Repetition frequency locking asynchronous electro-optical sampling device and method

Abstract

The invention belongs to the technical field of laser, and particularly discloses a repetition frequency locking asynchronous electro-optical sampling device and method, and the device comprises a pumping detection laser module, a calibration signal extraction module, and a terahertz receiving and transmitting module. Wherein the pumping detection laser module is used for providing a laser pulse and a laser difference frequency signal; the calibration signal extraction module is used for extracting higher harmonics of the laser difference frequency signals so that processing software can process the higher harmonics to obtain calibration signals, and then calibration and frequency relocking are carried out on the two lasers; and the terahertz receiving and transmitting module is used for receiving respective laser signals emitted by the two lasers subjected to calibration and frequency relocking so as to realize generation and detection of terahertz signals.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a repetition-frequency locked asynchronous electro-optical sampling device and method. Background Art

[0002] Terahertz waves are electromagnetic waves with a wavelength between microwaves and infrared light. Due to their unique frequency characteristics, they have been widely used in communication technology, material detection, imaging technology and other fields. Terahertz systems can be divided into synchronous optical sampling systems and asynchronous optical sampling systems according to different light sampling methods. Terahertz systems based on synchronous optical sampling usually use a single femtosecond laser to generate pump light and probe light, which are used to stimulate the terahertz generator and terahertz detector respectively. In this system, pump light is used to generate terahertz radiation, while probe light is used to sample these radiations. Since the pump light and probe light come from the same laser, they have a fixed phase relationship, which enables the system to achieve precise time control and synchronization. However, this sampling method relies on an external delay line to change the relative delay of the pump light and the probe light, thereby realizing the scanning of the entire terahertz signal, and the high-precision sampling time can reach several hours. Terahertz systems based on asynchronous optical sampling usually use two independent femtosecond lasers to generate pump light and probe light respectively. The two lasers in this system have close repetition frequencies and a small frequency difference between them, which can achieve higher sampling speed and spectral resolution, and can achieve high-speed acquisition while ensuring high precision. During asynchronous sampling, the repetition frequency difference between the two lasers is used as the delay of optical sampling and the synchronization signal during data acquisition. This method does not use a mechanical delay structure, but requires the two lasers to remain locked.

[0003] However, in asynchronous sampling, there is timing jitter between two free-running lasers with similar frequencies. When the jitter is greater than the period of the terahertz waveform (1ps), the terahertz waveform will be distorted or offset during data accumulation. Therefore, it is urgent to propose an asynchronous electro-optical sampling device and method with locked repetition rate to solve the above technical problems. Summary of the invention

[0004] The present invention provides a repetition-locked asynchronous electro-optical sampling device and method, which are used to solve the problem that in asynchronous sampling, there is timing jitter between two freely running lasers with similar frequencies. When the jitter is greater than the period of the terahertz waveform, the terahertz waveform will be distorted or offset in data accumulation.

[0005] In a first aspect, a repetition-frequency locked asynchronous electro-optical sampling device is provided, the device comprising:

[0006] Pump detection laser module, calibration signal extraction module and terahertz transceiver module; among them,

[0007] The pump-probe laser module is used to provide laser pulses and laser difference frequency signals;

[0008] The calibration signal extraction module is used to extract the higher harmonics of the laser difference frequency signal so as to be processed by the processing software to obtain the calibration signal, thereby calibrating and re-locking the frequency of the two lasers;

[0009] The terahertz transceiver module is used to receive the respective laser signals emitted by two calibrated and re-frequency-locked lasers to achieve the generation and detection of terahertz signals.

[0010] In a second aspect, a repetition-frequency locked asynchronous electro-optical sampling method is provided, the method comprising:

[0011] The pump-probe laser module provides laser pulses and laser difference frequency signals;

[0012] The calibration signal extraction module extracts the higher harmonics of the laser difference frequency signal for processing by the processing software to obtain the calibration signal, and then calibrates and re-locks the frequency of the two lasers;

[0013] The terahertz transceiver module receives the respective laser signals emitted by two calibrated and re-frequency-locked lasers to achieve the generation and detection of terahertz signals.

[0014] An asynchronous electro-optical sampling device and method for locking repetition rate provided in an embodiment of the present invention does not require the use of expensive piezoelectric elements, stable pulsed laser cavities, additional continuous lasers, etc. when locking the frequency difference between two lasers. The frequency difference of the lasers can be locked by real-time monitoring of high-order frequency difference signals using a calibration signal extraction module. In the calibration signal extraction module, except for a general equipment signal generator and a low-bandwidth photodetector, all other parts can be integrated into a circuit board, with extremely low cost.

[0015] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 A schematic diagram of the structure of a repetition-frequency locked asynchronous electro-optical sampling device provided according to an embodiment of the present invention;

[0018] Figure 2A schematic diagram of a circuit board of a calibration signal extraction module provided according to an embodiment of the present invention;

[0019] Figure 3 A schematic diagram of correction of phase distortion of a calibration signal provided according to an embodiment of the present invention;

[0020] Figure 4 The present invention is a schematic diagram of an implementation flow of a repetition-rate locked asynchronous electro-optical sampling method provided in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of this specification more clear, the technical solutions of this specification will be clearly and completely described below in combination with the specific embodiments of this specification and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this specification.

[0022] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0023] The technical solutions provided by the embodiments of this specification are described in detail below in conjunction with the accompanying drawings.

[0024] In order to enable an asynchronous sampling terahertz system to generate a more stable and accurate terahertz signal, an embodiment of the present invention provides a repetition-rate locked asynchronous electro-optical sampling device and method.

[0025] Figure 1 FIG. 1 is a schematic diagram of a structure of an asynchronous electro-optical sampling device with a locked repetition rate according to an embodiment of the present invention. Figure 1 , the device comprises:

[0026] Pump detection laser module, calibration signal extraction module and terahertz transceiver module; among them,

[0027] The pump-probe laser module is used to provide laser pulses and laser difference frequency signals;

[0028] The calibration signal extraction module is used to extract the higher harmonics of the laser difference frequency signal so as to be processed by the processing software to obtain the calibration signal, thereby calibrating and re-locking the frequency of the two lasers;

[0029] The terahertz transceiver module is used to receive the respective laser signals emitted by two calibrated and re-frequency-locked lasers to achieve the generation and detection of terahertz signals.

[0030] In a specific embodiment,

[0031] The pump-probe laser module includes: a femtosecond pulse laser 1, a femtosecond pulse laser 3, a photodetector 5, an optical mixer 4, an optical fiber 2 and a low-pass filter 6; wherein,

[0032] The femtosecond pulse laser 1 is used to provide a first laser pulse for the photodetector 13, and the laser repetition frequency is f1;

[0033] In a specific implementation, the laser repetition frequency f1 is about 100 MHz, and the central wavelength is 1550 nm;

[0034] The femtosecond pulse laser 3 is used to provide a second laser pulse to the photodetector 19, and the laser repetition frequency is f2; the repetition frequency f2 is close to the laser repetition frequency f1 of the femtosecond pulse laser 1, the laser frequency f2 is about 100MHz+10Hz, the central wavelength is 1550nm, the two lasers are in a free-running state, the frequencies of the two are close but not directly related, and the frequency difference Δf=f2-f1 of the two lasers is in the Hz order;

[0035] The optical mixer 4 is used to mix the first laser pulse and the second laser pulse and input the mixed pulses into the photodetector 5;

[0036] The photodetector 5 is used to convert the optical mixing signal into an electrical signal and then input it into the low-pass filter 6;

[0037] The low-pass filter 6 is used to filter the optical mixing electrical signal, and the cut-off frequency is f1. After filtering, a laser difference frequency signal Δf is obtained; wherein Δf=f2-f1;

[0038] The optical fiber 2 is used to transmit the first laser pulse and the second laser pulse emitted by the femtosecond pulse laser 1 and the femtosecond pulse laser 3 , and to transmit the optical mixing signal emitted by the optical mixer 4 .

[0039] In one embodiment, see Figure 2 ,

[0040] The calibration signal extraction module includes: a photodetector 13, a bandpass filter 14, a current amplifier 15, a mixer 16, a low-pass filter 23, a current amplifier 24, a power divider 18, a signal generator 17, a photodetector 19, a bandpass filter 20, a current amplifier 21, a mixer 22, a low-pass filter 25, a current amplifier 26, a mixer 27, a low-pass filter 28 and a current amplifier 29;

[0041] The photodetector 13 is used to convert the first laser pulse input by the laser 1 into an electrical signal with a frequency of f1, and input the electrical signal into the bandpass filter 14;

[0042] In the specific implementation, the photodetector uses an indium gallium arsenide photodetector DET08CFC, with a bandwidth of 5 GHz and an applicable wavelength of 800 nm to 1700 nm;

[0043] The bandpass filter 14 is used to extract the nth harmonic from the electrical signal with a frequency of f1; since the nth harmonic signal is relatively weak, a signal amplifier 15 is connected after the bandpass filter;

[0044] In specific implementation, the bandpass filter has an intermediate frequency of 1GHz and a bandwidth of -40dBc@±500MHz;

[0045] The current amplifier 15 is used to amplify the nth harmonic signal output by the bandpass filter 14;

[0046] In specific implementation, the current amplifier gain is 15dB;

[0047] The mixer 16 is used for mixing the nth harmonic signal of the laser 1 with the local oscillator signal provided by the signal generator 17;

[0048] The power divider 18 is used to divide the local oscillator signal provided by the signal generator 17 into two paths, and mix them with the nth harmonic of the laser 1 and the nth harmonic of the laser 3 respectively;

[0049] The signal generator 17 is used to provide a local oscillator signal;

[0050] In specific implementation, the local oscillator signal strength is 13dBm;

[0051] Among them, the frequency of the local oscillator signal is f LO =nf1+f L , where f L is a value close to the repetition frequency f1 of laser 1; the signal generator 17 is used here because the nth harmonic frequency is relatively high, and even after amplification, the signal is still relatively weak, and the effect of directly mixing the nth harmonic of laser 1 with the nth harmonic of laser 3 is extremely poor, so the signal generator is added to assist in signal extraction;

[0052] The low-pass filter 23 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 1, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L ;

[0053] The current amplifier 24 is used to amplify the current signal after low-pass filtering;

[0054] In specific implementation, the current amplifier gain is 15dB;

[0055] The photodetector 19 is used to convert the second laser pulse input by the laser 3 into an electrical signal with a frequency of f2, and input the electrical signal into the bandpass filter 20;

[0056] In the specific implementation, the photodetector uses an indium gallium arsenide photodetector DET08CFC, with a bandwidth of 5 GHz and an applicable wavelength of 800 nm to 1700 nm;

[0057] The bandpass filter 20 is used to extract the nth harmonic from the electrical signal with a frequency of f2; since the nth harmonic signal is relatively weak, a signal amplifier 21 is connected after the bandpass filter;

[0058] In specific implementation, the bandpass filter has an intermediate frequency of 1GHz and a bandwidth of -40dBc@±500MHz;

[0059] The current amplifier 21 is used to amplify the nth harmonic signal output by the bandpass filter 20;

[0060] In specific implementation, the current amplifier gain is 15dB;

[0061] The mixer 22 is used to mix the nth harmonic signal of the laser 3 with the local oscillator signal provided by the signal generator 17;

[0062] The low-pass filter 25 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 3, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L -nΔf, where Δf = f2-f1;

[0063] The current amplifier 26 is used to amplify the current signal after low-pass filtering;

[0064] In specific implementation, the current amplifier gain is 15dB;

[0065] The mixer 27 is used to convert the frequency f L -nΔf vs. f L The signal is mixed to obtain a signal with a frequency of nΔf;

[0066] The current amplifier 29 is used to amplify the calibration signal with a frequency of nΔf and output it to obtain an initial calibration signal with a frequency of nΔf.

[0067] In a specific embodiment,

[0068] The initial calibration signal has nonlinear distortion after passing through the amplification circuit, and also has jitter and drift because the two lasers are not completely locked.

[0069] The initial calibration signal is processed by the processing software to obtain the final calibration signal, which is specifically:

[0070] Take A, B, C, and D as the zero-crossing time position of the distorted signal, take the midpoints E, F, and G of the three segments AB, BC, and CD, and then take the midpoints of EF and FG as the zero-crossing position of the new time axis, and the calibration of the signal phase distortion is completed;

[0071] After calibration, an nΔf signal without jitter and drift is obtained, that is, the change of the frequency difference Δf between laser 1 and laser 2 is monitored, and then the change of the frequency difference Δf is corrected by post-processing software to keep the two lasers in a locked state at all times.

[0072] It should be noted that the current amplifier 29 is used to amplify the calibration signal with a frequency of nΔf to obtain a calibration signal with a frequency of nΔf. After passing through a series of amplification circuits, the signal will have nonlinear distortion. At the same time, since the lasers are not completely locked, there will be jitter and drift in the nΔf signal. The nΔf signal no longer appears as a perfect sine. The distortion of the calibration signal will cause its phase to be not proportional to time. Therefore, the time axis can be calibrated by analyzing the phase change of the signal. The calibration method is as follows: Figure 3 As shown, take A, B, C, and D as the zero-crossing time position of the distorted signal (in signal processing, the zero-crossing position is the easiest to judge), take the midpoints E, F, and G of the three segments AB, BC, and CD, and then take the midpoints of EF and FG as the zero-crossing position of the new time axis, and the calibration of the signal phase distortion can be completed.

[0073] After calibration, a nΔf signal without jitter and drift is obtained, which can monitor the change of the frequency difference Δf between laser 1 and laser 2. The change of the frequency difference Δf can be corrected by software post-processing to keep the two lasers in a locked state.

[0074] In a specific embodiment,

[0075] The terahertz transceiver module includes: a terahertz radiation source 7, a terahertz detector 10, a voltage source 8, a terahertz lens 9, a current amplifier 11 and an acquisition card 12;

[0076] The voltage source 8 is used to provide a bias voltage for the terahertz radiation source 7;

[0077] In a specific implementation, the voltage source 8 is used to provide a bias voltage of 100V for the terahertz radiation source 7;

[0078] The terahertz radiation source 7 is used to generate terahertz radiation when a bias voltage is externally provided to maintain a stable laser pulse generated by the femtosecond pulse laser 3 in a locked state;

[0079] In specific implementation, the terahertz radiation source uses a fiber-type terahertz photoconductive generating antenna with an excitation wavelength of 1550nm;

[0080] The terahertz lens 9 is used to converge the terahertz radiation beam and assist the transmission of the terahertz radiation beam;

[0081] In specific implementation, the terahertz lens 9 is used to converge the terahertz beam and assist the transmission of the terahertz beam. In the embodiment of the present invention, the size of the terahertz lens is 2 inches, and the focusing distance is 5 cm. After the terahertz radiation source 7 generates terahertz radiation, it is converged into a parallel beam through the terahertz lens, and the parallel beam is then converged into the terahertz detector 10 through the terahertz lens;

[0082] The terahertz detector 10 is used to respond to the terahertz radiation signal when the stable laser pulse is generated by the femtosecond pulse laser 1 provided externally and maintained in a locked state, and convert the terahertz radiation signal into a current signal for output;

[0083] In specific implementation, the terahertz detector uses a fiber-optic terahertz photoconductive detection antenna with an excitation wavelength of 1550nm;

[0084] The current amplifier 11 is used to amplify the current signal output by the terahertz detector 10 and input it into the acquisition card 12;

[0085] In a specific implementation, the current amplifier 11 is used to amplify the current signal output by the terahertz detector 10, with an amplification factor of 10^7, and input it into the acquisition card 12;

[0086] The acquisition card 12 is used to acquire current signals and display them on a display so that an operator can observe the terahertz signals.

[0087] In a specific implementation, the acquisition card 12 is used to acquire current signals and observe terahertz signals on a display, and the acquisition card uses NI's PXIe 5122.

[0088] The invention provides an asynchronous electro-optical sampling device with locked repetition rate, which has no additional requirements for lasers and allows two lasers to maintain a free-running state. Accurate frequency locking can be achieved by simply monitoring the repetition rate difference between the two lasers through a calibration signal extraction module and software post-processing. After frequency locking, highly stable asynchronous sampling can be achieved.

[0089] Based on the same inventive concept, the present invention also provides a repetition-frequency locked asynchronous electro-optical sampling method, see Figure 4 , the method comprising:

[0090] S400: The pump-probe laser module provides laser pulses and laser difference frequency signals;

[0091] S402: The calibration signal extraction module extracts the higher harmonics of the laser difference frequency signal for processing by the processing software to obtain the calibration signal, and then calibrates and re-locks the frequency of the two lasers;

[0092] S404: The terahertz transceiver module receives the respective laser signals emitted by the two calibrated and re-frequency-locked lasers to achieve the generation and detection of terahertz signals.

[0093] In a specific embodiment,

[0094] The pump-probe laser module includes: a femtosecond pulse laser 1, a femtosecond pulse laser 3, a photodetector 5, an optical mixer 4, an optical fiber 2 and a low-pass filter 6; wherein,

[0095] The femtosecond pulse laser 1 is used to provide a first laser pulse for the photodetector 13, and the laser repetition frequency is f1;

[0096] The femtosecond pulse laser 3 is used to provide a second laser pulse to the photodetector 19, and the laser repetition frequency is f2;

[0097] The optical mixer 4 is used to mix the first laser pulse and the second laser pulse and input the mixed pulses into the photodetector 5;

[0098] The photodetector 5 is used to convert the optical mixing signal into an electrical signal and then input it into the low-pass filter 6;

[0099] The low-pass filter 6 is used to filter the optical mixing electrical signal, and the cut-off frequency is f1. After filtering, a laser difference frequency signal Δf is obtained; wherein Δf=f2-f1;

[0100] The optical fiber 2 is used to transmit the first laser pulse and the second laser pulse emitted by the femtosecond pulse laser 1 and the femtosecond pulse laser 3 , and to transmit the optical mixing signal emitted by the optical mixer 4 .

[0101] In a specific embodiment,

[0102] The calibration signal extraction module includes: a photodetector 13, a bandpass filter 14, a current amplifier 15, a mixer 16, a low-pass filter 23, a current amplifier 24, a power divider 18, a signal generator 17, a photodetector 19, a bandpass filter 20, a current amplifier 21, a mixer 22, a low-pass filter 25, a current amplifier 26, a mixer 27, a low-pass filter 28 and a current amplifier 29;

[0103] The photodetector 13 is used to convert the first laser pulse input by the laser 1 into an electrical signal with a frequency of f1, and input the electrical signal into the bandpass filter 14;

[0104] The bandpass filter 14 is used to extract the nth harmonic from the electrical signal with a frequency of f1;

[0105] The current amplifier 15 is used to amplify the nth harmonic signal output by the bandpass filter 14;

[0106] The mixer 16 is used for mixing the nth harmonic signal of the laser 1 with the local oscillator signal provided by the signal generator 17;

[0107] The power divider 18 is used to divide the local oscillator signal provided by the signal generator 17 into two paths, and mix them with the nth harmonic of the laser 1 and the nth harmonic of the laser 3 respectively;

[0108] The signal generator 17 is used to provide a local oscillator signal;

[0109] Among them, the frequency of the local oscillator signal is f LO =nf1+f L , where f L is a value close to the repetition frequency f1 of laser 1;

[0110] The low-pass filter 23 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 1, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L ;

[0111] The current amplifier 24 is used to amplify the current signal after low-pass filtering;

[0112] The photodetector 19 is used to convert the second laser pulse input by the laser 3 into an electrical signal with a frequency of f2, and input the electrical signal into the bandpass filter 20;

[0113] The bandpass filter 20 is used to extract the nth harmonic from the electrical signal with a frequency of f2;

[0114] The current amplifier 21 is used to amplify the nth harmonic signal output by the bandpass filter 20;

[0115] The mixer 22 is used to mix the nth harmonic signal of the laser 3 with the local oscillator signal provided by the signal generator 17;

[0116] The low-pass filter 25 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 3, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L -nΔf, where Δf = f2-f1;

[0117] The current amplifier 26 is used to amplify the current signal after low-pass filtering;

[0118] The mixer 27 is used to convert the frequency f L -nΔf vs. f L The signal is mixed to obtain a signal with a frequency of nΔf;

[0119] The current amplifier 29 is used to amplify the calibration signal with a frequency of nΔf and output it to obtain an initial calibration signal with a frequency of nΔf.

[0120] In a specific embodiment,

[0121] The initial calibration signal has nonlinear distortion after passing through the amplification circuit, and also has jitter and drift because the two lasers are not completely locked.

[0122] The initial calibration signal is processed by the processing software to obtain the final calibration signal, which is specifically:

[0123] Take A, B, C, and D as the zero-crossing time position of the distorted signal, take the midpoints E, F, and G of the three segments AB, BC, and CD, and then take the midpoints of EF and FG as the zero-crossing position of the new time axis, and the calibration of the signal phase distortion is completed;

[0124] After calibration, an nΔf signal without jitter and drift is obtained, that is, the change of the frequency difference Δf between laser 1 and laser 2 is monitored, and then the change of the frequency difference Δf is corrected by post-processing software to keep the two lasers in a locked state at all times.

[0125] In a specific embodiment,

[0126] The terahertz transceiver module includes: a terahertz radiation source 7, a terahertz detector 10, a voltage source 8, a terahertz lens 9, a current amplifier 11 and an acquisition card 12;

[0127] The voltage source 8 is used to provide a bias voltage for the terahertz radiation source 7;

[0128] The terahertz radiation source 7 is used to generate terahertz radiation when a bias voltage is externally provided to maintain a stable laser pulse generated by the femtosecond pulse laser 3 in a locked state;

[0129] The terahertz lens 9 is used to converge the terahertz radiation beam and assist the transmission of the terahertz radiation beam;

[0130] The terahertz detector 10 is used to respond to the terahertz radiation signal when the stable laser pulse is generated by the femtosecond pulse laser 1 provided externally and maintained in a locked state, and convert the terahertz radiation signal into a current signal for output;

[0131] The current amplifier 11 is used to amplify the current signal output by the terahertz detector 10 and input it into the acquisition card 12;

[0132] The acquisition card 12 is used to acquire current signals and display them on a display so that an operator can observe the terahertz signals.

[0133] The present invention provides a frequency-locked asynchronous electro-optical sampling method. Compared with the traditional method of adding expensive laser cavities and additional lasers, the present application realizes real-time monitoring of frequency difference signals through software post-processing, is not limited by hardware conditions and can achieve precise locking, has a low processing price, and is easy to integrate.

[0134] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0135] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A repetition-locked asynchronous electro-optical sampling device, characterized in that: The device comprises: Pump detection laser module, calibration signal extraction module and terahertz transceiver module; among them, The pump-probe laser module is used to provide laser pulses and laser difference frequency signals; The calibration signal extraction module is used to extract the higher harmonics of the laser difference frequency signal so as to be processed by the processing software to obtain the calibration signal, thereby calibrating and re-locking the frequency of the two lasers; The terahertz transceiver module is used to receive the respective laser signals emitted by two calibrated and re-frequency-locked lasers to achieve the generation and detection of terahertz signals.

2. The device according to claim 1, characterized in that The pump-probe laser module includes: a femtosecond pulse laser 1, a femtosecond pulse laser 3, a photodetector 5, an optical mixer 4, an optical fiber 2 and a low-pass filter 6; wherein, The femtosecond pulse laser 1 is used to provide a first laser pulse for the photodetector 13, and the laser repetition frequency is f1; The femtosecond pulse laser 3 is used to provide a second laser pulse to the photodetector 19, and the laser repetition frequency is f2; The optical mixer 4 is used to mix the first laser pulse and the second laser pulse and input the mixed pulses into the photodetector 5; The photodetector 5 is used to convert the optical mixing signal into an electrical signal and then input it into the low-pass filter 6; The low-pass filter 6 is used to filter the optical mixing electrical signal, and the cut-off frequency is f1. After filtering, a laser difference frequency signal Δf is obtained; wherein Δf=f2-f1; The optical fiber 2 is used to transmit the first laser pulse and the second laser pulse emitted by the femtosecond pulse laser 1 and the femtosecond pulse laser 3 , and to transmit the optical mixing signal emitted by the optical mixer 4 .

3. The device according to claim 2, characterized in that The calibration signal extraction module includes: a photodetector 13, a bandpass filter 14, a current amplifier 15, a mixer 16, a low-pass filter 23, a current amplifier 24, a power divider 18, a signal generator 17, a photodetector 19, a bandpass filter 20, a current amplifier 21, a mixer 22, a low-pass filter 25, a current amplifier 26, a mixer 27, a low-pass filter 28 and a current amplifier 29; The photodetector 13 is used to convert the first laser pulse input by the laser 1 into an electrical signal with a frequency of f1, and input the electrical signal into the bandpass filter 14; The bandpass filter 14 is used to extract the nth harmonic from the electrical signal with a frequency of f1; The current amplifier 15 is used to amplify the nth harmonic signal output by the bandpass filter 14; The mixer 16 is used for mixing the nth harmonic signal of the laser 1 with the local oscillator signal provided by the signal generator 17; The power divider 18 is used to divide the local oscillator signal provided by the signal generator 17 into two paths, and mix them with the nth harmonic of the laser 1 and the nth harmonic of the laser 3 respectively; The signal generator 17 is used to provide a local oscillator signal; Among them, the frequency of the local oscillator signal is f LO =nf1+f L , where f L is a value close to the repetition frequency f1 of laser 1; The low-pass filter 23 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 1, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L ; The current amplifier 24 is used to amplify the current signal after low-pass filtering; The photodetector 19 is used to convert the second laser pulse input by the laser 3 into an electrical signal with a frequency of f2, and input the electrical signal into the bandpass filter 20; The bandpass filter 20 is used to extract the nth harmonic from the electrical signal with a frequency of f2; The current amplifier 21 is used to amplify the nth harmonic signal output by the bandpass filter 20; The mixer 22 is used to mix the nth harmonic signal of the laser 3 with the local oscillator signal provided by the signal generator 17; The low-pass filter 25 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 3, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L -nΔf, where Δf = f2-f1; The current amplifier 26 is used to amplify the current signal after low-pass filtering; The mixer 27 is used to convert the frequency f L -nΔf vs. f L The signal is mixed to obtain a signal with a frequency of nΔf; The current amplifier 29 is used to amplify the calibration signal with a frequency of nΔf and output it to obtain an initial calibration signal with a frequency of nΔf.

4. The device according to claim 3, characterized in that The initial calibration signal has nonlinear distortion after passing through the amplification circuit, and also has jitter and drift because the two lasers are not completely locked. The initial calibration signal is processed by the processing software to obtain the final calibration signal, which is specifically: Take A, B, C, and D as the zero-crossing time position of the distorted signal, take the midpoints E, F, and G of the three segments AB, BC, and CD, and then take the midpoints of EF and FG as the zero-crossing position of the new time axis, and the calibration of the signal phase distortion is completed; After calibration, an nΔf signal without jitter and drift is obtained, that is, the change of the frequency difference Δf between laser 1 and laser 2 is monitored, and then the change of the frequency difference Δf is corrected by post-processing software to keep the two lasers in a locked state at all times.

5. The device according to claim 4, characterized in that The terahertz transceiver module includes: a terahertz radiation source 7, a terahertz detector 10, a voltage source 8, a terahertz lens 9, a current amplifier 11 and an acquisition card 12; The voltage source 8 is used to provide a bias voltage for the terahertz radiation source 7; The terahertz radiation source 7 is used to generate terahertz radiation when a bias voltage is externally provided to maintain a stable laser pulse generated by the femtosecond pulse laser 3 in a locked state; The terahertz lens 9 is used to converge the terahertz radiation beam and assist the transmission of the terahertz radiation beam; The terahertz detector 10 is used to respond to the terahertz radiation signal when the stable laser pulse is generated by the femtosecond pulse laser 1 provided externally and maintained in a locked state, and convert the terahertz radiation signal into a current signal for output; The current amplifier 11 is used to amplify the current signal output by the terahertz detector 10 and input it into the acquisition card 12; The acquisition card 12 is used to acquire current signals and display them on a display so that an operator can observe the terahertz signals.

6. A repetition-locked asynchronous electro-optical sampling method, characterized in that: The device for asynchronous electro-optical sampling with repetition rate locking according to any one of claims 1 to 5, the method comprising: The pump-probe laser module provides laser pulses and laser difference frequency signals; The calibration signal extraction module extracts the higher harmonics of the laser difference frequency signal for processing by the processing software to obtain the calibration signal, and then calibrates and re-locks the frequency of the two lasers; The terahertz transceiver module receives the respective laser signals emitted by two calibrated and re-frequency-locked lasers to achieve the generation and detection of terahertz signals.

7. The method according to claim 6, characterized in that The pump-probe laser module includes: a femtosecond pulse laser 1, a femtosecond pulse laser 3, a photodetector 5, an optical mixer 4, an optical fiber 2 and a low-pass filter 6; wherein, The femtosecond pulse laser 1 is used to provide a first laser pulse for the photodetector 13, and the laser repetition frequency is f1; The femtosecond pulse laser 3 is used to provide a second laser pulse to the photodetector 19, and the laser repetition frequency is f2; The optical mixer 4 is used to mix the first laser pulse and the second laser pulse and input the mixed pulses into the photodetector 5; The photodetector 5 is used to convert the optical mixing signal into an electrical signal and then input it into the low-pass filter 6; The low-pass filter 6 is used to filter the optical mixing electrical signal, and the cut-off frequency is f1. After filtering, a laser difference frequency signal Δf is obtained; wherein Δf=f2-f1; The optical fiber 2 is used to transmit the first laser pulse and the second laser pulse emitted by the femtosecond pulse laser 1 and the femtosecond pulse laser 3 , and to transmit the optical mixing signal emitted by the optical mixer 4 .

8. The method according to claim 7, characterized in that The calibration signal extraction module includes: a photodetector 13, a bandpass filter 14, a current amplifier 15, a mixer 16, a low-pass filter 23, a current amplifier 24, a power divider 18, a signal generator 17, a photodetector 19, a bandpass filter 20, a current amplifier 21, a mixer 22, a low-pass filter 25, a current amplifier 26, a mixer 27, a low-pass filter 28 and a current amplifier 29; The photodetector 13 is used to convert the first laser pulse input by the laser 1 into an electrical signal with a frequency of f1, and input the electrical signal into the bandpass filter 14; The bandpass filter 14 is used to extract the nth harmonic from the electrical signal with a frequency of f1; The current amplifier 15 is used to amplify the nth harmonic signal output by the bandpass filter 14; The mixer 16 is used for mixing the nth harmonic signal of the laser 1 with the local oscillator signal provided by the signal generator 17; The power divider 18 is used to divide the local oscillator signal provided by the signal generator 17 into two paths, and mix them with the nth harmonic of the laser 1 and the nth harmonic of the laser 3 respectively; The signal generator 17 is used to provide a local oscillator signal; Among them, the frequency of the local oscillator signal is f LO =nf1+f L , where f L is a value close to the repetition frequency f1 of laser 1; The low-pass filter 23 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 1, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L ; The current amplifier 24 is used to amplify the current signal after low-pass filtering; The photodetector 19 is used to convert the second laser pulse input by the laser 3 into an electrical signal with a frequency of f2, and input the electrical signal into the bandpass filter 20; The bandpass filter 20 is used to extract the nth harmonic from the electrical signal with a frequency of f2; The current amplifier 21 is used to amplify the nth harmonic signal output by the bandpass filter 20; The mixer 22 is used to mix the nth harmonic signal of the laser 3 with the local oscillator signal provided by the signal generator 17; The low-pass filter 25 is used to perform low-pass filtering on the signal obtained by mixing the local oscillator signal with the nth harmonic of the laser 3, with a cutoff frequency of 2nf1. The frequency of the signal obtained after filtering is f L -nΔf, where Δf = f2-f1; The current amplifier 26 is used to amplify the current signal after low-pass filtering; The mixer 27 is used to convert the frequency f L -nΔf vs. f L The signal is mixed to obtain a signal with a frequency of nΔf; The current amplifier 29 is used to amplify the calibration signal with a frequency of nΔf and output it to obtain an initial calibration signal with a frequency of nΔf.

9. The method according to claim 8, characterized in that The initial calibration signal has nonlinear distortion after passing through the amplification circuit, and also has jitter and drift because the two lasers are not completely locked. The initial calibration signal is processed by the processing software to obtain the final calibration signal, which is specifically: Take A, B, C, and D as the zero-crossing time position of the distorted signal, take the midpoints E, F, and G of the three segments AB, BC, and CD, and then take the midpoints of EF and FG as the zero-crossing position of the new time axis, and the calibration of the signal phase distortion is completed; After calibration, an nΔf signal without jitter and drift is obtained, that is, the change of the frequency difference Δf between laser 1 and laser 2 is monitored, and then the change of the frequency difference Δf is corrected by post-processing software to keep the two lasers in a locked state at all times.

10. The method according to claim 9, characterized in that The terahertz transceiver module includes: a terahertz radiation source 7, a terahertz detector 10, a voltage source 8, a terahertz lens 9, a current amplifier 11 and an acquisition card 12; The voltage source 8 is used to provide a bias voltage for the terahertz radiation source 7; The terahertz radiation source 7 is used to generate terahertz radiation when a bias voltage is externally provided to maintain a stable laser pulse generated by the femtosecond pulse laser 3 in a locked state; The terahertz lens 9 is used to converge the terahertz radiation beam and assist the transmission of the terahertz radiation beam; The terahertz detector 10 is used to respond to the terahertz radiation signal when the stable laser pulse is generated by the femtosecond pulse laser 1 provided externally and maintained in a locked state, and convert the terahertz radiation signal into a current signal for output; The current amplifier 11 is used to amplify the current signal output by the terahertz detector 10 and input it into the acquisition card 12; The acquisition card 12 is used to acquire current signals and display them on a display so that an operator can observe the terahertz signals.

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