Electric rotating sample holder and method for detecting optical parameters of samples in terahertz frequency band

Abstract

The present invention discloses an electric rotating sample holder and method for detecting the optical parameters of a sample in the terahertz frequency band, which is suitable for a transmission terahertz time-domain spectroscopy system. The electric rotating sample holder includes a lifting platform, a drive system, and a scale plate. The scale plate is mounted on the lifting platform and its height is adjustable. The scale plate includes a scale plate body and an angle main scale plate, the angle main scale plate is provided with an angle main scale scale, and the scale plate body is provided with an angle vernier scale. Driven by the drive system, the angle main scale plate can rotate on the scale plate body. A placement groove for placing the sample to be tested is provided at the center position of the scale plate. After the sample to be tested is placed in the placement groove, the sample to be tested can rotate with the angle main scale plate. Utilizing the technical solution of the present invention, the optical axis direction of the birefringent crystal and the contactless thickness measurement of the sample can be achieved without any prior parameters and contact with the sample, and the measurement speed, stability, and accuracy of the optical parameters in the terahertz frequency band can be improved.

Description

Technical Field

[0001] The present invention relates to the field of terahertz optical measurement technology, and in particular to an electric rotating sample rack and method for detecting optical parameters of a sample in the terahertz frequency band, which is applicable to a transmission terahertz time-domain spectroscopy system. Background Art

[0002] Transmission-type terahertz time-domain spectroscopy (THz-TDS) can be used to detect the changes in amplitude and phase at each frequency component after the terahertz wave penetrates the sample to be tested. This is used to extract important terahertz optical parameters such as absorption characteristics and refractive index. It is the optimal tool for studying the interaction between light and matter in the terahertz band (0.3-3.0THz).

[0003] When using THz-TDS to characterize polarization-sensitive materials, it is often necessary to adjust the angular position of the sample and the polarization direction of the terahertz wave. When the terahertz wave is incident along the optical axis of the birefringent crystal, birefringence does not occur. However, when the propagation direction is different from the optical axis direction, the incident linearly polarized light can be equivalently decomposed into two light components with mutually perpendicular polarization directions. Among them, the component that satisfies the law of refraction is called ordinary light (o light), and the component that does not satisfy the law of refraction is called extraordinary light (e light). The two have different propagation speeds in the crystal. The speed difference is converted into a phase difference after passing through a medium of a certain thickness. The birefringence of the crystal can be calculated by measuring this phase difference. It can be seen that the measurement of birefringence depends on the determination of the optical axis direction and the thickness of the crystal.

[0004] For birefringent crystals with unknown optical axis orientation, polarization-sensitive measurement methods can be used to change the polarization direction of the terahertz generator or detector. However, this requires specialized instrument modification and prevents continuous measurement based on standard THz-TDS, resulting in poor universality. Changing the optical axis orientation by rotating the sample, combined with the optical axis azimuth calculated using the Jones matrix, is limited in its range by the cosine term. Furthermore, these methods rely on a priori parameters such as crystal thickness. However, in most current research, manual thickness measurements using vernier calipers or micrometers are still employed, which can result in significant errors and easily cause scratches that damage the sample.

[0005] Although the thickness can be estimated contactlessly in terahertz time-domain signals through the main peak and echo time difference between the sample and the reference, this method is only used for a rough estimate of the sample thickness; and the high-precision iterative method under appropriate initial values ​​has a low extraction efficiency due to the large amount of calculation. Summary of the Invention

[0006] The present invention provides an electric rotating sample holder and method for detecting the optical parameters of a sample in the terahertz frequency band, so as to solve the technical problems that existing equipment cannot perform continuous rotation measurement on birefringent crystal samples, and the measurement parameters are incomplete, the accuracy is low, and scratches are easily caused, thereby damaging the sample.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] On the one hand, the present invention provides an electric rotating sample holder for detecting optical parameters of a sample in the terahertz frequency band, which is suitable for a transmission terahertz time-domain spectroscopy system. The electric rotating sample holder for detecting optical parameters of a sample in the terahertz frequency band comprises: a lifting platform, a driving system, and a scale plate; wherein,

[0009] The scale plate is installed on the lifting platform, and after being installed and fixed, the plate surface of the scale plate is arranged in a vertical direction. Driven by the lifting platform, the height of the scale plate can be adjusted;

[0010] The scale plate includes a scale plate body and an angle main scale plate, the angle main scale plate being arranged concentrically with the scale plate body, an angle main scale scale being arranged on the inner side of the circumference of the angle main scale plate, and an angle vernier scale being arranged on the scale plate body along the circumference of the angle main scale plate; under the drive of the drive system, the angle main scale plate can rotate on the scale plate body, and the angle vernier scale cooperates with the angle main scale scale to display the rotation angle of the angle main scale plate;

[0011] A placement groove is provided at the center of the scale plate, and the placement groove is used to place the sample to be measured; after the sample to be measured is placed in the placement groove, the sample to be measured can rotate together with the angle main scale plate.

[0012] Furthermore, the lifting platform includes: a base and a height-adjustable lifting part; wherein the lifting part is installed on the base, and the dial is installed on the top of the lifting part.

[0013] Furthermore, the driving system includes: a controller, a driver, a stepping motor and a transmission mechanism;

[0014] The controller is used to generate a pulse signal for controlling the rotation direction and frequency of the stepper motor;

[0015] The driver is used to convert the pulse signal sent by the controller into angular displacement and send it to the stepping motor;

[0016] The stepper motor is connected to the main angle scale disk through the transmission mechanism; the transmission mechanism synchronously transmits the stepper motor rotation angle to the main angle scale disk to achieve automatic rotation control of the sample to be tested.

[0017] Furthermore, the controller includes a control unit and a communication unit; wherein the control unit is used to generate a pulse signal to control the rotation direction and frequency of the stepper motor through programming, and the pulse width is greater than 1.2 microseconds; the communication unit uses serial communication to upload the current position information of the stepper motor to the host computer;

[0018] The driver includes a housing and a terminal block; wherein the wiring leads from the terminal block are connected to the controller and the stepper motor respectively; the driver uses a subdivision setting of 3200 or above;

[0019] The stepper motor uses a two-phase four-wire 35 stepper motor.

[0020] Furthermore, the transmission mechanism includes: a scale plate synchronous wheel, a motor shaft synchronous wheel and a belt;

[0021] The motor shaft synchronous wheel is installed on the rotating shaft of the stepping motor, and the scale dial synchronous wheel is installed on the scale dial body. The scale dial synchronous wheel and the motor shaft synchronous wheel are connected by a belt; the scale dial synchronous wheel is provided with a driving gear which is concentric with the scale dial, and the rim of the angle main scale disk is provided with teeth along the circumference of the angle main scale disk, and the angle main scale disk is engaged with the driving gear.

[0022] Furthermore, the placement groove includes a circular slot and a square slot, and the circular slot is concentrically arranged with the square slot; and a wafer clamp for fixing a thin film wafer is also provided on the main angle scale disk.

[0023] Furthermore, the electric rotating sample holder is used to measure the angle of the optical axis by a delay line positioning method;

[0024] The process of measuring the optical axis angle using the delay line positioning method includes:

[0025] Place the electric rotating sample holder at the beam focus of the transmission terahertz time-domain spectroscopy system, adjust the height of the lifting platform so that the center of the dial coincides with the focus position of the terahertz wave, measure the air reference signal and save it;

[0026] The sample to be tested is embedded in the placement groove, and the linearly polarized terahertz wave is passed through the sample to be tested in any direction. The optical delay line of the transmission terahertz time-domain spectroscopy system is adjusted to scan the terahertz time-domain waveform and locate the double peak position of the time-domain waveform caused by birefringence;

[0027] The optical delay line is locked at the position of the first waveform peak, and the electric rotating sample holder is called to rotate the sample to be tested one circle. The output angle when the peak signal is maximum is the optical axis angle, thereby realizing automatic positioning of the optical axis of the sample to be tested. If the sample to be tested is a negative crystal, the optical delay line is positioned at the fast axis peak position; if the sample to be tested is a positive crystal, the optical delay line is positioned at the slow axis peak position.

[0028] Furthermore, the electric rotating sample holder is used to measure the thickness of the sample by using a transfer function iterative approximation method;

[0029] The process of measuring sample thickness using the transfer function iterative approximation method is as follows:

[0030] Unlock the optical delay line, scan the complete terahertz wave signal of the extraordinary optical axis, call the electric rotating sample holder to rotate the sample to be tested 90 degrees, and scan the complete terahertz wave signal of the ordinary optical axis again;

[0031] The thickness of the sample to be measured is extracted from the ordinary light and extraordinary light signals through the transfer function iterative approximation algorithm.

[0032] Furthermore, the method of extracting the thickness of the sample to be measured from the ordinary light and extraordinary light signals by using a transfer function iterative approximation algorithm includes:

[0033] Step 1: Calculate the initial estimated value of the thickness of the sample to be measured by the main peaks of the fast and slow light, the first echo peak, and the peak position of the air reference signal in the terahertz time domain signal, and use the initial estimated value as the current thickness value;

[0034] Step 2: Within the range of ±0.1 mm of the current thickness value, according to the Fresnel formula and the propagation coefficient inside the sample to be measured, establish a theoretical transfer function with the complex refractive index as a variable:

[0035]

[0036] in, is the complex refractive index that varies with frequency, d is the thickness of the sample to be measured, c is the speed of light in a vacuum, and m represents the number of multiple reflections of the terahertz signal inside the sample to be measured within the measurement time window;

[0037] Step 3: Perform Fourier transform on the sample signal to be tested and the air reference signal respectively to obtain the frequency domain signal E sam (ω) and E ref (ω), calculate the measured transfer function between the terahertz wave and the sample to be measured:

[0038]

[0039] Step 3: Calculate the complex refractive index through global optimization of multivariate functions and establish the error function between the theoretical and measured transfer functions:

[0040] E=|T th (ω)-T pr (ω)|;

[0041] Step 4: Apply Fourier transform to the obtained fast and slow axis refractive indices of the sample to be tested again to convert the periodic oscillation of the refractive index caused by the thickness inaccuracy into discrete peaks, and use the thickness corresponding to the minimum discrete peak as a more accurate thickness estimate;

[0042] Step 5: Narrow the iteration range, use the more accurate thickness estimation value obtained in step 4 as the current thickness value, repeat steps 2 to 4 for a preset number of times to improve the thickness estimation accuracy and obtain the final thickness value.

[0043] On the other hand, the present invention also provides a method for detecting optical parameters of a sample in the terahertz frequency band using the above-mentioned electric rotating sample holder for detecting optical parameters of the sample in the terahertz frequency band, which comprises:

[0044] Place the electric rotating sample holder at the beam focus of the transmission terahertz time-domain spectroscopy system, adjust the height of the lifting platform so that the center of the dial coincides with the focus position of the terahertz wave, measure the air reference signal and save it;

[0045] The sample to be tested is embedded in the placement groove, and the linearly polarized terahertz wave is passed through the sample to be tested in any direction. The optical delay line of the transmission terahertz time-domain spectroscopy system is adjusted to scan the terahertz time-domain waveform and locate the double peak position of the time-domain waveform caused by birefringence;

[0046] The optical delay line is locked at the position of the first waveform peak, and the electric rotating sample holder is called to rotate the sample to be tested one circle. The output angle when the peak signal is maximum is the optical axis angle, thereby realizing automatic positioning of the optical axis of the sample to be tested. If the sample to be tested is a negative crystal, the optical delay line is positioned at the fast axis peak position; if the sample to be tested is a positive crystal, the optical delay line is positioned at the slow axis peak position;

[0047] Unlock the optical delay line, scan the complete terahertz wave signal of the extraordinary optical axis, call the electric rotating sample holder to rotate the sample to be tested 90 degrees, and scan the complete terahertz wave signal of the ordinary optical axis again;

[0048] The thickness of the sample to be measured is extracted from the ordinary light and extraordinary light signals through the transfer function iterative approximation algorithm;

[0049] Based on the obtained optical axis direction and sample thickness, the optical parameters of the sample in the terahertz band are calculated.

[0050] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0051] 1. The present invention first provides a device and method for measuring information such as the optical axis direction, thickness, and refractive index of a birefringent crystal in the terahertz frequency band without any prior parameters. This solves the technical problems of existing equipment that cannot perform continuous rotation measurement of birefringent crystal samples, and that the measurement parameters are incomplete and the accuracy is low.

[0052] 2. The present invention realizes automatic measurement of the optical axis direction of the birefringent crystal by locking the optical delay line to rotate the sample, eliminating the positioning error caused by manual operation, improving the stability and accuracy of the measurement, and the angle reading in the present invention can be accurate to 10 minutes, with high measurement accuracy;

[0053] 3. The present invention uses a transfer function iterative approximation algorithm to achieve contactless measurement of birefringent crystal thickness. Compared with the manual measurement methods using vernier calipers or micrometers in most current research and practical operations, the present method is less likely to scratch the sample surface and damage the sample. The algorithm continuously narrows the thickness estimation range during the iterative process, improving the calculation speed and accuracy, and the standard deviation of the thickness estimation can be within 10 microns.

[0054] 4. The device of the present invention is not limited to the detection of optical parameters of circular birefringent wafers. By adding a thin film clip and a square card slot, it can be used for testing thin film devices and exploring the local electric field enhancement effect of periodic subwavelength artificial structures. It has great application value in the characterization of metamaterial spectral enhancement and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0056] Figure 1 This is a schematic diagram of the structure of a transmission terahertz time-domain spectroscopy system;

[0057] Figure 2 1 is a schematic structural diagram of an electric rotating sample rack provided by an embodiment of the present invention;

[0058] Figure 3 is a schematic structural diagram of a dial provided by an embodiment of the present invention;

[0059] Figure 4 This is a flow chart of a method for detecting optical parameters of a sample in the terahertz frequency band provided by an embodiment of the present invention;

[0060] Figure 5The following is a diagram showing the relationship between the THz-TDS system parameters and the operating timing. Ts represents the time window length for measuring a complete reference or sample signal, and Tc represents the detection time for one sample rotation during optical axis positioning.

[0061] Figure 6 is a schematic diagram of a birefringent crystal sample and a reference signal;

[0062] Figure 7 Schematic diagram of the optical parameters of the ordinary light and extraordinary light of a birefringent crystal solved by the method of the present invention; wherein (a) is a schematic diagram of the refractive index of the ordinary light and extraordinary light, and (b) is a schematic diagram of the birefringence;

[0063] Figure 8 The absorption spectra of ordinary light and extraordinary light of a birefringent crystal are solved by the method of the present invention.

[0064] Description of reference numerals:

[0065] 1. Electric rotating sample rack;

[0066] 11. Driver;

[0067] 12. Stepper motor;

[0068] 13. Synchronous wheel transmission mechanism; 131. Scale dial synchronous wheel; 132. Belt; 133. Motor shaft synchronous wheel;

[0069] 14. Dial; 141. Angle main scale; 142. Angle vernier scale; 143. Circular slot;

[0070] 144. Square card slot; 145. Wafer clamp; 146. Driving gear;

[0071] 15. Base;

[0072] 2. Femtosecond laser;

[0073] 3. Optical delay line;

[0074] 4. Terahertz transmitter;

[0075] 5. Terahertz detectors;

[0076] 61. Beam splitter; 62. Reflector; 63. Off-axis parabolic mirror. DETAILED DESCRIPTION

[0077] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0078] This embodiment provides a motorized rotating sample holder for detecting optical parameters of samples in the terahertz frequency band, which is suitable for a transmission terahertz time-domain spectroscopy system, such as Figure 1 As shown, the transmission terahertz time-domain spectroscopy system includes: an electric rotating sample holder 1, a femtosecond laser 2, an optical delay line 3, a terahertz emitter 4, a terahertz detector 5, and a series of optical lenses; wherein the electric rotating sample holder 1 is used to rotate the crystal to achieve optical axis positioning; the femtosecond laser 2 outputs ultrafast infrared laser for generating and detecting terahertz waves; its average power is 2.95 watts, and the pulse width is less than 100 femtoseconds; the optical delay line 3 includes a hollow total reflector and a stepper motor, which is placed in the pump light path to increase the optical path difference between the pump light and the detection light reaching the terahertz emitter 4 and the terahertz detector 5, thereby realizing discrete acquisition of terahertz signals. The sampling interval is determined by the step length Δs of the stepper motor: The terahertz emitter 4 and terahertz detector 5 adopt photoconductive antenna technology, which is realized by near-infrared laser pulses hitting biased semiconductor materials; they are used for terahertz signal emission and detection respectively; the optical lenses include a spectrometer 61, a reflector 62, an off-axis parabolic mirror 63, a half-wave plate, a polarizer, a lens, etc., which are used to change the optical path and propagation state of the infrared laser and the terahertz wave.

[0079] like Figure 2 As shown, the electric rotating sample rack 1 includes: a lifting platform, a driving system and a dial 14; wherein, the dial 14 is installed on the lifting platform, and after being installed and fixed, the disk surface of the dial 14 is set in a vertical direction, and driven by the lifting platform, the height of the dial 14 can be adjusted.

[0080] The scale plate 14 includes a scale body and an angle scale disc. The angle scale disc is arranged concentrically with the scale body. An angle scale scale 141 is provided on the inner side of the circumference of the angle scale disc. An angle vernier scale 142 is provided on the scale body along the circumference of the angle scale disc. Driven by the drive system, the angle scale disc can rotate on the scale body. The angle vernier scale 142 cooperates with the angle scale scale 141 to display the rotation angle of the angle scale disc. Specifically, in this embodiment, the scale disc adopts the universal angle scale reading principle, dividing the 2 degrees on the main scale into 12 equal parts, with a reading accuracy of up to 10 minutes. It is used to fix and rotate crystal samples and other polarization-sensitive materials to be measured, and can prepare to read the current rotation angle through the main scale and vernier scale.

[0081] A placement groove is provided at the center of the scale plate, and the placement groove is used to place the sample to be measured; after the sample to be measured is placed in the placement groove, the sample to be measured can rotate together with the angle main scale plate.

[0082] The lifting platform further comprises a base 15 and a height-adjustable lifting portion. The lifting portion is mounted on the base 15, and the scale plate 14 is mounted on top of the lifting portion. The lifting platform can adjust the scale plate height using a knob to ensure that the center of the crystal to be measured coincides with the focal position of the terahertz wave.

[0083] Furthermore, the drive system includes: a controller (not shown in the figure), a driver 11, a stepper motor 12 and a transmission mechanism 13; wherein, the controller is used to generate a pulse signal for controlling the rotation direction and frequency of the stepper motor 12. In order to obtain a reliable response, the pulse width should be greater than 1.2 microseconds; the driver 11 is used to convert the pulse signal emitted by the controller into an angular displacement and send it to the stepper motor 12. In order to ensure the accuracy of angle measurement, a subdivision setting of 3200 or above is selected; the stepper motor 12 is connected to the angle main scale disk through the transmission mechanism 13. The stepper motor 12 uses a two-phase four-wire 35 stepper motor, which makes the device volume as small as possible while meeting the torque required for rotating the dial; the transmission mechanism 13 synchronously transmits the rotation angle of the stepper motor 12 to the angle main scale disk to realize automatic rotation control of the sample to be measured.

[0084] The controller further includes a control unit and a communication unit. The control unit generates pulse signals to programmatically control the rotation direction and frequency of the stepper motor 12. The communication unit uses serial communication to upload the current position information of the stepper motor 12 to a host computer. The driver 11 includes a housing and wiring terminals. The wiring terminals lead to connections to the controller and the stepper motor 12, respectively.

[0085] Furthermore, the transmission mechanism 13 includes: a dial synchronization wheel 131, a motor shaft synchronization wheel 133 and a belt 132; the motor shaft synchronization wheel 133 is installed on the rotating shaft of the stepping motor 12, the dial synchronization wheel 131 is installed on the dial body, and the dial synchronization wheel 131 and the motor shaft synchronization wheel 133 are connected by a belt 132; the dial synchronization wheel 131 is provided with a driving gear 146 which is concentric with the dial synchronization wheel, the disc edge of the angle main scale disc is provided with teeth along the circumference of the angle main scale disc, the angle main scale disc is engaged with the driving gear 146, and transmission is achieved through gear transmission.

[0086] Furthermore, if Figure 3As shown, the mounting slots include a circular retaining slot 143 for securing a circular birefringent wafer and a square retaining slot 144 for securing a square birefringent wafer. The circular retaining slot 143 and the square retaining slot 144 are arranged concentrically. Furthermore, the main angle scale disk is provided with a wafer clamp 145 for securing a thin film wafer. Based on the above, the scale disk of this embodiment can not only be used for optical parameter testing of circular birefringent wafers, but also for testing thin film devices and exploring the localized electric field enhancement effects of periodic subwavelength artificial structures. It has significant application value in characterizing spectral enhancement of metamaterials.

[0087] The electric rotating sample holder of this embodiment can be used to measure the optical axis angle by the delay line positioning method; and the sample thickness can be measured by the transfer function iterative approximation method; specifically, the detection process is as follows Figure 4 Shown, including:

[0088] S1: Place the electric rotating sample holder at the beam focus of the transmission terahertz time-domain spectroscopy system. Adjust the height of the lifting platform so that the center of the sample to be measured (a birefringent crystal in this embodiment) coincides with the focal position of the terahertz wave. Rotate the sample around the terahertz beam as the axis, measure the air reference signal, and save it.

[0089] S2, embedding the birefringent crystal into the mounting groove, allowing the linearly polarized terahertz wave to pass through the sample to be measured in any direction, adjusting the optical delay line of the transmission terahertz time-domain spectroscopy system, scanning the terahertz time-domain waveform, and locating the double peak position of the time-domain waveform caused by birefringence;

[0090] S3, lock the optical delay line at the position of the first waveform peak, call the electric rotating sample holder to quickly rotate the sample to be tested for one circle, and the output angle when the peak signal is maximum is the optical axis angle. The optical axis angle is then measured using the delay line positioning method to achieve automatic positioning of the optical axis of the sample to be tested;

[0091] Among them, for the extraction of the optical axis direction, this embodiment takes the vertically polarized terahertz wave incident on a Z-Cut (optical axis parallel to the interface) uniaxial negative crystal as an example. The incident terahertz wave is decomposed into ordinary light (o light) that obeys the law of refraction and extraordinary light (e light) that does not satisfy the law of refraction. There is a phase difference between the two. The extraordinary light propagates faster and its polarization direction is parallel to the optical axis. Therefore, the optical axis direction can be calculated by locating the position of the fast axis peak. If the birefringent sample to be measured is a positive crystal, the optical delay line is positioned at the slow axis peak.

[0092] S4, unlock the optical delay line, scan the complete terahertz wave signal of the extraordinary optical axis, call the electric rotating sample holder to rotate the sample to be tested 90 degrees, and scan the complete terahertz wave signal of the ordinary optical axis again;

[0093] S5, extracting the thickness of the sample to be measured from the ordinary light and extraordinary light signals by using a transfer function iterative approximation algorithm;

[0094] S6. Calculate the optical parameters of the sample in the terahertz band based on the obtained optical axis direction and sample thickness.

[0095] Specifically, in this embodiment, the implementation process of the above S5 is as follows:

[0096] S51, calculating an initial estimated value of the thickness of the sample to be measured based on the main peaks of the fast and slow light, the first echo peak, and the peak position of the air reference signal in the terahertz time domain signal, and using the initial estimated value as the current thickness value;

[0097] S52: Within the range of ±0.1 mm of the current thickness value, based on the Fresnel formula and the propagation coefficient inside the sample to be measured, establish a theoretical transfer function with the complex refractive index as a variable:

[0098]

[0099] in, is the complex refractive index that varies with frequency, d is the thickness of the sample to be measured, c is the speed of light in a vacuum, and m represents the number of multiple reflections of the terahertz signal inside the sample to be measured within the measurement time window;

[0100] S53, perform Fourier transform on the sample signal to be tested and the air reference signal respectively to obtain the frequency domain signal E sam (ω) and E ref (ω), calculate the measured transfer function between the terahertz wave and the sample to be measured:

[0101]

[0102] S54, calculate the complex refractive index through global optimization of multivariate functions, and establish the error function between the theoretical and measured transfer functions:

[0103] E=|T th (ω)-T pr (ω)|;

[0104] S55, Fourier transform is applied again to the obtained fast and slow axis refractive indices of the sample to be measured, and the periodic oscillation of the refractive index caused by the thickness inaccuracy is converted into discrete peaks:

[0105]

[0106] Among them, N represents the number of sampling points, n s (ω) represents the complex refractive index The real part of

[0107] S56, taking the thickness corresponding to the minimum discrete peak value as a more accurate thickness estimation value;

[0108] S57, narrowing the iteration range, taking the more accurate thickness estimation value obtained in S56 as the current thickness value, and repeating S52 to S56 for a preset number of times to improve the thickness estimation accuracy and realize non-contact thickness measurement of birefringent crystals.

[0109] After obtaining the optical axis direction and sample thickness, the corresponding optical parameters such as the refractive index and absorption coefficient can be calculated and output. Furthermore, it should be noted that this embodiment minimizes the peak value to weaken the influence of multiple reflections within the sample, narrowing the iteration range and obtaining a more accurate thickness estimate.

[0110] Specifically, in this embodiment, the relationship between system parameters and working timing is as follows: Figure 5 As shown, after measuring and saving the air reference signal, the birefringent crystal is embedded in the mounting groove of the scale plate 14, so that the linearly polarized terahertz wave passes through the crystal in any direction to obtain the sample signal. The signal can clearly distinguish the two peaks corresponding to the fast and slow axes. If only one peak is recognized, the stepper motor 12 automatically rotates 45 degrees and re-measures. The extraordinary light velocity of the negative crystal is faster, corresponding to Figure 6 The fast light shown has a polarization direction parallel to the optical axis. The optical delay line 3 is locked at the position of the first waveform peak. The rotating frame is called to rotate the crystal quickly for one circle. The output angle when the peak signal is maximum is the optical axis angle. The optical axis direction and thickness of the crystal are obtained, and the refractive index of the ordinary light and extraordinary light are calculated, as shown in Figure 2. Figure 7 As shown, the absorption spectrum, such as Figure 8 shown.

[0111] In summary, this embodiment provides an electric rotating sample holder and method for detecting the optical parameters of samples in the terahertz frequency band, which is suitable for a transmission terahertz time-domain spectroscopy system. By using the electric rotating sample holder and method of this embodiment, the optical axis direction positioning of the birefringent crystal and the contactless thickness measurement of the sample can be achieved without any prior parameters and sample contact, and the refractive index, absorption coefficient and other terahertz frequency band optical parameters of ordinary light and extraordinary light can be calculated, thereby eliminating problems such as sample damage and positioning errors caused by manual operation, and achieving the effect of improving the measurement speed, stability and accuracy of the optical parameters of the birefringent crystal in the terahertz frequency band.

[0112] Furthermore, it should be noted that the present invention may be provided as a method, apparatus, or computer program product. Thus, embodiments of the present invention may take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, embodiments of the present invention may take the form of a computer program product embodied on one or more computer-usable storage media containing computer-usable program code.

[0113] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, an embedded processor, or other programmable data processing terminal device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the process in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0114] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device, so that a series of operation steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for implementing the process in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0115] It should also be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The terms "comprises," "includes," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or terminal device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. In the absence of further restrictions, an element defined by the phrase "comprises a ..." does not exclude the presence of additional identical elements in the process, method, article, or terminal device that includes the element.

[0116] Finally, it should be noted that the above is a preferred embodiment of the present invention. It should be noted that although the preferred embodiment of the present invention has been described, it is clear that those skilled in the art, once they understand the basic inventive concept of the present invention, can make various improvements and modifications without departing from the principles of the present invention. Such improvements and modifications should also be considered as within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims

1. A method for detecting optical parameters of a sample in the terahertz frequency band, implemented by using an electrically rotating sample holder, characterized in that:

7. The swiftly and minutely adjusting device for a wood-planer working table as claimed in claim 1, wherein said linking rod and said adjusting base are pivotally connected to each other with a bolt, and said bolt has a round shank to contact with said linking rod. said linking rod has a round shank to contact with said linking rod. The method comprises: Place the electric rotating sample holder at the beam focus of the transmission terahertz time-domain spectroscopy system, adjust the height of the lifting platform so that the center of the dial coincides with the focus position of the terahertz wave, measure the air reference signal and save it; The sample to be tested is embedded in the placement tank, and the linearly polarized terahertz wave is allowed to pass through the sample to be tested in any direction. The optical delay line of the transmission terahertz time-domain spectroscopy system is adjusted to scan the terahertz time-domain waveform and locate the double peak position of the time-domain waveform caused by birefringence; The optical delay line is locked at the position of the first waveform peak, and the electric rotating sample holder is called to rotate the sample to be tested one circle. The output angle when the peak signal is maximum is the optical axis angle, thereby realizing automatic positioning of the optical axis of the sample to be tested. If the sample to be tested is a negative crystal, the optical delay line is positioned at the fast axis peak position; if the sample to be tested is a positive crystal, the optical delay line is positioned at the slow axis peak position; Unlock the optical delay line, scan the complete terahertz wave signal of the extraordinary optical axis, call the electric rotating sample holder to rotate the sample to be tested 90 degrees, and scan the complete terahertz wave signal of the ordinary optical axis again; The thickness of the sample to be measured is extracted from the ordinary light and extraordinary light signals through the transfer function iterative approximation algorithm; Based on the obtained optical axis direction and sample thickness, the optical parameters of the sample in the terahertz band are calculated.

2. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 1, wherein: The lifting platform includes a base and a height-adjustable lifting portion; wherein the lifting portion is installed on the base, and the scale plate is installed on the top end of the lifting portion.

3. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 1, wherein: The driving system includes: a controller, a driver, a stepping motor and a transmission mechanism; The controller is used to generate a pulse signal for controlling the rotation direction and frequency of the stepper motor; The driver is used to convert the pulse signal sent by the controller into angular displacement and send it to the stepping motor; The stepper motor is connected to the main angle scale disk through the transmission mechanism; the transmission mechanism synchronously transmits the stepper motor rotation angle to the main angle scale disk to achieve automatic rotation control of the sample to be tested.

4. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 3, wherein: The controller includes a control unit and a communication unit; wherein the control unit is used to generate a pulse signal to control the rotation direction and frequency of the stepper motor through programming, and the pulse width is greater than 1.2 microseconds; the communication unit uses serial communication to upload the current position information of the stepper motor to the host computer; The driver includes a housing and a terminal block; wherein the wiring leads from the terminal block are connected to the controller and the stepper motor respectively; the driver uses a subdivision setting of 3200 or above; The stepper motor uses a two-phase four-wire 35 stepper motor.

5. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 3, wherein: The transmission mechanism includes: a scale plate synchronous wheel, a motor shaft synchronous wheel and a belt; The motor shaft synchronous wheel is installed on the rotating shaft of the stepping motor, and the scale dial synchronous wheel is installed on the scale dial body. The scale dial synchronous wheel and the motor shaft synchronous wheel are connected by a belt; the scale dial synchronous wheel is provided with a driving gear which is concentric with the scale dial, and the rim of the angle main scale disk is provided with teeth along the circumference of the angle main scale disk, and the angle main scale disk is engaged with the driving gear.

6. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 1, wherein: The placement slot includes a circular slot and a square slot, and the circular slot is concentrically arranged with the square slot; and a wafer clamp for fixing a thin film wafer is also provided on the main angle scale disk.

7. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 1, wherein: The electric rotating sample holder is used to measure the angle of the optical axis by a delay line positioning method; The process of measuring the optical axis angle using the delay line positioning method includes: Place the electric rotating sample holder at the beam focus of the transmission terahertz time-domain spectroscopy system, adjust the height of the lifting platform so that the center of the dial coincides with the focus position of the terahertz wave, measure the air reference signal and save it; The sample to be tested is embedded in the placement groove, and the linearly polarized terahertz wave is passed through the sample to be tested in any direction. The optical delay line of the transmission terahertz time-domain spectroscopy system is adjusted to scan the terahertz time-domain waveform and locate the double peak position of the time-domain waveform caused by birefringence; The optical delay line is locked at the position of the first waveform peak, and the electric rotating sample holder is called to rotate the sample to be tested one circle. The output angle when the peak signal is maximum is the optical axis angle, thereby realizing automatic positioning of the optical axis of the sample to be tested. If the sample to be tested is a negative crystal, the optical delay line is positioned at the fast axis peak position; if the sample to be tested is a positive crystal, the optical delay line is positioned at the slow axis peak position.

8. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 7, wherein: The electric rotating sample holder is used to measure the thickness of the sample by using the transfer function iterative approximation method; The process of measuring sample thickness using the transfer function iterative approximation method is as follows: Unlock the optical delay line, scan the complete terahertz wave signal of the extraordinary optical axis, call the electric rotating sample holder to rotate the sample to be tested 90 degrees, and scan the complete terahertz wave signal of the ordinary optical axis again; The thickness of the sample to be measured is extracted from the ordinary light and extraordinary light signals through the transfer function iterative approximation algorithm.

9. The method for detecting optical parameters of a sample in the terahertz frequency band according to claim 8, wherein: The method of extracting the thickness of the sample to be measured from the ordinary light and extraordinary light signals by using a transfer function iterative approximation algorithm includes: Step 1: Calculate the initial estimated value of the thickness of the sample to be measured by the main peaks of the fast and slow light, the first echo peak, and the peak position of the air reference signal in the terahertz time domain signal, and use the initial estimated value as the current thickness value; Step 2: Within the range of ±0.1 mm of the current thickness value, according to the Fresnel formula and the propagation coefficient inside the sample to be measured, establish a theoretical transfer function with the complex refractive index as a variable: in, is the complex refractive index that varies with frequency, d is the thickness of the sample to be measured, c is the speed of light in a vacuum, and m represents the number of multiple reflections of the terahertz signal inside the sample to be measured within the measurement time window; Step 3: Perform Fourier transform on the sample signal to be tested and the air reference signal respectively to obtain the frequency domain signal E sam (ω) and E ref (ω), calculate the measured transfer function between the terahertz wave and the sample to be measured: Step 3: Calculate the complex refractive index through global optimization of multivariate functions and establish the error function between the theoretical and measured transfer functions: E=|T th (ω)-T pr (oh)|; Step 4: Apply Fourier transform to the obtained fast and slow axis refractive indices of the sample to be tested again to convert the periodic oscillation of the refractive index caused by the thickness inaccuracy into discrete peaks, and use the thickness corresponding to the minimum discrete peak as a more accurate thickness estimate; Step 5: Narrow the iteration range, use the more accurate thickness estimation value obtained in step 4 as the current thickness value, repeat steps 2 to 4 for a preset number of times to improve the thickness estimation accuracy and obtain the final thickness value.

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