A terahertz wave band substance dielectric property measurement system and method

Abstract

The application discloses a terahertz waveband substance dielectric property measuring system and method, and relates to the technical field of terahertz waveband substance detection. The system comprises a laser frequency doubling unit, an optical parametric oscillator, an ultra-wideband terahertz difference frequency generating crystal, a transmission type test platform, a terahertz intensity detection device and a spectral data acquisition and processing device. The laser frequency doubling unit is used for emitting laser with a preset wavelength. The optical parametric oscillator is used for controllably outputting double-wavelength difference frequency pumping light. The ultra-wideband terahertz difference frequency generating crystal is used for outputting difference frequency terahertz waves. The transmission type test platform is used for carrying test samples with different preset thicknesses Li. The spectral data acquisition and processing device is internally provided with a spectral intensity determination model of the test sample, a dielectric property real part determination model, a dielectric property imaginary part determination model and a dielectric property determination model. The spectral data acquisition and processing device is electrically connected with the terahertz intensity detection device and the optical parametric oscillator.

Description

Technical Field

[0001] This invention relates to the field of terahertz band material detection technology, and in particular to a system and method for measuring the dielectric properties of terahertz band materials. Background Technology

[0002] Terahertz (THz) waves lie between microwaves and optical wavelengths in the electromagnetic spectrum, at the intersection of electronics and optics. They possess characteristics such as water sensitivity, characteristic macromolecular vibrational-rotational energy level fingerprints, low photon energy, and high transmittance to polar materials. Based on these characteristics, THz waves hold significant promise for applications in material identification, medical diagnostics, and non-destructive testing. However, due to limitations in THz wave generation methods, research on the properties of materials across the entire THz band has been very limited, leaving the spectral characteristics of materials in this band largely unexplored. Currently, THz time-domain spectroscopy (THz-TDS) and far-infrared Fourier transform spectrometry (FT-IR) are primarily used to obtain the dielectric properties of materials in the terahertz band, including refractive index and absorption coefficient. However, THz-TDS is limited by the material properties of the transmitting antenna, with an effective spectral range typically between 0.5 and 2.5 THz, resulting in limited information on the spectral characteristics of materials that can be characterized. FT-IR offers a wider effective spectral range, but the overall system size is generally large and the structure is complex. It requires liquid helium-cooled detectors for measurement, resulting in high costs and long measurement times. Using nanosecond pulse pumping, and based on novel organic crystals, an ultrawideband tunable quasi-monochromatic polarized THz wave output within the 0.1-20 THz range can be achieved through nonlinear optical processes. This allows for incoherent direct measurement of the THz spectral information of materials; such systems are called THz frequency domain spectroscopy systems (THz-FDS). This approach offers advantages such as simple process, room temperature operation, wide effective spectral range, and low cost. However, directly using incoherent measurement techniques only obtains the intensity information of the material's spectrum, making it difficult to separately obtain the dielectric properties of the material, such as refractive index and absorption coefficient.

[0003] Currently, there is no method for measuring the dielectric properties of materials in the ultra-wideband THz band using an ultra-wideband tunable transmission THz-FDS system employing incoherent direct measurement techniques. Summary of the Invention

[0004] The purpose of this invention is to provide a terahertz band dielectric property measurement system and method, filling the gap in the measurement of ultra-wideband THz band dielectric properties of materials using an ultra-wideband coordinateable transmission THz-FDS system employing incoherent direct measurement technology.

[0005] Firstly, to achieve the above objectives, the present invention provides a measurement system for the dielectric properties of materials in the terahertz band, comprising a laser frequency doubling unit, an optical parametric oscillator, an ultra-wideband terahertz difference frequency generating crystal, a transmission-type testing platform, a terahertz intensity detection device, and a spectral data acquisition and processing device. The laser frequency doubling unit emits a laser with a preset wavelength. The optical parametric oscillator selects a laser with a preset wavelength and controllably outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal, upon receiving the dual-wavelength difference frequency pump light, outputs a difference frequency terahertz wave. The transmission-type platform carries multiple test samples with different preset thicknesses Li, where i is the number of test samples, 1 ≤ i ≤ N; the difference frequency terahertz wave is emitted after passing through the test samples. When the test sample is mounted on a transmission-type testing platform, the terahertz intensity detection device measures the spectral intensity of the difference-frequency terahertz wave emitted from the test sample, defined as the transmission spectral intensity. When the transmission-type testing platform is not mounted on the test sample, the terahertz intensity detection device also measures the spectral intensity of the difference-frequency terahertz wave emitted from the transmission-type testing platform, defined as the background spectral intensity. The spectral data acquisition and processing device is equipped with a spectral intensity determination model, a dielectric property real part determination model, a dielectric property imaginary part determination model, and a dielectric property determination model for the test sample. The spectral intensity determination model includes the transmission spectral intensity, the background spectral intensity, and a preset thickness Li of the test sample. The spectral data acquisition and processing device is electrically connected to both the terahertz intensity detection device and the optical parametric oscillator. The spectral data acquisition and processing device is used to acquire the transmission spectral intensity and the background spectral intensity obtained from the terahertz intensity detection device; it also controls the optical parametric oscillator to adjust the output of the dual-wavelength difference-frequency pump light.

[0006] In practical applications, multiple test samples with a preset thickness Li can be prefabricated. The test samples can be labeled as L1, L2, L3, L4, etc. according to their thickness from smallest to largest. The test thickness Li of the test samples can be configured into the spectral intensity determination model.

[0007] Before measuring the dielectric properties of multiple test samples with different preset thicknesses of Li at different frequencies in the terahertz band using the terahertz band dielectric property measurement system provided by this invention, the dual-wavelength difference-frequency pump light output by the optical parametric oscillator can be calibrated first. This involves adjusting the phase matching conditions of the output dual-wavelength difference-frequency pump light by adjusting the optical parametric oscillator. The calibrated dual-wavelength difference-frequency pump light is then emitted to an ultra-wideband terahertz difference-frequency generating crystal, thereby outputting a difference-frequency terahertz wave. Further, the difference-frequency terahertz wave penetrates the transmission-type test platform. It should be understood that at this time, the transmission-type test platform does not contain multiple test samples with different preset thicknesses of Li. Under the control of the spectral data acquisition and processing device, the terahertz intensity detection device directly measures the spectral intensity output from the transmission-type test platform. For distinction, this spectral intensity can be defined as the background spectral intensity. If the measured background spectral intensity does not meet the preset spectral intensity, it can be adjusted by adjusting the optical parametric oscillator until the background spectral intensity meets the preset spectral intensity range.

[0008] When measuring the dielectric properties of multiple test samples with different preset thicknesses of Li at different frequencies in the terahertz band using the terahertz band dielectric property measurement system provided by this invention, multiple test samples with different preset thicknesses of Li can be sequentially mounted on a transmission-type test platform. It should be understood that the test samples should be capable of transmitting terahertz waves. Based on this, the laser frequency doubling unit emits a laser with a preset wavelength, and the calibrated optical parametric oscillator selects the laser with the preset wavelength and outputs a dual-wavelength difference-frequency pump light. The dual-wavelength difference-frequency pump light is then processed by an ultra-wideband terahertz difference-frequency generation crystal to output a difference-frequency terahertz wave. Further, the difference-frequency terahertz wave is emitted from the test sample. At this time, under the control of the spectral data acquisition and processing device, the terahertz intensity detection device directly measures the spectral intensity output from the test sample. For distinction, the above spectral intensity can be defined as the transmission spectral intensity.

[0009] After the terahertz intensity detection device acquires the background spectral intensity and the transmission spectral intensity, these intensities are sent to the spectral data acquisition and processing device. At this point, the spectral intensity determination model, based on the background spectral intensity, the transmission spectral intensity, and the preset thickness Li of the test sample, can fit the material refractive index and the material absorption coefficient of the test sample. Furthermore, the dielectric property real part determination model and the dielectric property imaginary part determination model determine the real and imaginary parts of the dielectric property based on the material refractive index and the material absorption coefficient. Finally, the dielectric property determination model, based on the real and imaginary parts of the dielectric property, determines the dielectric properties of test samples with different preset thicknesses Li at a specific frequency in the terahertz band.

[0010] As can be seen from the above application process, by using the terahertz band material dielectric property measurement system provided by the present invention, the transmission spectral intensity of test samples with different preset thicknesses Li at each frequency point in the ultra-wideband THz frequency range can be obtained through experiments, adding the thickness information dimension of the test sample, effectively avoiding the limitation of limited information in incoherent measurement methods.

[0011] Furthermore, by comprehensively considering the Fresnel loss and absorption loss of the test sample end face, the refractive index and absorption coefficient of the test sample are obtained by fitting calculation, and finally the dielectric properties of each frequency point in the ultra-wideband THz frequency range are obtained. A method for obtaining the dielectric properties of samples in the ultra-wideband THz band based on a novel ultra-wideband tunable THz radiation source and incoherent intensity measurement method is established, filling the gap in spectral data of the THz band, especially the high-frequency THz band.

[0012] As one possible implementation, the spectral intensity determination model is as follows:

[0013]

[0014] Among them, T i This represents the transmission spectral intensity of test samples with different preset thicknesses, which is obtained by the terahertz intensity detection device. T 0 T represents the non-background spectral intensity. noise Indicates the noise intensity of the terahertz intensity detection device; n 0 L represents the refractive index of air or the refractive index of the end face material of the transparent container used to hold the test sample. i n represents the thickness of the test sample. m α represents the refractive index of the test sample material. m This represents the absorption coefficient of the test sample material;

[0015] In T i T 0 T noise n 0 and L i With all parameters determined, the refractive index n of the test sample material is obtained by fitting. m and the absorption coefficient α of the test sample material. m .

[0016] As one possible implementation, the model for determining the real part of the dielectric property is as follows:

[0017]

[0018] The model for determining the imaginary part of dielectric properties is as follows:

[0019]

[0020] The dielectric property determination model is as follows:

[0021]

[0022] in, For terahertz wavelength, For weights.

[0023] As one possible implementation, the laser frequency doubling unit includes a laser, a half-wave plate, and a frequency doubling crystal. The laser emits laser light with an initial wavelength λ0. The half-wave plate, upon receiving laser light from the laser, adjusts the polarization state of the laser. The frequency doubling crystal, upon receiving laser light from the half-wave plate, adjusts the initial wavelength λ0 of the laser to a preset wavelength λ1, where λ0 > λ1.

[0024] Using the above technical solution, a half-wave plate is used to control the energy of the laser emitted by the laser, thereby maximizing the energy of the laser output through the frequency doubling crystal. Based on this, when the optical parametric oscillator receives a high-energy laser from the frequency doubling crystal, the energy of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator can be increased, ultimately resulting in a high-energy difference-frequency terahertz wave output by the ultra-wideband terahertz difference-frequency generating crystal.

[0025] As one possible implementation, the optical parametric oscillator includes a cavity, a first mirror, a second mirror, a first KTP parametric crystal, a second KTP parametric crystal, and a rotating platform. The first mirror is located at the front end of the cavity, and the second mirror, opposite the first mirror, is located at the rear end of the cavity. Laser light with a preset wavelength enters the cavity and oscillates back and forth under the reflection of the first and second mirrors. The first and second KTP parametric crystals are spaced apart between the two mirrors, with the length of the first KTP crystal being shorter than the length of the second KTP crystal. Dual-wavelength difference-frequency pump light is generated based on the first and second KTP parametric crystals. The rotating platform carries the first KTP parametric crystal and is electrically connected to a spectral data acquisition and processing device. The spectral data acquisition and processing device controls the rotation of the rotating platform, changing the wavelength of the dual-wavelength difference-frequency pump light generated by the first and second KTP parametric crystals by altering the phase-matching conditions of the first KTP parametric crystal.

[0026] When using the above technical solution, the optical parametric oscillator selects a preset wavelength of λ. 1 Furthermore, the laser beam is oriented in the same direction; that is, the optical parametric oscillator will produce a beam with a wavelength not equal to the preset wavelength λ. 1The laser light is filtered out; the laser light entering the optical parametric oscillator oscillates in the reciprocating reflection of the first and second mirrors, thereby increasing the laser energy. Based on this, a dual-wavelength difference-frequency pump light is generated using a first and second KTP parametric crystal of unequal lengths, based on the high-energy laser light. More importantly, the rotation platform can be controlled by a spectral data acquisition and processing device (which includes parameters to be calibrated for the optical parametric oscillator, such as the output frequency or wavelength of the dual-wavelength difference-frequency pump light), thereby controlling the rotation of the first KTP parametric crystal by a certain angle until the wavelength of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator matches the wavelength set in the spectral data acquisition and processing device. In summary, the wavelength of the dual-wavelength difference-frequency pump light to be calibrated can be determined based on the thickness of the test sample, and then the first KTP parametric crystal can be rotated by the rotation platform to match the wavelength of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator with the wavelength set in the spectral data acquisition and processing device. Based on this, the terahertz band dielectric property measurement device provided by the present invention has good applicability.

[0027] As one possible implementation, the measurement system also includes a beam splitter positioned between the laser frequency doubling unit and the optical parametric oscillator to select laser light with a preset wavelength for delivery into the optical parametric oscillator.

[0028] Using the above technical solution, a beam splitter can be used to split a beam with an initial wavelength λ. 0 The laser light is filtered out, while the light with a preset wavelength λ is filtered out. 1 The laser is delivered to the optical parametric oscillator. Based on this, while ensuring that the wavelength of the laser input to the optical parametric oscillator meets the requirements, the wavelength of the dual-wavelength difference frequency pump light output from the optical parametric oscillator also meets the requirements.

[0029] As one possible implementation, the measurement system also includes a parabolic mirror terahertz beam shaping device, which is set between the ultra-wideband terahertz difference frequency generating crystal and the transmission test platform, and is used to shape the difference frequency terahertz wave emitted by the ultra-wideband terahertz difference frequency generating crystal and having a large divergence angle.

[0030] With the above technical solution, in practical applications, the parabolic mirror terahertz beam shaping device can be used to shape the terahertz waves with a large divergence angle emitted from the ultra-wideband terahertz difference frequency generating crystal, so as to effectively reduce the risk of energy loss of terahertz waves due to divergence.

[0031] As one possible implementation, the initial wavelength λ0 = 1064 nm and the preset wavelength λ1 = 532 nm.

[0032] Secondly, the present invention also provides a method for measuring the dielectric properties of materials in the terahertz band, comprising the following steps:

[0033] A terahertz band dielectric property measurement system is constructed, wherein the terahertz band dielectric property measurement system is the terahertz band dielectric property measurement system disclosed in the first aspect and / or any possible implementation of the first aspect.

[0034] Prepare test samples, the number of test samples is i, 1≤i≤N, and each test sample has a different preset thickness Li;

[0035] Calibrate the optical parametric oscillator and control the frequency of the dual-wavelength difference-frequency pump light emitted by the optical parametric oscillator to meet the preset frequency or preset wavelength; calibrate the frequency or wavelength of the difference-frequency terahertz wave based on the preset frequency or preset wavelength of the dual-wavelength difference-frequency pump light and using a spectral data acquisition and processing device.

[0036] When the transmission test platform is not carrying the test sample, the terahertz band dielectric property measurement system is activated. At this time, the laser frequency doubling unit emits a laser with a preset wavelength. After receiving the laser, the optical parametric oscillator outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal outputs a difference frequency terahertz wave based on the dual-wavelength difference frequency pump light. The difference frequency terahertz wave penetrates the transmission platform and is emitted. The terahertz intensity detection device measures the spectral intensity of the emitted difference frequency terahertz wave under the control of the spectral data acquisition and processing device, which is defined as the background spectral intensity.

[0037] With the test sample supported on the transmission test platform, the terahertz dielectric property measurement system is activated. At this time, the laser frequency doubling unit emits a laser with a preset wavelength. After receiving the laser, the optical parametric oscillator outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal outputs a difference frequency terahertz wave based on the dual-wavelength difference frequency pump light. After the difference frequency terahertz wave penetrates the test sample, it is emitted. The terahertz intensity detection device measures the spectral intensity of the emitted difference frequency terahertz wave under the control of the spectral data acquisition and processing device, which is defined as the transmission spectral intensity.

[0038] The terahertz intensity detection device sends the background spectral intensity and the transmission spectral intensity to the spectral data acquisition and processing device, and finally determines the dielectric properties of the test sample at each frequency point in the difference frequency terahertz band based on the spectral intensity determination model, the dielectric property real part determination model, the dielectric property imaginary part determination model, and the dielectric property determination model.

[0039] As one possible implementation, the spectral intensity determination model is as follows:

[0040]

[0041] Among them, T iThis represents the transmission spectral intensity of test samples with different preset thicknesses. The transmission spectral intensity is obtained by a terahertz intensity detection device. (T) 0 T represents the non-background spectral intensity. noise Indicates the noise intensity of the terahertz intensity detection device; n 0 L represents the refractive index of air or the refractive index of the end face material of a transparent container used to hold test samples. i n represents the thickness of the test sample. m α represents the refractive index of the test sample material. m Indicates the absorption coefficient of the test sample material;

[0042] In T i T 0 T noise n 0 and L i With all parameters fixed, the refractive index n of the test sample material is obtained by fitting. m And the absorption coefficient α of the test sample material. m ; and / or,

[0043] The model for determining the real part of dielectric properties is as follows:

[0044]

[0045] The model for determining the imaginary part of dielectric properties is as follows:

[0046]

[0047] The dielectric property determination model is as follows:

[0048]

[0049] in, For terahertz wavelength, For weights.

[0050] The beneficial effects of the terahertz band material dielectric property measurement method provided by the present invention are the same as those of the terahertz band material dielectric property measurement system provided by the first aspect and / or any implementation of the first aspect of the present invention, and will not be repeated here. Attached Figure Description

[0051] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0052] Figure 1 A schematic diagram of the structure of the terahertz band material dielectric property measurement system provided in an embodiment of the present invention;

[0053] Figure 2 A flowchart of a method for measuring the dielectric properties of materials in the terahertz band provided in an embodiment of the present invention.

[0054] Figure label:

[0055] 1-Laser frequency doubling unit, 2-Optical parametric oscillator, 3-Ultra-wideband terahertz difference frequency generation crystal,

[0056] 4- Transmission-type testing platform; 5- Terahertz intensity detection device; 6- Spectral data acquisition and processing device.

[0057] 7-Beam splitter, 8-Parametric mirror terahertz beam shaping device.

[0058] 9-Computer;

[0059] 10 - Laser, 11 - Half-wave plate, 12 - Frequency doubling crystal,

[0060] 20 - Cavity, 21 - First reflecting mirror, 22 - Second reflecting mirror

[0061] 23-First KTP parametric crystal, 24-Second KTP parametric crystal, 25-Rotating platform. Detailed Implementation

[0062] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0063] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0064] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0065] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0066] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0067] See Figure 1 The terahertz band dielectric property measurement system provided in this embodiment of the invention includes a laser frequency doubling unit, an optical parametric oscillator, an ultra-wideband terahertz difference frequency generating crystal, a transmission-type testing platform, a terahertz intensity detection device, and a spectral data acquisition and processing device. The laser frequency doubling unit emits a laser with a preset wavelength. The optical parametric oscillator selects a laser with a preset wavelength and controllably outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal, upon receiving the dual-wavelength difference frequency pump light, outputs a difference frequency terahertz wave. The transmission-type platform carries multiple test samples with different preset thicknesses Li, where i is the number of test samples, 1 ≤ i ≤ N; the difference frequency terahertz wave is emitted after passing through the test samples. When the test sample is mounted on a transmission-type test platform, the terahertz intensity detection device measures the spectral intensity of the difference-frequency terahertz wave emitted from the test sample, defined as the transmission spectral intensity. When the transmission-type test platform is not mounted on the test sample, the terahertz intensity detection device also measures the spectral intensity of the difference-frequency terahertz wave emitted from the transmission-type test platform, defined as the background spectral intensity. The spectral data acquisition and processing device is equipped with a spectral intensity determination model, a dielectric property real part determination model, a dielectric property imaginary part determination model, and a dielectric property determination model for the test sample. The spectral intensity determination model includes the transmission spectral intensity, the background spectral intensity, and a preset thickness Li of the test sample. The spectral data acquisition and processing device is electrically connected to both the terahertz intensity detection device and the optical parametric oscillator. The spectral data acquisition and processing device controls the terahertz intensity detection device to acquire and receive the transmission and background spectral intensities; it also controls the optical parametric oscillator to adjust the output of the dual-wavelength difference-frequency pump light.

[0068] In practical applications, multiple test samples with a preset thickness Li can be prefabricated. The test samples can be labeled as L1, L2, L3, L4, etc. according to their thickness from smallest to largest. The test thickness Li of the test samples can be configured into the spectral intensity determination model.

[0069] Before measuring the dielectric properties of multiple test samples with different preset Li thicknesses at different frequencies in the terahertz band using the terahertz band dielectric property measurement system provided by this invention, the dual-wavelength difference-frequency pump light output by the optical parametric oscillator can be calibrated first. This involves adjusting the wavelength and frequency of the output dual-wavelength difference-frequency pump light by adjusting the optical parametric oscillator. The calibrated dual-wavelength difference-frequency pump light is then emitted to an ultra-wideband terahertz difference-frequency generating crystal, thereby outputting a difference-frequency terahertz wave. Further, the difference-frequency terahertz wave penetrates the transmission-type testing platform. It should be understood that at this time, the transmission-type testing platform does not contain multiple test samples with different preset Li thicknesses. The spectral data acquisition and processing device acquires the spectral intensity output from the transmission-type testing platform, directly measured by the terahertz intensity detection device. For differentiation, this spectral intensity can be defined as the background spectral intensity. If the measured background spectral intensity does not meet the preset spectral intensity, it can be adjusted by adjusting the optical parametric oscillator until the background spectral intensity meets the preset spectral intensity range.

[0070] When measuring the dielectric properties of multiple test samples with different preset thicknesses of Li at different frequencies in the terahertz band using the terahertz band dielectric property measurement system provided by this invention, multiple test samples with different preset thicknesses of Li can be sequentially (it should be understood that sequentially refers to replacing one test sample with another after the previous test is completed) placed on a transmission-type test platform. It should be understood that the test samples should be capable of transmitting terahertz waves. Based on this, the laser frequency doubling unit emits a laser with a preset wavelength, and the calibrated optical parametric oscillator selects the laser with the preset wavelength and outputs a dual-wavelength difference-frequency pump light. The dual-wavelength difference-frequency pump light is then processed by an ultra-wideband terahertz difference-frequency generation crystal to output a difference-frequency terahertz wave. Further, the difference-frequency terahertz wave is emitted from the test sample. At this time, the spectral data acquisition and processing device acquires the spectral intensity output from the test sample, which is directly measured by the terahertz intensity detection device. For distinction, the above spectral intensity can be defined as the transmission spectral intensity.

[0071] After the terahertz intensity detection device acquires the background spectral intensity and the transmission spectral intensity, these intensities are sent to the spectral data acquisition and processing device. At this point, the spectral intensity determination model, based on the background spectral intensity, the transmission spectral intensity, and the preset thickness Li of the test sample, can fit the material refractive index and the material absorption coefficient of the test sample. Furthermore, the dielectric property real part determination model and the dielectric property imaginary part determination model determine the real and imaginary parts of the dielectric property based on the material refractive index and the material absorption coefficient. Finally, the dielectric property determination model, based on the real and imaginary parts of the dielectric property, determines the dielectric properties of test samples with different preset thicknesses Li at a specific frequency in the terahertz band.

[0072] As can be seen from the above application process, using the terahertz band dielectric property measurement system provided by this invention, the transmission spectral intensity of test samples with different preset thicknesses Li at various frequency points in the ultra-wideband THz frequency range can be obtained experimentally. Adding the thickness information dimension of the test sample effectively avoids the limitation of limited information in incoherent measurement methods. In other words, by adding the thickness information dimension of the test sample, the real and imaginary parts of the test sample can be calculated using both the real part determination model and the imaginary part determination model. Based on this, the dielectric properties of the test sample are then determined from the real and imaginary parts. This effectively improves the accuracy of the measurement results. Furthermore, although the embodiments of this invention utilize laser (coherent light) as the incident light, since only spectral intensity is measured, it is actually an incoherent measurement device. Compared with coherent measurement devices, it is more convenient, and compared with traditional incoherent devices, the measurement accuracy is higher.

[0073] Furthermore, by comprehensively considering the Fresnel loss and absorption loss of the test sample end face, the refractive index and absorption coefficient of the test sample are obtained by fitting calculation, and finally the dielectric properties of each frequency point in the ultra-wideband THz frequency range are obtained. A method for obtaining the dielectric properties of samples in the ultra-wideband THz band based on a novel ultra-wideband tunable THz radiation source and incoherent intensity measurement method is established, filling the gap in spectral data of the THz band, especially the high-frequency THz band.

[0074] As one possible implementation, the aforementioned laser frequency doubling unit may include a laser, a half-wave plate, and a frequency doubling crystal. The laser emits laser light with an initial wavelength λ0. The half-wave plate, upon receiving laser light from the laser, adjusts the polarization state of the laser. The frequency doubling crystal, upon receiving laser light from the half-wave plate, adjusts the initial wavelength λ0 of the laser to a preset wavelength λ1, where λ0 > λ1.

[0075] As an example, the aforementioned laser could be a high-energy pulsed 1064 laser, such as a high-energy pulsed Nd:YAG laser, which employs electro-optic modulation to output a single pulse energy of 200 mJ, a pulse width of 10 ns, a repetition frequency of 10 Hz, a laser spot diameter of 5 mm, and an initial wavelength λ. 0 The wavelength is 1064nm. The aforementioned frequency doubling crystal can be a KTP frequency doubling crystal. After the polarization state of the 1064nm laser is adjusted by a half-wave plate, it enters the KTP frequency doubling crystal. After the 1064nm laser enters the KTP frequency doubling crystal, it generates high-energy 532nm green light for subsequent pumping. In the example, the pump energy of the 1064nm laser and the half-wave plate can be adjusted to control the energy of the 532nm green light, ensuring the energy (signal strength) of the subsequent difference frequency output ultra-wideband terahertz wave.

[0076] Using the above technical solution, a half-wave plate is used to control the energy of the laser emitted by the laser, thereby maximizing the energy of the laser output through the frequency doubling crystal. Based on this, when the optical parametric oscillator receives a high-energy laser from the frequency doubling crystal, the energy of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator can be increased, ultimately resulting in a high-energy difference-frequency terahertz wave output by the ultra-wideband terahertz difference-frequency generating crystal.

[0077] As an example, a beam splitter can be placed between the laser frequency doubling unit and the optical parametric oscillator (OPO). The 532nm green light emitted from the KTP frequency doubling crystal passes through the beam splitter and enters the OPO. The beam splitter filters out the remaining 1064nm laser light. This effectively avoids the 1064nm laser light from damaging the OPO, and further, it effectively avoids the risk of damage to the KTP crystal caused by the 1064nm laser light entering the OPO. Moreover, it effectively reduces the interference of the 1064nm laser light with the 532nm green light.

[0078] As one possible implementation, the optical parametric oscillator includes a cavity, a first mirror, a second mirror, a first KTP parametric crystal, a second KTP parametric crystal, and a rotating platform. The first mirror is located at the front end of the cavity, and the second mirror, opposite the first mirror, is located at the rear end of the cavity. Laser light with a preset wavelength enters the cavity and oscillates back and forth under the reflection of the first and second mirrors. The first and second KTP parametric crystals are spaced apart between the two mirrors, with the length of the first KTP crystal being shorter than the length of the second KTP crystal. The first and second KTP parametric crystals each generate dual-wavelength difference-frequency pump light. The rotating platform carries the first KTP parametric crystal and is electrically connected to a spectral data acquisition and processing device. The spectral data acquisition and processing device controls the rotation of the rotating platform, changing the wavelength of the dual-wavelength difference-frequency pump light generated by the first KTP parametric crystal by altering its phase.

[0079] When using the above technical solution, the optical parametric oscillator selects a preset wavelength of λ. 1 Furthermore, the laser beam is oriented in the same direction; that is, the optical parametric oscillator will produce a beam with a wavelength not equal to the preset wavelength λ. 1 The laser light is filtered out; the laser light entering the optical parametric oscillator oscillates in the reciprocating reflection of the first and second mirrors, thereby increasing the laser energy. Based on this, a dual-wavelength difference-frequency pump light is generated using a first and second KTP parametric crystal of unequal lengths, based on the high-energy laser light. More importantly, the rotation platform can be controlled by a spectral data acquisition and processing device (which includes parameters to be calibrated for the optical parametric oscillator, such as the output frequency or wavelength of the dual-wavelength difference-frequency pump light), thereby controlling the rotation of the first KTP parametric crystal by a certain angle until the wavelength of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator matches the wavelength set in the spectral data acquisition and processing device. In summary, the wavelength of the dual-wavelength difference-frequency pump light to be calibrated can be determined based on the thickness of the test sample, and then the first KTP parametric crystal can be rotated by the rotation platform to match the wavelength of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator with the wavelength set in the spectral data acquisition and processing device. Based on this, the terahertz band dielectric property measurement device provided by the present invention has good applicability.

[0080] As an example, after 532nm green light enters the optical parametric oscillator, a first KTP parametric crystal and a second KTP parametric crystal are placed one after the other inside the cavity. The two crystals generate dual-wavelength difference-frequency pump light, with the second crystal achieving wavelength tuning through rotation. Specifically, the rotating platform directly controls the rotation angle of the first KTP parametric crystal inside the cavity. By changing the phase-matching angle of the first KTP parametric crystal, the output wavelength is tuned, achieving rapid frequency sweep control of the wavelength interval of the dual-wavelength difference-frequency pump light.

[0081] As an example, the chamfers of both the first and second KTP parametric crystals satisfy the phase matching condition for generating 1.3-1.5μm idler light using 532nm pumping. The first KTP parametric crystal is selected with a length of 15mm, and the second KTP parametric crystal with a length of 30mm, to ensure that the energy of the dual-wavelength difference-frequency pump light output by the optical parametric oscillator is close under strong pumping conditions.

[0082] As an example, the ultra-wideband terahertz difference frequency generation crystal is a novel high-performance organic nonlinear optical crystal represented by DAST crystal. It employs a type 0 phase-matching condition and selects a crystal thickness of less than 1 mm to avoid strong absorption of the generated terahertz wave. For example, it can include DAST, DSTMS, OH1, and OHI-T crystals. DAST crystal's full name is 4-(4-dimethylaminostyryl)methylpyridine p-toluenesulfonate; DSTMS crystal's full name is 4-(4-dimethylaminostyryl)methylpyridine 2,4,6-trimethylbenzenesulfonate; OH1 crystal's full name is 2-(3-(4-hydroxystyryl)-5,5-dimethylphenylhex-2-enyl)malonitrile; and OHI-T crystal uses 1,2-(4-hydroxystyryl)-3,3-trimethylindoline (OHI) as the cation group and p-methanesulfonate (T) as the anion group. The difference frequency output terahertz wave tuning range is 0.5~20THz.

[0083] As an example, the parabolic mirror terahertz beam shaping device selects a set of short-focal off-axis parabolic mirrors as the beam shaping device, which has the function of shaping the terahertz waves with a large divergence angle emitted from the ultra-wideband terahertz difference frequency generating crystal.

[0084] As an example, the transmission-type sample measurement platform uses white polyethylene or white polytetrafluoroethylene as the sample container and has the function of acquiring intensity information in the high signal-to-noise ratio ultra-wideband terahertz band.

[0085] As an example, the terahertz intensity detection device uses a liquid helium-cooled Bolometer (microbolometer) as the intensity detector to ensure the signal-to-noise ratio of the spectral measurement.

[0086] As an example, the spectral data acquisition and processing device uses LabVIEW as the data acquisition and processing system. It uses a computer to synchronously control a 1064nm laser frequency doubling unit, a rotating platform, and a terahertz intensity detection device to acquire spectral intensity data in the ultra-wideband terahertz range and fit the dielectric properties of the material in the entire terahertz band.

[0087] As an example, the test sample is a solid-state test sample. In this case, it is necessary to prepare solid-state test sample sheets with different preset Li thicknesses. The solid-state test sample must be internally homogeneous and without interfaces.

[0088] As a second example, the test sample is a liquid test sample. In this case, white polyethylene or white polytetrafluoroethylene is needed as the sample container to encapsulate the liquid test sample with different preset thicknesses of Li in the sample container to ensure that the inside is uniform and free of bubbles.

[0089] It should be understood that the absorption characteristics in the terahertz band must be considered for both solid and liquid test samples. If the test sample has significant absorption, the preset thickness Li must be strictly controlled to ensure the transmitted spectral intensity. If the sample absorption is not significant, a relatively thicker thickness can be selected to ensure the contrast of the transmitted spectral intensity signals for test samples of different thicknesses. During the experiment, the transmission sample measurement platform must maintain normal incidence conditions with the incident terahertz wave.

[0090] In practical applications, the preset thickness Li of each test sample is recorded, and they are placed sequentially on a transmission test platform to ensure that parameters such as the measurement spectral range, scan step size, and number of spectral measurements in the measurement system are the same as those in the background spectral data acquisition conditions. Using a terahertz intensity detection device and a data acquisition and processing system, the transmission spectral intensity at each frequency point of the measurement system is recorded. Given that the background spectral intensity, the aforementioned transmission spectral intensity, and the thickness of the test sample are all determined, the dielectric properties of the test sample at each test frequency point in the terahertz band can be finally obtained using the spectral intensity determination model, the real part determination model, the imaginary part determination model, and the dielectric property determination model configured in the spectral data acquisition and processing device.

[0091] Specifically, the model for determining spectral intensity is as follows:

[0092]

[0093] Among them, T i This represents the transmission spectral intensity of test samples with different preset thicknesses, which is obtained by the terahertz intensity detection device. T 0 T represents the non-background spectral intensity. noise Indicates the noise intensity of the terahertz intensity detection device; n 0L represents the refractive index of air or the refractive index of the end face material of the transparent container used to hold the test sample. i n represents the thickness of the test sample. m α represents the refractive index of the test sample material. m This represents the absorption coefficient of the test sample material;

[0094] In T i T 0 T noise n 0 and L i With all parameters determined, the refractive index n of the test sample material is obtained by fitting. m and the absorption coefficient α of the test sample material. m .

[0095] As one possible implementation, the model for determining the real part of the dielectric property is as follows:

[0096]

[0097] The model for determining the imaginary part of dielectric properties is as follows:

[0098]

[0099] The dielectric property determination model is as follows:

[0100]

[0101] in, For terahertz wavelength, For weights.

[0102] Secondly, see Figure 2 This invention also provides a method for measuring dielectric properties in the terahertz band, comprising the following steps:

[0103] S10. Construct a terahertz band dielectric property measurement system, wherein the terahertz band dielectric property measurement system is the terahertz band dielectric property measurement system disclosed in the first aspect and / or any possible implementation of the first aspect.

[0104] S11. Prepare test samples. The number of test samples is i, 1≤i≤N. Each test sample has a different preset thickness Li.

[0105] S12. Calibrate the optical parametric oscillator and control the frequency of the dual-wavelength difference-frequency pump light emitted by the optical parametric oscillator to meet the preset frequency or preset wavelength; calibrate the frequency or wavelength of the difference-frequency terahertz wave based on the preset frequency or preset wavelength of the dual-wavelength difference-frequency pump light and using a spectral data acquisition and processing device; for example, the preset frequency can be 0.1-25THz.

[0106] S13. When the transmission test platform is not carrying the test sample, start the terahertz band dielectric property measurement system. At this time, the laser frequency doubling unit emits a laser with a preset wavelength. After receiving the laser, the optical parametric oscillator outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal outputs a difference frequency terahertz wave based on the dual-wavelength difference frequency pump light. After the difference frequency terahertz wave penetrates the transmission platform, it is emitted. Under the control of the spectral data acquisition and processing device, the terahertz intensity detection device measures the spectral intensity of the emitted difference frequency terahertz wave, which is defined as the background spectral intensity.

[0107] S14. With the test sample supported on the transmission test platform, the terahertz band dielectric property measurement system is started. At this time, the laser frequency doubling unit emits a laser with a preset wavelength. After receiving the laser, the optical parametric oscillator outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal outputs a difference frequency terahertz wave based on the dual-wavelength difference frequency pump light. After the difference frequency terahertz wave penetrates the test sample, it is emitted. The terahertz intensity detection device measures the spectral intensity of the emitted difference frequency terahertz wave under the control of the spectral data acquisition and processing device, which is defined as the transmission spectral intensity.

[0108] S15 and the terahertz intensity detection device send the background spectral intensity and the transmission spectral intensity to the spectral data acquisition and processing device, respectively. Based on the spectral intensity determination model, the dielectric property real part determination model, the dielectric property imaginary part determination model, and the dielectric property determination model, the dielectric properties of the test sample at each frequency point in the difference frequency terahertz band are finally determined.

[0109] As one possible implementation, the spectral intensity determination model is as follows:

[0110]

[0111] Among them, T i This represents the transmission spectral intensity of test samples with different preset thicknesses. The transmission spectral intensity is obtained by a terahertz intensity detection device. (T) 0 T represents the non-background spectral intensity. noise Indicates the noise intensity of the terahertz intensity detection device; n 0 L represents the refractive index of air or the refractive index of the end face material of a transparent container used to hold test samples. i n represents the thickness of the test sample. m α represents the refractive index of the test sample material. m Indicates the absorption coefficient of the test sample material;

[0112] In T i T 0 T noise n 0 and Li With all parameters fixed, the refractive index n of the test sample material is obtained by fitting. m And the absorption coefficient α of the test sample material. m ; and / or,

[0113] The model for determining the real part of dielectric properties is as follows:

[0114]

[0115] The model for determining the imaginary part of dielectric properties is as follows:

[0116]

[0117] The dielectric property determination model is as follows:

[0118]

[0119] in, For terahertz wavelength, For weights.

[0120] The beneficial effects of the terahertz band material dielectric property measurement method provided by the present invention are the same as those of the terahertz band material dielectric property measurement system provided by the first aspect and / or any implementation of the first aspect of the present invention, and will not be repeated here.

[0121] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0122] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A terahertz band dielectric property measurement system, characterized in that, include: A laser frequency doubling unit, wherein the laser frequency doubling unit is used to emit laser light, the laser light having a preset wavelength; An optical parametric oscillator, wherein the optical parametric oscillator selects the laser with a preset wavelength and controllably outputs dual-wavelength difference frequency pump light; An ultra-wideband terahertz difference frequency generating crystal is used to output difference frequency terahertz waves when receiving the dual-wavelength difference frequency pump light. A transmission-type testing platform is used to carry multiple test samples with different preset thicknesses Li, where i is the number of test samples, 1≤i≤N; the difference-frequency terahertz wave is emitted after passing through the test samples. The terahertz intensity detection device, when the test sample is supported on the transmission test platform, is used to measure the spectral intensity of the difference-frequency terahertz wave emitted from the test sample, which is defined as the transmission spectral intensity; when the transmission test platform is not supported by the test sample, the terahertz intensity detection device is also used to measure the spectral intensity of the difference-frequency terahertz wave emitted from the transmission test platform, which is defined as the background spectral intensity. A spectral data acquisition and processing device is provided, which includes a spectral intensity determination model, a dielectric property real part determination model, a dielectric property imaginary part determination model, and a dielectric property determination model for the test sample. The spectral intensity determination model includes transmission spectral intensity, background spectral intensity, and a preset thickness Li of the test sample. The spectral data acquisition and processing device is electrically connected to a terahertz intensity detection device and an optical parametric oscillator. It is used to acquire the transmission spectral intensity and background spectral intensity obtained by the terahertz intensity detection device. The spectral data acquisition and processing device is also used to control the optical parametric oscillator to adjust the output of the dual-wavelength difference-frequency pump light. The spectral intensity determination model is as follows: Among them, T i This represents the transmission spectral intensity of test samples with different preset thicknesses, which is obtained by the terahertz intensity detection device. T 0 T represents the non-background spectral intensity. noise Indicates the noise intensity of the terahertz intensity detection device; n 0 L represents the refractive index of air or the refractive index of the end face material of the transparent container used to hold the test sample. i n represents the thickness of the test sample. m α represents the refractive index of the test sample material. m This represents the absorption coefficient of the test sample material; In T i T 0 T noise n 0 and L i With all parameters determined, the refractive index n of the test sample material is obtained by fitting. m and the absorption coefficient α of the test sample material. m ; The model for determining the real part of the dielectric property is as follows: The model for determining the imaginary part of the dielectric property is as follows: The dielectric property determination model is as follows: in, For terahertz wavelength, For weights.

2. The terahertz band material dielectric property measurement system according to claim 1, characterized in that, The laser frequency doubling unit includes: A laser for emitting laser light having an initial wavelength λ. 0 ; A half-wave plate, which, upon receiving laser light from the laser, is used to adjust the polarization state of the laser light; A frequency doubling crystal, which, upon receiving laser light from the half-wave plate, reduces the initial wavelength λ of the laser light... 0 Adjusted to the preset wavelength λ 1 , λ 0 >λ 1 .

3. The terahertz band material dielectric property measurement system according to claim 1, characterized in that, The optical parametric oscillator includes: cavity, A first reflector and a second reflector are provided. The first reflector is located at the front end of the cavity, and the second reflector is located at the rear end of the cavity, opposite to the first reflector. When a laser with a preset wavelength enters the cavity, it travels back and forth under the reflection of the first and second reflectors to generate oscillations. A first KTP parametric crystal and a second KTP parametric crystal are disposed between the two reflectors, with the length of the first KTP parametric crystal being less than the length of the second KTP crystal; dual-wavelength difference frequency pump light is generated based on the first KTP parametric crystal and the second KTP parametric crystal. A rotating platform is provided to support the first KTP parametric crystal. The rotating platform is electrically connected to the spectral data acquisition and processing device, which controls the rotation of the rotating platform and changes the wavelength of the dual-wave difference frequency pump light generated by the first KTP parametric crystal and the second KTP parametric crystal by changing the phase matching conditions of the first KTP parametric crystal.

4. The terahertz band material dielectric property measurement system according to claim 1, characterized in that, The measurement system also includes: A beam splitter is disposed between the laser frequency doubling unit and the optical parametric oscillator to select laser light with a preset wavelength for delivery into the optical parametric oscillator.

5. The terahertz band material dielectric property measurement system according to claim 1, characterized in that, The measurement system also includes: A parabolic mirror terahertz beam shaping device is disposed between the ultra-wideband terahertz difference frequency generating crystal and the transmission test platform, and is used to shape the difference frequency terahertz wave emitted from the ultra-wideband terahertz difference frequency generating crystal and having a large divergence angle.

6. The terahertz band material dielectric property measurement system according to claim 2, characterized in that, The initial wavelength λ 0 =1064nm, the preset wavelength λ 1 =532nm.

7. A method for measuring the dielectric properties of materials in the terahertz band, characterized in that, Includes the following steps: A terahertz band dielectric property measurement system is constructed, wherein the terahertz band dielectric property measurement system is the terahertz band dielectric property measurement system according to any one of claims 1 to 6; Prepare test samples, wherein the number of test samples is i, 1≤i≤N, and each test sample has a different preset thickness Li; The optical parametric oscillator is calibrated to control the frequency of the dual-wavelength difference-frequency pump light emitted by the optical parametric oscillator to meet the preset frequency; the frequency of the difference-frequency terahertz wave is calibrated based on the preset frequency of the dual-wavelength difference-frequency pump light and using the spectral data acquisition and processing device. When the test sample is not supported on the transmission test platform, the terahertz dielectric property measurement system is activated. At this time, the laser frequency doubling unit emits a laser with a preset wavelength. After receiving the laser, the optical parametric oscillator outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal outputs a difference frequency terahertz wave based on the dual-wavelength difference frequency pump light. The difference frequency terahertz wave penetrates the transmission platform and is emitted. Under the control of the spectral data acquisition and processing device, the terahertz intensity detection device measures the spectral intensity of the emitted difference frequency terahertz wave, which is defined as the background spectral intensity. With the test sample supported on the transmission test platform, the terahertz dielectric property measurement system is activated. At this time, the laser frequency doubling unit emits a laser with a preset wavelength. After receiving the laser, the optical parametric oscillator outputs a dual-wavelength difference frequency pump light. The ultra-wideband terahertz difference frequency generating crystal outputs a difference frequency terahertz wave based on the dual-wavelength difference frequency pump light. The difference frequency terahertz wave penetrates the test sample and is emitted. Under the control of the spectral data acquisition and processing device, the terahertz intensity detection device measures the spectral intensity of the emitted difference frequency terahertz wave, which is defined as the transmission spectral intensity. The terahertz intensity detection device sends the background spectral intensity and the transmission spectral intensity to the spectral data acquisition and processing device, and based on the spectral intensity determination model, the dielectric property real part determination model, the dielectric property imaginary part determination model, and the dielectric property determination model, finally determines the dielectric properties of the test sample at each frequency point in the difference frequency terahertz band. The spectral intensity determination model is as follows: Among them, T i This represents the transmission spectral intensity of test samples with different preset thicknesses, which is obtained by the terahertz intensity detection device. T 0 T represents the non-background spectral intensity. noise Indicates the noise intensity of the terahertz intensity detection device; n 0 L represents the refractive index of air or the refractive index of the end face material of the transparent container used to hold the test sample. i n represents the thickness of the test sample. m α represents the refractive index of the test sample material. m This represents the absorption coefficient of the test sample material; In T i T 0 T noise n 0 and L i With all parameters determined, the refractive index n of the test sample material is obtained by fitting. m and the absorption coefficient α of the test sample material. m ; and / or, The model for determining the real part of the dielectric property is as follows: The model for determining the imaginary part of the dielectric property is as follows: The dielectric property determination model is as follows: in, For terahertz wavelength, For weights.

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