A mid-infrared discrete-time stretch spectroscopy method

Abstract

The application discloses a kind of mid-infrared discrete time stretching spectrum method, its characteristics are as follows:1) prepare the double-color pulse light source with slightly different repetition frequency;2) the pulse of pulse light source 1 is output wavelength broadening and time stretching for the signal light of nonlinear difference frequency, and the pulse of pulse light source 2 is output power amplification, for the pump light of nonlinear difference frequency;3) the time-domain broadening spectrum optical sampling of signal light by pump light pulse, obtain the pulse sequence of mid-infrared discrete time stretching;4) mid-infrared discrete chirp pulse is measured through low bandwidth mid-infrared detector after passing through the sample to be measured, and absorption spectrum information is obtained.The application has the advantages of wide band, high speed and high resolution compared with prior art, and the measurement of mid-infrared spectrum is completed by means of low bandwidth single-point detector, without dispersion spectrometer element and mechanical scanning device, which solves the problem of lack of time and high dispersion time-domain stretching medium in mid-infrared band, and expands the application of time stretching technology in mid-infrared band.

Description

Technical Field

[0001] The present invention relates to the technical field of mid-infrared spectroscopy, in particular to a mid-infrared discrete time stretching spectroscopy method. Background Art

[0002] The mid-infrared (MIR) band lies in the molecular fingerprint spectral region, encompassing the vibrational and rotational energy level transitions of numerous molecules. It can provide distinct infrared absorption signatures of the sample being measured, providing a crucial tool for qualitatively or quantitatively extracting molecular composition and structural information. It has become a commonly used and indispensable tool in modern structural chemistry and analytical chemistry, and is widely used in various fields, including physics, biology, and chemistry. Mid-infrared spectroscopy is widely applicable to a wide range of samples, capable of characterizing solid, liquid, and gaseous samples. It exhibits exceptional performance in the detection of inorganic, organic, and polymeric compounds, characterized by rapid testing, ease of operation, excellent reproducibility, high sensitivity, and minimal sample usage. The development of high-rate MIR spectroscopy has long been a frontier in this field, crucial for measuring rapidly changing dynamic spectra, such as those associated with studying random or non-repeating phenomena like gas combustion or protein conformational changes. Furthermore, high-frame-rate MIR spectroscopy provides a high-throughput means of acquiring and analyzing spectral information, playing a crucial role in areas such as substance detection, atmospheric remote sensing, and environmental monitoring.

[0003] However, existing mid-infrared spectral measurement technologies, limited by their operating mechanisms or device performance, have long faced the dilemma of insufficient spectral measurement speed. For example, common dispersive spectrometers utilize spectroscopic devices such as gratings and prisms to spatially spread the spectrum to be measured. Linear or planar array detectors are then used to capture the resulting spatially chirped beam, allowing spectral information to be obtained through a single exposure. To ensure the resolution of spectral measurements, the linear or planar array detectors employed are generally required to have a sufficient number of pixels. This results in a generally low frame rate for mid-infrared multi-pixel detectors, severely limiting the refresh rate of mid-infrared spectral measurements. Fourier transform infrared spectrometers, another widely used spectral measurement tool, utilize a Michelson interferometer as their core. They obtain the interference pattern of the measured light field by scanning the optical path difference between the two arms of the interferometer. A Fourier transform operation is then performed to restore the spectral information of the measured light source. These spectrometers offer advantages such as high light flux and high resolution. Although Fourier transform infrared spectrometers can perform interferogram measurements using a single-point detector, the acquisition process inevitably relies on mechanical scanning, which significantly limits the spectral refresh rate.

[0004] In recent years, the emerging technology of time-stretch spectroscopy has emerged, offering an effective approach for high-speed infrared spectral measurements. Based on the fundamental principle of the spatiotemporal duality of light fields, this technique maps pulse spectral information into the time domain via a dispersive Fourier transform process. Using a single-pixel detector to measure the time-varying intensity information, the measured spectrum can be restored, ultimately enabling ultra-high-speed single-shot pulse spectral measurements. Typically, time-stretch spectroscopy requires the introduction of a large group velocity dispersion delay (typically reaching 0.1 ns / nm) to meet far-field diffraction requirements and achieve a one-to-one correspondence between the spectra on the time axis. Furthermore, achieving high spectral resolution places high demands on the bandwidth of the detection and acquisition systems (typically exceeding 10 GHz). Given these two stringent requirements, time-stretch spectroscopy currently primarily operates in the near-infrared (NIR). In contrast, the mid-infrared (MIIR) lacks low-loss, high-dispersion transmission media. Traditional glass optical fibers suffer from severe absorption losses in the MIR. Furthermore, the bandwidth of photodetectors in this band is limited, typically to sub-GHz. Therefore, the lack of efficient time-stretching media and high-speed infrared detection devices is the main obstacle restricting the expansion of time-stretching technology into the mid-infrared band. Summary of the Invention

[0005] The purpose of the present invention is to provide a mid-infrared discrete time stretch spectroscopy method in response to the deficiencies of the prior art. By utilizing the discrete time stretch effect, the bandwidth limitation of the mid-infrared detection and acquisition system is effectively reduced, and high-speed, high-resolution mid-infrared spectroscopy measurement can be achieved through a low-bandwidth single-pixel detector. Through the nonlinear difference frequency process of asynchronous optical sampling, a time-domain chirped mid-infrared pulse sequence is directly prepared, which circumvents the dilemma of lacking low-loss, high-dispersion time-domain stretching media in the mid-infrared band. This method does not require any dispersive spectroscopic elements and mechanical scanning devices, and can achieve mid-infrared stretch spectroscopy measurement with the help of a single-point detector. It has the advantages of simple structure, stable system, and easy operation. It can better solve the problem of lacking high-dispersion time-domain stretching media in the mid-infrared band, further expand the application of time stretching technology in the mid-infrared band, and provide strong support for applications in the fields of material detection, atmospheric remote sensing, and environmental monitoring.

[0006] The specific technical solution for achieving the purpose of the present invention is: a mid-infrared discrete time stretching spectroscopy method, which is characterized in that the method specifically includes the following steps:

[0007] 1) Prepare a two-color pulse light source with slightly different repetition frequencies: the central wavelength of pulse light source 1 is 1550nm, the repetition frequency is fr1, the central wavelength of pulse light source 2 is 1030nm, the repetition frequency is fr=fr-Δfr, where Δfr is the repetition frequency difference between the two lasers.

[0008] 2) Control the pulse output characteristics of the two-color light source: wavelength broaden and time stretch the output pulse of pulse light source 1, which serves as the signal light for the subsequent nonlinear difference frequency; power amplify the output pulse of pulse light source 2, which serves as the pump light for the subsequent nonlinear difference frequency.

[0009] 3) Nonlinear difference frequency sampling of asynchronous optical sampling: The pump light pulse performs high-speed optical sampling on the time-domain broadened spectrum of the signal light, generating a mid-infrared idler light with a central wavelength that varies with time, thus obtaining a mid-infrared discrete time-stretched pulse sequence.

[0010] 4) Measuring mid-infrared absorption spectra: After the mid-infrared discrete chirped pulse passes through the sample to be tested, the absorption degree of each spectral component will be directly mapped onto the time domain envelope of the mid-infrared pulse sequence. The absorption spectrum information can be quickly and conveniently measured using a low-bandwidth mid-infrared detector.

[0011] The nonlinear asynchronous optical sampling method uses a pump pulse to perform high-precision wavelength scanning on the time-domain stretched signal pulse, so that the generated mid-infrared chirped spectrum is amplified N times in the time domain (N=fr / Δfr). High-precision spectral resolution can be obtained using a low-bandwidth detector, greatly reducing the requirements for detection bandwidth for high-precision spectral measurement.

[0012] Compared with the prior art, the present invention has the following significant technical effects and improvements:

[0013] 1) Through nonlinear difference frequency sampling using asynchronous optical sampling, a mid-infrared chirped pulse train was generated, resulting in the acquisition of a mid-infrared time-stretched discrete spectrum. This technique overcomes the long-standing technical bottleneck that has limited the expansion of traditional time-stretched spectroscopy into the mid-infrared band, providing a new approach for achieving wide-band, high-speed, and high-resolution mid-infrared spectral measurements.

[0014] 2) High-precision spectral resolution can be achieved using a low-bandwidth detector, which greatly reduces the requirements for detection bandwidth for high-precision spectral measurement.

[0015] 3) Through nonlinear asynchronous optical sampling technology, the generated mid-infrared chirped spectrum is amplified N times in the time domain (N = fr / Δfr). This technology does not require any spectroscopic elements or mechanical scanning devices and has the advantages of simple structure, stable system and easy operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the spectrum detection system structure constructed for the present invention;

[0017] Figure 2 Schematic diagram of mid-infrared discrete time stretching spectroscopy measurement;

[0018] Figure 3This is a graph showing the relationship between mid-infrared discrete time stretch spectral resolution and influencing factors;

[0019] Figure 4 Schematic diagram of the spectrum detection system structure of Example 1. DETAILED DESCRIPTION

[0020] See Figure 1 The present invention directly prepares a time-domain chirped mid-infrared pulse train based on the nonlinear difference frequency process of asynchronous optical sampling. The method mainly includes the following steps:

[0021] 1) Prepare a two-color pulse light source with slightly different repetition frequencies: the central wavelength of pulse light source 1 is 1550nm, the repetition frequency is fr, the central wavelength of pulse light source 2 is 1030nm, the repetition frequency is fr = fr-Δfr, where Δfr is the repetition frequency difference between the two lasers.

[0022] 2) Control the pulse output characteristics of the two-color light source: wavelength broaden and time stretch the output pulse of pulse light source 1 to serve as the signal light for the subsequent nonlinear difference frequency; power amplify the output pulse of pulse light source 2 to serve as the pump light for the subsequent nonlinear difference frequency.

[0023] 3) Nonlinear difference frequency sampling of asynchronous optical sampling: The pump light pulse performs high-speed optical sampling on the time-domain broadened spectrum of the signal light, generating a mid-infrared idler light with a central wavelength that varies with time, thus obtaining a mid-infrared discrete time-stretched pulse train.

[0024] 4) Measuring mid-infrared absorption spectra: After the mid-infrared discrete chirped pulse passes through the sample to be tested, the absorption degree of each spectral component will be directly mapped onto the time domain envelope of the mid-infrared pulse sequence. The absorption spectrum information can be quickly and conveniently measured using a low-bandwidth mid-infrared detector.

[0025] The nonlinear difference frequency process based on asynchronous optical sampling is the core step in the present invention to achieve mid-infrared discrete time stretch spectroscopy. The basic principles of this process are explained below with reference to the accompanying figures, and the relevant important parameters are derived and analyzed to provide useful guidance for optimizing spectral measurement performance in specific implementations.

[0026] See Figure 2 The relevant parameters in the figure are defined as follows: the central wavenumbers of the output spectra of pulse source 1 and pulse source 2 are υ and υ, respectively; the repetition frequencies are fr and fr-Δfr, respectively; the pulse widths are t and t, respectively; and the pulse periods are T = 1 / fr and T = 1 / (fr-Δfr), respectively. The output pulses of pulse source 1 are time-stretched to achieve spectrum-to-time mapping, assuming that the time-stretched pulse width can occupy the entire pulse period, that is, t = T.

[0027] The pump pulse generated by the pulse light source 2 performs nonlinear asynchronous optical sampling on the signal pulse after time stretching of the pulse light source 1. The relative time delay between each pair of dual-color pulses increases linearly with the pulse sequence number, so the pump pulse can sequentially sample the signal pulses in the signal spectrum. The components interact with each other, the effective step size of optical asynchronous scanning is Δτ = (TT) = Δfr / fr, and the scanning period is T = 1 / Δfr.

[0028] The present invention utilizes a nonlinear difference frequency process to generate mid-infrared idler light with a central wave number of υ. According to the law of conservation of energy, the following relationship is satisfied: υ = υ - υ. Assuming the spectral widths of the signal light, pump light, and idler light pulses to be Δ, Δ, and Δ, respectively, the signal spectrum width Δ collected from a single pump pulse can be expressed as: Δ = D·t = Δ / T·t = Δ·fr·t, where the time stretch amplitude is D = Δ / T. Assuming the pump pulse to be Gaussian and satisfying the Fourier transform limit, the corresponding pulse width can be expressed as The time-bandwidth product κ is 0.441, and the mid-infrared spectral performance is derived and analyzed using the above-defined parameters.

[0029] 1) Spectral resolution: The wavenumber width of the infrared idler is: Δυ = Δυ + Δυ, where Δυ is the spectral wavenumber width of the signal collected from a single pump pulse. The spectral wavenumber width Δυ of the mid-infrared discrete pulse can be deduced to be expressed by the following formula (a):

[0030]

[0031] In this spectral measurement system, spectral resolution refers to the wavenumber spacing between discrete pulses. According to the Rayleigh criterion, to achieve effective spectral resolution of a mid-infrared pulse train, the wavenumber spacing between adjacent pulses must be no less than the wavenumber width of the pulse itself. Therefore, the maximum resolution of a mid-infrared spectrum is the spectral width Δυ corresponding to the discrete pulses.

[0032] From formula (a), we can see that when the pump pulse spectrum width Δλ is the only independent variable, the mid-infrared pulse spectrum width Δυ has a minimum value when Δυ=Δυ. At this time, we can get When Δυ s >>Δυ2, that is, when Δλ2→0, the second term in formula (a) can be ignored, and we can get When Δυ s When Δυ2<Δυ2, that is, Δλ2→+∞, the first term in formula (a) can be ignored, and we can get

[0033] 2) Spectral scanning frame rate: In this spectral measurement system, the spectral scanning frame rate is determined by the repetition frequency difference Δfr of the two pulse light sources. Although a larger Δfr can achieve a higher spectral measurement rate, the scanning step length Δτ=Δfr / fr1 in the asynchronous optical sampling process 2 It will also become larger. When Δfr is very large, it will cause a larger sampling time interval, making the central wavenumber interval of adjacent mid-infrared pulses too large, reducing the spectral resolution; when Δfr is relatively small, the time interval is too small, causing the spectra of adjacent mid-infrared pulses to overlap with each other, sacrificing the spectral scanning frame rate while not improving the spectral resolution. Therefore, while ensuring the highest spectral resolution, by selecting a suitable repetition frequency difference, the scanning frame rate can be optimized to meet the requirement that the wavenumber interval corresponding to adjacent pulses of mid-infrared discrete pulses should be equal to the wavenumber width of the pulse itself. Based on this, it can be deduced that the optimal frame rate is expressed by the following (b):

[0034]

[0035] See Figure 3 , the figure plots the relationship between spectral resolution and pump pulse spectral width under different repetition frequency conditions. Set the central wavelength of the signal light to 1550nm, the spectral width to 200nm (can cover the wavelength range of 1450~1650nm), and the pulse width fills the entire repetition period after time stretching. The central wavelength of the pump light is 1030nm, and the idler light with a central wavelength of 3070nm can be generated by nonlinear difference frequency. The spectral range corresponding to the obtained mid-infrared discrete chirped pulse sequence is 2741~3556nm. Through the above parameter conditions, the relationship curve between different pump pulse spectral widths (i.e. different pump pulse widths) and mid-infrared spectral resolution is plotted. As shown Figure 3 The graphs below show the relationship between the repetition rates of 20, 200, and 2000 MHz, respectively. The point at the minimum of the curve represents the highest mid-infrared spectral resolution corresponding to the pump pulse parameters. At a repetition rate of 20 MHz, the optimal spectral width of the pump pulse is 0.05 nm, and the spectral resolution is 0.92 nm. Formula (b) indicates that the spectral scanning frame rate is approximately 24 kHz. As the repetition rate increases, the optimal spectral resolution also increases.

[0036] Generally, spectral resolution, spectral frame rate, and spectral width constrain each other. During the specific implementation process, different parameters can be optimized as needed to obtain the characteristic spectral measurement performance of interest. For example, if you want to increase the coverable spectral width, you can use spectral broadening to increase the signal pulse spectral width to 400nm (1350-1750nm). The corresponding mid-infrared spectral width can be covered (2503-4345nm). At this time, the spectral resolution is 1.3nm and the scanning frame rate is 17kHz. If you want to increase the scanning frame rate, you can increase the repetition frequency to 2000MHz, the scanning frame rate can reach 24MHz, and the spectral resolution is reduced to 9.2nm. If you want to improve the spectral resolution, you can appropriately reduce the signal pulse spectral coverage range to 5nm. At this time, the spectral resolution can reach 0.14nm and the spectral scanning frame rate is 0.15MHz.

[0037] The following is a further detailed description of the features of the present invention and other related features in conjunction with the accompanying drawings and schematic diagrams of embodiments, so as to facilitate understanding by those skilled in the art:

[0038] Example 1

[0039] See Figure 4 The spectrum detection system includes: a clock source 101, a pulse light source 102, a pulse light source 103, a highly nonlinear optical fiber 104, a single-mode optical fiber 105, a wavelength division multiplexer 106, a collimator 107, a plano-convex lens 201, a nonlinear difference frequency crystal 202, a plano-convex lens 203, a filter 204, mirrors 205 and 206, a sample to be measured 301, a mid-infrared detector 302, and a computer 303. The specific implementation process is as follows:

[0040] 1) Prepare a dual-color pulse light source with a repetition frequency of Δfr: Use clock source 101 as a precise frequency standard to control the stability of the repetition frequency of the dual-color pulse light source. The repetition frequency of pulse light source 102 is 20 MHz, the central wavelength is 1030 nm, the spectral width is 0.08 nm, and the pulse width is 20 ps. The repetition frequency of pulse light source 103 is 20.025 MHz, and the central wavelength is 1550 nm.

[0041] 2) Controlling the pulse output characteristics of the dual-color light source: The output pulses of pulse light source 103 are first spectrally broadened to 200 nm (1450-1650 nm) by highly nonlinear fiber 104. They are then time-stretched through single-mode fiber 105 to fill the entire 50 ns period, achieving spectrum-to-time mapping. The time-stretch amplitude is 4 nm / ns. The wavelength-broadened and time-stretched output pulses of pulse light source 103 serve as the signal light for the subsequent nonlinear difference frequency generation, while the power-amplified output pulses of pulse light source 2 serve as the pump light for the subsequent nonlinear difference frequency generation.

[0042] 3) Nonlinear difference frequency sampling for asynchronous optical sampling: The signal light and pump light are combined via wavelength division multiplexer 106 and collimated for output via fiber collimator 107. The signal light and pump light for asynchronous optical sampling are focused by plano-convex lens 201 and projected onto nonlinear difference frequency crystal 202. The output light is collimated by plano-convex lens 203 and filtered by filter 204 to obtain mid-infrared idler light, thus obtaining a mid-infrared discrete time-stretched pulse train. The corresponding mid-infrared discrete spectrum has a wavelength range of 2741 to 3556 nm, a resolution of 1 nm, and a scanning frame rate of 25 kHz.

[0043] 4) Measuring the mid-infrared absorption spectrum: Discrete mid-infrared chirped pulses pass through two reflectors 205 and 206 and enter the sample to be measured 301. The absorption degree of each spectral component will be directly mapped to the time domain envelope of the mid-infrared pulse sequence. A low-bandwidth mid-infrared detector 302 is used to measure the time-varying amplitude information of each discrete pulse in the envelope. The absorption spectrum of the sample is then processed and analyzed by a computer 303.

[0044] The clock source 101 is an atomic clock such as a hydrogen clock or a rubidium clock that can be used as a frequency standard. This technology can also modulate the repetition frequency of the pump pulse with the help of a signal generator and other equipment to change the repetition frequency difference between the two-color light sources to achieve reciprocating scanning of the pump pulse on the specific wavelength spectrum in the signal pulse, thereby reducing the scanning time. The pulse light source 102 is an ytterbium-doped fiber laser, which can output watt-level narrow-band picosecond pulses after power amplification. The pulse light source 103 is an erbium-doped fiber laser, which outputs milliwatt-level broadband femtosecond pulses. The highly nonlinear fiber 104 has a high nonlinear coefficient and provides sufficient nonlinear effect to achieve nonlinear broadening of the spectrum. The single-mode fiber 105 mainly uses G652D single-mode fiber, and devices such as fiber Bragg gratings can also be used to achieve time stretching. The purpose of the wavelength division multiplexer 106 is to combine the pump light and the signal light into a bundle, which can achieve the transmission of high-power optical pulses. The collimator 107 is a high-power fiber collimator that collimates the combined pump light and signal light for output.

[0045] The plano-convex lens 201 is used to focus the combined pump light and signal light onto the crystal; the nonlinear difference frequency crystal 202 is a lithium niobate crystal with a chirped polarization structure, in which the chirped polarization period effectively expands the phase matching bandwidth, thereby realizing broadband frequency conversion. The nonlinear crystal used in this embodiment has a polarization period of 25.2-32μm, and the temperature is set to 60°C, which can achieve broadband nonlinear difference frequency. The plano-convex lens 203 is a CaF lens, the purpose of which is to collimate the mid-infrared idler light diverging after passing through the sample to achieve efficient spectral detection; the filter 204 is a 2μm long-pass filter, which is used for mid-infrared pulse light filtering, filtering out 1030nm pump light, 1550nm signal light, and ambient stray light; the reflectors 205 and 206 have high reflectivity in the infrared band and are used to change the direction of the light path;

[0046] The sample to be tested 301 includes but is not limited to biological tissues, chemical materials, etc. The detection target has different light absorption rates at different wavelengths, and the absorption rate of each wavelength can be obtained. The mid-infrared detector 302 is a mercury cadmium telluride detector, which aims to detect the time-varying intensity information of each discrete pulse in the envelope in real time. According to the Nyquist sampling theory, the sampling rate (N·fr) in conventional time stretching technology should be greater than the required minimum bandwidth fr ＝>t Twice the minimum detector bandwidth fr ＝>t >fr / 2=20MHz 2 / 2×25kFz=8GFz. This method combines asynchronous optical sampling technology to amplify the sampling time axis by N=20MHz / 25kHz=800 times, so the required minimum detection bandwidth is 10MHz. When the detector bandwidth is lower than the minimum detection bandwidth, the discrete pulse is distorted, thereby reducing the spectral resolution; when the detector bandwidth is higher than the minimum detection bandwidth, too much data is not conducive to the acquisition of time-varying pulse amplitude, and will also increase the work of data storage and processing; the computer 303 divides the two sets of data with and without the sample to be tested to obtain the absorption spectrum information of the sample. In this process, the conversion rate and detection rate of the detection system for each wavelength do not affect the spectral absorbance calibration result due to the data division;

[0047] This spectrum detection system is suitable for operation with light sources of more wavelengths. It can obtain pulsed light of different wavelength bands by using lasers with different gain media, spectrum broadening, wavelength tuning, etc. For example, a thulium-doped pulse laser with a wavelength of 1800nm ​​can be used, or a ytterbium-doped pulse laser with a wavelength of 1030nm can be used to broaden the spectrum to 1200-1400nm through nonlinear devices.

[0048] The above-mentioned spectral detection system can use other nonlinear crystals for frequency conversion to obtain wide-spectrum pulsed light in the mid-infrared and even far-infrared. For example, using nonlinear silver gallium sulfide crystals, the signal light in the 1200nm band and the pump light in the 1030nm band can be nonlinearly differentiating to produce a mid-infrared and far-infrared spectrum in the 8-11μm band.

[0049] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mid-infrared discrete time stretch spectroscopy method, characterized in that: The method specifically comprises the following steps: 1) Preparation of asynchronous two-color pulse light source Prepare a pulse light source with a central wavelength of 1550 nm and a repetition frequency of fr1; another pulse light source with a central wavelength of 1030 nm and a repetition frequency of ,in is the repetition frequency difference between the two lasers; 2) Control the pulse output characteristics of the dual-color light source The output pulse of one pulse light source is wavelength-broadened and time-stretched to serve as the signal light for the subsequent nonlinear difference frequency; the output pulse of another pulse light source is power-amplified to serve as the pump light for the subsequent nonlinear difference frequency; 3) Nonlinear difference frequency of asynchronous optical sampling The pump light pulse is used to perform nonlinear asynchronous optical sampling on the time-domain broadened spectrum of the signal light, generating a mid-infrared idler light with a time-varying central wavelength as a mid-infrared chirped pulse light, thereby obtaining a mid-infrared discrete time-stretched pulse train. 4) Measuring mid-infrared absorption spectra After the mid-infrared discrete chirped pulse passes through the sample to be tested, the absorption degree of each spectral component will be directly mapped on the time domain envelope of the mid-infrared discrete time-stretched pulse sequence, and the absorption spectrum information can be measured by a low-bandwidth mid-infrared detector.

2. The mid-infrared discrete time stretch spectroscopy method according to claim 1, characterized in that: The pump light pulse performs wavelength scanning on the time-domain stretched signal pulse, so that the generated mid-infrared chirped spectrum is amplified N times in the time domain. , high-precision spectral resolution can be achieved using a low-bandwidth detector.

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