Asynchronous optical sampling and phase-locked amplification integrated terahertz spectrum system

Abstract

The invention provides a terahertz spectrum system integrating asynchronous optical sampling and phase-locked amplification. The terahertz spectrum system comprises a pumping, detection and repetition frequency stabilization femtosecond laser emission module, a terahertz signal generation module, a terahertz signal detection module and a data phase-locked amplification and acquisition module. As the voltage pulse power supply with a terahertz signal modulation function and the phase-locked amplifier for amplifying and demodulating radio-frequency signals are introduced into the spectrum system, the terahertz asynchronous optical sampling spectrum system measurement method based on the phase-locked amplification technology has the advantages that compared with an existing standard terahertz asynchronous optical sampling spectrum system, the measurement accuracy is improved; both the time domain peak value signal-to-noise ratio and the frequency domain peak value dynamic range are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of terahertz spectroscopy, and in particular relates to a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification technology. Background Art

[0002] Terahertz (THz) waves are electromagnetic waves between microwaves and far infrared, with wide frequency range, high biosafety, rich fingerprint spectrum, high coherence and ultrafast transient characteristics. These characteristics make THz waves have wide application potential in space communications, radar detection, aerospace and biomedicine. In recent years, with the development of ultrafast laser technology, the generation of THz pulses has a stable and reliable excitation light source, enabling people to study the characteristics of THz waves and their interaction with matter.

[0003] As an important part of terahertz spectroscopy technology, terahertz time-domain spectroscopy (THz-TDS) can accurately characterize the optical, electrical and dielectric properties of samples that change with terahertz frequency. However, the development of THz-TDS technology is limited by the acquisition speed of terahertz pulses. Early technologies have limitations in rapid detection. For example, traditional technologies use a single light source plus moving parts (such as Michelson interferometers or optical delay lines) to achieve the acquisition of spectral signals during spectral scanning. This acquisition method is slow and can only collect time-domain signal information, resulting in low spectral resolution and poor system stability. In order to solve these problems, asynchronous optical sampling technology (ASOPS) came into being. By realizing optical delay without moving components, it greatly improves the delayed scanning speed and expands the scanning range. It can combine the advantages of wide spectral coverage, high detection sensitivity, high frequency resolution, and fast measurement that cannot be obtained simultaneously in traditional spectral measurements, showing unparalleled comprehensive performance.

[0004] In addition, the application of phase-locked amplification technology in terahertz spectroscopy technology provides new possibilities for the accurate measurement of terahertz waves. This technology effectively suppresses 1 / f noise through modulation and demodulation, thereby improving the quality of the signal and achieving a higher signal-to-noise ratio and dynamic range. However, to date, the phase-locked amplification technology and terahertz asynchronous optical sampling technology have not been integrated. Therefore, the present invention realizes a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification to overcome the limitations of the prior art and promote the application of terahertz technology in a wider range of fields. Summary of the invention

[0005] The purpose of the present invention is to provide a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification with a higher signal-to-noise ratio than traditional terahertz spectroscopy technology. To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification, which has the following characteristics: a femtosecond laser emission module, which is used to emit a femtosecond laser with a locked repetition frequency and an adjustable repetition frequency; a signal generation module, which is used to emit a terahertz signal; a signal detection module, which is used to detect the emitted terahertz signal; and a data phase-locked amplification and acquisition module, which is used to modulate, amplify and demodulate the terahertz signal, so that low-frequency 1 / f noise is effectively suppressed, thereby forming a signal with a higher signal-to-noise ratio.

[0007] The terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following features: wherein the laser emission module includes: a first femtosecond laser, used to emit femtosecond pump laser pulses with a first set repetition frequency; a second femtosecond laser, used to emit femtosecond detection laser pulses with a second set repetition frequency; the two laser pulses have a small repetition frequency difference; a repetition frequency stabilization and synchronization system, used to precisely lock the first and second repetition frequencies and the repetition frequency difference between the two femtosecond lasers.

[0008] The terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following characteristics: wherein the central wavelength of the femtosecond laser is 780 nm, the pulse width is 100 fs, and the output average power is greater than 100 mW.

[0009] The terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following characteristics: wherein the first set repetition frequency is 100 MHz, and the frequency difference between the first set repetition frequency and the second set repetition frequency ranges from 5 Hz to 1000 Hz.

[0010] The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following feature: wherein the repetition frequency difference is 5 Hz.

[0011] The terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following features: wherein the signal generating module includes an attenuation plate for adjusting the light intensity of the femtosecond laser incident on the first photoconductive antenna, thereby ensuring that the light intensity of the femtosecond laser incident on the first photoconductive antenna is less than the damage threshold; a focusing lens for focusing the optical path of the pump laser to form a first focal spot, and the first focal spot is located on the first photoconductive antenna; and the first photoconductive antenna, a bias voltage is applied to the antenna, so that when the pump laser passes through the first photoconductive antenna, the first set repetition frequency is down-converted to the terahertz frequency band, thereby emitting a terahertz signal.

[0012] The asynchronous optical sampling and phase-locked amplification integrated terahertz spectroscopy system provided by the present invention may also have the following features: wherein the signal detection module includes an attenuation plate for adjusting the light intensity of the femtosecond laser incident on the second photoconductive antenna, thereby ensuring that the light intensity of the femtosecond laser incident on the second photoconductive antenna is less than a damage threshold; a focusing lens for focusing the optical path of the detection laser to form a second focal spot, and the second focal spot is located on the second photoconductive antenna; and the second photoconductive antenna, the emitted terahertz signal and the detection laser coincide at a convergence point on the second photoconductive antenna, generating an asynchronous optical sampling terahertz time-domain electric field signal.

[0013] The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following features: wherein, the data phase-locked amplification and acquisition module includes: a voltage pulse generator for modulating the terahertz emission signal; a current amplifier for receiving and amplifying the asynchronous optical sampling terahertz electric field signal; a phase-locked amplifier for amplifying and demodulating the modulated asynchronous optical sampling terahertz electric field signal; and a data acquisition recorder for receiving the amplified asynchronous optical sampling terahertz electric field signal and displaying the signal waveform.

[0014] The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following feature: wherein the voltage pulse generator applies a pulse bias voltage to the first photoconductive antenna, and the modulation frequency is 1 MHz.

[0015] The terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification provided by the present invention may also have the following characteristics: wherein the amplification gain of the current amplifier is V / A.

[0016] Functions and Effects of the Invention

[0017] According to the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification involved in the present invention, because it has a voltage pulse generator for modulating terahertz signals and a phase-locked amplifier for amplifying and demodulating asynchronous optically sampled terahertz electric field signals, the measurement method combining the phase-locked amplification technology with the terahertz asynchronous optical sampling technology of the present invention has a significant improvement in both the time domain peak signal-to-noise ratio and the frequency domain peak dynamic range compared to the existing terahertz asynchronous optical sampling spectroscopy technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification in an embodiment of the present invention;

[0019] Figure 2It is a time domain signal diagram of the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification in an embodiment of the present invention;

[0020] Figure 3 It is a frequency domain signal diagram of the terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments and the accompanying drawings specifically illustrate the terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification of the present invention.

[0022] <Example>

[0023] This embodiment provides a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification.

[0024] Figure 1 It is a schematic diagram of the structure of a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification in an embodiment of the present invention.

[0025] like Figure 1 As shown, the asynchronous optical sampling and phase-locked amplification integrated terahertz spectroscopy system 100 of this embodiment includes a femtosecond laser emission module 10 , a signal generation module 20 , a signal detection module 30 , and a data phase-locked amplification and acquisition module 40 .

[0026] The femtosecond laser emission module 10 is used to emit femtosecond laser pulses with locked repetition frequency and adjustable repetition frequency. The laser emission module 10 includes a first femtosecond laser 11 , a second femtosecond laser 12 , and a frequency stabilization synchronization system 13 .

[0027] The first femtosecond laser 11 is used to emit repetition-frequency locked femtosecond pump laser pulses; in this embodiment, the first predetermined repetition frequency is preferably 100 MHz.

[0028] The second femtosecond laser 12 is used to emit repetition frequency locked femtosecond detection laser pulses; the two laser pulses have a small repetition frequency difference, and the frequency difference between the first set repetition frequency and the second set repetition frequency ranges from 5 Hz to 1000 Hz; in this embodiment, the repetition frequency difference is preferably 5 Hz.

[0029] In this embodiment, the central wavelength of the femtosecond laser is 780 nm, the pulse width is 100 fs, and the output average power is greater than 100 mW.

[0030] The frequency stabilization synchronization system 13 is used to precisely lock the repetition frequency and the difference between the repetition frequencies of the two femtosecond lasers.

[0031] The signal generating module 20 is used for transmitting the terahertz signal, and comprises an attenuation plate 21 , a focusing lens 22 and a first photoconductive antenna 23 .

[0032] The attenuation plate 21 is used to adjust the light intensity of the femtosecond laser incident on the first photoconductive antenna 23, so as to ensure that the light intensity of the femtosecond laser incident on the first photoconductive antenna is less than the damage threshold.

[0033] The focusing lens 22 is used to focus the optical path of the pump laser to form a first focal spot, and the first focal spot is located on the first photoconductive antenna 23 .

[0034] A bias voltage is applied to the first photoconductive antenna 23, so that when the pump laser passes through the first photoconductive antenna, the first set repetition frequency drops to the terahertz frequency band, thereby emitting a terahertz signal. In this embodiment, the model of the first photoconductive antenna 23 is Teravil, ETM-8.

[0035] The signal detection module 30 is used to detect the emitted terahertz signal, and includes an attenuation plate 31 , a focusing lens 32 and a second photoconductive antenna 33 .

[0036] The attenuation plate 31 is used to adjust the light intensity of the femtosecond laser incident on the second photoconductive antenna 33, so as to ensure that the light intensity of the femtosecond laser incident on the second photoconductive antenna is less than the damage threshold.

[0037] The focusing lens 32 is used to focus the optical path of the detection laser to form a second focal spot, and the second focal spot is located on the second photoconductive antenna 33 .

[0038] The second photoconductive antenna 33 is located at the focusing point, and the emitted terahertz signal and the detection laser coincide with the convergence point on the second photoconductive antenna, generating an asynchronous optical sampling terahertz time-domain electric field signal.

[0039] The data lock-in amplifier and acquisition module 40 is used to modulate, amplify and demodulate the terahertz signal, so that the low-frequency 1 / f noise is effectively suppressed, thereby forming a signal with a higher signal-to-noise ratio. It includes a voltage pulse generator 41, a current amplifier 42, a lock-in amplifier 43 and a data acquisition recorder 44.

[0040] The voltage pulse generator 41 is used to modulate the terahertz emission signal and applies a pulse bias voltage to the first photoconductive antenna 23. In this embodiment, the voltage pulse generator 41 is Agilent 8114A, 100V / 2A, the modulation frequency is preferably 1 MHz, and the bias voltage is preferably 20V.

[0041] The current amplifier 42 is used to receive and amplify the asynchronous optical sampling terahertz electric field signal. In this embodiment, the model of the current amplifier 42 is FEMTO, DHPCA-100 I / V, and the amplification gain of the current amplifier is preferably V / A.

[0042] The lock-in amplifier 43 is used to amplify and demodulate the modulated asynchronous optical sampling terahertz electric field signal. In this embodiment, the model of the lock-in amplifier 43 is Zurich Instruments, HF2LI 50 MHz.

[0043] The data acquisition record 44 is used to receive the amplified asynchronous optical sampling terahertz electric field signal and display the signal waveform.

[0044] The following combination Figure 1 The workflow of the THz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification is described, including the following steps:

[0045] Step 1: A pump laser pulse with a first predetermined repetition frequency is emitted by the first femtosecond laser 11, and a detection laser pulse with a second predetermined repetition frequency is emitted by the second femtosecond laser 12. The two laser pulses have a small repetition frequency difference and the repetition frequency difference is precisely locked by a frequency stabilization synchronization system.

[0046] Step 2: The intensity of the pump femtosecond laser incident on the first photoconductive antenna 23 is adjusted by the attenuation plate 21, and then focused by the focusing lens 22 to the first photoconductive antenna, and the second photoconductive antenna 33 is driven by the voltage pulse generator 41. When the femtosecond laser is irradiated on the electrode gap, photogenerated carriers are generated, and the carriers are accelerated under the pulse bias voltage and radiate modulated terahertz pulse signals.

[0047] Step 3: The detection laser passes through the attenuation plate 31 and the focusing lens 32 and is focused on the second photoconductive antenna 33. At this time, the terahertz pulse and the detection laser converge on the second photoconductive antenna, and signal collection is performed based on the asynchronous optical sampling principle.

[0048] Step 4: The photocurrent output by the second photoconductive antenna 33 is amplified by the current amplifier 42 and then connected to the phase-locked amplifier 43 to achieve demodulation and amplification of the modulated signal.

[0049] Step 5: The terahertz time-domain pulse signal is collected through the data collection record 44, and the spectrum information is obtained after Fourier transformation.

[0050] Figure 2 is a time domain signal diagram of a terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification in an embodiment of the present invention; Figure 3It is a frequency domain signal diagram of the terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification in an embodiment of the present invention.

[0051] Functions and Effects of the Embodiments

[0052] According to the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification involved in this embodiment, because it has a first femtosecond laser that emits pump laser, a second femtosecond laser that emits detection laser, and a frequency stabilization synchronization system, the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification in this embodiment can stably emit two femtosecond laser pulses with locked repetition frequency and a small repetition frequency difference.

[0053] Furthermore, because the frequency difference between the first predetermined repetition frequency and the second predetermined repetition frequency in this embodiment ranges from 5 Hz to 1000 Hz, the difference between the first predetermined repetition frequency and the second predetermined repetition frequency can be flexibly selected within a larger range according to actual needs.

[0054] Because the asynchronous optical sampling and phase-locked amplification integrated terahertz spectroscopy system involved in this embodiment is provided with an attenuation plate and a focusing lens between the femtosecond laser and the photoconductive antenna, it is capable of adjusting the light intensity of the femtosecond laser incident on the photoconductive antenna and converging it, so that the light intensity of the femtosecond laser incident on the photoconductive antenna can be ensured to be less than the damage threshold, and the pump laser can be more efficiently converted into the emission terahertz signal without damaging the photoconductive antenna.

[0055] Because the terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification involved in this embodiment has a voltage pulse generator, which is combined with a phase-locked amplifier to modulate, amplify and demodulate the original terahertz electric field time domain signal and effectively suppress low-frequency 1 / f noise, the terahertz asynchronous optical sampling spectroscopy system based on phase-locked amplification in this embodiment improves the signal-to-noise ratio compared with the existing terahertz asynchronous optical sampling spectroscopy technology and can obtain a wide dynamic range.

[0056] Because the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification involved in this embodiment first detects the time domain waveform and then performs Fourier transform to quickly obtain the frequency domain spectrum when collecting and recording the signal, the terahertz spectroscopy system integrated with asynchronous optical sampling and phase-locked amplification in this embodiment can obtain the full frequency domain spectrum information of the signal.

[0057] The above-mentioned implementation modes are preferred cases of the present invention and are not used to limit the protection scope of the present invention. Various deformations or modifications that can be made by ordinary technicians in this field without creative work within the scope of the attached claims are still within the protection scope of this patent.

Claims

1. A terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification, having the following characteristics: A femtosecond laser emission module, used for emitting femtosecond laser pulses with locked repetition frequency and adjustable repetition frequency; A signal generating module, used for transmitting a terahertz signal; A signal detection module, used for detecting the emitted terahertz signal; The data phase-locked amplification and acquisition module is used to modulate, amplify and demodulate the terahertz signal so that the low-frequency 1 / f noise is effectively suppressed, thereby forming a signal with a higher signal-to-noise ratio.

2. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 1, characterized in that: It also includes: wherein the femtosecond laser emission module includes: a first femtosecond laser, used to emit a repetition frequency locked femtosecond pump laser pulse; a second femtosecond laser, used to emit a repetition frequency locked femtosecond detection laser pulse; the two laser pulses have a small repetition frequency difference; a repetition frequency locking and synchronization system, used to precisely lock the repetition frequency and the repetition frequency difference between the two femtosecond lasers.

3. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 2, characterized in that: Also includes: The central wavelength of the femtosecond laser is 780 nm, the pulse width is 100 fs, and the output average power is greater than 100 mW.

4. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 2, characterized in that: Also includes: The first set repetition frequency is 100 MHz, and the frequency difference between the first set repetition frequency and the second set repetition frequency ranges from 5 Hz to 1000 Hz.

5. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 2, characterized in that: Also includes: The repetition frequency difference is 5 Hz.

6. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 1, characterized in that: Also includes: The signal generating module includes an attenuation plate for adjusting the light intensity of the femtosecond laser incident on the first photoconductive antenna, thereby ensuring that the light intensity of the femtosecond laser incident on the first photoconductive antenna is less than a damage threshold; A focusing lens, used for focusing the optical path of the pump laser to form a first focal spot, wherein the first focal spot is located on the first photoconductive antenna; and a first photoconductive antenna, a bias voltage is applied to the antenna, so that when the pump laser passes through the first photoconductive antenna, the first predetermined repetition frequency is reduced to the terahertz frequency band, thereby emitting a terahertz signal.

7. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 1, characterized in that: Also includes: The signal detection module includes an attenuation plate for adjusting the light intensity of the femtosecond laser incident on the second photoconductive antenna, thereby ensuring that the light intensity of the femtosecond laser incident on the second photoconductive antenna is less than a damage threshold; A focusing lens, used for focusing the optical path of the detection laser to form a second focal spot, wherein the second focal spot is located on the second photoconductive antenna; and a second photoconductive antenna, wherein the emitted terahertz signal and the detection laser coincide with a convergence point on the second photoconductive antenna to generate an asynchronous optically sampled terahertz time-domain electric field signal.

8. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 1, characterized in that: Also includes: The data phase-locked amplification and acquisition module includes a voltage pulse generator for modulating the terahertz emission signal; A current amplifier, used for receiving and amplifying the asynchronous optically sampled terahertz electric field signal; A lock-in amplifier, used for amplifying and demodulating the modulated asynchronous optical sampling terahertz electric field signal; and data acquisition and recording, used to receive the amplified asynchronous optical sampling terahertz electric field signal and display the signal waveform.

9. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification according to claim 8, characterized in that: Also includes: The voltage pulse generator applies a pulse bias voltage to the first photoconductive antenna, and the modulation frequency is 1 MHz.

10. The terahertz spectroscopy system integrating asynchronous optical sampling and phase-locked amplification technology according to claim 8, characterized in that: Also includes: The amplification gain of the current amplifier is V / A.

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