CN116183536A - A mid-infrared up-conversion spectral detection method with multi-wavelength pumping - Google Patents

Abstract

The invention discloses a mid-infrared up-conversion spectrum detection method of multi-wavelength pumping, which is characterized in that the method uses multi-wavelength narrow-band laser as a non-linear conversion pumping source, and simultaneously uses a multi-period quasi-phase matching crystal as a non-linear up-conversion medium, thereby realizing mid-infrared signal broadband and high-efficiency conversion, and finally obtaining mid-infrared spectrum detection with wide band, high resolution and ultrasensitivity by combining a high-performance near-infrared spectrum measurement and control element. Compared with the existing up-conversion spectrum technology, the method has the characteristics of large bandwidth and high efficiency, can high-fidelity and resolve the spectrum information of the middle infrared, provides an effective means for realizing the ultra-sensitive middle infrared spectrum measurement with wide band and high resolution, and is expected to be applied to important fields such as molecular spectroscopy, trace substance detection, infrared remote sensing, atmosphere monitoring and the like.

Description

A mid-infrared up-conversion spectral detection method with multi-wavelength pumping

technical field

The invention relates to the technical field of mid-infrared spectroscopy, in particular to a multi-wavelength pumped mid-infrared up-conversion spectrum detection method.

Background technique

The mid-infrared band corresponds to the vibrational energy level transition peaks of many molecules, and is directly related to the molecular composition and structure of most biological tissues and chemical materials. It is called the molecular "fingerprint" spectral region and is widely used in qualitative and quantitative detection of substances. The development of mid-infrared spectroscopy technology has important application prospects in life sciences, environmental monitoring, materials engineering, medical diagnosis, infrared remote sensing, etc. In particular, broadband mid-infrared spectroscopy technology is beneficial to obtain the spectral line characteristics of multiple components at one time. High-resolution mid-infrared spectroscopy technology provides a powerful means for obtaining fine characterization of spectral lines. Under the condition of irradiance, a higher signal-to-noise ratio can be obtained. At present, mid-infrared spectroscopy technology is constantly changing and improving, and it is urgent to develop a new technology for mid-infrared spectroscopy detection with a wide band, high resolution, and ultra-sensitivity, so as to meet the requirements of multi-component material detection and high-precision spectral lines in the scientific and industrial fields. There is an urgent need for analysis and trace substance detection.

Currently, mid-infrared spectrometers are generally based on grating dispersive detection or use Fourier transform infrared (FTIR) detection. The grating spectrometer uses a grating to separate the mid-infrared spectrum spatially, and then is detected by a linear array detector. However, limited by the limited pixels of the mid-infrared detection array and the low frame rate, the resolution of the grating spectrometer is usually very low and the spectral forming speed is slow. Although the Fourier transform infrared spectrometer can use a single-point detector to achieve higher spectral resolution and a wider spectral range, it relies on mechanical scanning, which greatly limits the speed of spectral formation, so it is not suitable for fast acquisition. In addition, the detection elements of mid-infrared spectrometers are generally based on narrow-bandgap semiconductor materials (such as: HgCdTe, InSb), which are limited by intrinsic noise. Usually, it is necessary to suppress dark current and thermal noise by means of an extremely low-temperature multi-stage cooling system to improve Sensitivity of the detection system. Even so, its sensitivity is still far from that of detectors working in the near-infrared band. Therefore, mid-infrared spectroscopy technology is limited by spectroscopic methods and infrared detection devices, and breakthroughs are urgently needed in terms of spectral formation speed, spectral resolution, and detection sensitivity.

In view of the difficulties faced by the current mid-infrared spectroscopy technology, mid-infrared frequency up-conversion detection technology has developed rapidly in recent years. This technology converts the weak mid-infrared signal to the visible/near-infrared band with high fidelity through a nonlinear sum-frequency process. Visible/near-infrared detection array detection with lower and faster response speed realizes ultra-sensitive and rapid spectrum formation in the mid-infrared band. However, the existing up-conversion spectroscopy technology is limited by the quasi-phase matching bandwidth, resulting in the spectral window for efficient conversion is generally only tens of nanometers, which is far from meeting the needs of broadband detection scenarios such as infrared remote sensing, environmental monitoring, and astronomical observation. To break through the limitation of matching bandwidth, the matching bandwidth is often widened by tuning the nonlinear crystal temperature, changing the grating period of the nonlinear medium, and tuning the incident angle of signal light. However, these methods all rely on mechanical tuning, which is a slow process, which severely limits the spectral acquisition speed. In addition, another commonly used method is to use a chirped nonlinear medium with a continuously changing period to increase the bandwidth. Although this method avoids tuning transformation, the limited nonlinear action distance limits the conversion efficiency, thereby sacrificing the detection sensitivity. Therefore, up-conversion spectroscopy technology faces the mutual constraints of detection bandwidth and detection efficiency, and it is urgent to develop a mid-infrared up-conversion spectroscopy detection technology with both broadband conversion and high conversion efficiency.

Contents of the invention

The purpose of the present invention is to provide a multi-wavelength pumped mid-infrared up-conversion spectral detection method for the deficiencies of the prior art, adopting the corresponding quasi-phase matching cycle extremum under different pump wavelengths, and designing a multi-cycle nonlinear The medium, under the action of multi-wavelength single-frequency narrow-linewidth laser pumping, broadens the overall bandwidth of nonlinear phase matching, and uses multi-wavelength single-frequency pumping and multi-period nonlinear media to achieve high-efficiency mid-infrared frequency up-conversion detection. Finally, the mature near-infrared dispersive element and single-photon detection array are used to realize high-sensitivity, high-speed, and high-resolution spectral analysis in the mid-infrared wide spectral range. This method overcomes the mutual constraints between mid-infrared wide-spectrum detection and high conversion efficiency, and can achieve wide-band, high-efficiency, high-resolution ultra-sensitive detection of mid-infrared spectroscopy. It provides strong support for applications such as remote sensing detection and atmospheric monitoring.

The specific technical solution to realize the object of the present invention is: a multi-wavelength pumped mid-infrared up-conversion spectral detection method, which is characterized in that a multi-wavelength single-frequency narrow-band laser is used as the pump light, and a multi-period nonlinear medium is used to realize broadband Mid-infrared coverage and efficient mid-infrared frequency up-conversion, the converted spectral components do not overlap, using high-performance near-infrared dispersion and detection elements to achieve high-resolution and ultra-sensitive detection of mid-infrared broadband spectra, the method specifically includes the following The above steps:

1) Using multi-wavelength single-frequency narrow-linewidth lasers as pump light breaks through the dilemma of limited phase-matching bandwidth under traditional single-wavelength pumping. Different pump wavelengths can achieve simultaneous and efficient conversion of multiple mid-infrared signal bands. The converted spectral components have no overlap, and after simple up-conversion spectral splicing, a wide-band mid-infrared spectral detection range can be obtained.

2) Using a multi-period nonlinear medium as the medium for frequency up-conversion, refer to the quasi-phase period extremum corresponding to the nonlinear conversion under different pump wavelength conditions, design a crystal or waveguide with discrete periodic changes, and obtain broadband through a multi-period structure The phase matching window can be obtained, and at the same time, a longer nonlinear interaction length can be obtained to achieve more efficient nonlinear frequency up-conversion.

3) The pump light source uses a narrow-band single-frequency laser. Because of its single longitudinal mode, low noise, and narrow spectrum characteristics, it can ensure that the wavelength after nonlinear conversion corresponds to the wavelength of the mid-infrared signal, thereby maintaining the mid-infrared signal with high fidelity. Spectral information, combined with visible light, near-infrared high-resolution dispersion elements and multi-pixel detection elements, provides a guarantee for high-resolution mid-infrared spectral analysis.

The multi-period nonlinear medium includes structures such as crystals and waveguides, and uses non-collinear quasi-phase matching to broaden the matching bandwidth of mid-infrared signals. The materials of the nonlinear crystals and waveguides include but are not limited to: periodically poled niobium lithium oxide (PPLN) crystal/waveguide, periodically poled potassium titanyl phosphate (PPKTP) crystal/waveguide, periodically poled lithium tantalate (PPLT) crystal/waveguide, etc.; The quasi-phase cycle extremum of the up-conversion is selected to ensure the coverage of the mid-infrared spectral range required for detection. The cycle selection of the nonlinear medium includes but is not limited to 34.8 μm, 28.1 μm, 25.8 μm, and 24.1 μm; the nonlinear medium’s Crystal and waveguide structure designs include but are not limited to: multi-period cascade arrangement, multi-period staggered arrangement, etc.

The multi-wavelength single-frequency narrow-linewidth laser as the pump light is a pump light source that uses multi-wavelength beam combining. The pump light source is composed of a plurality of single-frequency narrow-linewidth continuous lasers, which can maintain Broad-band mid-infrared spectral information, the number of pump laser sources includes but not limited to 4; the wavelength of the pump light includes but not limited to: 1.55 μm, 1.35 μm, 1.20 μm and 1.10 μm.

The visible light and near-infrared high-resolution dispersive elements include, but are not limited to, prisms, gratings, virtual imaging arrays, and the like.

The envelope of the multi-pixel detection element is not limited to CCD, EMCCD, CMOS, sCMOS and other detector arrays.

Compared with the prior art, the present invention has the following remarkable technical effects and progress:

1) Multi-wavelength continuous lasers are used as pump light, and the up-conversion spectra corresponding to different pump wavelengths do not overlap. Through band splicing, a wide-band mid-infrared spectral detection window can be obtained, which breaks through the traditional single-wavelength pump Put down the dilemma of limited bandwidth of phase matching. At the same time, the pump light source uses a narrow-band single-frequency laser, because of its single longitudinal mode, low noise, and narrow spectrum characteristics, it can ensure that the wavelength after nonlinear conversion corresponds to the wavelength of the mid-infrared signal, thereby maintaining the mid-infrared signal with high fidelity. The spectral information provides a guarantee for the realization of high-resolution mid-infrared spectral analysis.

2) The multi-period nonlinear medium is used as the medium for frequency up-conversion. The mid-infrared incident crystal can obtain a wide-band phase matching window without tuning temperature, period, and angle, avoiding the limitation of mechanical tuning on the spectral speed. At the same time, compared with the nonlinear medium of the chirped structure, a longer nonlinear interaction distance can be obtained, thereby improving the efficiency of broadband nonlinear frequency up-conversion.

3) Convert the mid-infrared signal to the near-infrared by performing frequency up-conversion in a nonlinear medium, and use superior performance, economical and effective near-infrared dispersion elements and ultra-sensitive detection arrays to overcome the performance bottleneck of existing mid-infrared devices, Realized higher spectral resolution, faster spectroscopic speed, and higher detection sensitivity.

Description of drawings

Fig. 1 is a schematic diagram of phase matching of three-wave nonlinear sum frequency under the collinear situation;

Figure 2 is a diagram of the collinear quasi-phase period Λ relationship corresponding to each band in the mid-infrared under different wavelength pumping conditions;

Fig. 3 is a graph showing the relationship between the mid-infrared wavelength and the up-conversion efficiency under the extreme period of Fig. 2;

Fig. 4 is a diagram of the relationship between the range and intensity of the near-infrared band corresponding to the mid-infrared band in Fig. 3 after frequency up-conversion;

FIG. 5 is a schematic structural diagram of the spectral detection device of Embodiment 1.

Detailed ways

The present invention uses a multi-wavelength single-frequency narrow-linewidth laser to pump a multi-period nonlinear medium, wherein the light field involved satisfies the law of conservation of energy and momentum, a pump photon with a frequency of _ωp and a low-frequency photon with a frequency of _ωs The energetic mid-infrared signal photon annihilates, producing an upconverted photon of frequency ω _u . In the frequency conversion process, when the phase matching condition is satisfied, and Δk=k _u -k _s -k _p is zero, there is the maximum conversion efficiency. The prior art requires strict angle and temperature phase matching, and the mid-infrared matching bandwidth that can realize efficient frequency conversion is often only a few tens of nanometers. In order to overcome the above technical difficulties and broaden the spectral range of mid-infrared frequency conversion, the present invention adopts a Quasi-phase matching technology, through the design of the periodic distribution of the polarized crystal, selects the appropriate inversion period Λ to compensate for the mismatch of Δk, so as to ensure that the mid-infrared spectra of different wavelengths can meet the phase matching conditions, thereby realizing frequency conversion.

Referring to Figure 1, the three waves of pump light, mid-infrared signal light and up-converted light propagate collinearly along the distribution direction of the periodic row in the nonlinear medium, and the phase mismatch in the process of sum-frequency interaction is expressed by the following formula (a):

为非线性介质周期性结构引入的光栅波矢。在非线性介质制作工艺上，Λ_i可灵活调整，所以通过对特定非线性过程设计周期，能容易地满足Λk＝0，实现准相位匹配作用，保证能量流动的方向始终是由基波到和频波。in,

Introduced grating wavevectors for periodic structures in nonlinear media. In the nonlinear medium manufacturing process, _Λi can be adjusted flexibly, so by designing the cycle for a specific nonlinear process, it can easily satisfy Λk=0, realize the quasi-phase matching effect, and ensure that the direction of energy flow is always from the fundamental wave to and frequency wave.

和/>

的条件为例，中红外波长与其匹配的共线准相位周期Λ存在图2中所示的关系，可以发现，每条曲线都有一个周期极值点，且该极值点位置会随着泵浦光波长的选择而变化。Referring to Figure 2, the second-order nonlinear MgO-PPLN crystal and the pumping wavelength are respectively

and />

As an example, the mid-infrared wavelength and its matching collinear quasi-phase period Λ have the relationship shown in Figure 2. It can be found that each curve has a period extreme point, and the position of the extreme point will vary with the pump The choice of the wavelength of the pump light varies.

Referring to Figure 3, if the domain period Λ near the extreme point corresponding to a single pump wavelength is selected to design a nonlinear crystal, the matching bandwidth of mid-infrared signals under each pump wavelength can reach the order of hundreds of nanometers. Therefore, by designing the crystal period Λ, the pump wavelength, and choosing an appropriate crystal material, the frequency up-conversion process can be matched to a specific mid-infrared wavelength range.

由分段的上转换光谱/>

与频率之间的转换关系，通过下述(b)式获得各分段的中红外光谱强度分布/>

Referring to FIG. 4 , the matched mid-infrared bands under various pumping conditions have no overlap in the near-infrared spectrum after nonlinear frequency up-conversion. Therefore, the mid-infrared spectral information can be uniquely deduced according to the corresponding pumping conditions, and the mid-infrared broadband spectrum can be obtained through simple spectral calculation and splicing. Specifically, it is first necessary to segment the upconversion spectral intensity distribution I _u (λ _u ) obtained at one time according to each pumping condition, and the upconversion spectral intensity distribution corresponding to different pumping wavelengths is

Up-converted spectra by segmenting />

The conversion relationship between frequency and frequency, the mid-infrared spectral intensity distribution of each segment is obtained by the following (b) formula />

后，通过下(c)式获得中红外全探测范围内的光谱强度分布I_s(λ_s)：Next, after obtaining the mid-infrared spectral intensity distribution of each segment

Finally, the spectral intensity distribution I _s (λ _s ) in the full detection range of the mid-infrared is obtained by the following formula (c):

Through the above method, measure the spectral intensity distribution curve σ(λ _s )I _s (λ _s ) when the sample is placed and the spectral intensity distribution curve I _s (λ _s ) when the sample is not placed, and divide the two to obtain The broadband mid-infrared absorption line σ(λ _s ) of the sample was measured.

Referring to Figure 2, under the condition of multi-wavelength pumping, multi-period nonlinear crystals are used to obtain efficient conversion of multiple mid-infrared signal bands at the same time, which effectively broadens the bandwidth of mid-infrared efficient conversion. Since the up-conversion spectra of each cycle do not overlap, the wide-band mid-infrared spectral information can be obtained by selecting the corresponding pump light for wavelength conversion. Compared with single-wavelength pumping and single-period crystal schemes, this method can obtain a wider phase-matching bandwidth. In the way of obtaining broadband, compared with the traditional temperature adjustment, period adjustment, and angle adjustment methods, the complicated tuning process is eliminated. Compared with using a chirped crystal with a continuously changing period to achieve broadband conversion, the advantage of using Long nonlinear interaction length for more efficient nonlinear conversion. The invention adopts a combination of multiple narrow-band single-frequency lasers, and when interacting with broadband infrared spectral signals, it can obtain spectral patterns corresponding to mid-infrared in the near-infrared band, thereby realizing high-fidelity infrared spectral information transfer, which is high-precision Mid-infrared spectral analysis provides assurance.

The near-infrared mature dispersion element and ultra-sensitive single-photon detection array adopted in the present invention have more mature technology and better performance. Near-infrared dispersive elements, such as gratings, have denser lines and higher grating efficiency than mid-infrared dispersive elements. In addition, compared with mid-infrared detectors, near-infrared detection arrays have the advantages of more pixels, lower noise, and faster response speed. Therefore, through the frequency up-conversion process, the mid-infrared signal is converted to the near-infrared band, which can achieve spectral analysis with spectral resolution, higher sensitivity, and faster spectroscopic speed.

In the following, the present invention will be further described in detail through the implementation of a multi-wavelength pumped mid-infrared up-conversion spectrum detection.

Example

Referring to Fig. 5, the spectral detection device implementing the present invention specifically includes: a broadband mid-infrared light source 1, a germanium window 2, an off-axis parabolic mirror 3, a sample to be measured 4, a calcium fluoride lens 5, and a single-frequency continuous pump laser 6 , b single-frequency continuous pumping laser 7, c single-frequency continuous pumping laser 8, d single-frequency continuous pumping laser 9, wavelength division multiplexer 10, achromatic focusing lens 11, binomial mirror 12, multi-period stages Connected waveguide 13, temperature control furnace 14, a lens 16, filter 16, b lens 17, near-infrared grating 18, metal mirror 19, c lens 20, COMS detection array 21 and computer 22.

The broadband mid-infrared light source 1 can be an active light source generated by a continuum such as a waveguide or a soft glass fiber, or a passive light source such as a thermal light source, and its wavelength range can cover 3-5 μm.

The germanium window 2 is used to block any incident visible light, and the window is coated with a broadband anti-reflection coating with an average reflectance of less than 3% within 3-5 μm.

The purpose of the off-axis parabolic mirror 3 is to collect infrared signals, and the average reflectivity is greater than 96% in the broadband range of 800nm-20μm.

The purpose of the sample to be tested 4 is to measure the absorption/transmission spectrum of the sample. The sample to be tested has different degrees of light absorption at different wavelengths. The absorbance of the wavelength. Samples to be tested include but are not limited to: solid, gas, liquid, etc.

The purpose of the calcium fluoride lens 5 is to focus the mid-infrared carrying spectral information into the multi-period cascaded waveguide 13 .

和/>

谱宽3KHz，偏振对比度大于20dB，输出功率能达到10W。将这四个激光器输出光合束后作为频率上转换的泵浦光源，可以实现中红外上千纳米范围的上转换。The single-frequency continuous pump lasers 6, 7, 8, and 9 of a, b, c, and d are external cavity diode lasers with tunable center wavelengths, and their center wavelengths are respectively

and />

The spectral width is 3KHz, the polarization contrast is greater than 20dB, and the output power can reach 10W. The output of these four lasers is combined as a pump light source for frequency upconversion, which can realize upconversion in the range of thousands of nanometers in the mid-infrared.

The purpose of the wavelength division multiplexer 10 is to combine the pump lights of different wavelengths together and output them coaxially.

The purpose of the achromatic focusing lens 11 is to transform the pump light and focus it into the multi-period cascaded waveguide 13 .

The purpose of the dichroic mirror 12 is to combine the pump light and the mid-infrared light. The dichroic mirror has a high transmittance to the mid-infrared light and a high reflectance to the multicolor pump light.

The multi-period cascaded waveguide 13 adopts a multi-period cascaded lithium niobate waveguide as a frequency up-conversion nonlinear medium, and its polarization periods are cascaded arrangements of 34.8 μm, 28.1 μm, 25.8 μm, and 24.1 μm, which can be Broadband mid-infrared light is converted to the near-infrared band. The optical channel of the waveguide can provide a long-distance strong confinement field, and its narrow structure can increase the average power of the multicolor pump light field, thereby improving the broadband frequency up-conversion efficiency.

The temperature-controlled furnace 14 is used to control the temperature of the crystal and stabilize the refractive index of the laser in the crystal, thereby improving the stability of the optical resonant cavity of the system.

The purpose of the a-lens 15 is to collimate the light exiting the waveguide.

The filter 16 is a combination of near-infrared bandpass filters, and the transmission range is 800nm-1100nm. The filter is used for idle frequency photon filtering, filtering out multicolor pump light, pump light up-conversion fluorescence, ambient stray light, etc.

The purpose of the b-lens 17 is to collect the up-converted light and focus it into the grating.

The purpose of the near-infrared grating 18 is to spatially separate the up-converted spectrum, wherein the number of lines is 1200 lines/mm, and the wavelength range is 400-1600 nm.

The purpose of the metal mirror 19 is to change the propagation direction of the light path, and the average reflectance in the range of 800nm-1100nm is greater than 99%.

The purpose of the c-lens 20 is to collect the light spatially separated by the dispersive system to focus the upconverted spectrum onto the detection array.

The purpose of the CMOS array 21 is to realize ultra-sensitive detection of the near-infrared spectrum generated by up-conversion. The detection wavelength range covers 600-1700 nm, the resolution reaches 0.02 nm, and the fast measurement takes 0.2 s.

The purpose of the computer 22 is to process the up-converted spectrum acquired by the near-infrared spectrometer and convert it into mid-infrared spectral information.

Referring to Figure 5, the specific implementation process of a multi-wavelength pumped mid-infrared up-conversion spectrum detection is as follows:

1) Design multi-period cascaded waveguides as the medium for nonlinear frequency conversion. Specifically, multi-period cascaded waveguides 13 with inversion periods including 34.8 μm, 28.1 μm, 25.8 μm, and 24.1 μm are designed and placed on a temperature-controlled furnace 14 .

2) The broadband mid-infrared signal 1 is collected into the multi-period cascaded waveguide 13 through the germanium window 2, the off-axis parabolic mirror 3, the sample to be tested 4, the calcium fluoride lens 5, and the dichroic mirror 12. The conversion process converts to the near-infrared band. Specifically, the broadband blackbody radiation emitted by a thermal light source, as a mid-infrared continuous light source, passes through the germanium window 2 to filter out visible light, is collected by the off-axis parabolic mirror 3, and after being absorbed by the sample 4 to be tested, carries the Infrared Absorption Spectral Information. Subsequently, the mid-infrared signal is focused by the calcium fluoride lens 5 , passes through the dichroic mirror 12 and combines with the high-power polychromatic pump light source in space, and enters the optical channel of the multi-period cascaded waveguide 13 .

3) The high-power continuous pump light emitted by the single-frequency continuous pump lasers 6, 7, 8 and 9 of a, b, c and d enters through the wavelength division multiplexer 10, the achromatic focusing lens 11 and the dichroic mirror 12 In the multi-period cascaded waveguide 13, it participates in the broadband mid-infrared frequency up-conversion process. Specifically, the multi-wavelength pump light is combined by the wavelength division multiplexer 10, and after coaxial output, it is focused by the achromatic lens 11, combined with the broadband mid-infrared space by the dichroic mirror 12, and enters the multi-period cascaded waveguide 13 In the waveguide structure, a stable high-power mixed pump light field is formed.

4) The mid-infrared signal light is converted to the near-infrared band through a broadband frequency up-conversion method, and is detected by a near-infrared detection array with superior performance, realizing mid-infrared high-performance detection with fine spectral resolution capabilities in the range of thousands of nanometers. Specifically, the frequency up-converted signal spectrum transmitted in the multi-period cascaded waveguide 13 is collimated by the a-lens 15, and the filter 16 filters out multicolor pump light, pump light up-converted fluorescence, and ambient stray light. Then, the b-lens 17 performs spatial focusing, and is spatially separated by the near-infrared grating 18 , refracted by the optical path of the metal mirror 19 , and collected and focused by the c-lens 20 . Finally, it is detected by the near-infrared CMOS array 21, and converted into the spectral absorption curve of the sample in the mid-infrared band through image processing by the computer 22, finally realizing broadband mid-infrared ultra-sensitive up-conversion spectral resolution, its resolution, Compared with traditional mid-infrared spectrometers, the sensitivity and spectrum forming speed will be improved by orders of magnitude.

The content not described in detail in the foregoing embodiments belongs to the prior art known to those skilled in the art. The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be described in the foregoing embodiments. Modifications are made to the recorded technical solutions, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (4)

1. The method is characterized in that a multi-wavelength single-frequency narrow-band laser is adopted as pumping light, a multi-period nonlinear frequency up-conversion medium is used for realizing broadband mid-infrared coverage and high-efficiency mid-infrared frequency up-conversion, and a high-performance near-infrared dispersion and detection element is utilized for realizing mid-infrared spectrum detection with broadband, high resolution and ultrasensitivity, and the method specifically comprises the following steps:

step 1: irradiating a sample to be detected by a broadband mid-infrared light source to obtain broadband mid-infrared light of sample absorption spectrum information;

step 2: forming a multicolor pumping field by using the multi-wavelength pumping light beam, and spatially combining the multi-wavelength pumping light beam and the middle infrared signal light beam by using a dichroic mirror;

step 3: performing broadband frequency up-conversion under the action of a multi-wavelength pumping field through a multi-period nonlinear medium, and converting infrared signals into visible/near infrared bands;

step 4: and (3) utilizing a visible/near infrared dispersion element to split light, and utilizing a visible/near infrared detection array to obtain a spectrum, dividing the spectrum intensity of the sample and the spectrum intensity of the sample without the sample, and splicing the up-conversion spectrum to obtain an absorption spectrum line of the sample to be detected for the middle infrared.

2. The method for detecting mid-infrared up-conversion spectrum of multi-wavelength pump according to claim 1, wherein the wavelengths of the polychromatic pump fields are selected to ensure that up-conversion spectra under each pump condition do not overlap.

3. The method for detecting the mid-infrared up-conversion spectrum of the multi-wavelength pump according to claim 1, wherein the multi-wavelength pump light adopts single-frequency narrow-band laser, so that the wavelength after nonlinear conversion corresponds to the wavelength of the mid-infrared signal one by one, and the spectrum information of the mid-infrared signal is kept.

4. The method for detecting mid-infrared up-conversion spectrum of multi-wavelength pump according to claim 1, wherein the multi-period nonlinear medium refers to quasi-phase period extremum corresponding to nonlinear conversion under different pump wavelength conditions, and a crystal or waveguide structure with discrete period change is designed to obtain a broadband phase matching window to cover the mid-infrared spectrum range to be detected.

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