Ultrafast spectrum transient signal acquisition method and system based on high-speed signal acquisition card

Abstract

The invention discloses an ultrafast spectrum transient signal acquisition device and method based on a high-speed signal acquisition card, and the device comprises an external clock which generates a modulation synchronization signal, and inputs the modulation synchronization signal to an optical modulation device and a high-speed data acquisition card to achieve synchronization; an optical modulation device which receives the modulation synchronization signal, changes the frequency of the input optical pulse to be the same as the synchronization signal, and generates a modulation optical pulse; the photoelectric detector generates an analog electric signal based on the modulated detection light; the high-speed data acquisition card generates a digital electric signal based on the analog electric signal; and the data processing center is used for receiving the digital electric signal and carrying out modulation processing based on a time integral window to obtain an ultrafast spectrum transient signal acquisition result. The high-speed acquisition card is adopted to directly record the voltage value of the detector, so that waiting time is avoided; the voltage values and the difference value in the pump on state and the pump off state are obtained through the time integral window, the light intensity of the pump off and the light intensity difference brought by modulation are collected at the same time, and the collection efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafast spectroscopy, and in particular to an ultrafast spectroscopy transient signal acquisition method and system based on a high-speed signal acquisition card. Background Art

[0002] Femtosecond ultrafast spectroscopy, which uses ultrashort pulses to improve temporal resolution, has proven to be an important tool for studying photogenerated carriers in semiconductor materials. The nonlinear effects of ultrafast pulses allow the probe light range to extend from microwaves to the ultraviolet. Since semiconductors have different spectral responses at different wavelengths—for example, free carriers are more sensitive in the terahertz and microwave bands, while signals from tightly bound exciton states in strongly confined systems are mostly in the visible or ultraviolet—selecting the appropriate wavelength of probe light, combined with pump-probe techniques, allows the spectral response of the semiconductor material's non-equilibrium state to be captured, thereby extracting the desired excited state information. Different types of ultrafast spectroscopy require different information from the probe light, necessitating different signal acquisition methods. For example, transient absorption spectroscopy systems using broadband supercontinuum white light as the probe light often employ a combination of a grating and an externally triggered area array CCD (charge-coupled device) camera to simultaneously detect the intensity of white light across different wavelengths. For ultrafast spectroscopy systems such as time-resolved terahertz spectroscopy, terahertz time-domain spectroscopy, time-resolved Kerr rotation spectroscopy, and single-wavelength transient absorption spectroscopy, it is only necessary to collect changes in the pulse light characteristics (light intensity, phase) of a specific wavelength. Usually, people obtain such changes through phase-locked amplifiers.

[0003] The scheme of using a lock-in amplifier to measure the detection light in a single wavelength transient absorption detection system is as follows: Figure 1 As shown in the figure, the chopper controller reduces the frequency of the laser's synchronization signal to half, and then inputs it to the chopper-modulated pump light and the phase-locked amplifier as a reference signal. At the same time, the detection light and the pump light overlap in time and space at the sample and are sent to the photodetector. The pulsed electrical signal detected by the photodetector is then sent to the signal input of the phase-locked amplifier. At this time, if the pump pulse arrives at the sample earlier than the detection pulse, the sample's absorption of the detection light can be directly obtained, thereby achieving the measurement of transient absorption. Although the phase-locked amplifier combined with the synchronization signal can directly obtain the measurement of transient signals, there are still some problems that reduce the efficiency of ultrafast spectroscopy acquisition. The specific problems are as follows:

[0004] (1) The low-pass filter limits the signal acquisition rate. Since a low-pass filter is used in the design, the time constant variable needs to be set when the phase-locked amplifier acquires the signal. The larger the time constant value is, the smoother the signal will be. However, when the input signal changes, the output signal does not change directly, but gradually approaches the true output value through the e exponential method. The change of the output signal over time is as follows: Figure 2 Therefore, a time constant of 3 to 5 times the signal acquisition time is typically set in the signal acquisition program to ensure that the signal reaches a stable value after a change, thereby achieving the best signal-to-noise ratio. However, for ultrafast spectroscopy that requires the acquisition of a large number of different data points, this can significantly increase signal acquisition time and reduce efficiency.

[0005] (2) Single output signal. By design, the phase-locked amplifier can only output a signal with the same frequency as the reference frequency, and can only output one signal value at a time. However, in ultrafast spectroscopy experiments, the signal of the detection light itself and the change in the detection light signal caused by the pump light are often measured. Therefore, in the experiment, the modulation frequency of the pump light and the modulation frequency of the detection light need to be input into the phase-locked amplifier separately to complete the test requirements, which increases the acquisition time. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems in the prior art.

[0007] The technical solution adopted by the present invention to solve the technical problem is to provide an ultrafast spectral transient signal acquisition device based on a high-speed signal acquisition card, comprising:

[0008] An optical modulation device receives a modulation synchronization signal, changes the frequency of an input optical pulse to be the same as the synchronization signal, and generates a modulated optical pulse;

[0009] A photodetector, configured to detect modulated detection light and generate a corresponding analog electrical signal; the modulated detection light is detection light altered by a modulated light pulse, and the detection light is a known laser;

[0010] A high-speed data acquisition card receives the analog electrical signal from the photodetector and generates a corresponding digital electrical signal;

[0011] External clock, which uses the clock signal to generate a modulation synchronization signal, which is input into the optical modulation device and the high-speed data acquisition card to achieve synchronization;

[0012] The data processing center receives the digital electrical signal from the high-speed data acquisition card, modulates the digital electrical signal based on the time integration window, and obtains the ultrafast spectral transient signal acquisition result.

[0013] The present invention also provides an ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card, comprising the following steps:

[0014] The preparation step includes generating a modulation synchronization signal using an external clock signal, and synchronizing the optical modulation device and the high-speed data acquisition card using the generated modulation synchronization signal; connecting the high-speed data acquisition card to the photodetector via the analog voltage signal port, and setting the acquisition parameters of the high-speed data acquisition card; and creating two square wave curves with a phase difference of 180 degrees as a pump-on time integration window and a pump-off time integration window based on the acquisition parameters of the high-speed data acquisition card at the data processing center.

[0015] Modulation step: the ultrafast spectral signal modulates the input optical pulse after passing through the optical modulation device to obtain a modulated optical pulse of the same frequency;

[0016] In the acquisition step, the high-speed data acquisition card collects the voltage signal of the detected light through the photodetector; the data processing center modulates the voltage signal using the pump-on time integration window and the pump-off time integration window to obtain the modulation result;

[0017] The delay step changes the relative distance between the modulated light pulse and the detection light to control the delay between the pulses. The modulation step and the acquisition step are repeated to obtain the change in the voltage value received by the detector after modulation under different delays, thereby obtaining an ultrafast spectral signal.

[0018] Preferably, the method of generating a modulation synchronization signal by using an external clock signal and synchronizing the optical modulation device and the high-speed data acquisition card by using the generated modulation synchronization signal comprises the following steps:

[0019] Input an external clock signal to the NI PCIe-6612 channel counter to generate a modulated synchronization signal. The frequency of the modulated synchronization signal is 1 / N of the clock signal frequency F, where N is an even number and the duty cycle is greater than 50%.

[0020] The modulation synchronization signal is output to the optical modulation device and the high-speed data acquisition card respectively. The trigger mode of the optical modulation device and the acquisition mode of the data acquisition card are set to external triggering to achieve synchronization of the two devices.

[0021] Preferably, the acquisition parameters of the high-speed data acquisition card are set as follows:

[0022] Based on the detection limit of the photodetector and the acquisition limit of the data acquisition card, set the voltage measurement range, acquisition rate, and number of voltage points for a single acquisition of the high-speed acquisition card.

[0023] Preferably, the data processing center creates two square wave curves as a pump on time integration window and a pump off time integration window based on the acquisition parameters of the high-speed data acquisition card, specifically:

[0024] The number of voltage points acquired in a single time is used as the signal length, the acquisition rate divided by the frequency of the modulation synchronization signal is used as the period, and the pulse signal attenuation interval is used as the integration interval. Two square wave curves, pump on and pump off, are created respectively. The integration interval value is 1, and the non-integration interval value is 0.

[0025] Preferably, the data processing center modulates the voltage signal using the pump on time integration window and the pump off time integration window to obtain a modulation result, comprising the following steps:

[0026] Multiply the voltage signal by the pump-on time integration window to obtain the pump-on curve;

[0027] The voltage signal is multiplied by the pump off time integration window to obtain the pump off curve;

[0028] The two curves are integrated to obtain the intensity of the modulated detection light, and the variation of the detection light after modulation is obtained by subtracting them.

[0029] Preferably, when the ultrafast spectral signal is a terahertz spectral signal, the laser synchronization signal is used as an external clock signal to be input into the PCIe-6612 channel counter, and the output frequency is a modulated synchronization signal, which is output to the optical chopper controller and the high-speed data acquisition card PCIe-6374 respectively;

[0030] After passing through a polarizer, a detection crystal and a quarter-wave plate, the detection light will be modulated into a circularly polarized light, and then passed through a Wollaston prism to split the detection light into two beams of equal intensity with perpendicular polarization directions. If there is a terahertz electric field, the detection light will pass through the detection crystal and its polarization will be twisted by a certain angle. After passing through the quarter-wave plate, an elliptically polarized light will be obtained, which will be split into two beams of inconsistent light intensity by the Wollaston prism. After passing through a balanced detector, an analog signal is generated and input into a high-speed data acquisition card.

[0031] Preferably, the setting range of the synchronization signal of the laser is 0.1 to 500 KHz.

[0032] Preferably, when the ultrafast spectral signal is a time-resolved Kerr rotation spectral signal, the external clock signal and the detection light are obtained by a fiber femtosecond laser, specifically: the laser emits a laser with a central wavelength of approximately 1030 nm and a repetition frequency of 100 kHz, which is split into two beams by a beam splitter, one of which is further passed through a 9:1 beam splitter to obtain two beams of light, the relatively weaker beam being used as the detection light, and the relatively stronger beam being passed through a BBO frequency doubling and optical modulation device as a modulated light pulse;

[0033] After passing through the delay optical path and delay line, the detection light is focused on the same position of the sample as the modulated light pulse. At the same time, the polarization states of the modulated light pulse and the detection light are controlled separately by the polarizer. Finally, the detection light is collimated by the lens and then passed through the 1 / 4 wave plate and Wollaston prism again to be divided into two beams of light with mutually perpendicular polarizations, which are sent to the balanced detector for detection.

[0034] The present invention has the following beneficial effects: the present invention provides a solution for acquiring changes in detection light signals by combining synchronous signal modulation with a high-speed data acquisition card, creates a current / voltage signal integration window by setting the acquisition speed and the modulation frequency of the pump, and performs mathematical processing on the acquired voltage or current signal to acquire changes in the detection light; the supported femtosecond laser repetition rate range is 0.1 to 500 kHz, basically covering common femtosecond laser models on the market. Taking terahertz time-domain spectroscopy as an example, compared with a phase-locked amplifier, this method increases the acquired terahertz signal-to-noise ratio by 6 times while increasing the acquisition speed by 3 times.

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of using a lock-in amplifier to measure detection light in a single-wavelength transient absorption detection system;

[0037] Figure 2 is a schematic diagram of the output signal of the lock-in amplifier changing with time;

[0038] Figure 3 Schematic diagram of the system structure of an embodiment of the present invention;

[0039] Figure 4 1. The pump-on square wave curve and the pump-off square wave curve of the embodiment of the present invention;

[0040] Figure 5 This is a flowchart of a signal extraction process after the modulated detection light is modulated by the time integration window according to an embodiment of the present invention;

[0041] Figure 6 A diagram showing the steps of a method according to an embodiment of the present invention;

[0042] Figure 7 This is a schematic diagram of the principle of terahertz spectrum signal acquisition according to an embodiment of the present invention;

[0043] Figure 8 This is a logic diagram of terahertz pulse detection under 1KHz repetition rate laser and 500Hz modulation;

[0044] Figure 9Schematic diagram of time window integration modulation for terahertz pulse detection under 1 kHz repetition rate laser and 500 Hz modulation;

[0045] Figure 10 The time domain and frequency domain images are obtained by detecting terahertz pulses with a 1 kHz repetition rate laser and 500 Hz modulation.

[0046] Figure 11 The working timing diagram of terahertz pulse detection under 100KHz repetition rate laser and 500Hz modulation and the schematic diagram of time window integral modulation;

[0047] Figure 12 The time domain and frequency domain images are obtained by detecting terahertz pulses with a 100KHz repetition rate laser and 500Hz modulation.

[0048] Figure 13 This is the optical path diagram for ultrafast signal detection in time-resolved Kerr rotation spectroscopy and the time-resolved optical Kerr rotation dynamics curves of two-dimensional perovskite materials with different layer numbers. DETAILED DESCRIPTION

[0049] The present invention provides an ultrafast spectral transient signal acquisition device based on a high-speed signal acquisition card, comprising:

[0050] An optical modulation device receives a modulation synchronization signal, changes the frequency of an input optical pulse to be the same as the synchronization signal, and generates a modulated optical pulse;

[0051] A photodetector, configured to detect modulated detection light and generate a corresponding analog electrical signal; the modulated detection light is detection light altered by a modulated light pulse, and the detection light is a known laser;

[0052] A high-speed data acquisition card receives the analog electrical signal from the photodetector and generates a corresponding digital electrical signal;

[0053] External clock, which uses the clock signal to generate a modulation synchronization signal, which is input into the optical modulation device and the high-speed data acquisition card to achieve synchronization;

[0054] The data processing center receives the digital electrical signal from the high-speed data acquisition card, modulates the digital electrical signal based on the time integration window, and obtains the ultrafast spectral transient signal acquisition result.

[0055] See also Figure 3 Figure 1 is a schematic diagram of a device according to an embodiment of the present invention. An external clock signal is used to trigger a chopper and a high-speed acquisition card, and a coordinated time integration window is used in software to extract transient signals from ultrafast spectroscopy. The signal processing flow in this embodiment of the present invention is as follows, using NI's PCIe-6612 channel counter and PCIe-6374 high-speed signal acquisition card as an example:

[0056] (1) Preparation of modulation synchronization signal: The laser synchronization signal is used as an external trigger source and input into the NI PCIe-6612 channel counter to output the modulation synchronization signal. Through LabView programming control, the output synchronization digital signal rate is F / N (N is an even number) of the laser synchronization signal frequency, and the duty cycle is greater than 50%;

[0057] (2) Synchronization of the optical modulation device and the data acquisition card: The generated modulation synchronization signal is output to the optical modulation device (such as an optical chopper, an acousto-optic modulator) and the high-speed data acquisition card respectively, and the trigger mode of the optical modulation device and the acquisition mode of the data acquisition card are set to external triggering to synchronize the two devices;

[0058] (3) Photodetector voltage signal measurement: Connect the photodetector to the analog voltage signal port of the high-speed data acquisition card. According to the detection limit of the photodetector and the acquisition limit of the data acquisition card, set the voltage measurement range, acquisition rate and number of voltage points of a single acquisition of the high-speed acquisition card.

[0059] (4) Time integration window creation: The number of voltage points collected in a single time is the signal length, the acquisition rate divided by the frequency of the modulation synchronization signal is the period, and the pulse signal attenuation interval is the integration interval. Two square wave curves, pump on and pump off, are created respectively, where the integration interval value is 1 and the non-integration interval value is 0. The square wave waveform example is as follows: Figure 4 As shown, the acquisition rate is set to 2MS / s and the external trigger frequency is 500Hz.

[0060] (5) Extraction of the modulation change of the detection light signal: The voltage signal collected by the photodetector is multiplied by the pump on and pump off time integration windows respectively to obtain the voltage value of the detector in the two states. Then, the two curves are integrated to obtain the detection light parameters (light intensity / polarization) in the corresponding states. After subtraction, the change in the detection light modulation can also be obtained. The LabView program block diagram of the signal extraction is as follows Figure 5 shown.

[0061] See also Figure 6 FIG. 1 is a diagram showing a method for collecting ultrafast spectral transient signals based on a high-speed signal acquisition card according to an embodiment of the present invention, comprising the following steps:

[0062] S601, a preparation step, using an external clock signal to generate a modulation synchronization signal, and using the generated modulation synchronization signal to synchronize the optical modulation device and the high-speed data acquisition card; the high-speed data acquisition card is connected to the photodetector via the analog voltage signal port, and the acquisition parameters of the high-speed data acquisition card are set; based on the acquisition parameters of the high-speed data acquisition card, the data processing center creates two square wave curves with a phase difference of 180 degrees as the pump-on time integration window and the pump-off time integration window;

[0063] S602, a modulation step, wherein the ultrafast spectral signal modulates the input optical pulse after passing through an optical modulation device to obtain a modulated optical pulse of the same frequency;

[0064] S603, acquisition step: the high-speed data acquisition card acquires the voltage signal of the detection light through the photodetector; the data processing center modulates the voltage signal using the pump-on time integration window and the pump-off time integration window to obtain the modulation result;

[0065] S604, a delay step, changes the relative distance between the modulated light pulse and the detection light to control the delay between the pulses, repeats the modulation step and the acquisition step, obtains the change in the voltage value received by the detector after modulation under different delays, and obtains the ultrafast spectral signal.

[0066] The following is a detailed explanation of the measurement of terahertz pulses in time-resolved terahertz spectroscopy and the acquisition of ultrafast signals in time-resolved Kerr rotation spectroscopy.

[0067] Measurement of terahertz pulses in time-resolved terahertz spectroscopy. Compared to the thermal radiation method that can only measure terahertz intensity, people usually use the electro-optical effect of the detection crystal to measure terahertz pulses. This technology can simultaneously obtain the electric field intensity and phase of the terahertz wave packet, bringing an analytical perspective to semiconductor research. Utilizing the strong nonlinear effect of femtosecond lasers, a specific crystal with a strong phase match between the femtosecond fundamental frequency light and the terahertz pulse is selected. When the terahertz pulse and the detection (fundamental frequency) light are simultaneously focused on the crystal in time and space, the electric field of the terahertz pulse will change the polarization of the detection light. And because the time scale of the main wave packet of the terahertz pulse is about 1 to 2 picoseconds, the time scale of the femtosecond fundamental frequency light is usually between 35 and 200 femtoseconds, which is much lower than that of the terahertz pulse. Therefore, when the terahertz and detection light reach the detection crystal at the same time, the terahertz electric field applied to the crystal can be approximated as a static electric field relative to the detection light. By changing the time delay between the detection light and the terahertz, the electric field intensity of the terahertz pulse in the time domain can be sampled and detected, thereby obtaining the time domain waveform of the terahertz electric field.

[0068] The specific detection principle is as follows Figure 7 As shown, Figure 7(a) is a simplified diagram comparing the THz pulse and the detection light pulse wave packet in the time domain. Figure 7 (b) in the figure is a balanced diagram of electro-optical detection. First, the detection light passes through a polarizer to obtain a detection light with complete linear polarization. If there is no terahertz electric field, the detection light will be modulated into a circularly polarized light after passing through the detection crystal and a quarter-wave plate. The detection light will then pass through a Wollaston prism to split the detection light into two equal-intensity beams with perpendicular polarization directions. If there is a terahertz electric field, the detection light will pass through the detection crystal, and the detection light polarization will be twisted by a certain angle. After passing through the quarter-wave plate, an elliptically polarized light will be obtained. The intensities of the two beams split by the Wollaston prism will be inconsistent. The difference in light intensity is proportional to the terahertz electric field strength. Therefore, controlling the time delay between the terahertz wave packet and the detection light can achieve terahertz electric field intensity scanning.

[0069] Specifically, take the measurement of terahertz pulses with a 1KHz repetition rate laser and 500Hz modulation as an example. The terahertz pulse measurement system with a femtosecond laser repetition rate of 1KHz is as follows: Figure 8 As shown in (a). The 1KHz synchronization signal of the laser is used as an external trigger source and input into the PCIe-6612 channel counter to output a modulated synchronization signal with a frequency of Hz. The generated modulated synchronization signal is then output to the optical chopper controller and the high-speed data acquisition card PCIe-6374 respectively to synchronize the two devices. Because both use the high level of the same signal as the judgment of whether the chopper is blocking light, it is only necessary to fix the phase of the chopper to ensure the synchronous operation between the two. The timing diagram of the system at work is shown in Figure 8 As shown in (b), it can be seen that the frequency of the terahertz pulse is half of the detection light. The adjacent pulses of the detection light modulated by the terahertz pulse must not be modulated. Since the change in the polarization state of the detection light is proportional to the electric field of the terahertz pulse, the relative electric field strength of the terahertz pulse can be directly obtained by subtracting the voltage signals of the two adjacent pulses, that is, E THz =I pump-on -I pump-off .

[0070] After the pump on and pump off integration windows are multiplied by the photodetector output voltage, the output voltage of a single pulse time interval is amplified as follows: Figure 9 (a) is shown. After multiplying with the output voltage, since the voltage value of the integration window is 1 and the voltage value of the non-window interval is 0, the voltage signal between the integration window partitions is retained, and the signals of other intervals without signals are all 0. While retaining the signal, the noise brought by other intervals is reduced, and the signal-to-noise ratio is improved to a certain extent. The voltage values ​​obtained by the detector in the two states of pump on and pump off are as follows Figure 9As shown in (b), by integrating the two curves separately and then subtracting them, the terahertz voltage at the delay time can be directly obtained.

[0071] The relative position of the terahertz and detection light pulses is controlled by the translation stage, and the voltage of the terahertz pulses with different delays is recorded to obtain the waveform of the terahertz pulse, such as Figure 10 (a) As shown in the figure, it can be seen that the period of the main terahertz wave packet is about 1ps, and a pulse wave packet contains multiple oscillation periods. The frequency domain distribution of the pulse can be obtained by performing a fast Fourier transform (FFT) on the terahertz waveform, as shown in Figure 10 As shown in (b). Because a 1mm thick (110) ZnTe crystal is used for THz generation and detection, the detection bandwidth of this system is 0.2 to 2.2 THz. The absorption of water in air at 1.1 THz and 1.7 THz in the spectrum is due to the absorption of water in this band.

[0072] Specifically, take the measurement of terahertz pulses with a 100KHz repetition rate laser and 500Hz modulation as an example. When the laser repetition rate increases, and the optical modulation device cannot modulate adjacent pulses, for example, a 100KHz repetition rate laser requires 50KHz to modulate adjacent pulses, a low modulation frequency can be used for optical modulation. The working sequence of the specific scheme is as follows: Figure 11 (a). When the chopper frequency is much lower than the laser repetition rate, the pulses in the pump on and pump off intervals will change from one to multiple pulses. Since the pump pulses and the probe pulses are one-to-one corresponding, and the probe light affected by the pump light is also within a certain time range, by integrating the probe light intensity over a period of time in the pump on and pump off intervals, as long as the integration time and the number of pulses are the same, the total probe light intensity in the pump on and pump off states can be obtained. The extracted pulse distribution is shown in Figure 1. Figure 11 (b) By subtracting the two, the relative electric field intensity of the terahertz pulse can also be obtained.

[0073] By using this processing method, terahertz pulses were successfully collected on a femtosecond laser platform with a repetition rate of 100KHz and a central wavelength of 1030nm. Using a gallium phosphide crystal, the relative displacement of the terahertz pulse and the detection light was controlled, and the terahertz time domain waveform was also obtained. The frequency domain distribution was obtained by fast Fourier transforming the terahertz time domain waveform, which is basically consistent with the reports in the literature. The time domain and frequency domain diagrams of the terahertz waveform are shown as follows: Figure 12 As shown in (a) and (b).

[0074] Acquisition of ultrafast signals in time-resolved Kerr rotation spectroscopy. By combining Kerr rotation spectroscopy with pump-probe technology, time-resolved Kerr rotation spectroscopy can directly obtain the evolution process of the optical anisotropy of the sample after light excitation. This technology is widely used to measure the transient polarization response of molecular solutions, the transient evolution of magnetic order of ferromagnetic and antiferromagnetic materials after light excitation, and other processes. The optical path diagram of the time-resolved Kerr rotation spectroscopy (TR-OKE) designed in this embodiment is shown in the figure below. Figure 13 As shown in (a). The entire system is based on a domestic fiber femtosecond laser with a central wavelength of approximately 1030nm and a repetition rate of 100KHz. Before being introduced into the system, the beam splitter splits the initially output 1030nm laser into two beams. One of the beams passes through a 9:1 beam splitter again, and the weaker beam is used as the detection light of the TR-OKE system, while the stronger beam is used as the excitation light of the system after BBO frequency doubling. Subsequently, the detection light passes through the delayed optical path and the delay line, and is focused at the same position of the sample as the pump light. At the same time, the polarization states of the pump light and the detection light are controlled separately by the polarizer. Finally, the detection light is collimated by the lens, and then passes through the 1 / 4 wave plate and the Wollaston prism again to be divided into two beams of light with mutually perpendicular polarizations, which are respectively sent to the balanced detector for detection. In the experiment, the ultrafast Kerr rotation signal extraction logic and Figure 11 The signal intensity directly reflects the change in the polarization state of the detection light after the sample is excited, and thus reflects the transient evolution of the optical anisotropy of the sample. Based on this spectrum, it was successfully observed that the Kerr rotation lifetime of a single-layer two-dimensional perovskite is much higher than that of a double-layer or triple-layer sample, such as Figure 13 (b) shown.

[0075] Specifically, a voltage or current acquisition method using a channel counter of another brand and a high-speed signal acquisition card may be used instead of the acquisition method of the embodiment of the present invention.

[0076] Specifically, other programming languages ​​may be used instead of LabView in the embodiment of the present invention to implement the processing of experimental data.

[0077] When implementing the present invention, a tunable modulated synchronization signal is used to synchronously control a high-speed voltage acquisition card and an optical modulation device, and the duty cycle of the synchronization signal is modulated to greater than 50% to achieve phase stability between the two. A software integration window is used to extract pump-on and pump-off signals, from which the relative intensity of the detection light in the pump-on and pump-off states and the intensity difference caused by the modulation can be directly obtained, thereby directly acquiring ultrafast transient signals. By rationally controlling the distribution and length of the integration window, transient experimental data acquisition under different repetition rate laser conditions can be achieved without hardware adjustment.

[0078] It can be seen that the present invention provides an ultrafast spectral transient signal acquisition method and system based on a high-speed signal acquisition card, which has a faster response speed and saves acquisition time. Due to the presence of a low-pass filter, the phase-locked amplifier needs to wait for an additional 3 to 5 time constant values ​​when the acquired signal occurs to ensure the stability of the output value. This solution uses a high-speed acquisition card to directly record the output voltage value of the detector, which avoids waiting time, saves acquisition time, and has more data output types, thereby improving acquisition efficiency. The output value of the phase-locked amplifier is related to the frequency of the input synchronization signal, and usually only one data can be output at a time. Since the high-speed acquisition card completely records the detector voltage output value within a certain time range, and through the time integration window, the voltage values ​​in the two states of pump on and pump off and their difference can be obtained respectively. For the ultrafast spectrum, the light intensity of the pump off and the light intensity difference caused by modulation need to be collected simultaneously, and they can be obtained at the same time, thereby improving acquisition efficiency.

[0079] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ultrafast spectral transient signal acquisition device based on a high-speed signal acquisition card, characterized in that: include: An optical modulation device receives a modulation synchronization signal, changes the frequency of an input optical pulse to be the same as the synchronization signal, and generates a modulated optical pulse; A photodetector, configured to detect modulated detection light and generate a corresponding analog electrical signal; the modulated detection light is detection light altered by a modulated light pulse, and the detection light is a known laser; A high-speed data acquisition card receives the analog electrical signal from the photodetector and generates a corresponding digital electrical signal; External clock, which uses the clock signal to generate a modulation synchronization signal, which is input into the optical modulation device and the high-speed data acquisition card to achieve synchronization; The data processing center receives the digital electrical signal from the high-speed data acquisition card, modulates the digital electrical signal based on the time integration window, and obtains the ultrafast spectral transient signal acquisition result.

2. A method for collecting ultrafast spectral transient signals based on a high-speed signal acquisition card, characterized in that: The following steps are involved: The preparation step includes generating a modulation synchronization signal using an external clock signal, and synchronizing the optical modulation device and the high-speed data acquisition card using the generated modulation synchronization signal; connecting the high-speed data acquisition card to the photodetector via the analog voltage signal port, and setting the acquisition parameters of the high-speed data acquisition card; and creating two square wave curves with a phase difference of 180 degrees as a pump-on time integration window and a pump-off time integration window based on the acquisition parameters of the high-speed data acquisition card at the data processing center. Modulation step: the ultrafast spectral signal modulates the input optical pulse after passing through the optical modulation device to obtain a modulated optical pulse of the same frequency; In the acquisition step, the high-speed data acquisition card collects the voltage signal of the detected light through the photodetector; the data processing center modulates the voltage signal using the pump-on time integration window and the pump-off time integration window to obtain the modulation result; In the delay step, the relative distance between the modulated light pulse and the detection light is changed to control the delay between the pulses. The modulation step and the acquisition step are repeated to obtain the change in the voltage value received by the detector after modulation under different delays, thereby obtaining the ultrafast spectral signal.

3. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 2, characterized in that: The method of generating a modulation synchronization signal by using an external clock signal and synchronizing an optical modulation device and a high-speed data acquisition card by using the generated modulation synchronization signal comprises the following steps: Input an external clock signal to the NI PCIe-6612 channel counter to generate a modulated synchronization signal. The frequency of the modulated synchronization signal is 1 / N of the clock signal frequency F, where N is an even number and the duty cycle is greater than 50%. The modulation synchronization signal is output to the optical modulation device and the high-speed data acquisition card respectively. The trigger mode of the optical modulation device and the acquisition mode of the data acquisition card are set to external triggering to achieve synchronization of the two devices.

4. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 2, characterized in that: The acquisition parameters of the high-speed data acquisition card are specifically set as follows: Based on the detection limit of the photodetector and the acquisition limit of the data acquisition card, set the voltage measurement range, acquisition rate, and number of voltage points for a single acquisition of the high-speed acquisition card.

5. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 2, characterized in that: The data processing center creates two square wave curves as the pump on time integration window and the pump off time integration window based on the acquisition parameters of the high-speed data acquisition card, specifically: The number of voltage points acquired in a single time is used as the signal length, the acquisition rate divided by the frequency of the modulation synchronization signal is used as the period, and the pulse signal attenuation interval is used as the integration interval. Two square wave curves, pump on and pump off, are created respectively. The integration interval value is 1, and the non-integration interval value is 0.

6. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 2, characterized in that: The data processing center modulates the voltage signal using the pump-on time integration window and the pump-off time integration window to obtain a modulation result, including the following steps: Multiply the voltage signal by the pump-on time integration window to obtain the pump-on curve; The voltage signal is multiplied by the pump off time integration window to obtain the pump off curve; The two curves are integrated to obtain the intensity of the modulated detection light, and the variation of the detection light after modulation is obtained by subtracting them.

7. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 2, characterized in that: When the ultrafast spectral signal is a terahertz spectral signal, the laser synchronization signal is used as an external clock signal to be input into the PCIe-6612 channel counter, and the output frequency is a modulated synchronization signal, which is output to the optical chopper controller and the high-speed data acquisition card PCIe-6374 respectively; After passing through a polarizer, a detection crystal and a quarter-wave plate, the detection light will be modulated into a circularly polarized light, and then passed through a Wollaston prism to split the detection light into two beams of equal intensity with perpendicular polarization directions. If there is a terahertz electric field, the detection light will pass through the detection crystal and its polarization will be twisted by a certain angle. After passing through the quarter-wave plate, an elliptically polarized light will be obtained, which will be split into two beams of inconsistent light intensity by the Wollaston prism. After passing through a balanced detector, an analog signal is generated and input into a high-speed data acquisition card.

8. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 7, characterized in that: The setting range of the synchronization signal of the laser is 0.1~500KHz.

9. The ultrafast spectral transient signal acquisition method based on a high-speed signal acquisition card according to claim 2, characterized in that: When the ultrafast spectral signal is a time-resolved Kerr rotation spectral signal, the external clock signal and detection light are obtained by a fiber femtosecond laser. Specifically, the laser emits a laser with a central wavelength of approximately 1030 nm and a repetition frequency of 100 kHz, which is split into two beams by a beam splitter. One of the beams is further passed through a 9:1 beam splitter to obtain two beams of light, the relatively weaker beam being used as the detection light, and the relatively stronger beam being passed through a BBO frequency doubling and optical modulation device as a modulated light pulse. After passing through the delay optical path and delay line, the detection light is focused on the same position of the sample as the modulated light pulse. At the same time, the polarization states of the modulated light pulse and the detection light are controlled separately by the polarizer. Finally, the detection light is collimated by the lens and then passed through the 1 / 4 wave plate and Wollaston prism again to be divided into two beams of light with mutually perpendicular polarizations, which are sent to the balanced detector for detection.

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