CN118347957A - High-speed high-resolution mid-infrared spectrum detection method and device - Google Patents

Abstract

The present invention belongs to the technical field of mid-infrared spectrum detection, and specifically is a high-speed and high-resolution mid-infrared spectrum detection method and device. The method includes using a first chirped polarization structure nonlinear crystal, based on the nonlinear broadband difference frequency process of time-stretched near-infrared signal and single-frequency continuous pumping, to generate a broadband mid-infrared stretch signal with a time-spectrum mapping relationship; using a second chirped polarization structure nonlinear crystal, through the broadband nonlinear sum frequency process of femtosecond pump pulse and mid-infrared time-domain stretch signal passing through the sample, the mid-infrared signal is converted to the visible/near-infrared band; by controlling the repetition frequency difference between the femtosecond pump pulse and the mid-infrared time-domain stretch signal, optical asynchronous scanning is achieved, and then high-precision optical sampling of the spectrum of the mid-infrared time-domain stretch signal is obtained. This technical solution can achieve extremely high spectral resolution, effectively improve the spectrum formation speed, and at the same time avoid the influence of the detector's own time jitter on the stretch spectrum measurement.

Description

A high-speed and high-resolution mid-infrared spectrum detection method and device

Technical Field

The present invention belongs to the technical field of mid-infrared spectrum detection, and specifically relates to a high-speed and high-resolution mid-infrared spectrum detection method and device.

Background technique

Time-stretch spectroscopy technology uses the different propagation speeds of different wavelength components of pulsed light in dispersive media to achieve the mapping relationship between signal spectrum and time. The spectrum can be inferred by measuring the difference in time. Among them, the dispersive media used in this technology are usually single-mode optical fiber, multi-mode optical fiber, chirped fiber Bragg grating, etc. Compared with the low spectral detection resolution of spectral spatial dispersion combined with mechanical scanning scheme and the low spectrum formation rate of Fourier transform infrared spectroscopy technology, time-stretch spectroscopy detection is widely used in chemistry, biology, materials, physics and other fields due to its simple structure, high spectral resolution and fast spectrum formation rate to achieve high-speed qualitative and quantitative detection and analysis of substances.

In particular, the mid-infrared band contains many characteristic spectral lines of molecular vibrational energy levels, covering many characteristic absorption peaks of functional groups, and is located in the molecular "fingerprint" spectrum range. Realizing sensitive spectral detection in this band is an important means of identifying material components and a key technology for a large number of analytical applications. However, due to the lack of high-performance, low-loss, and low-cost dispersion media in the mid-infrared band, time-stretch spectroscopy technology is usually limited to the visible/near-infrared band. Although the mid-infrared pulse can be stretched to the nanosecond level through the free-space angular chirp enhanced delay (FACED) system, the spectral resolution of tens of nanometers achieved is still limited by the time resolution accuracy of the electrical measurement equipment and the sampling bandwidth of the digital display device. On the other hand, existing mid-infrared detectors are usually implemented using semiconductor materials with narrow band gaps (such as mercury cadmium telluride and indium antimonide), have large intrinsic dark noise, and usually require complex and expensive low-temperature refrigeration devices. In terms of core parameters such as resolution bandwidth and response wavelength range, they are far inferior to silicon-based devices in the visible light band, resulting in great limitations in the spectral sensitivity, detection wavelength range, and spectral speed of mid-infrared spectral detection.

Summary of the invention

The purpose of the present invention is to propose a high-speed and high-resolution mid-infrared spectral detection method, which can achieve extremely high spectral resolution, effectively improve the spectrum formation speed, and at the same time avoid the influence of the detector's own time jitter on the stretched spectrum measurement.

To achieve the above objectives, in a first aspect, the present disclosure provides a high-speed and high-resolution mid-infrared spectrum detection method, comprising:

The first chirped polarization structure nonlinear crystal is used to generate a broadband mid-infrared stretched signal with a time-spectrum mapping relationship based on the nonlinear broadband difference frequency process of the time-stretched near-infrared signal and the single-frequency continuous pump.

The second chirped polarization structure nonlinear crystal is used to convert the mid-infrared signal into the visible/near-infrared band through the broadband nonlinear sum frequency process of the femtosecond pump pulse and the mid-infrared time-domain stretching signal passing through the sample;

Optical asynchronous scanning is achieved by controlling the repetition frequency difference between the femtosecond pump pulse and the mid-infrared time-domain stretching signal, thereby obtaining high-precision optical sampling of the spectrum of the mid-infrared time-domain stretching signal.

As an implementable preferred solution, the stretched near-infrared signal prepared by the near-infrared dispersion element is converted to the mid-infrared band to obtain a mid-infrared time-domain stretched signal with a time-wavelength mapping relationship.

As an implementable preferred solution, broadband nonlinear frequency up-conversion of mid-infrared time-domain stretching signals is realized based on a nonlinear crystal with a second chirped polarization structure, and mid-infrared signals are detected using a high-performance silicon-based detector.

As an implementable preferred solution, fine nonlinear asynchronous time sampling is performed on the mid-infrared time-domain stretching spectrum based on ultrashort pulses.

Beneficial effects of this solution: This technical solution combines time stretching technology with a broadband nonlinear difference frequency method to generate a mid-infrared stretched signal with a time-spectrum mapping relationship, avoiding the limitations of small dispersion and large loss of dispersive elements in the mid-infrared band; adopts broadband nonlinear frequency up-conversion technology, and uses high-performance silicon-based detectors to achieve high-sensitivity mid-infrared spectrum detection, avoiding the limitation of insufficient sensitivity of existing infrared detectors; based on ultrashort pulses, nonlinear fine time sampling of mid-infrared time-domain stretched spectra is performed, and only intensity information needs to be measured at the detection end, thereby avoiding the detection time jitter of electrical detection equipment, and has the characteristics of high spectral resolution; high-speed asynchronous optical sampling technology is used to realize nonlinear asynchronous time sampling and detection of time-domain stretched mid-infrared signals, eliminating the mechanical scanning process, reducing the complexity of the spectral detection system, and significantly improving the spectrum formation rate.

The differences between this method and traditional stretching spectroscopy technology are as follows: the time measurement resolution is determined by the pump pulse width in the nonlinear process and is not affected by the detector time jitter; the wavelength of the stretching signal is extended to the mid-infrared band through the nonlinear frequency conversion process; asynchronous time sampling is used to eliminate the mechanical scanning process and effectively improve the spectrum generation rate.

In the second aspect, the embodiments of the present disclosure also provide a high-speed and high-resolution mid-infrared spectrum detection device, which uses a high-speed and high-resolution mid-infrared spectrum detection method as described above, including a near-infrared broadband light source, a high-precision repetition rate locking system, a femtosecond pump light source, a beam collimator, a dispersive medium, a high-power single-frequency continuous light source, a dichroic mirror, a _CaF2 lens, a chirped polarized lithium niobate crystal, a filter, and a silicon-based detector.

As an implementable preferred solution, the near-infrared broadband light source is used as a seed source to combine the time stretching technology and the broadband nonlinear difference frequency technology to generate a mid-infrared time-domain stretching signal light source; the high-precision repetition frequency locking system is used to lock the repetition frequency of the near-infrared broadband light source and the femtosecond pump light source with high precision so that they have a fixed repetition frequency difference; the high-power single-frequency continuous light source is used as a pump source for the broadband nonlinear difference frequency process;

The beam collimator comprises a first beam collimator and a second beam collimator; the first beam collimator is used to couple the near-infrared broadband light source output in space into the dispersive optical fiber; the dispersive medium is used to achieve the dispersion separation of the spectral components of the near-infrared broadband light source in the time domain; the second beam collimator is used to spatially collimate and output the stretched near-infrared signal after being transmitted through the dispersive optical fiber;

The dichroic mirror includes a first dichroic mirror, which is used to combine the stretched near-infrared signal with the high-power single-frequency continuous light source output to form a first spatial beam; the chirped polarized lithium niobate crystal includes a first chirped polarized lithium niobate crystal, which is used to generate a mid-infrared time-domain stretched signal; the _CaF2 lens includes a first _CaF2 lens, which is used to focus the first spatial beam into the first chirped polarized lithium niobate crystal; the filter includes a first filter, which is used to filter out the high-power single-frequency continuous laser and the near-infrared stretched signal.

As an implementable preferred solution, the dispersive medium is one of single-mode dispersive optical fiber, multi-mode optical fiber or chirped fiber Bragg grating.

As an implementable preferred solution, a femtosecond pump light source is used as the pump light for the subsequent mid-infrared signal frequency up-conversion process to achieve high-precision optical sampling of the mid-infrared time-domain stretching signal;

The dichroic mirror also includes a second dichroic mirror, which is used to combine the mid-infrared time-domain stretching signal passing through the sample with the femtosecond pump light source to output a second spatial beam; the chirped polarized lithium niobate crystal includes a second chirped polarized lithium niobate crystal, which is used to convert the mid-infrared time-domain stretching signal to the visible/near-infrared band to obtain an up-conversion signal; the _CaF2 lens includes a third _CaF2 lens, which is used to focus the second spatial beam into the second chirped polarized lithium niobate crystal; the filter includes a second filter, which is used to filter out the femtosecond pump light source.

As an implementable preferred solution, the silicon-based detector is used to measure the intensity of the up-conversion signal.

As an implementable preferred solution, it also includes an oscilloscope for displaying and collecting the signal intensity information of each wavelength measured by the silicon-based detector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a high-speed and high-resolution mid-infrared spectroscopy detection method;

FIG2 is a resolution numerical simulation curve diagram of a high-speed and high-resolution mid-infrared spectrum detection method;

FIG3 is a flow chart of a high-speed and high-resolution mid-infrared spectroscopy detection method;

FIG4 is a schematic diagram of a high-speed and high-resolution mid-infrared spectroscopy detection device.

Detailed ways

In order to make the technical solution and advantages of the present application clearer, the technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings. It will be understood that the specific embodiments described herein are only partial embodiments of the present invention, which are only used to explain the present application, rather than to limit the present application. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated, and they can be combined with each other to achieve better technical effects. The same reference numerals appearing in the drawings of the following embodiments represent the same features or components, which can be applied to different embodiments.

In addition, unless otherwise defined, the technical terms or scientific terms used in the description of the present invention should have the common meanings understood by those skilled in the art in the art to which the present invention belongs.

In addition, it should be noted that, in the description of the present invention, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

The present invention is further described in detail below in conjunction with the accompanying drawings:

Explanation of the reference numerals: near-infrared broadband light source 101, high-precision repetition rate locking system 102, femtosecond pump light source 103, first beam collimator 104, dispersive medium 105, second beam collimator 106, high-power single-frequency continuous light source 107, first dichroic mirror 108, first reflector 109, first _CaF2 lens 110, first chirped-polarized lithium niobate crystal 111, second _CaF2 lens 112, first filter 113, second reflector 114, position for placing the sample to be tested 115, second dichroic mirror 116, third _CaF2 lens 117, second chirped-polarized lithium niobate crystal 118, fourth _CaF2 lens 119, second filter 120, silicon-based detector 121, oscilloscope 122.

Referring to FIG1 , a high-speed and high-resolution mid-infrared spectrum detection method includes:

Step S100, using a first chirped polarization structure nonlinear crystal, based on a nonlinear broadband difference frequency process of a time-stretched near-infrared signal and single-frequency continuous pumping, generates a broadband mid-infrared stretched signal with a time-spectrum mapping relationship.

The purpose of time stretching is to separate the spectral components of broadband near-infrared femtosecond pulses in the time domain and obtain a time-spectrum mapping relationship, so that the subsequent femtosecond pump pulse can obtain the sample spectral information by only performing nonlinear optical sampling on the time domain envelope of the mid-infrared signal pulse.

Specifically, broadband near-infrared femtosecond pulses are time stretched, and a time-domain stretched mid-infrared signal is obtained by a broadband nonlinear difference frequency process. The near-infrared dispersion elements used include but are not limited to: single-mode dispersion fiber, multimode fiber, chirped fiber Bragg grating. The group delay dispersion introduced by the dispersion element is ,in is the group velocity dispersion of the dispersive element. For example, the group velocity dispersion of the G652D fiber commonly used in the communication band for 1550 nm is , is the action length of the dispersion element. If we assume that the spectral width of the near-infrared femtosecond pulse is , then the near-infrared pulse time domain stretching width is .

The nonlinear crystal of the first chirped polarization structure has a larger phase matching bandwidth than the periodic polarization structure, and the purpose is to realize the broadband nonlinear difference frequency process of the near-infrared stretching signal under single-frequency continuous pumping, and then generate a time-domain stretched mid-infrared light source as the signal light for subsequent sample spectrum detection. In this nonlinear difference frequency process, the following energy conservation relationship is satisfied:

in, , , They are the wavelength of single-frequency continuous pump, the center wavelength of near-infrared femtosecond pulse laser, and the center wavelength of mid-infrared signal light source generated by difference frequency. Single-frequency continuous pump is a narrow linewidth light source, and the effect of spectral width on nonlinear difference frequency can be ignored. Since near-infrared femtosecond pulse laser has spectral width , then the spectrum width of the mid-infrared signal source generated by the nonlinear difference frequency is As follows:

.

Step S200. Using a second chirped polarization structure nonlinear crystal, the mid-infrared signal is converted to the visible/near-infrared band through a broadband nonlinear frequency sum process of a femtosecond pump pulse and a mid-infrared time-domain stretching signal passing through the sample.

The purpose of the nonlinear crystal of the second chirped polarization structure is to realize the broadband nonlinear sum frequency process of the femtosecond pump pulse and the broadband mid-infrared stretched signal, thereby generating a time-domain stretched visible/near-infrared up-conversion signal, so that sensitive detection can be achieved using a high-performance silicon-based detector. This avoids the defects of existing infrared detection devices such as large intrinsic dark noise and the need for low-temperature refrigeration operation.

Step S300, optical asynchronous scanning is achieved by controlling the repetition frequency difference between the femtosecond pump pulse and the mid-infrared time-domain stretching signal, thereby obtaining high-precision optical sampling of the spectrum of the mid-infrared time-domain stretching signal.

The up-conversion detection of each spectral component of the mid-infrared is achieved by the optical asynchronous scanning method, referring to Figures 1 and 3, that is, the broadband near-infrared pulse and the femtosecond pump pulse have a fixed repetition frequency difference through the control system. （ Refers to the broadband near-infrared pulse repetition frequency, refers to the repetition frequency of the femtosecond pump pulse), then the time delay between the mid-infrared stretching signal and each cycle of the femtosecond pump pulse is （ Refers to the central repetition frequency of broadband near-infrared pulses and femtosecond pump pulses. Generally speaking, the repetition frequency difference between the two is small, and it can be approximately considered when calculating time delay and period. ). In other words, the pump light pulses are The mid-infrared time-stretched spectrum is sampled once in a period of , and the relative time position of each sampling will exist time difference.

Thus, the time required to scan a complete mid-infrared stretch spectrum is , that is, the scanning rate is , which can generally be achieved The measurement is above the level of the detector, thus achieving high-speed spectral measurement without mechanical scanning. The influence of the detector's own time jitter on the stretched spectral measurement is avoided, the requirements for the detector and oscilloscope resolution bandwidth are reduced, the spectral resolution capability is significantly improved, and the mechanical scanning process is eliminated.

If the infrared time-domain spectrum is stretched to fill the entire pulse period, then The femtosecond pump pulse can achieve nonlinear sum-frequency conversion only in a very narrow time window in the mid-infrared time-domain stretching signal. If the femtosecond pump pulse width is , and assuming that the spectral components of the mid-infrared stretch signal are linearly and uniformly expanded in the time domain, the spectral resolution accuracy of a single optical sampling is As follows:

From the above formula, we can see that the spectral sampling accuracy is proportional to the pump pulse width. A narrower pump pulse width will enable the system to obtain higher spectral resolution accuracy. Therefore, this technical solution selects infrared pulses of the order of hundreds of femtoseconds as the pump light source. If high-resolution spectral acquisition is performed with the spectral resolution accuracy as the scanning step, then , the spectrum detection refresh rate at this time is .

When the mid-infrared time-stretched signal is frequency up-converted with the femtosecond pump pulse, the time walk-off effect introduced will reduce the spectral sampling resolution accuracy due to the different group velocities of the two-color pulses in the nonlinear medium, as expressed by the following formula:

in, is the walk-off time of the two-color pulse, is the nonlinear medium length, are the inverse of the mid-infrared signal and femtosecond pump pulse group velocity, That is, it represents the time walk-off of the two-color pulse per unit length in the nonlinear medium. Considering the above factors, the final system detection spectral resolution accuracy is shown in the following formula:

Referring to Figure 2, for the up-conversion pump light and difference frequency near-infrared broadband light source with central wavelengths of 1030 nm and 1550 nm, respectively, the numerical simulation results of the mid-infrared spectral detection resolution changing with the dispersion amount under different sampling pulse widths are given. The nonlinear frequency up-conversion medium used in the numerical simulation is a lithium niobate crystal with a chirped polarization structure of 10 mm in length, and its time walk-off between the mid-infrared pulse signal near 3 μm and the 1030 nm pump pulse signal is 52 ps/m. As can be seen from the figure, the system detection spectral resolution increases with the increase of time dispersion stretching. For shorter sampling pump pulse widths, the spectral resolution can reach the pm level.

In addition, the high-performance silicon-based detector used in this technical solution only needs to record intensity information, and the detector's own time jitter does not affect the measured spectral resolution. The kHz spectrum rate and pm-level mid-infrared spectral resolution achieved by this technology are unattainable by traditional methods.

4 , a high-speed and high-resolution mid-infrared spectrum detection device includes a near-infrared broadband light source 101, a high-precision repetition rate locking system 102, a femtosecond pump light source 103, a first beam collimator 104, a dispersive medium 105, a second beam collimator 106, a high-power single-frequency continuous light source 107, a first dichroic mirror 108, a first reflector 109, a first _CaF2 lens 110, a first chirped polarized lithium niobate crystal 111, a second _CaF2 lens 112, a first filter 113, a second reflector 114, a sample placement position 115, a second dichroic mirror 116, a third _CaF2 lens 117, a second chirped polarized lithium niobate crystal 118, a fourth _CaF2 lens 119, a second filter 120, a silicon-based detector 121, and an oscilloscope 122.

The near-infrared broadband light source 101 is used as a seed source to combine the time stretching technology and the broadband nonlinear difference frequency technology to generate a mid-infrared time-domain stretching signal light source. In one embodiment, the infrared signal spectrum needs to cover 3000-4000 nm, so the spectrum of the near-infrared broadband light source 101 needs to cover 1387-1569 nm.

The high-precision repetition frequency locking system 102 is used to lock the repetition frequency of the near-infrared broadband light source 101 and the femtosecond pump light source 103 with high precision so that they have a fixed repetition frequency difference. The locking method is an active feedback frequency locking based on a piezoelectric ceramic actuator. In one embodiment, the repetition frequency of the near-infrared broadband light source 101 and the femtosecond pump light source 103 is locked by a high-precision repetition frequency locking system 102. The central repetition frequency is 20 MHz, and the repetition frequency difference is .

The femtosecond pump light source 103 is used as the pump light for the subsequent mid-infrared signal frequency up-conversion process to achieve high-precision optical sampling of the mid-infrared time-domain stretched signal. In one embodiment, the pulse width is 300 fs and the central wavelength is 1 μm.

The first beam collimator 104 is used to couple the spatially output near-infrared broadband light source 101 into the dispersive optical fiber.

The dispersion medium 105 includes but is not limited to single-mode dispersion optical fiber, multimode optical fiber, chirped fiber Bragg grating, etc., which is used to separate the spectral components of the near-infrared broadband light source 101 in the time domain. The development of communication band transmission optical fiber is very mature, and the transmission loss in the near-infrared band is low, so it is used as a preferred solution. In one embodiment, 15 km of G652D optical fiber is used as the dispersion medium, and its zero dispersion point is at 1310 nm, and there is a large positive dispersion near 1550 nm, and the dispersion coefficient is Through long-distance time stretching, the near-infrared light source can stretch the delay to about 50 ns.

The second beam collimator 106 is used to spatially collimate the stretched near-infrared signal after being transmitted through the dispersion optical fiber to output it, so as to facilitate the subsequent participation in the broadband nonlinear difference frequency process.

The high-power single-frequency continuous light source 107 is used as a pump source for the broadband nonlinear difference frequency process. In one embodiment, its central wavelength is 1030 nm and its output power can reach 10 W.

The first dichroic mirror 108 is used to spatially combine the stretched near-infrared signal with the output of the high-power single-frequency continuous light source 107 (first spatial combination) to facilitate the subsequent participation in the broadband nonlinear difference frequency process. The dichroic mirror is a 1.3 μm short-wave pass dichroic mirror, which has a high reflectivity for 1387-1569 nm near-infrared signal light and a high transmittance for 1030 nm pump light.

The first reflector 109 and the second reflector 114 are used to change the direction of the light path.

The first CaF ₂ lens 110 and the second CaF ₂ lens 112 are used to focus the signal light and the pump light involved in the nonlinear frequency conversion into the first chirped polarized lithium niobate crystal 111. The third CaF ₂ lens 117 and the fourth CaF ₂ lens 119 are used to focus the signal light and the pump light involved in the nonlinear frequency conversion into the second chirped polarized lithium niobate crystal 118 to achieve efficient frequency conversion.

The first chirped polarized lithium niobate crystal 111 is used as a nonlinear medium in the frequency down-conversion process to generate a 3-4 μm mid-infrared time-domain stretching signal. In one embodiment, its polarization period covers 25 to 32 μm.

The first filter 113 is used to filter out high-power single-frequency continuous laser and near-infrared stretching signals. In one embodiment, a 2.4 μm long-pass filter is used, which has a high transmittance for 3-4 μm mid-infrared time-domain stretching signals.

The target to be detected is placed at the sample placement position 115. The target to be detected has different light absorption degrees at different wavelengths. The experimental system can obtain the absorption rate of the target to be detected at each wavelength by measuring the spectral intensity distribution with and without samples.

The second dichroic mirror 116 is used to spatially combine the mid-infrared time-domain stretched signal with the output of the femtosecond pump light source 103 (second spatial combination) to facilitate subsequent participation in the broadband nonlinear sum frequency process. In this embodiment, the dichroic mirror is a 1.3 μm short-wave pass dichroic mirror, which has a high reflectivity for 3-4 μm near-infrared signal light and a high transmittance for 1030 nm pump light.

The second polarized lithium niobate crystal 118 is used as a nonlinear medium in the frequency up-conversion process to convert the 3-4 μm mid-infrared time-domain stretching signal to the visible/near infrared band. In one embodiment, its polarization period covers 19 to 24 μm and the length is 10 mm.

The second filter 120 is used to filter out the femtosecond pump light source 103. In one embodiment, a 900 nm low-pass filter is used, which has a high transmittance for 700-900 nm up-conversion signals.

The silicon-based detector 121 is used to realize ultra-sensitive intensity detection of the up-conversion signal, and its detection wavelength range is 400-1100 nm.

The oscilloscope 122 is used to display and collect the signal strength information of each wavelength measured by the silicon-based detector 121. Since the repetition frequency of the dual-color pulse is about 20 MHz, that is, the asynchronous sampling time interval is about 50 ns, the resolution bandwidth of the oscilloscope needs to be better than 20 MHz.

This embodiment is implemented as follows: first, the high-precision repetition frequency locking system 102 locks the repetition frequency of the near-infrared broadband light source 101 to 20 MHz, and its spatial output is coupled into the G652D single-mode optical fiber by the first beam collimator 104, and its spectral range 1387-1569 nm is linearly and uniformly stretched to 50 ns. The near-infrared stretching signal is spatially output by the second beam collimator 106, and spatially combined with the high-power single-frequency continuous light source 107 through the first dichroic mirror 108 (first spatial beam combination), and is focused by the first _CaF2 lens 110 into the first chirped polarized lithium niobate crystal 111 to achieve broadband nonlinear difference frequency mid-infrared time domain stretching signal generation, and then spatially collimated by the second _CaF2 lens 112, and the high-power single-frequency continuous laser and near-infrared stretching signal are filtered out by the first filter 113. The wavelength of the generated mid-infrared time domain stretching signal covers 3-4 μm, and the stretching delay is still 50ns, that is, the mid-infrared stretching spectrum dispersion is 50 ps/nm.

Subsequently, the pulse outputted by the femtosecond pump light source 103 locked by the high-precision repetition frequency locking system 102 is spatially combined (second spatial beam combination) with the mid-infrared time-domain stretching signal passing through the detected target (sample) through the second dichroic mirror 116, and is focused by the third _CaF2 lens 117 into the second chirped polarized lithium niobate crystal 118 to generate a frequency up-conversion signal. Subsequently, the up-conversion signal is spatially collimated by the fourth _CaF2 lens 119, and the femtosecond pump pulse is filtered out by the second filter 120, and the intensity is measured by the silicon-based detector 121, and the data is collected and displayed by the oscilloscope 122.

Since the mid-infrared time-domain stretching signal has a time-spectrum mapping relationship, the intensity information of different wavelengths can be obtained by performing nonlinear optical sampling on the mid-infrared signal at different times. In this embodiment, the near-infrared broadband light source 101 and the femtosecond pump light source 103 have a fixed repetition frequency difference through the high-precision repetition frequency locking system 102. , then the sampling delay between the mid-infrared stretching signal and the femtosecond pump pulse is . Femtosecond pump light source 103 every The mid-infrared time-domain stretched signal is sampled once every time, and each sampling will step the relative time. In this way, the time required to scan a complete mid-infrared stretched spectrum is , that is, the scanning rate is , thus achieving high-speed spectral measurement without mechanical scanning. The spectral resolution accuracy in this case is:

For high-resolution acquisition mode, the acquisition step time should be The spectrum resolution is 11.8 pm and the spectrum refresh rate is If the repetition frequency difference between the near-infrared broadband light source 101 and the femtosecond pump light source 103 is increased, such as , the spectral scanning rate will be further increased to 10 kHz, and the spectral resolution accuracy is still 11.8 pm, the sampling step time is 25 ps, and the corresponding spectral resolution is 0.5 nm, which is still better than the existing mid-infrared spectrometer. At the same time, the high-performance silicon-based detector used in this technical solution only records intensity information, and the detector's own time jitter is much smaller than the sampling time interval, so it does not affect the measured spectral resolution. The kHz spectrum rate and pm-level mid-infrared spectral resolution achieved by this technology are unattainable by traditional means, and can provide strong support for applications such as rapid spectral diagnosis of tissue pathology and non-destructive testing of materials.

As an extension, this technical solution can also be combined with a time-correlated single-photon counter to be applied to single-photon high-resolution spectral detection. The sum frequency signal of the near-infrared broadband pulse after time stretching by the dispersion medium 105 and the femtosecond pump light source 103 is used as the trigger start signal, and the intensity signal measured by the silicon-based detector 121 is used as the trigger end signal. The time-domain distribution of the spectral intensity is statistically analyzed by the time-correlated single-photon counter to achieve high-resolution spectral detection at the single-photon level without mechanical scanning, which can provide strong support for applications such as non-phototoxic biomedical sample observation, trace substance analysis, and long-distance spectral detection.

As an extension, this technical solution can also be used for mid-infrared hyperspectral imaging. By replacing the silicon-based detector 121 with a silicon-based high-speed camera, assuming that the number of imaging spectral bands is 1000, the camera working frame rate is 1 kHz, and the image spectrum acquisition step is 1 nm, the two-color pulse repetition frequency difference needs to be controlled to 1 Hz, so that the total sampling range of the camera within the 1 ms exposure time is 1 nm. The mid-infrared hyperspectral imaging realized based on this method eliminates the spectral scanning acquisition process and has the advantages of high speed and high resolution.

The above contents are only embodiments of the present invention. Common knowledge such as the known specific structures and characteristics in the scheme is not described in detail here. Ordinary technicians in the relevant field know all the common technical knowledge in the technical field to which the invention belongs before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply conventional experimental means before that date. Ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the scope of protection of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to explain the content of the claims.

Claims (10)

1. A high-speed and high-resolution mid-infrared spectrum detection method, characterized in that it includes: The first chirped polarization structure nonlinear crystal is used to generate a broadband mid-infrared stretched signal with a time-spectrum mapping relationship based on the nonlinear broadband difference frequency process of the time-stretched near-infrared signal and the single-frequency continuous pump. The second chirped polarization structure nonlinear crystal is used to convert the mid-infrared signal into the visible/near-infrared band through the broadband nonlinear sum frequency process of the femtosecond pump pulse and the mid-infrared time-domain stretching signal passing through the sample; Optical asynchronous scanning is achieved by controlling the repetition frequency difference between the femtosecond pump pulse and the mid-infrared time-domain stretching signal, thereby obtaining high-precision optical sampling of the spectrum of the mid-infrared time-domain stretching signal. 2. A high-speed and high-resolution mid-infrared spectrum detection method according to claim 1, characterized in that: the stretched near-infrared signal prepared by the near-infrared dispersion element is converted to the mid-infrared band to obtain a mid-infrared time-domain stretched signal with a time-wavelength mapping relationship. 3. A high-speed and high-resolution mid-infrared spectrum detection method according to claim 1, characterized in that: a nonlinear crystal based on a second chirped polarization structure realizes broadband nonlinear frequency up-conversion of mid-infrared time-domain stretching signals, and a high-performance silicon-based detector is used to detect mid-infrared signals. 4. A high-speed and high-resolution mid-infrared spectrum detection method according to claim 3, characterized in that: fine nonlinear asynchronous time sampling is performed on the mid-infrared time-domain stretching spectrum based on ultrashort pulses. 5. A high-speed and high-resolution mid-infrared spectrum detection device, characterized in that: it uses a high-speed and high-resolution mid-infrared spectrum detection method as described in any one of claims 1 to 4, including a near-infrared broadband light source, a high-precision repetition rate locking system, a femtosecond pump light source, a beam collimator, a dispersive medium, a high-power single-frequency continuous light source, a dichroic mirror, a _CaF2 lens, a chirped polarized lithium niobate crystal, a filter, and a silicon-based detector. 6. A high-speed and high-resolution mid-infrared spectrum detection device according to claim 5, characterized in that: the near-infrared broadband light source is used as a seed source to combine time stretching technology and broadband nonlinear difference frequency technology to generate a mid-infrared time-domain stretching signal light source; the high-precision repetition frequency locking system is used to lock the repetition frequency of the near-infrared broadband light source and the femtosecond pump light source with high precision so that they have a fixed repetition frequency difference; the high-power single-frequency continuous light source is used as a pump source for the broadband nonlinear difference frequency process; The beam collimator comprises a first beam collimator and a second beam collimator; the first beam collimator is used to couple the near-infrared broadband light source output in space into the dispersive optical fiber; the dispersive medium is used to achieve the dispersion separation of the spectral components of the near-infrared broadband light source in the time domain; the second beam collimator is used to spatially collimate and output the stretched near-infrared signal after being transmitted through the dispersive optical fiber; The dichroic mirror includes a first dichroic mirror, which is used to combine the stretched near-infrared signal with the high-power single-frequency continuous light source output to form a first spatial beam; the chirped polarized lithium niobate crystal includes a first chirped polarized lithium niobate crystal, which is used to generate a mid-infrared time-domain stretched signal; the _CaF2 lens includes a first _CaF2 lens, which is used to focus the first spatial beam into the first chirped polarized lithium niobate crystal; the filter includes a first filter, which is used to filter out the high-power single-frequency continuous laser and the near-infrared stretched signal. 7. A high-speed and high-resolution mid-infrared spectrum detection device according to claim 6, characterized in that the dispersion medium adopts one of single-mode dispersion optical fiber, multi-mode optical fiber or chirped fiber Bragg grating. 8. A high-speed and high-resolution mid-infrared spectrum detection device according to claim 6, characterized in that: a femtosecond pump light source is used as a pump light for a subsequent mid-infrared signal frequency up-conversion process to achieve high-precision optical sampling of the mid-infrared time-domain stretched signal; The dichroic mirror also includes a second dichroic mirror, which is used to combine the mid-infrared time-domain stretching signal passing through the sample with the femtosecond pump light source to output a second spatial beam; the chirped polarized lithium niobate crystal includes a second chirped polarized lithium niobate crystal, which is used to convert the mid-infrared time-domain stretching signal to the visible/near-infrared band to obtain an up-conversion signal; the _CaF2 lens includes a third _CaF2 lens, which is used to focus the second spatial beam into the second chirped polarized lithium niobate crystal; the filter includes a second filter, which is used to filter out the femtosecond pump light source. 9. A high-speed and high-resolution mid-infrared spectrum detection device according to claim 8, characterized in that the silicon-based detector is used to measure the intensity of the up-conversion signal. 10. A high-speed and high-resolution mid-infrared spectrum detection device according to claim 9, characterized in that it also includes an oscilloscope for displaying and collecting signal intensity information of each wavelength measured by the silicon-based detector.