up to 2.5mm. The recessed area is used to place the sample to be tested; the diameter of the through hole on the plate 602 can be set to 1cm, and the through hole can allow the complete terahertz wave to pass through while ensuring the cooling effect.

[0044] A serpentine cooling channel 603 is machined inside the sample support plate 602 to facilitate the flow of low-temperature nitrogen gas generated during the vaporization of liquid nitrogen during extraction. The inlet of the serpentine cooling channel 603 is connected to the cold nitrogen inlet pipe 605, and the outlet of the cooling channel 603 is connected to the cold nitrogen outlet pipe 606 via compression fittings 604. A sealing ring is provided at the fitting to ensure reliable connection in low-temperature environments.

[0045] The cold nitrogen inlet pipe 605 and the cold nitrogen outlet pipe 606 can be made of stainless steel braided hose or polytetrafluoroethylene low-temperature resistant hose. The hose is wrapped with heat insulation cotton. The flexible low-temperature resistant hose connection method ensures that the liquid nitrogen inlet and outlet will not cause mechanical stress to the plate during thermal expansion and contraction. Therefore, there is no need to change the interface size, and only a matching compression fitting is required.

[0046] In addition, the sample carrier plate 602 can be provided with 4 M6 through holes at its tail end, which can be used to fix it stably on the three-dimensional displacement stage, so as to flexibly adjust the position of the sample being measured.

[0047] When the measurement system is in use, the liquid nitrogen storage device 601 can be connected to the compression fitting 604 via the cold nitrogen inlet pipe 605, and the evacuation device 607 can be connected to another compression fitting 604 via the cold nitrogen outlet pipe 606. When cooling begins, the evacuation device 607 is adjusted to its maximum setting, so that the liquid nitrogen is rapidly vaporized into cold nitrogen during the extraction process, which is then transported in the cold nitrogen inlet pipe 605 and flows into the cooling channel 603.

[0048] According to embodiments of this disclosure, the terahertz near-field spectral signal measurement system may further include a temperature sensor mounted on a sample carrier plate to detect the temperature of the near-field region, so as to activate the emission source module and the photoconductive microprobe module when the temperature of the near-field region is lower than a preset temperature.

[0049] According to embodiments of this disclosure, a temperature sensor can be used to detect the temperature in the near-field region of the sample to be tested, thereby determining the time for terahertz wave acquisition.

[0050] Continue to refer to Figure 2A temperature sensor 608 can be installed on the lower surface of the sample support plate 602 near the through hole to detect the temperature of the sample in real time. When cold nitrogen flows into the cooling channel 603, the sample area of ​​the sample support plate 602 is rapidly reduced to below the preset temperature.

[0051] After detecting a temperature change, the temperature sensor 608 can feed back the signal to its display unit. Furthermore, by controlling the flow rate of the suction device 607, dynamic equilibrium of the near-field temperature of the sample can be achieved. The temperature can be controlled within the range of 90–300 K by controlling the suction device.

[0052] Preferably, the nitrogen extracted by the vacuuming device can be returned to the vicinity of the sample to be tested and the sample testing area can be purged, so that the nitrogen can continuously flow near the sample surface, so that a low-temperature dry local area is formed on the sample surface, thus maintaining a low-temperature surface without frost in an open environment.

[0053] According to embodiments of this disclosure, a closed-loop nitrogen circulation cooling circuit can be formed by using liquid nitrogen storage devices and pumping devices at both ends of the cooling channel. The forced convection of the low-temperature nitrogen gas after vaporization directly removes heat from the near-field region, rapidly reducing the surface temperature of the sample support plate from room temperature to below a preset temperature. Since nitrogen is used as the cooling medium, there are no harmful risks of flammability, conductivity, or residual pollution. It also does not chemically corrode the emission source or the photoconductive microprobe, thus improving the safety of the entire measurement system. Furthermore, the temperature sensor monitors the near-field temperature in real time, allowing the emission source and microprobe module to be activated only when the temperature falls below a preset threshold. This avoids measurement errors caused by high-temperature drift and prevents frost formation or structural stress damage due to low-temperature overshoot, enabling rapid and convenient measurement of the low-temperature near-field spectral signal of the sample. Simultaneously, it simplifies the piping layout and reduces maintenance and operating costs.

[0054] According to an embodiment of this disclosure, the emission source module includes: a laser source unit for generating pump light pulses and probe light pulses; and a terahertz emission unit for being excited by the pump light pulses to generate terahertz waves and guiding the terahertz waves through a through-hole to pass through the sample to be tested.

[0055] According to an embodiment of this disclosure, the laser source unit includes a fiber femtosecond laser and a beam splitter, wherein the beam splitter is used to split the pulsed laser emitted by the fiber femtosecond laser into the pump light pulse and the probe light pulse.

[0056] Based on embodiments of this disclosure, and referring again to Figure 1The laser source unit 1 can split the laser generated by the laser in it into two beams through the beam splitter to obtain pump light pulse and probe light pulse. After the pump light pulse is transmitted to the terahertz emission unit 3 through the optical fiber, a terahertz wave can be obtained.

[0057] According to embodiments of this disclosure, the laser source unit 1 may include a fiber femtosecond laser, an attenuator, a lens group for collimating the optical path, a fiber coupler, and a beam splitter. The fiber femtosecond laser is used to generate a center wavelength. repetition frequency Pulse width less than The linearly polarized light is attenuated by an attenuator, collimated by a lens group, and then coupled into a beam splitter through an optical fiber coupler. Then, the pulsed light is split into a pump pulse and a probe pulse for the generation of terahertz waves and the excitation of the optical guide microprobe.

[0058] Furthermore, the emission source module may also include a polarization controller 2; the pump light pulse split by the beam splitter is connected to the terahertz emission unit 3 through a dispersion-compensating fiber and a polarization-maintaining fiber. In addition, a polarization controller 2 may also be installed in the dispersion-compensating fiber, and the probe light pulse is connected to the optical guide microprobe module 4 through the dispersion-compensating fiber and the polarization-maintaining fiber.

[0059] According to embodiments of this disclosure, the polarization controller 2 may include multiple functions, such as maintaining the pump light pulse with parallel polarization to maximize terahertz generation efficiency; adjusting the polarization of the probe light pulse to match the direction of the terahertz electric field and improve the signal-to-noise ratio; and compensating for random polarization drift in the optical fiber or optical path to achieve long-term stable measurement.

[0060] According to embodiments of this disclosure, a beam splitter is used in the transmitting module, enabling synchronized output of pump and probe pulses within a single laser. This eliminates the need for an additional laser head and an external laser synchronization path, and ensures that the center wavelengths and repetition frequencies of the generated pump and probe pulses are identical. This single-laser and beam splitter design allows for low-cost, highly integrated, and highly stable terahertz near-field spectral signal measurement across the entire measurement system, reducing system setup and maintenance complexity and improving measurement efficiency.

[0061] According to an embodiment of this disclosure, the terahertz transmitting unit includes: a terahertz transmitting antenna, a voltage source, and a terahertz lens, wherein a pump light pulse irradiates an irradiated area in the terahertz transmitting antenna to generate a first photogenerated carrier, and the first photogenerated carrier radiates a terahertz wave under the action of a bias voltage of the voltage source; the terahertz lens is used to collimate the terahertz wave radiated by the transmitting antenna and guide the terahertz wave through a through-hole to pass through the sample under test.

[0062] According to embodiments of this disclosure, a pump light pulse, upon irradiating a region in a low-temperature GaAs photoconductive antenna, can instantaneously generate a high concentration of electron-hole pairs. Under the influence of a bias electric field provided by an external voltage source, the charge carriers accelerate extremely rapidly to form a sub-picosecond transient current, radiating a broadband terahertz electromagnetic wave according to Ampere's law. The terahertz wave is collimated by a lens and guided to the sample under test, resulting in a terahertz wave passing through the sample.

[0063] According to embodiments of this disclosure, the terahertz transmitting unit further includes an optical fiber delay line, which is used to delay the pump light pulse to change the optical path length of the pump light pulse relative to the probe light pulse.

[0064] Figure 3 A schematic diagram illustrating the connection structure of the terahertz emitting unit and the optical guide microprobe module according to an embodiment of the present disclosure is shown.

[0065] like Figure 3 As shown, the terahertz transmitting unit may include: an optical fiber delay line 301, a terahertz transmitting antenna 302, a terahertz lens 303, a voltage source 304, and an antenna support 305. The pump light pulse split by the beam splitter is transmitted through the dispersion-compensating fiber, the polarization-maintaining fiber, and the optical fiber delay line 301 into the terahertz transmitting antenna 302 of the terahertz transmitting unit, exciting photogenerated carriers. These carriers accelerate under square wave bias, radiating terahertz waves. The optical fiber delay line 301 can be controlled by the host computer 5 to change the optical path difference between the pump light pulse and the probe light pulse, thereby acquiring the complete terahertz signal. The divergent terahertz signal is collimated by a terahertz lens into a parallel light spot with a diameter of about 6 mm. The terahertz lens 303 and the terahertz transmitting antenna 302 are fixed on the antenna support 305. The polarization direction of the terahertz wave can be changed by rotating the antenna support 305. A two-dimensional displacement stage is provided under the antenna support 305, which can adjust the position of the light spot formed by the terahertz radiation in three dimensions.

[0066] According to embodiments of this disclosure, the optical path of the pump light pulse, after being finely adjusted by the fiber delay line, enables the terahertz wave and the probe pulse to arrive at the photoconductive microprobe synchronously with femtosecond precision, eliminating time-domain drift. The terahertz emitting unit in this disclosure achieves high integration, and the directional radiation of the terahertz wave can be improved through the terahertz lens, thereby improving the detection accuracy of the sample under test. The terahertz emitting unit can provide stable and repeatable terahertz wave radiation for the measurement of near-field spectral signals.

[0067] According to embodiments of this disclosure, the terahertz near-field spectral signal measurement system further includes a host computer; the photoconductive microprobe module includes: a microprobe and a current amplifier; a probe light pulse irradiates the irradiated area in the microprobe to generate a second photogenerated carrier; the terahertz wave passing through the sample under test causes the second photogenerated carrier to move in a directional manner, generating a target photocurrent signal; the current amplifier converts the target photocurrent signal into a voltage signal and amplifies it to obtain a target voltage signal; the host computer is configured to obtain the terahertz spectral signal of the sample under test based on the target voltage signal.

[0068] According to embodiments of this disclosure, when a probe light pulse illuminates the tip region of a microprobe, photogenerated charge carriers are instantaneously generated. Simultaneously, an arriving terahertz wave drives these charge carriers to form a transient current, the magnitude of which is proportional to the field strength of the terahertz wave. This current can be recorded by a current amplifier and converted into a voltage signal. A host computer can then convert the acquired voltage signal into a spectral signal of the sample under test, enabling the measurement of the terahertz near-field spectral signal.

[0069] Based on embodiments of this disclosure, and further referenced Figure 3 In addition to the microprobe 404 and the current amplifier 408, the optical microprobe module may also include: an optical fiber collimator 401, a lens group 402, a reflector 403, a vertical plate 405, support rods 406 and 407, and a lock-in amplifier 409.

[0070] According to embodiments of this disclosure, the fiber optic collimator 401, lens group 402, reflector 403, and microprobe 404 are fixed on a vertical plate 405 of a three-dimensional translation support. The vertical plate 405 is connected to an electric three-dimensional translation stage 407 via a support rod 406, which can move in three dimensions to change the probe position.

[0071] The probe light pulse is guided through an optical fiber to the fiber collimator 401 in the optical fiber microprobe module. The fiber collimator 401 converts the probe light pulse transmitted in the optical fiber into free-space transmission. After collimation and beam contraction by the lens group 402 and reflection by the mirror 403, it is focused on the optical switch of the microprobe 404. At this time, the optical fiber microprobe can generate photogenerated carriers. The photogenerated carriers accelerate under the action of the terahertz continuous wave to form a photocurrent. The generated photocurrent is transmitted to the current amplifier 408 through the circuit. The current amplifier amplifies the current signal with a certain bandwidth and converts it into a voltage signal. Then, it is transmitted to the lock-in amplifier 409 through the circuit for signal extraction and noise filtering. Finally, the acquired near-field terahertz signal is processed by the host computer. The host computer can directly extract the time domain signal and observe the peak-to-peak value change trend of the electric field to obtain time domain information. The amplitude, intensity, phase and other information of the spectrum can be obtained by performing a fast Fourier transform on the time domain signal to obtain the spectral signal of the sample under test.

[0072] According to embodiments of this disclosure, the relative position and spacing between the optical guide microprobe and the sample support plate can be precisely controlled through microscopic observation and adjustment of a three-dimensional displacement stage, ensuring accurate measurement of terahertz waves in the near-field region of a specific location on the sample under test. The entire temperature-controlled sample support module is an open design, without sealed cavities or vacuum vents, and can be used directly in ambient air.

[0073] According to embodiments of this disclosure, by using an optically guided microprobe, high detection sensitivity and spatial resolution can be achieved. The specific tip size of the microprobe determines the detection area, which can be as small as sub-micrometers, breaking through the terahertz wavelength limitation. Furthermore, the microprobe tip does not contact the sample, thus avoiding mechanical damage or dielectric disturbance. In terahertz near-field spectroscopy and imaging, the optically guided microprobe can simultaneously acquire micrometer-scale spatial images, femtosecond time-resolved spectra, and phase information, providing a precise and real-time measurement method for measuring the terahertz spectral signals of the sample under test.

[0074] Figure 4 A flowchart illustrating a terahertz near-field spectral signal measurement method according to an embodiment of the present disclosure is shown schematically.

[0075] like Figure 4 As shown, the terahertz near-field spectral signal measurement system method of this embodiment includes operations S410 to S430.

[0076] In operation S410, the sample to be tested is supported by a sample carrier plate, and the temperature of the near-field region of the sample to be tested is reduced to below a preset temperature.

[0077] When operating the S420, the transmitter module is used to emit probe light pulses and terahertz waves, and guide the terahertz waves through the sample to be tested.

[0078] In operation of S430, within the near-field region of the sample to be tested, the photoconductive microprobe module receives the terahertz wave passing through the sample under the action of the probe light pulse, thereby obtaining the terahertz spectral signal of the sample to be tested.

[0079] The following combination Figures 1 to 4 An example description is given of the process of measuring terahertz near-field spectral signals.

[0080] According to an embodiment of this disclosure, in operation S410, the sample can be placed in the center of the sample support plate. The recessed area, with a depth of 2.5 mm, can be laterally limited. Then, the flow rate controllable pumping device is started, and liquid nitrogen is vaporized in the hose to form cold nitrogen gas, which enters the serpentine cooling channel. The temperature sensor display unit provides real-time temperature feedback. After 30 seconds, the temperature of the near-field area of ​​the sample under test can be stabilized at 100 K. The pumping device can automatically reduce its speed to maintain thermal balance, so that the near-field area of ​​the sample under test is reduced to below the preset temperature and maintained.

[0081] Preferably, low-temperature nitrogen purging can be performed in a local area near the sample to form a stable low-temperature dry gas area around the sample, which can isolate external moisture interference.

[0082] When operating the S420, the fiber femtosecond laser outputs... , The laser pulse is split into two beams by a beam splitter and used as a pump pulse. The beam is then incident on a low-temperature GaAs terahertz transmitting antenna via an optical fiber delay line. The antenna radiates terahertz waves under square wave bias. The terahertz waves are collimated into a parallel beam by a terahertz lens and pass perpendicularly through the through hole in the center of the sample carrier plate.

[0083] While operating S430, another probe light pulse is focused by an optical fiber collimator, lens group, and mirror onto the tip of the optical guide microprobe; the tip is located 50° above the surface of the sample to be tested. μ In the near-field region within m, the terahertz wave and the probe light are collinearly coupled at the needle tip. Photogenerated carriers are driven by the terahertz field to form a transient current. The current is converted into a voltage signal by a current amplifier, and a lock-in amplifier performs phase-sensitive detection with the frequency of a square wave voltage source as a reference to suppress background noise. The host computer performs an FFT on the time-domain voltage waveform obtained by the delayed line scan to extract the amplitude and phase, thus obtaining the terahertz complex spectrum of that pixel. The motorized three-dimensional translation stage moves the sample under test in 2μm steps. Then, the steps S420–S430 can be repeated point by point on the sample under test to finally stitch together a spatially resolved terahertz near-field spectral image.

[0084] According to embodiments of this disclosure, program code for executing the computer programs provided in embodiments of this disclosure can be written in any combination of one or more programming languages. Specifically, these computational programs can be implemented using high-level procedural and / or object-oriented programming languages, and / or assembly / machine languages. Programming languages ​​include, but are not limited to, languages ​​such as Java, C++, Python, "C", or similar programming languages. The program code can execute entirely on a user's computing device, partially on a user's device, partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0085] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions. Those skilled in the art will understand that the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways, even if such combinations are not explicitly described in the present disclosure. In particular, the features described in the various embodiments of this disclosure may be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0086] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A terahertz near-field spectral signal measurement system, characterized in that, include: A sample carrier plate is provided with through holes and cooling channels. The sample to be tested is placed in the through holes, and the cooling channels are used for the flow of cooling medium. The emission source module is used to emit probe light pulses and terahertz waves, and guide the terahertz waves through the through-hole to pass through the sample under test; as well as The optical guide microprobe module is configured to be placed in the near-field region of the sample to be tested; Wherein, when the cooling medium flows through the cooling channel to make the temperature of the near-field region lower than the preset temperature, the photoguide microprobe module is configured to receive the terahertz wave passing through the sample under the action of the probe light pulse, and obtain the terahertz spectral signal of the sample.

2. The terahertz near-field spectral signal measurement system according to claim 1, characterized in that, It also includes a cooling unit; The cooling units are respectively connected to the ports at both ends of the cooling channel; The cooling unit is configured to transfer cooling medium from a port at one end of the cooling channel to a port at the other end of the cooling channel.

3. The terahertz near-field spectral signal measurement system according to claim 2, characterized in that: The cooling medium includes nitrogen; The cooling unit includes a liquid nitrogen storage device and an air extraction device, wherein; The outlet of the liquid nitrogen storage device is connected to one end of the cooling channel, and the inlet of the air extraction device is connected to the other end of the cooling channel. The air extraction device is configured to allow the vaporized liquid nitrogen to flow through the cooling channel in order to reduce the temperature of the near-field region.

4. The terahertz near-field spectral signal measurement system according to claim 2, characterized in that, Also includes: A temperature sensor, mounted on the sample carrier plate, is used to detect the temperature of the near-field region, so that the emission source module and the photoguide microprobe module are activated when the temperature of the near-field region is lower than a preset temperature.

5. The terahertz near-field spectral signal measurement system according to claim 1, characterized in that: The transmitter module includes: The laser source unit is used to generate pump light pulses and probe light pulses; A terahertz emission unit is used to generate terahertz waves by being excited by the pump light pulse, and to guide the terahertz waves through the through-hole to pass through the sample under test.

6. The terahertz near-field spectral signal measurement system according to claim 5, characterized in that: The laser source unit includes a fiber femtosecond laser and a beam splitter, wherein the beam splitter is used to split the pulsed laser emitted by the fiber femtosecond laser into the pump light pulse and the probe light pulse.

7. The terahertz near-field spectral signal measurement system according to claim 5, characterized in that, The terahertz transmitting unit includes: a terahertz transmitting antenna, a voltage source, and a terahertz lens, wherein... The pump light pulse irradiates the irradiation area in the terahertz transmitting antenna, generating a first photogenerated carrier. The first photogenerated carrier radiates a terahertz wave under the bias voltage of the voltage source. The terahertz lens is used to collimate the terahertz wave radiated by the terahertz transmitting antenna and guide the terahertz wave through the through-hole into the sample under test.

8. The terahertz near-field spectral signal measurement system according to claim 7, characterized in that: The terahertz transmitting unit also includes an optical fiber delay line, which is used to delay the pump light pulse to change the optical path length of the pump light pulse relative to the probe light pulse.

9. The terahertz near-field spectral signal measurement system according to claim 1, characterized in that, It also includes the host computer; The optical guide microprobe module includes: a microprobe and a current amplifier; The probe light pulse irradiates the irradiated area in the micro probe, generating a second photogenerated carrier; the terahertz wave passing through the sample under test causes the second photogenerated carrier to move in a directional manner, generating a target photocurrent signal; The current amplifier converts the target photocurrent signal into a voltage signal and amplifies it to obtain the target voltage signal; The host computer is configured to obtain the terahertz spectral signal of the sample under test based on the target voltage signal.

10. A method for measuring terahertz near-field spectral signals, applied to the measurement system according to any one of claims 1 to 9, characterized in that, The measurement method includes: The sample to be tested is supported by a sample carrier plate, and the temperature of the near-field region of the sample to be tested is reduced to below a preset temperature. Using a source module, probe light pulses and terahertz waves are emitted, and the terahertz waves are guided through the sample to be tested. In the near-field region of the sample to be tested, the photoconductive microprobe module receives the terahertz wave passing through the sample under the action of the probe light pulse, thereby obtaining the terahertz spectral signal of the sample to be tested.

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