CN118347957A - High-speed high-resolution mid-infrared spectrum detection method and device - Google Patents
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Abstract
The invention belongs to the technical field of mid-infrared spectrum detection, and particularly relates to a high-speed high-resolution mid-infrared spectrum detection method and device. The method comprises the steps of adopting a nonlinear crystal with a first chirp polarization structure, and generating a broadband mid-infrared stretching signal with a time-spectrum mapping relation based on a nonlinear broadband difference frequency process of time stretching near infrared signals and single-frequency continuous pumping; the second chirp polarization structure nonlinear crystal is adopted, and the middle infrared signal is converted into a visible/near infrared band through the broadband nonlinear sum frequency process of the femtosecond pump pulse and the middle infrared time domain stretching signal passing through the sample; the optical asynchronous scanning is realized by controlling the repetition frequency difference of the femtosecond pump pulse and the mid-infrared time domain stretching signal, so that the high-precision optical spectrum sampling of the mid-infrared time domain stretching signal is obtained. According to the technical scheme, extremely high spectrum resolution capability can be realized, the spectrum forming speed is effectively improved, and meanwhile, the influence of the time jitter of the detector on the measurement of the stretching spectrum is avoided.
Description
Technical Field
The invention belongs to the technical field of mid-infrared spectrum detection, and particularly relates to a high-speed high-resolution mid-infrared spectrum detection method and device.
Background
The time stretching spectrum technology utilizes different propagation speeds of different wavelength components of pulse light in a dispersion medium to realize the mapping relation between signal spectrum and time, and can calculate the spectrum by measuring the difference of time. Among them, the dispersion medium used in this technology is typically a single-mode fiber, a multimode fiber, a chirped fiber bragg grating, or the like. Compared with the low spectral detection resolution of the spectrum space dispersion and the low spectral formation rate of the Fourier infrared transformation spectrum technology, the time stretching spectrum detection has the advantages of simple structure, high spectral resolution and high spectral formation rate, and is widely applied to various fields of chemistry, biology, materials, physics and the like to realize high-speed qualitative and quantitative detection analysis of substances.
In particular, the mid-infrared band contains a number of molecular vibrational energy level characteristic spectral lines, covering a number of functional group characteristic absorption peaks, located in the molecular "fingerprint" spectral interval. The sensitive spectrum detection of the wave band is an important means for identifying the components of substances and a key technology for mass analysis application. However, due to the lack of high performance, low loss, low cost dispersive media in the mid-infrared band, time-stretched spectroscopy techniques are typically limited to the visible/near infrared band. Although mid-infrared pulses can be stretched to nanosecond levels by the free space angle chirp enhanced delay (FACED) system, the tens of nanometers of spectral resolution they achieve is still limited by the time resolution accuracy of the electrical measurement device and the sampling bandwidth of the digital display device. On the other hand, the existing mid-infrared detector is usually implemented by adopting a semiconductor material (such as tellurium cadmium mercury and indium antimonide) with a relatively narrow band gap, has relatively large intrinsic dark noise, generally needs a complex and expensive low-temperature refrigeration device, and is far less than a silicon-based device in a visible light wave band in terms of core parameters such as resolution bandwidth, response wavelength range and the like, so that the spectral sensitivity, detection wavelength range, spectral speed and the like of mid-infrared spectrum detection are greatly limited.
Disclosure of Invention
The invention aims at: the technical scheme can realize extremely high spectrum resolution capability, effectively improve the spectrum forming speed and avoid the influence of the self time jitter of the detector on the measurement of the stretching spectrum.
To achieve the above object, in a first aspect, an embodiment of the present disclosure provides a high-speed and high-resolution mid-infrared spectrum detection method, including:
A nonlinear crystal with a first chirp polarization structure is adopted, and a broadband mid-infrared stretching signal with a time-spectrum mapping relation is generated based on a nonlinear broadband difference frequency process of time stretching near infrared signals and single-frequency continuous pumping;
the second chirp polarization structure nonlinear crystal is adopted, and the middle infrared signal is converted into a visible/near infrared band through the broadband nonlinear sum frequency process of the femtosecond pump pulse and the middle infrared time domain stretching signal passing through the sample;
The optical asynchronous scanning is realized by controlling the repetition frequency difference of the femtosecond pump pulse and the mid-infrared time domain stretching signal, so that the high-precision optical spectrum sampling of the mid-infrared time domain stretching signal is obtained.
As a practical preferred scheme, the stretching near infrared signal prepared by the near infrared dispersion element is converted into a middle infrared band to obtain a middle infrared time domain stretching signal with a time-wavelength mapping relation.
As an implementation preferred scheme, the broadband nonlinear frequency up-conversion of the mid-infrared time domain stretching signal is realized based on the nonlinear crystal of the second chirped polarization structure, and the mid-infrared signal is detected by using the high-performance silicon-based detector.
As a practical preferred scheme, the ultra-short pulse-based fine nonlinear asynchronous time sampling is performed on the mid-infrared time domain stretching spectrum.
The beneficial effect of this scheme: the technical scheme combines a time stretching technology and a broadband nonlinear difference frequency method to generate a mid-infrared stretching signal with a time-spectrum mapping relation, so that the limitations of small dispersion quantity, large loss and the like of a mid-infrared band dispersion element are avoided; the high-sensitivity mid-infrared spectrum detection can be realized by using a high-performance silicon-based detector by adopting a broadband nonlinear frequency up-conversion technology, so that the limitation of insufficient sensitivity of the conventional infrared detector is avoided; nonlinear fine time sampling is carried out on the intermediate infrared time domain stretching spectrum based on the ultra-short pulse, only intensity information needs to be measured at a detection end, so that detection time jitter of electrical detection equipment is avoided, and the method has the characteristic of high spectrum resolution; by adopting the high-speed asynchronous optical sampling technology, nonlinear asynchronous time sampling detection of infrared signals in time domain stretching is realized, the mechanical scanning process is avoided, the complexity of a spectrum detection system is reduced, and the spectrum forming rate is remarkably improved.
The method is different from the traditional stretching spectrum technology in that: the time measurement resolution is determined by the pump pulse width in the nonlinear process and is not affected by the time jitter of the detector; the wavelength of the stretching signal is expanded to a middle infrared band through a nonlinear frequency conversion process; and asynchronous time sampling is adopted, so that a mechanical scanning process is avoided, and the spectral rate is effectively improved.
In a second aspect, an embodiment of the present disclosure further provides a high-speed and high-resolution mid-infrared spectrum detection device, which uses the above-mentioned high-speed and high-resolution mid-infrared spectrum detection method, and includes a near-infrared broadband light source, a high-precision heavy-frequency 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 CaF 2 lens, a chirped polarized lithium niobate crystal, a filter, and a silicon-based detector.
As an implementation preferred scheme, the near infrared broadband light source is used as a seed source to combine a time stretching technology and a 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 for locking the repetition frequencies of the near infrared broadband light source and the femtosecond pumping light source to ensure that the repetition frequencies have fixed repetition frequency difference; the high-power single-frequency continuous light source is used as a pumping source of a broadband nonlinear difference frequency process;
The beam collimator comprises a first beam collimator and a second beam collimator; the first beam collimator is used for coupling the near infrared broadband light source output in space into the dispersion optical fiber; the dispersion medium is used for realizing the dispersion separation of each spectrum component of the near infrared broadband light source in the time domain; the second beam collimator is used for spatially collimating and outputting the stretched near infrared signal transmitted by the dispersive optical fiber;
The dichroic mirror comprises a first dichroic mirror and is used for outputting a first spatial beam combination of the stretching near infrared signal and a high-power single-frequency continuous light source; the chirped polarized lithium niobate crystal comprises a first chirped polarized lithium niobate crystal used for generating a mid-infrared time domain stretching signal; the CaF 2 lens comprises a first CaF 2 lens for focusing a first spatially combined beam into a first chirped polarized lithium niobate crystal; the filter plate comprises a first filter plate used for filtering high-power single-frequency continuous laser and near infrared stretching signals.
As a practical preferred embodiment, the dispersion medium is one of a single-mode dispersion fiber, a multimode fiber or a chirped fiber bragg grating.
As an implementation preferred scheme, the femtosecond pump light source is used as pump light in the subsequent middle infrared signal frequency up-conversion process to realize time high-precision optical sampling of the middle infrared time domain stretching signal;
The dichroic mirror further comprises a second dichroic mirror, and the second dichroic mirror is used for outputting a second spatial beam combination of the middle infrared time domain stretching signal passing through the sample and the femtosecond pumping light source; the chirped polarized lithium niobate crystal comprises a second chirped polarized lithium niobate crystal and is used for converting the middle infrared time domain stretching signal into a visible/near infrared wave band to obtain an up-conversion signal; the CaF 2 lens comprises a third CaF 2 lens for focusing the second spatially combined beam into a second chirped polarized lithium niobate crystal; the filter comprises a second filter for filtering the femtosecond pump light source.
As an implementation preference, the silicon-based detector is used to measure the intensity of the up-converted signal.
As a practical preferred scheme, the system also comprises an oscilloscope which is used for displaying and acquiring the signal intensity information of each wavelength measured by the silicon-based detector.
Drawings
FIG. 1 is a schematic diagram of a high-speed high-resolution mid-infrared spectrum detection method;
FIG. 2 is a graph of a high-speed high-resolution mid-IR spectrum detection method resolution simulation;
FIG. 3 is a flow chart of a high-speed high-resolution mid-infrared spectrum detection method;
FIG. 4 is a schematic diagram of a high-speed high-resolution mid-IR spectrum detection device.
Detailed Description
In order to make the technical scheme of the present application and the advantages thereof more clear, the technical scheme of the present application will be described in further detail with reference to the accompanying drawings. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not limiting thereof. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be regarded as being isolated, and they may be combined with each other to achieve a better technical effect. The same reference numerals appearing in the drawings of the embodiments described below represent the same features or components and are applicable to the different embodiments.
Furthermore, unless defined otherwise, technical or scientific terms used in the description of the invention should be given the ordinary meaning as understood by one of ordinary skill in the art to which the invention pertains.
Furthermore, it should be noted that in the description of the present invention, the terms "first," "second," "third," and the like are used merely to distinguish between descriptions and are not to be construed as indicating or implying relative importance.
The invention is described in further detail below with reference to the accompanying drawings:
Reference numerals illustrate: the system comprises a near infrared broadband light source 101, a high-precision repetition frequency locking system 102, a femtosecond pumping light source 103, a first light beam collimator 104, a dispersion medium 105, a second light beam collimator 106, a high-power single-frequency continuous light source 107, a first dichroic mirror 108, a first reflecting mirror 109, a first CaF 2 lens 110, a first chirped polarized lithium niobate crystal 111, a second CaF 2 lens 112, a first filter 113, a second reflecting mirror 114, a sample placement position 115 to be measured, a second dichroic mirror 116, a third CaF 2 lens 117, a second chirped polarized lithium niobate crystal 118, a fourth CaF 2 lens 119, a second filter 120, a silicon-based detector 121 and an oscilloscope 122.
Referring to fig. 1, a high-speed high-resolution mid-infrared spectrum detection method includes:
step S100, a nonlinear crystal with a first chirp polarization structure is adopted, and a broadband mid-infrared stretching signal with a time-spectrum mapping relation is generated based on a nonlinear broadband difference frequency process of time stretching near infrared signals and single-frequency continuous pumping.
The time stretching aims at separating each spectrum component of the broadband near-infrared femtosecond pulse in the time domain to obtain a time-spectrum mapping relation, so that the subsequent femtosecond pumping pulse only carries out nonlinear optical sampling on the time domain envelope of the middle infrared signal pulse to obtain sample spectrum information.
Specifically, the infrared signal in the time domain stretching is obtained by stretching the time of the broadband near-infrared femtosecond pulse and relying on the broadband nonlinear difference frequency process, and the near-infrared dispersion element comprises but is not limited to: single mode dispersion optical fiber, multimode optical fiber, chirped fiber bragg grating. The group delay dispersion quantity introduced by the dispersion element isWhereinGroup velocity dispersion of dispersive element, such as group velocity dispersion of G652D optical fiber pair 1550 nm commonly used in communication band, is，Acting as a dispersive element. If the spectrum width of the near infrared femtosecond pulse is assumed to beThe near infrared pulse time domain stretching width is。
Compared with a periodic polarization structure, the chirp polarization structure of the nonlinear crystal of the first chirp polarization structure has larger phase matching bandwidth, and the nonlinear crystal aims to realize a broadband nonlinear difference frequency process of near infrared stretching signals under single-frequency continuous pumping, so that a time-domain stretching mid-infrared light source is generated and used as signal light for spectrum detection of a subsequent sample. In the nonlinear difference frequency process, the following energy conservation relation is satisfied:
Wherein, ，，The laser is respectively single-frequency continuous pumping wavelength, near infrared femtosecond pulse laser center wavelength and middle infrared signal light source center wavelength generated by difference frequency. The single-frequency continuous pump is a narrow linewidth light source, and the influence of the spectrum width on the nonlinear difference frequency is negligible. Due to the spectral width of near infrared femtosecond pulse laserSpectrum width of light source of middle infrared signal generated by nonlinear difference frequencyThe formula is as follows:
。
S200, a second chirp polarization structure nonlinear crystal is adopted, and the middle infrared signal is converted into a visible/near infrared band through a broadband nonlinear sum frequency process of the femtosecond pump pulse and the middle infrared time domain stretching signal passing through the sample.
The nonlinear crystal of the second chirp polarization structure aims to realize the broadband nonlinear sum frequency process of the femtosecond pumping pulse and the infrared stretching signal in the broadband, so as to generate the visible/near infrared up-conversion signal of the time domain stretching, thereby realizing the sensitive detection by utilizing the high-performance silicon-based detector. The defects of high intrinsic dark noise, low-temperature refrigeration operation requirement and the like of the conventional infrared detection device are overcome.
And step S300, optical asynchronous scanning is realized by controlling the repetition frequency difference of the femtosecond pump pulse and the mid-infrared time domain stretching signal, and further, the spectrum high-precision optical sampling of the mid-infrared time domain stretching signal is obtained.
The method realizes the up-conversion detection of each spectrum component of the mid-infrared by an optical asynchronous scanning method, referring to fig. 1 and 3, that is, the control system leads the broadband near-infrared pulse and the femtosecond pumping pulse to have fixed frequency difference（Refers to the wideband near infrared pulse repetition frequency,Refers to the repetition frequency of the femtosecond pump pulse), the time delay of each period of the mid-infrared stretching signal and the femtosecond pump pulse is（The center repetition frequencies of the broadband near infrared pulse and the femtosecond pump pulse are generally smaller, and the difference of the two repetition frequencies can be approximately considered when calculating the time delay and the period). In other words, every other pump light pulseIs sampled once for the mid-infrared time stretch spectrum, and the relative time position of each sample existsIs a time difference of (2).
Thus, the time required for scanning the complete mid-infrared stretching spectrum once isI.e. scan rate ofIn general, it can be achieved thatAbove the level, thereby enabling high-speed spectroscopic measurements without mechanical scanning. The influence of the self time jitter of the detector on the tensile spectrum measurement is avoided, the requirements on the resolution bandwidths of the detector and the oscilloscope are reduced, the spectrum resolution capability is obviously improved, and the mechanical scanning process is avoided.
If the infrared time domain spectrum is stretched to fill the entire pulse period, then. Nonlinear and frequency conversion is realized only in extremely narrow time window in mid-infrared time domain stretching signal by femtosecond pump pulse once, if the pulse width of the femtosecond pump pulse isAnd assuming that each spectral component of the mid-infrared stretching signal is linearly and uniformly spread in the time domain, the spectral resolution precision of the single optical samplingThe formula is as follows:
The spectrum sampling precision is proportional to the pumping pulse width, and the narrower pumping pulse width can lead the system to obtain higher spectrum resolution precision, so the technical scheme selects the infrared pulse with the hundred femtoseconds as a pumping light source. If the spectrum resolution precision is taken as the scanning step to carry out high-resolution spectrum acquisition, then The spectral detection refresh rate at this time is。
When the frequency up-conversion is carried out on the mid-infrared time domain stretching signal and the femtosecond pumping pulse, the introduced time walk-off effect reduces the spectrum sampling resolution precision due to the different group velocities of the bicolor pulse in the nonlinear medium, and the spectrum sampling resolution precision is expressed by the following formula:
Wherein, For the off-time of the bi-color pulse,For a non-linear media length,The inverse of the group velocity of the mid-infrared signal and the femtosecond pump pulse respectively,I.e. the amount of time per unit length of the bi-color pulse in the non-linear medium. Considering the above factors, the final system detects the spectral resolution accuracy as shown in the following formula:
Referring to fig. 2, for the up-conversion pump light and the difference frequency near infrared broadband light source with the center wavelength of 1030 nm and 1550 nm respectively, the numerical simulation result of the mid-infrared spectrum detection resolution changing with the dispersion under different sampling pulse widths is given. The nonlinear frequency up-conversion medium adopted in the numerical simulation is a lithium niobate crystal with a chirp polarization structure and a length of 10mm, and the time walk-off quantity of the lithium niobate crystal to a mid-infrared pulse signal and a 1030 nm pump pulse signal which are near 3 μm is 52 ps/m. From the graph, the system detection spectral resolution is improved with the increase of the time dispersion stretching amount, and the spectral resolution can reach pm level for shorter sampling pump pulse width.
In addition, the high-performance silicon-based detector used in the technical scheme only needs to record intensity information, and the time jitter of the detector does not influence the measured spectral resolution. The kHz spectral rate and pm-magnitude mid-infrared spectral resolution realized by the technology are not compatible with the traditional means.
Referring to fig. 4, a high-speed high-resolution mid-infrared spectrum detection device includes a near-infrared broadband light source 101, a high-precision repetition frequency locking system 102, a femtosecond pump light source 103, a first beam collimator 104, a dispersion medium 105, a second beam collimator 106, a high-power single-frequency continuous light source 107, a first dichroic mirror 108, a first reflecting mirror 109, a first CaF 2 lens 110, a first chirped polarized lithium niobate crystal 111, a second CaF 2 lens 112, a first filter 113, a second reflecting mirror 114, a sample placement bit 115 to be detected, a second dichroic mirror 116, a third CaF 2 lens 117, a second chirped polarized lithium niobate crystal 118, a fourth CaF 2 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 is required to cover 3000-4000 nm, and the near infrared broadband light source 101 spectrum is required to cover 1387-1569 nm.
A high-precision repetition frequency locking system 102 for locking the repetition frequencies of the near infrared broadband light source 101 and the femtosecond pump light source 103 to have a fixed repetition frequency differenceThe locking method is active feedback frequency locking based on a piezoelectric ceramic actuator, in one embodiment, the high-precision repetition frequency locking system 102 locks the repetition frequencies of the near infrared broadband light source 101 and the femtosecond pumping light source 103, the central repetition frequency is 20 MHz, and the repetition frequency difference is。
The femto-second pump light source 103 is used as pump light in the subsequent mid-infrared signal frequency up-conversion process to realize time high-precision optical sampling of the mid-infrared time domain stretching signal, and in one embodiment, the pulse width is 300 fs, and the center wavelength is 1 μm.
The first beam collimator 104 is used to couple the spatially output near infrared broadband light source 101 into a dispersive optical fiber.
The dispersive medium 105 includes, but is not limited to, a single-mode dispersive fiber, a multimode fiber, a chirped fiber Bragg grating, etc., for effecting time-domain separation of the spectral components of the near infrared broadband light source 101. The transmission optical fiber of the communication band has very mature development and low transmission loss to the near infrared band, thus being a preferable scheme. In one embodiment, a 15 km G650D fiber is used as the dispersive medium, with a zero dispersion point at 1310 nm and a large positive dispersion near 1550 nm, with a dispersion coefficient of. By long-distance time stretching, the stretching delay of the near infrared light source can reach about 50 ns.
The second beam collimator 106 is used for spatially collimating and outputting the stretched near-infrared signal transmitted by the dispersive optical fiber, 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 pumping source for a broadband nonlinear difference frequency process, and in one embodiment, the center wavelength is 1030 nm, and the output power can reach 10W.
The first dichroic mirror 108 is configured to spatially combine the stretched near infrared signal with the output of the high-power single-frequency continuous light source 107 (the first spatially combined beam), so as to facilitate the subsequent participation in the broadband nonlinear difference frequency process. The dichroic mirror is a 1.3 mu m short-wave through dichroic mirror, has higher reflectivity for 1387-1569 nm near infrared signal light and higher transmissivity for 1030 nm pump light.
The first mirror 109 and the second mirror 114 are used to change the path direction.
The first CaF 2 lens 110 and the second CaF 2 lens 112 are used to focus the signal light and the pump light participating 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 for focusing the signal light and the pump light participating in nonlinear frequency conversion into the second chirped polarized lithium niobate crystal 118, so as to realize efficient frequency conversion.
The first chirped polarized lithium niobate crystal 111, as a nonlinear medium for the frequency down conversion process, is used to generate a 3-4 μm mid-infrared time domain stretched signal, and in one embodiment, has a polarization period ranging from 25 μm to 32 μm.
The first filter 113 is used for filtering out high-power single-frequency continuous laser and near infrared stretching signals, and in one embodiment, a 2.4 μm long-pass filter is used, so that the high-power single-frequency continuous laser and near infrared stretching signals have higher transmittance to the infrared time domain stretching signals in the range of 3-4 μm.
The sample to be tested is placed in the placing position 115, the detected targets have different light absorption degrees for different wavelengths, and the experimental system can obtain the absorption rate of the detected targets for each wavelength by measuring the spectral intensity distribution of the sample without the sample or with the sample.
The second dichroic mirror 116 is configured to spatially combine the mid-infrared time domain stretching signal with the output of the femtosecond pump light source 103 (second spatial combining), so as to facilitate the 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, has a high reflectivity for 3-4 μm near infrared signal light, and has a high transmissivity for 1030 nm pump light.
The second polarized lithium niobate crystal 118, which is a nonlinear medium for the frequency up-conversion process, is used to convert the infrared time domain stretching signal in the 3-4 μm range to the visible/near infrared band, and in one embodiment, has a polarization period ranging from 19 μm to 24 μm and a length of 10 mm.
The second filter 120 is used for filtering the femtosecond pump light source 103, and in one embodiment, a 900 nm low-pass filter is used, which has a higher transmittance for the 700-900 nm up-conversion signal.
The silicon-based detector 121 is used for realizing ultrasensitive intensity detection on the up-converted signal, and the detection wavelength range is 400-1100 nm.
The oscilloscope 122 is used for displaying and collecting the signal intensity information of each wavelength measured by the silicon-based detector 121, and the resolution bandwidth of the oscilloscope is better than 20 MHz because the repetition frequency of the bicolor pulse is about 20 MHz, i.e. the asynchronous sampling time interval is about 50 ns.
This embodiment is implemented by first locking the near infrared broadband light source 101 with the high precision repetition frequency of 20 MHz by the high precision repetition frequency locking system 102, coupling it into the G652D single mode fiber by the first beam collimator 104 after spatial output, and linearly and uniformly stretching the spectral range 1387-1569 nm to 50 ns. The near infrared stretching signal is spatially output by the second beam collimator 106, spatially combined with the high-power single-frequency continuous light source 107 through the first dichroic mirror 108 (first spatially combined), focused by the first CaF 2 lens 110 into the first chirped polarized lithium niobate crystal 111, so as to generate a broadband nonlinear difference-frequency mid-infrared time domain stretching signal, spatially collimated by the second CaF 2 lens 112, and filtered by the first filter 113 to obtain the high-power single-frequency continuous laser and near infrared stretching signal. The wavelength of the generated mid-infrared time domain stretching signal is covered by 3-4 mu m, the stretching delay amount is 50 ns, namely the dispersion amount of the mid-infrared stretching spectrum is 50 ps/nm.
Subsequently, the output pulse of the femtosecond pump light source 103 locked by the high-precision repetition frequency locking system 102 is spatially combined (second spatially combined) with the mid-infrared time domain stretching signal passing through the detected target (sample) through the second dichroic mirror 116, and focused into the second chirped polarized lithium niobate crystal 118 by the third CaF 2 lens 117, so as to realize frequency up-conversion signal generation. The up-converted signal is then spatially collimated by the fourth CaF 2 lens 119, filtered out of the femtosecond pump pulses by the second filter 120, intensity measured by the silicon-based detector 121, and data acquired and displayed by the oscilloscope 122.
Because the mid-infrared time domain stretching signal has a time-spectrum mapping relation, the intensity information of different wavelengths can be obtained by performing nonlinear optical sampling on the mid-infrared signals of different times. In this embodiment, the near infrared broadband light source 101 and the femto-second pump light source 103 have a fixed difference in frequency by the high-precision frequency-repetition locking system 102The sampling delay of the mid-infrared stretching signal and the femtosecond pumping pulse is. Every other femto second pump light source 103Is to sample the mid-infrared time domain stretched signal once, and each sample is to be stepped relative in time. Thus, the time required for scanning the complete mid-infrared stretching spectrum once isI.e. scan rate ofThereby enabling high-speed spectroscopic measurements without mechanical scanning. The spectrum resolution accuracy in this case is:
for high resolution acquisition mode, the acquisition step time should be The acquired 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 asThe spectrum scanning rate is further improved to 10 kHz, the spectrum resolution precision is still 11.8 pm, the sampling step time is 25 ps, the corresponding spectrum resolution is 0.5 nm, and the spectrum resolution is still superior to the existing mid-infrared spectrometer. Meanwhile, the high-performance silicon-based detector used in the technical scheme only records intensity information, and the time jitter of the detector is far smaller than a sampling time interval, so that the measured spectral resolution is not influenced. The kHz spectral rate and pm-magnitude mid-infrared spectral resolution realized by the technology are not achieved by the traditional means, and can provide powerful support for applications such as rapid spectral diagnosis of histopathology and nondestructive detection of materials.
As an expansion, the technical scheme can be also applied to single photon high resolution spectrum detection by combining with a time-dependent single photon counter. The near infrared broadband pulse stretched in time by the dispersive medium 105 and the sum frequency signal of the femtosecond pump light source 103 are used as trigger starting signals, the intensity signal measured by the silicon-based detector 121 is used as trigger terminating signals, the time domain distribution of the spectrum intensity is counted by a time-dependent single photon counter, the high-resolution spectrum detection of single photon magnitude without mechanical scanning is realized, and powerful support can be provided for applications such as non-toxic biomedical sample observation, trace substance analysis, remote spectrum detection and the like.
As an expansion, the technical scheme 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 imaging spectrum is 1000, the working frame frequency of the camera is 1 kHz, the image spectrum acquisition step is 1 nm, the double-color pulse repetition frequency difference is required to be controlled to be 1 Hz, and the total sampling range of the camera 1ms within the exposure time is 1 nm. The mid-infrared hyperspectral imaging realized based on the mode avoids the spectrum scanning acquisition process and has the advantages of high speed, high resolution and the like.
The foregoing is merely exemplary of the present application, and the specific structures and features well known in the art will not be described in any way, so that those skilled in the art will be able to ascertain all prior art in the field, and will not be able to ascertain any prior art to which the application pertains, without the general knowledge of the specific structures and features of the application, before the filing date or the priority date, with the ability to apply the conventional practice of the application, as it would be well known to those skilled in the art, with the benefit of this disclosure, to make various embodiments with the ability to work in mind, and to make certain typical structures or methods well known to those skilled in the art. It should be noted that modifications and improvements can be made by those skilled in the art without departing from the structure of the present application, and these should also be considered as the scope of the present application, which does not affect the effect of the implementation of the present application and the utility of the patent. The protection scope of the present application is subject to the content of the claims, and the description of the specific embodiments and the like in the specification can be used for explaining the content of the claims.
Claims (10)
1. A high-speed high-resolution mid-infrared spectrum detection method is characterized in that: comprising the following steps:
A nonlinear crystal with a first chirp polarization structure is adopted, and a broadband mid-infrared stretching signal with a time-spectrum mapping relation is generated based on a nonlinear broadband difference frequency process of time stretching near infrared signals and single-frequency continuous pumping;
the second chirp polarization structure nonlinear crystal is adopted, and the middle infrared signal is converted into a visible/near infrared band through the broadband nonlinear sum frequency process of the femtosecond pump pulse and the middle infrared time domain stretching signal passing through the sample;
The optical asynchronous scanning is realized by controlling the repetition frequency difference of the femtosecond pump pulse and the mid-infrared time domain stretching signal, so that the high-precision optical spectrum sampling of the mid-infrared time domain stretching signal is obtained.
2. The high-speed high-resolution mid-infrared spectrum detection method according to claim 1, wherein the method comprises the following steps: and converting the stretching near infrared signal prepared by the near infrared dispersion element into a middle infrared band to obtain a middle infrared time domain stretching signal with a time-wavelength mapping relation.
3. The high-speed high-resolution mid-infrared spectrum detection method according to claim 1, wherein the method comprises the following steps: the nonlinear crystal based on the second chirped polarization structure realizes the broadband nonlinear frequency up-conversion of the mid-infrared time domain stretching signal, and the mid-infrared signal is detected by the high-performance silicon-based detector.
4. A high-speed high-resolution mid-infrared spectrum detection method as defined in claim 3, wherein: and performing fine nonlinear asynchronous time sampling on the mid-infrared time domain stretching spectrum based on the ultra-short pulse.
5. A high-speed high-resolution mid-infrared spectrum detection device is characterized in that: a high-speed high-resolution mid-infrared spectrum detection method as claimed in any one of claims 1-4, comprising a near-infrared broadband light source, a high-precision repetition frequency locking system, a femtosecond pump light source, a beam collimator, a dispersion medium, a high-power single-frequency continuous light source, a dichroic mirror, a CaF 2 lens, a chirped polarization lithium niobate crystal, a filter and a silicon-based detector.
6. The high-speed high-resolution mid-infrared spectrum detection device according to claim 5, wherein: the near infrared broadband light source is used as a seed source to combine a time stretching technology and a 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 for locking the repetition frequencies of the near infrared broadband light source and the femtosecond pumping light source to ensure that the repetition frequencies have fixed repetition frequency difference; the high-power single-frequency continuous light source is used as a pumping source of a broadband nonlinear difference frequency process;
The beam collimator comprises a first beam collimator and a second beam collimator; the first beam collimator is used for coupling the near infrared broadband light source output in space into the dispersion optical fiber; the dispersion medium is used for realizing the dispersion separation of each spectrum component of the near infrared broadband light source in the time domain; the second beam collimator is used for spatially collimating and outputting the stretched near infrared signal transmitted by the dispersive optical fiber;
The dichroic mirror comprises a first dichroic mirror and is used for outputting a first spatial beam combination of the stretching near infrared signal and a high-power single-frequency continuous light source; the chirped polarized lithium niobate crystal comprises a first chirped polarized lithium niobate crystal used for generating a mid-infrared time domain stretching signal; the CaF 2 lens comprises a first CaF 2 lens for focusing a first spatially combined beam into a first chirped polarized lithium niobate crystal; the filter plate comprises a first filter plate used for filtering high-power single-frequency continuous laser and near infrared stretching signals.
7. The high-speed high-resolution mid-infrared spectrum detection device according to claim 6, wherein: the dispersion medium adopts one of single-mode dispersion optical fiber, multimode optical fiber or chirped fiber Bragg grating.
8. The high-speed high-resolution mid-infrared spectrum detection device according to claim 6, wherein: the femtosecond pump light source is used as pump light in the subsequent intermediate infrared signal frequency up-conversion process to realize time high-precision optical sampling of the intermediate infrared time domain stretching signal;
The dichroic mirror further comprises a second dichroic mirror, and the second dichroic mirror is used for outputting a second spatial beam combination of the middle infrared time domain stretching signal passing through the sample and the femtosecond pumping light source; the chirped polarized lithium niobate crystal comprises a second chirped polarized lithium niobate crystal and is used for converting the middle infrared time domain stretching signal into a visible/near infrared wave band to obtain an up-conversion signal; the CaF 2 lens comprises a third CaF 2 lens for focusing the second spatially combined beam into a second chirped polarized lithium niobate crystal; the filter comprises a second filter for filtering the femtosecond pump light source.
9. The high-speed high-resolution mid-infrared spectrum detection device according to claim 8, wherein: the silicon-based detector is used for measuring the intensity of the up-conversion signal.
10. The high-speed high-resolution mid-infrared spectrum detection device according to claim 9, wherein: the oscilloscope is used for displaying and collecting the signal intensity information of each wavelength measured by the silicon-based detector.
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