A pump-probe carrier anisotropy automatic measurement method based on sample rotation

Abstract

The application discloses a kind of pump-probe carrier anisotropy automatic measurement methods based on sample rotation.The method is through automatic control and data processing unit to the delay execution mechanism, electric rotary table, pump state control device and probe and signal detection unit are cooperatively controlled;After determining pump-probe measurement time delay, set sample rotation angle range and step, control electric rotary table is positioned to each target azimuth in turn, and reference signal of pump closed state and photoexcitation signal of pump opened state are respectively collected under each azimuth;Measurement signal is processed and is associated with current sample azimuth and is saved, if angle scanning is not ended, then automatically enter next target angle, until the anisotropy curve of carrier response with sample azimuth change is formed.The method realizes the integration automatic operation of sample rotation control and pump-probe measurement process.

Description

Technical Field

[0001] This invention relates to an automatic measurement method for pump-probe anisotropy based on sample rotation. Background Technology

[0002] Femtosecond pump-probe carrier anisotropy measurement requires continuously changing the azimuth angle of the sample relative to the incident light or the probe direction under a given pump-probe delay, and repeating the positioning, reference signal measurement, photoexcitation signal measurement, and data processing at each sample angle.

[0003] This type of measurement requires strict matching of the sample azimuth, delay position, and corresponding experimental signal. The method of manually rotating the sample and recording point by point involves many steps and is prone to errors in angle positioning, data correspondence, and consistency of experimental conditions, which is not conducive to continuously obtaining the direction-dependent characteristics of the charge carrier response. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an automatic measurement method for pump-probe anisotropy based on sample rotation. The method uses the sample azimuth angle as the main scanning variable and obtains the carrier anisotropy through the coordinated operation of the sample rotation mechanism and pump-probe measurement.

[0005] This invention is achieved through the following technical solution: an automatic measurement method for pump-probe anisotropy based on sample rotation, wherein the method uses an automatic control and data processing unit to coordinate the control of a delayed execution mechanism, an electric rotary table, a pump state control device, and a detection and signal detection unit, including: (1) Equipment initialization and status reading: The host computer initializes the delayed execution mechanism, electric rotary table, detection and signal detection unit, and pump status control device, and reads the current equipment status; (2) Delay position adjustment and pre-scan: Determine the effective pump-probe signal through delay position adjustment and pre-scan, and determine the time conditions used for anisotropic measurement; (3) Set angle scanning parameters: The sample is placed on the electric rotary table, and the sample rotation start angle, end angle, angle step size and corresponding signal acquisition parameters are set. (4) Positioning the sample to the current target angle: Control the electric rotary table to move the sample to the current set azimuth angle and confirm the current position; (5) Acquire current angle measurement signal: Under the current sample azimuth angle and the predetermined pump-detection time delay, the automatic control and data processing unit controls the pump state control device to establish the pump off and pump on states respectively, and the detection and signal detection unit collects the reference signal and photoexcitation signal; (6) Calculate the current angle carrier response: Perform corresponding data processing based on the measurement signal, and automatically associate the obtained carrier response with the current sample azimuth angle; (7) Angle Cycle: If the set angle range has not been scanned, the electric rotary table is controlled to rotate to the next target angle and the signal acquisition and data processing are repeated; (8) Results output: After completing the azimuth scanning of all samples, the carrier responses corresponding to each angle are arranged and processed in a unified manner to form a curve of carrier response changing with sample azimuth angle, thereby characterizing anisotropy.

[0006] Furthermore, equipment initialization and status reading include establishing communication between the automatic control and data processing unit and the delayed execution mechanism, electric rotary table, detection and signal detection unit, and pump status control device, completing equipment initialization, and reading the current status of each device.

[0007] Furthermore, the delayed position adjustment and pre-scan include adjusting the position of the delayed actuator, finding an effective pump-probe signal through manual adjustment and / or pre-scan, and determining the time conditions used for anisotropic measurements.

[0008] Furthermore, the electric rotary stage automatically changes the sample azimuth angle according to the set start angle, end angle, and angle step size, and can read and provide feedback on the current position. After completing the measurement at one angle, the system automatically moves to the next target angle.

[0009] Furthermore, the current angle measurement signal is acquired: the reference signal in the pump-off state and the photoexcitation response in the pump-on state are measured respectively, and the carrier response corresponding to the current sample direction is obtained by integration, ratio or normalization.

[0010] The advantages of this invention are: it integrates sample rotation control with the femtosecond pump-probe measurement process, realizing integrated operation of equipment initialization, delay position adjustment, pre-scanning, sample angle scanning, reference signal measurement, excitation signal measurement, data processing, and result display.

[0011] The system can automatically change the sample azimuth angle according to the set angle range and step size, and automatically correspond each angle position with the corresponding pump-probe measurement result.

[0012] By continuously recording and processing the carrier responses obtained at different sample azimuth angles, a curve of carrier response changing with sample azimuth angle can be directly generated, thereby characterizing the anisotropy of photoexcited carriers and improving the automation, repeatability, and accuracy of the correspondence between angle and data in angle scanning measurements. Attached Figure Description

[0013] Figure 1This is a flowchart of the automatic measurement method of the present invention.

[0014] Figure 2 This is a schematic diagram of the equipment and control relationship of the automatic measurement system of the present invention.

[0015] Figure 3 This is a schematic diagram of the host computer control relationship.

[0016] Figure 4 This is a flowchart of the host computer control instructions.

[0017] Figure 5 The results of automatic measurement of carrier anisotropy of the flat ZnTe sample in Example 2 under different pump polarizations are shown.

[0018] Figure 6 Figure 2 shows the evolution of carrier anisotropy in the flat ZnTe sample of Example 2 with pump-probe delay. Figure (a) shows the periodic oscillation of terahertz transmittance with crystal azimuth angle under different pump-probe delays. Figure (b) shows the change of oscillation amplitude with pump-probe delay, with the maximum value appearing around 35 ps.

[0019] Figure 7 Figure 1 shows the automatic measurement results of carrier anisotropy of the prestructured ZnTe sample in Example 3. Figures (a) and (b) compare the optical pump transmission angle response of flat ZnTe and prestructured ZnTe under different pump energy flux densities; Figure (c) compares the static terahertz transmission with and without surface ripple structure; Figure (d) shows the pump-probe delay of 35 ps and the pump energy flux density of 0.25 mJ / cm². 2 Furthermore, the dynamic terahertz transmission angle response obtained under horizontal polarization conditions. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments: Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; unless otherwise specified, the materials and devices used can be those commonly used in the art.

[0021] Example 1, see attached document Figure 1-4 An automatic measurement method for pump-probe anisotropy based on sample rotation is disclosed. The method utilizes an automatic control and data processing unit to coordinate the control of a delayed execution mechanism, an electric rotary table, a pump state control device, and a detection and signal detection unit. The method includes: (1) Equipment initialization and status reading: The host computer initializes the delayed execution mechanism, electric rotary table, detection and signal detection unit, and pump status control device, and reads the current equipment status; (2) Delay position adjustment and pre-scan: The effective pump-probe signal is determined by the delay position adjustment and pre-scan of the delay actuator, and the time conditions used for anisotropic measurement are determined. (3) Set angle scanning parameters: The sample is placed on the electric rotary table, and the sample rotation start angle, end angle, angle step size and corresponding signal acquisition parameters are set. (4) Positioning the sample to the current target angle: Control the electric rotary table to move the sample to the current set azimuth angle and confirm the current position; (5) Acquire current angle measurement signal: Under the current sample azimuth angle and the predetermined pump-detection time delay, the automatic control and data processing unit controls the pump state control device to establish the pump off and pump on states respectively, and the detection and signal detection unit collects the reference signal and photoexcitation signal; (6) Calculate the current angle carrier response: Perform corresponding data processing based on the measurement signal, and automatically associate the obtained carrier response with the current sample azimuth angle; (7) Angle Cycle: If the set angle range has not been scanned, the electric rotary table is controlled to rotate to the next target angle and the signal acquisition and data processing are repeated; (8) Results output: After completing the azimuth scanning of all samples, the carrier responses corresponding to each angle are arranged and processed in a unified manner to form a curve of carrier response changing with sample azimuth angle, thereby characterizing anisotropy.

[0022] An automatic measurement method for pump-probe anisotropy based on sample rotation, wherein the delay actuator includes a pump delay stage and a probe delay stage.

[0023] An automatic measurement method for pump-probe carrier anisotropy based on sample rotation is provided. The equipment initialization and status reading include establishing communication between the automatic control and data processing unit and the pump delay stage, the probe delay stage, the electric rotary stage, the probe and signal detection unit, and the pump status control device, completing the equipment initialization and reading the current status of each device.

[0024] An automatic measurement method for pump-probe carrier anisotropy based on sample rotation is provided. The delay position adjustment and pre-scan include adjusting the positions of the pump delay stage and the probe delay stage respectively, finding effective pump-probe signals through manual adjustment and / or pre-scan, and determining the time conditions used for anisotropy measurement.

[0025] An automatic measurement method for pump-probe anisotropy of charge carriers based on sample rotation is proposed. The electric rotary stage automatically changes the sample azimuth angle according to the set start angle, end angle and angle step size, and can read and feed back the current position. After completing the measurement at one angle, the system automatically enters the next target angle.

[0026] An automatic measurement method for pump-probe anisotropy based on sample rotation is proposed, which acquires the current angle measurement signal, measures the reference signal in the pump-off state and the photoexcitation response in the pump-on state, and obtains the carrier response corresponding to the current sample direction through integration, ratio or normalization.

[0027] An automatic measurement method for pump-probe anisotropy of charge carriers based on sample rotation is proposed. The host computer controls the delay execution mechanism to establish the measurement delay conditions, the electric rotary stage is responsible for point-by-point positioning of the sample azimuth angle, the pump state control device is responsible for switching between reference and excitation states, the detection and signal detection unit is responsible for signal acquisition at each angle, and the automatic control and data processing unit is responsible for associating the sample azimuth angle with the measurement results and determining the angle cycle.

[0028] An automatic measurement method for pump-probe carrier anisotropy based on sample rotation is disclosed in this embodiment. The automatic control and data processing unit is implemented by a host computer running a LabVIEW automatic measurement program. The host computer sequentially sends corresponding control commands to the delayed execution mechanism, the electric rotary table, and the pump state control device according to a predetermined measurement procedure, while simultaneously reading measurement data from the detection and signal detection unit. The program automatically correlates the measurement results with the current sample azimuth angle and completes angle cycling and anisotropy measurements accordingly.

[0029] Specifically, in the initialization phase: the host computer initializes the pump delay stage, the detection delay stage, the electric rotary stage, the pump status control device, and the detection and signal detection unit, and sets the sample rotation angle range and step size, the pump-detection delay, and the corresponding acquisition parameters.

[0030] Specifically, the delay condition setting is as follows: the host computer sends the target position command to the delayed execution mechanism, so that the system establishes the current pump-probe delay condition.

[0031] Specifically, sample angle positioning: the host computer sends a target angle command to the electric rotary table, causing the sample to rotate to the current measurement azimuth angle.

[0032] Specifically, reference state acquisition: at the current sample azimuth angle, the host computer sends a pump shutdown command to the pump state control device and reads the reference signal from the detection and signal detection unit.

[0033] Specifically, the excitation state acquisition and processing: the host computer then sends a pump start command to the pump state control device and reads the signal under the photoexcitation state; the reference signal and the photoexcitation signal are processed, and the processing result is associated with and saved with the current sample azimuth angle.

[0034] Specifically, proceeding to the next angle: After the current angle measurement is completed, the host computer sends the next target angle command to the electric rotary table and repeats the above process; after all angles are completed, the carrier anisotropy curve is formed; if it is necessary to study the evolution of anisotropy over time, the pump-probe delay can be changed and the angle scan can be repeated.

[0035] Example 2 (Reference Appendix) Figure 5-6 An automated method for measuring the anisotropy of pump-probe carriers based on sample rotation, for the automated measurement of carrier anisotropy in flat ZnTe samples. Test sample: Semi-insulating ZnTe crystal, 500μm thick, with a flat, unstructured surface.

[0036] Test objective: To verify that the system can automatically control sample rotation and synchronously acquire terahertz reference signals and pump excitation signals under fixed pump-probe delay conditions, thereby outputting anisotropic curves of terahertz transmittance as a function of crystal orientation; and to repeat the process under different pump-probe delays to obtain anisotropic evolution.

[0037] Parameter settings (main embodiment): Sample rotation range 0–360°, 1 point collected every 10°, for a total of 36 angle points; commonly used pump energy flux density 0.125 mJ / cm³ 2 The pump polarization was set to horizontal and vertical, respectively; the pump-probe time delay was fixed near the location where carrier absorption was strong. In the supplementary control experiment, the pump energy flux density was also set to 0.1 mJ / cm². 2 With 0.01 mJ / cm 2 .

[0038] Automated testing process: 1. Complete the initialization of the lock-in amplifier, probe delay stage, pump delay stage, and rotary stage; 2. Set fixed pump-detection delay and pump polarization; 3. The rotary table rotates the sample point by point according to a preset step size (e.g., 10°); 4. At each angular position, automatically acquire the terahertz reference signal in the unpumped state and the terahertz signal in the pumped state; 5. Calculate the corresponding terahertz transmittance and record it as an angle function; 6. After completing the 360° scan, smooth and post-process the curve to output the final anisotropy result; 7. If it is necessary to study the evolution of anisotropy over time, the above angle scanning process can be repeated after changing the pump-probe time delay.

[0039] Experimental results and conclusions: at 0.125 mJ / cm 2Under certain conditions, terahertz transmittance varies with the crystal. <001> The axis angle exhibits a clear periodic oscillation, and the oscillation curve changes accordingly after the pump polarization changes from horizontal to vertical; the fitted parameter is B≈0.23. Control experiments show that at 0.1 mJ / cm... 2 Oscillations are still visible below, and at 0.01 mJ / cm 2 The time oscillations essentially disappeared, leaving only noise, indicating that the system measured the intrinsic anisotropy generated by pump-induced two-photon absorption. Further, at 0.14 mJ / cm... 2 By changing the pump-probe delay and repeating the 360° scan, it can be seen that the anisotropic amplitude reaches its maximum at about 35 ps, proving that the system can not only measure the static angular response, but also automatically measure the evolution of anisotropy over time.

[0040] refer to Figure 5 The pump energy flux density is 0.125 mJ / cm³. 2 A 360° angle scan was performed on the sample near a fixed pump-probe delay. The figures show the variations in optical pump transmission and terahertz transmission under horizontal and vertical pump polarization conditions, and a comparison between experimental data and theoretical models; the terahertz response varies with... <001> The crystal axis azimuth angle exhibits obvious periodic oscillations, and the anisotropy parameter B obtained by fitting is approximately 0.23, verifying that the intrinsic anisotropy of the charge carriers can be directly obtained through rotating scanning and synchronous signal acquisition.

[0041] refer to Figure 6 The pump energy flux density is 0.14 mJ / cm³. 2 The pump polarization is horizontal, and 360° sample angle scans are performed at multiple pump-probe delay positions. The results show that the system can not only automatically obtain the anisotropy curve under a single delay, but also reconstruct the temporal evolution of anisotropy by changing the delay and repeating the angle scan.

[0042] Example 3 (Reference Appendix) Figure 7 An automated method for measuring pump-probe anisotropy of charge carriers based on sample rotation, for the automated measurement of charge carrier anisotropy in prestructured ZnTe samples. Test sample: ZnTe sample with laser-induced periodic surface ripple prestructure.

[0043] Test objective: To verify that the automated measurement system can measure angular responses that differ from those of flat samples on samples with permanent surface anisotropy, thereby distinguishing between intrinsic and extrinsic anisotropy.

[0044] Parameter settings: When comparing static / dynamic anisotropy, a fixed pump-probe delay of 35 ps is commonly used, and the pump flux density can be 0.25 mJ / cm³. 2The pump polarization is horizontal; the angle scan still uses the 360° automatic scanning mode. For pump transmission contrast, it is also possible to perform tests at 0.01, 0.125, and 0.25 mJ / cm². 2 The following compares samples with and without surface ripple structures.

[0045] Automated testing process: 1. Replace with a pre-structured ZnTe sample and realign; 2. Set fixed pump-probe delay, pump polarization, and rotational scanning parameters; 3. The rotary table automatically completes a 360° point-by-point scan; 4. Automatically acquire signals at various angular positions and calculate terahertz transmittance; 5. Compare the results with the angular response of the flat ZnTe sample.

[0046] Experimental Results and Conclusions: The optical pump transmission behavior with angle in the prestructured sample differs significantly from that in the flat sample; at 0.125 mJ / cm 2 At the input energy flux density, the surface corrugated structure significantly reduces the optical pump transmission power (by about 7 times), and the static terahertz transmittance decreases by about 30%, but its angle dependence does not change much. Conversely, in dynamic terahertz transmittance measurements, the prestructured sample exhibits a significant angle-dependent phase shift relative to the flat sample, indicating that the automatic measurement system can effectively measure the extrinsic anisotropy introduced by the surface prestructure.

[0047] Reference Appendix Figure 7 The pre-structured sample exhibited significant angular correlation response changes and phase shifts compared to the flat sample, verifying that the automatic rotation measurement system has the ability to resolve extrinsic anisotropy introduced by surface structure. The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make equivalent substitutions or corresponding adjustments to the actuators, control devices, scanning parameters, or data processing methods without departing from the concept of the present invention, and all such substitutions or adjustments can be implemented according to the automatic cooperative control relationship described in the present invention; the scope of protection of the present invention is defined by the claims.

Claims

1. An automatic measurement method for pump-probe anisotropy based on sample rotation, characterized in that: The method utilizes an automatic control and data processing unit to coordinate the control of the delayed execution mechanism, the electric rotary table, the pump status control device, and the detection and signal detection unit, including: (1) Equipment initialization and status reading: The host computer initializes the delayed execution mechanism, electric rotary table, detection and signal detection unit, and pump status control device, and reads the current equipment status; (2) Delay position adjustment and pre-scan: Determine the effective pump-probe signal through delay position adjustment and pre-scan, and determine the time conditions used for anisotropic measurement; (3) Set angle scanning parameters: The sample is placed on the electric rotary table, and the sample rotation start angle, end angle, angle step size and corresponding signal acquisition parameters are set. (4) Positioning the sample to the current target angle: Control the electric rotary table to move the sample to the current set azimuth angle and confirm the current position; (5) Acquire current angle measurement signal: Under the current sample azimuth angle and the predetermined pump-detection time delay, the automatic control and data processing unit controls the pump state control device to establish the pump off and pump on states respectively, and the detection and signal detection unit collects the reference signal and photoexcitation signal; (6) Calculate the current angle carrier response: Perform corresponding data processing based on the measurement signal, and automatically associate the obtained carrier response with the current sample azimuth angle; (7) Angle Cycle: If the set angle range has not been scanned, the electric rotary table is controlled to rotate to the next target angle and the signal acquisition and data processing are repeated; (8) Results output: After completing the azimuth scanning of all samples, the carrier responses corresponding to each angle are arranged and processed in a unified manner to form a curve of carrier response changing with sample azimuth angle, thereby characterizing anisotropy.

2. The automatic measurement method for pump-probe anisotropy based on sample rotation according to claim 1, characterized in that: Equipment initialization and status reading include establishing communication between the automatic control and data processing unit and the delayed execution mechanism, electric rotary table, detection and signal detection unit, and pump status control device, completing equipment initialization, and reading the current status of each device.

3. The automatic measurement method for pump-probe anisotropy based on sample rotation according to claim 1, characterized in that: The delayed position adjustment and pre-scan include adjusting the position of the delayed actuator separately, finding an effective pump-probe signal through manual adjustment and / or pre-scan, and determining the time conditions used for anisotropic measurements.

4. The automatic measurement method for pump-probe anisotropy based on sample rotation according to claim 1, characterized in that: The electric rotary table automatically changes the sample azimuth angle according to the set start angle, end angle and angle step size, and can read and provide feedback on the current position. After completing the measurement at one angle, the system automatically moves to the next target angle.

5. The automatic measurement method for pump-probe anisotropy based on sample rotation according to claim 1, characterized in that: Acquire the current angle measurement signal: Measure the reference signal in the pump-off state and the photoexcitation response in the pump-on state, and obtain the carrier response corresponding to the current sample direction through integration, ratio or normalization.

Images