A multi-wavelength pumped mid-infrared upconversion spectral probing method

Abstract

The application discloses a kind of multi-wavelength pumped mid-infrared upconversion spectral detection methods, its characteristics are that the method uses multi-wavelength narrowband laser as the pump source of nonlinear conversion, simultaneously adopt multi-period quasi-phase matching crystal as nonlinear upconversion medium, realize mid-infrared signal broadband and efficient conversion, and combine high-performance near-infrared spectral measurement and control element, finally obtain wide band, high resolution, ultra-sensitive mid-infrared spectral detection.The application has the characteristics of large bandwidth and high efficiency compared with existing upconversion spectral technology, simultaneously can high fidelity resolution mid-infrared spectral information, for realizing wide band, high resolution, ultra-sensitive mid-infrared spectral measurement provides effective means, is expected to be applied to molecular spectroscopy, trace substance detection, infrared remote sensing and atmospheric monitoring and other important fields.

Description

Technical Field

[0001] This invention relates to the field of mid-infrared spectroscopy, and more particularly to a multi-wavelength pumped mid-infrared upconversion spectroscopy detection method. Background Technology

[0002] The mid-infrared band corresponds to the vibrational-rotational 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 known as the molecular "fingerprint" spectral region and is widely used for qualitative and quantitative detection of substances. The development of mid-infrared spectroscopy technology has significant application prospects in life sciences, environmental monitoring, materials engineering, medical diagnostics, and infrared remote sensing. In particular, wide-band mid-infrared spectroscopy is beneficial for acquiring the spectral characteristics of multiple components in a single operation, high-resolution mid-infrared spectroscopy provides a powerful means for obtaining fine characterization of spectral lines, and ultra-sensitive mid-infrared spectroscopy can achieve a high signal-to-noise ratio under low irradiance conditions. Currently, mid-infrared spectroscopy technology is constantly evolving and progressing, and there is an urgent need to develop new mid-infrared spectral detection technologies that combine wide bandwidth, high resolution, and ultra-sensitivity to meet the pressing needs of scientific and industrial fields for multi-component substance detection, high-precision spectral line analysis, and trace substance detection.

[0003] Currently, mid-infrared spectrometers are generally based on grating dispersion detection or Fourier transform infrared (FTIR) detection. Grating spectrometers use gratings to separate the mid-infrared spectral space, which is then detected by a linear array detector. However, due to the limited pixels and low frame rate of the mid-infrared detector array, grating spectrometers typically have low resolution and slow spectrogramming speed. While Fourier transform infrared spectrometers can use single-point detectors to achieve higher spectral resolution and a wider spectral range, their reliance on mechanical scanning greatly limits the spectrogramming speed, making them unsuitable for rapid acquisition. Furthermore, the detection elements of mid-infrared spectrometers are generally based on narrow-bandgap semiconductor materials (such as HgCdTe and InSb), which are limited by intrinsic noise. Therefore, they typically require multi-stage cooling systems with extremely low temperatures to suppress dark current and thermal noise, thereby improving the sensitivity of the detection system. Even so, their sensitivity is still far inferior to detectors operating in the near-infrared band. Therefore, mid-infrared spectroscopy technology, limited by the dispersion method and infrared detection devices, urgently needs breakthroughs in spectrogramming speed, spectral resolution, and detection sensitivity.

[0004] Given the current challenges in mid-infrared spectroscopy, mid-infrared frequency upconversion detection technology has developed rapidly in recent years. This technology converts weak mid-infrared signals to the visible / near-infrared band with high fidelity through a nonlinear sum-frequency process. This not only allows for higher spectral resolution using mature dispersive spectrometers but also enables ultra-sensitive and rapid spectral generation in the mid-infrared band using visible / near-infrared detector arrays with more pixels, lower noise, and faster response. However, existing upconversion spectroscopy techniques are limited by quasi-phase-matching bandwidth, resulting in a spectral window for efficient conversion that is typically only tens of nanometers, far from meeting the needs of broadband detection scenarios such as infrared remote sensing, environmental monitoring, and astronomical observation. Overcoming the limitation of matching bandwidth often involves widening the matching bandwidth by tuning the temperature of the nonlinear crystal, changing the grating period of the nonlinear medium, and tuning the incident angle of the signal light. However, these methods all rely on mechanical tuning, which is slow and severely limits the speed of spectral acquisition. In addition, another common method is to use a chirped nonlinear medium with continuously varying periods to increase the bandwidth. Although this method avoids tuning transformation, the limited nonlinear action distance limits the conversion efficiency, thus sacrificing detection sensitivity. Therefore, upconversion spectroscopy technology faces the mutual constraint of detection bandwidth and detection efficiency, and there is an urgent need to develop a mid-infrared upconversion spectroscopy detection technology that combines broadband conversion and high conversion efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-wavelength pumped mid-infrared upconversion spectral detection method to address the shortcomings of existing technologies. This method utilizes the quasi-phase-matching periodic extrema corresponding to different pump wavelengths to design a multi-periodic nonlinear medium. Under the pumping action of a multi-wavelength single-frequency narrow-linewidth laser, the overall bandwidth of the nonlinear phase matching is broadened. By employing multi-wavelength single-frequency pumping and a multi-periodic nonlinear medium, high-efficiency mid-infrared frequency upconversion detection is achieved. Finally, by utilizing mature near-infrared dispersive elements and single-photon detector arrays, high-sensitivity, high-speed, and high-resolution spectral analysis is achieved over a wide mid-infrared spectral range. This method overcomes the mutual constraint between wide-band spectral detection and high conversion efficiency in the mid-infrared band, enabling ultra-sensitive mid-infrared spectral detection with wide band, high efficiency, and high resolution. This provides strong support for applications such as infrared molecular spectroscopy, trace substance detection, infrared remote sensing, and atmospheric monitoring.

[0006] The specific technical solution to achieve the objective of this invention is: a multi-wavelength pumped mid-infrared upconversion spectral detection method, characterized by using a multi-wavelength single-frequency narrowband laser as the pump light, employing a multi-period nonlinear medium to achieve broadband mid-infrared coverage and efficient mid-infrared frequency upconversion, with no overlap in the converted spectral components, and using high-performance near-infrared dispersion and detection elements to achieve high-resolution and ultra-sensitive detection of the mid-infrared broadband spectrum. The method specifically includes the following steps:

[0007] 1) Using multi-wavelength single-frequency narrow-linewidth lasers as pump light breaks through the limitation of limited phase matching bandwidth under traditional single-wavelength pumping. Different pump wavelengths can achieve efficient conversion of multiple mid-infrared signal spectral bands at the same time. The converted spectral components do not overlap, and a wide-band mid-infrared spectral detection range can be obtained by simple upconversion spectral splicing.

[0008] 2) Using a multi-period nonlinear medium as the frequency upconversion medium, and referencing the quasi-phase periodic extrema corresponding to the nonlinear conversion under different pump wavelengths, a crystal or waveguide with discrete periodic variations is designed. A wideband phase matching window is obtained through the multi-period structure, while a longer nonlinear interaction length is obtained, thus achieving more efficient nonlinear frequency upconversion.

[0009] 3) The pump source uses a narrowband single-frequency laser. Because it has single longitudinal mode, low noise and narrow spectrum characteristics, it can ensure that the wavelength after nonlinear conversion corresponds one-to-one with the wavelength of the mid-infrared signal, thus maintaining the spectral information of the mid-infrared signal with high fidelity. Combined with high-resolution dispersive elements and multi-pixel detection elements in visible light and near-infrared, it provides a guarantee for realizing high-resolution mid-infrared spectral analysis.

[0010] The multi-period nonlinear medium includes structures such as crystals and waveguides. It utilizes 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 polarized lithium niobate (PPLN) crystals / waveguides, periodically polarized potassium titanium oxyphosphate (PPKTP) crystals / waveguides, and periodically polarized lithium tantalate (PPLT) crystals / waveguides. The multi-period should be selected with reference to the extreme values ​​of the quasi-phase period of upconversion at different pump wavelengths to ensure coverage of the required mid-infrared spectral range. The period 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 crystal and waveguide structure design of the nonlinear medium includes, but is not limited to: multi-period cascaded arrangement and multi-period staggered arrangement.

[0011] The multi-wavelength single-frequency narrow-linewidth laser used as pump light is a multi-wavelength beam combining pump source, which is composed of multiple single-frequency narrow-linewidth continuous lasers. During the beam combining process, it can maintain the mid-infrared spectral information in a wide band. The number of pump laser sources is not limited to four. The pump light wavelength is not limited to 1.55μm, 1.35μm, 1.20μm, and 1.10μm.

[0012] The high-resolution dispersive elements for visible light and near-infrared light include, but are not limited to, prisms, gratings, and virtual imaging arrays.

[0013] The multi-pixel detection element is not limited to, but includes, detector arrays such as CCD, EMCCD, CMOS, and sCMOS.

[0014] Compared with the prior art, the present invention has the following significant technical effects and advancements:

[0015] 1) Using multi-wavelength continuous lasers as pump light, the upconversion spectra corresponding to different pump wavelengths do not overlap. Through spectral band splicing, a wide-band mid-infrared spectral detection window can be obtained, overcoming the limitation of limited phase-matching bandwidth under traditional single-wavelength pumping. Simultaneously, the pump source employs narrow-band single-frequency lasers, which, due to their single longitudinal mode, low noise, and narrow spectral characteristics, ensure a one-to-one correspondence between the wavelength after nonlinear conversion and the mid-infrared signal wavelength. This guarantees high-fidelity preservation of the spectral information of the mid-infrared signal, ensuring high-resolution mid-infrared spectral analysis.

[0016] 2) Using multi-period nonlinear media as the frequency upconversion medium, mid-infrared incident crystals can obtain a wide-bandgap phase-matching window without tuning temperature, period, or angle, thus avoiding the limitation of spectral formation speed imposed by mechanical tuning. Furthermore, compared to chirped nonlinear media, it can achieve a longer nonlinear interaction distance, thereby improving the efficiency of wide-bandgap nonlinear frequency upconversion.

[0017] 3) By performing frequency up-conversion in a nonlinear medium, the mid-infrared signal is converted to the near-infrared. By using high-performance, cost-effective near-infrared dispersive elements and ultra-sensitive detection arrays, the performance bottleneck of existing mid-infrared devices is overcome, achieving higher spectral resolution, faster spectral speed, and higher detection sensitivity. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of phase matching for the nonlinear sum and frequency of three waves under collinearity.

[0019] Figure 2 The diagram shows the collinear quasi-phase period Λ relationship for each band in the mid-infrared region under different wavelength pumping conditions.

[0020] Figure 3 for Figure 2 Relationship between mid-infrared wavelength and upconversion efficiency under extreme period conditions;

[0021] Figure 4 for Figure 3 The relationship between the range and intensity of the near-infrared spectral bands corresponding to the mid-infrared spectral bands after frequency upconversion;

[0022] Figure 5 This is a schematic diagram of the spectral detection device in Example 1. Detailed Implementation

[0023] This invention employs a multi-wavelength, single-frequency, narrow-linewidth laser to pump a multi-period nonlinear medium, wherein the optical field involved satisfies the laws of conservation of energy and momentum, and the frequency is ω. pThe pump photon and a frequency of ω s The low-energy mid-infrared signal photon annihilation produces a frequency of ω u The upconverted photon. During the frequency conversion process, when the phase matching condition is met, Δk = k u -k s -k p The conversion efficiency is highest when the phase ratio is zero. Existing technologies have strict requirements for angle and temperature phase matching, and the mid-infrared matching bandwidth that can achieve efficient frequency conversion is often only tens of nanometers. To overcome these technical difficulties and broaden the mid-infrared frequency conversion spectral range, this invention employs a highly flexible quasi-phase matching technique. By designing the periodic distribution of the polarized crystal, a suitable inversion period Λ is selected to compensate for the mismatch of Δk, ensuring that the phase matching conditions are met for mid-infrared spectra of different wavelengths, thereby achieving frequency conversion.

[0024] See Figure 1 The pump light, mid-infrared signal light, and upconversion light propagate collinearly along the periodic distribution direction of the nonlinear medium. The phase mismatch during the sum-frequency interaction is expressed by the following equation (a):

[0025]

[0026] in, The grating wave vector introduced for the periodic structure of a nonlinear dielectric. In the fabrication process of nonlinear dielectrics, Λ i It can be flexibly adjusted, so by designing the period for a specific nonlinear process, it is easy to satisfy Λk=0, achieve quasi-phase matching, and ensure that the direction of energy flow is always from the fundamental wave to the sum frequency wave.

[0027] See Figure 2 Using a second-order nonlinear MgO-PPLN crystal and pump wavelengths of [missing information], and Taking the condition as an example, the mid-infrared wavelength and its collinear quasi-phase period Λ exist. Figure 2 As shown in the diagram, each curve has a periodic extreme point, and the location of this extreme point varies with the selection of the pump light wavelength.

[0028] See Figure 3 If the domain period Λ near the extreme point corresponding to a single pump wavelength is selected to design the nonlinear crystal, the mid-infrared signal matching bandwidth under each pump wavelength condition can reach approximately 100 nanometers. Therefore, by designing the crystal period Λ, the pump wavelength, and selecting appropriate crystal materials, the frequency up-conversion process can be matched to a specific mid-infrared wavelength range.

[0029] See Figure 4Under various pump conditions, the mid-infrared spectral bands matched by the pumps, after nonlinear frequency upconversion, exhibit no spectral overlap in the near-infrared region. Therefore, the mid-infrared spectral information can be uniquely deduced from the corresponding pump conditions, and a broadband mid-infrared spectrum can be obtained through simple spectral calculations and splicing. Specifically, the intensity distribution I of the upconversion spectrum obtained in one step needs to be... u (λ u The upconversion spectral intensity distribution corresponding to different pump wavelengths is segmented according to various pump conditions. From segmented upconversion spectra The conversion relationship between frequency and intensity is obtained by formula (b) below, which gives the mid-infrared spectral intensity distribution of each segment.

[0030]

[0031] Next, the mid-infrared spectral intensity distribution of each segment was obtained. Then, the spectral intensity distribution I across the entire mid-infrared detection range is obtained using the following equation (c). s (λ s ):

[0032]

[0033] Using the above method, the spectral intensity distribution curve σ(λ) during sample placement was measured. s )I s (λ s ) and the spectral intensity distribution curves without a sample I s (λ s Dividing the two yields the broadband mid-infrared absorption spectrum σ(λ) of the sample. s ).

[0034] See Figure 2Under multi-wavelength pumping conditions, a multi-period nonlinear crystal is used to simultaneously achieve efficient conversion of multiple mid-infrared signal bands, effectively broadening the bandwidth of efficient mid-infrared conversion. Since the upconversion spectra of each period do not overlap, a wide-band mid-infrared spectral information can be obtained by selecting the appropriate pump light for wavelength conversion. Compared to single-wavelength pumping and single-period crystal schemes, this method achieves a wider phase-matching bandwidth. Regarding the method of obtaining broadband, compared to traditional methods of adjusting temperature, period, and angle, it eliminates the complex tuning process. Compared to using chirped crystals with continuously varying periods to achieve broadband conversion, it utilizes a longer nonlinear interaction length, thus achieving more efficient nonlinear conversion. This invention employs a combination of multiple narrowband single-frequency lasers, which, when interacting with broadband infrared spectral signals, can obtain spectral modes in the near-infrared band that correspond one-to-one with the mid-infrared band, thereby achieving high-fidelity infrared spectral information transfer and ensuring high-precision mid-infrared spectral analysis.

[0035] This invention utilizes mature near-infrared dispersive elements and an ultra-sensitive single-photon detector array, offering more mature technology and superior performance. Near-infrared dispersive elements, such as gratings, have denser scribe lines and higher grating efficiency compared to mid-infrared dispersive elements. Furthermore, near-infrared detector arrays offer advantages over mid-infrared detectors, including more pixels, lower noise, and faster response speed. Therefore, by up-converting mid-infrared signals to the near-infrared band through a frequency up-conversion process, spectral analysis with higher spectral resolution, greater sensitivity, and faster dispersive speed can be achieved.

[0036] The present invention will be further described in detail below through a specific implementation of a multi-wavelength pumped mid-infrared upconversion spectroscopy detection.

[0037] Example

[0038] See Figure 5 The spectral detection device for 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 tested 4, a calcium fluoride lens 5, an a single-frequency continuous-pump laser 6, a b single-frequency continuous-pump laser 7, a c single-frequency continuous-pump laser 8, a d single-frequency continuous-pump laser 9, a wavelength division multiplexer 10, an achromatic focusing lens 11, a dichroic mirror 12, a multi-period cascaded waveguide 13, a temperature-controlled furnace 14, an a lens 16, a filter 16, a b lens 17, a near-infrared grating 18, a metal mirror 19, a c lens 20, a CMOS detector array 21, and a computer 22.

[0039] The broadband mid-infrared light source 1 can be an active light source generated by a continuous spectrum such as a waveguide or soft glass optical fiber, or a passive light source such as a thermal light source, and its wavelength range can cover 3 to 5 μm.

[0040] The germanium window 2 is used to block any incident visible light, and the window is coated with a broadband antireflection film with an average reflectivity of less than 3% within a 3-5 μm range.

[0041] The purpose of the off-axis parabolic mirror 3 is to collect infrared signals, with an average reflectivity greater than 96% in a broadband range of 800nm-20μm.

[0042] The purpose of the test sample 4 is to measure the absorption / transmission spectrum of the sample. The test sample absorbs light of different wavelengths to different degrees. The experimental system can obtain the absorbance of the test sample at each wavelength by measuring the spectrum with and without the sample. The test sample includes, but is not limited to, solids, gases, and liquids.

[0043] The purpose of the calcium fluoride lens 5 is to focus the mid-infrared rays carrying spectral information into the multi-period cascaded waveguide 13.

[0044] The single-frequency continuous-pump lasers 6, 7, 8, and 9 (a, b, c, d) are external cavity diode lasers with tunable center wavelengths, and their center wavelengths are respectively... and With a spectral width of 3kHz, a polarization contrast greater than 20dB, and an output power reaching 10W, these four lasers can be combined and used as a pump source for frequency upconversion, enabling upconversion in the mid-infrared range of thousands of nanometers.

[0045] The purpose of the wavelength division multiplexer 10 is to combine pump light of different wavelengths together and output them coaxially.

[0046] The purpose of the achromatic focusing lens 11 is to transform the pump light and focus it into the multi-period cascaded waveguide 13.

[0047] The purpose of the dichroic mirror 12 is to combine the pump light with the mid-infrared light. The dichroic mirror has high transmittance for mid-infrared light and high reflectance for multicolor pump light.

[0048] The multi-period cascaded waveguide 13 employs a multi-period cascaded lithium niobate waveguide as the frequency up-conversion nonlinear medium. Its cascaded arrangement with polarization periods of 34.8 μm, 28.1 μm, 25.8 μm, and 24.1 μm can convert broadband mid-infrared light to the near-infrared band. The waveguide's optical channel provides a long-distance, strongly confined field, and its narrow structure increases the average power of the multicolor pump light field, thereby improving the broadband frequency up-conversion efficiency.

[0049] The temperature-controlled furnace 14 is used to control the crystal temperature and stabilize the refractive index of the laser within the crystal, thereby improving the stability of the optical resonant cavity of the system.

[0050] The purpose of the lens 15 is to collimate the light emitted from the waveguide.

[0051] The filter 16 is a near-infrared bandpass filter assembly with a transmission wavelength range of 800nm-1100nm. This filter is used for idler photon filtering to remove multicolor pump light, pump light upconversion fluorescence, ambient stray light, etc.

[0052] The purpose of the b lens 17 is to collect the upconverted light and focus it onto the incident grating.

[0053] The purpose of the near-infrared grating 18 is to spatially separate the upconversion spectrum, wherein the grating has 1200 lines / mm and the wavelength range is 400–1600 nm.

[0054] The purpose of the metal mirror 19 is to change the direction of light propagation, with an average reflectivity greater than 99% in the 800nm-1100nm range.

[0055] The purpose of the c-lens 20 is to collect the light that has been spatially separated by the dispersion system, so that the upconverted spectrum is focused onto the detector array.

[0056] The purpose of the CMOS array 21 is to achieve ultrasensitive detection of the near-infrared spectrum generated by upconversion, with a detection wavelength range of 600–1700 nm, a resolution of 0.02 nm, and a rapid measurement speed of 0.2 s.

[0057] The purpose of the computer 22 is to process the upconversion spectrum acquired by the near-infrared spectrometer and convert it into mid-infrared spectral information.

[0058] See Figure 5 The specific implementation process of a multi-wavelength pumped mid-infrared upconversion spectral detection is as follows:

[0059] 1) Design a multi-period cascaded waveguide as the medium for nonlinear frequency conversion. Specifically, design a multi-period cascaded waveguide 13 with inversion periods of 34.8μm, 28.1μm, 25.8μm, and 24.1μm, and place it on a temperature-controlled furnace 14.

[0060] 2) The broadband mid-infrared signal 1 is collected by the germanium window 2, off-axis parabolic mirror 3, sample 4, calcium fluoride lens 5, and dichroic mirror 12 into the multi-period cascaded waveguide 13, and converted to the near-infrared band through a broadband frequency up-conversion process. Specifically, broadband blackbody radiation emitted by a thermal source, as a continuous mid-infrared light source, is filtered out by the germanium window 2 and collected by the off-axis parabolic mirror 3. After being absorbed by the sample 4, it carries the infrared absorption spectrum information of the sample. Subsequently, the mid-infrared signal is focused by the calcium fluoride lens 5, and spatially combined with the high-power multicolor pump source through the dichroic mirror 12 into the optical channel of the multi-period cascaded waveguide 13.

[0061] 3) The high-power continuous pump light emitted from single-frequency continuous-pump lasers 6, 7, 8, and 9 (a, b, c, and d) enters the multi-period cascaded waveguide 13 via wavelength division multiplexing (WDM) 10, achromatic focusing lens 11, and dichroic mirror 12, participating in the broadband mid-infrared frequency upconversion process. Specifically, the multi-wavelength pump light is combined by WDM 10, output coaxially, focused by achromatic lens 11, and then combined with the broadband mid-infrared spatial beam by dichroic mirror 12 before entering the multi-period cascaded waveguide 13, forming a stable high-power hybrid pump light field within the waveguide's guide structure.

[0062] 4) The mid-infrared signal light is converted to the near-infrared band via a broadband frequency up-conversion method and detected by a high-performance near-infrared detector array, achieving high-performance mid-infrared detection with fine spectral resolution within a range of thousands of nanometers. Specifically, the signal spectrum transmitted through the multi-period cascaded waveguide 13 is collimated by lens a 15, and filtered by filter 16 to remove multicolor pump light, pump light up-conversion fluorescence, and ambient stray light. Next, it is spatially focused by lens b 17, spatially separated by a near-infrared grating 18, refracted by a metal mirror 19, and collected and focused by lens c 20. Finally, it is detected by a near-infrared CMOS array 21, and after image processing by computer 22, it is converted into the sample's spectral absorption curve in the mid-infrared band, ultimately achieving broadband mid-infrared ultrasensitive up-conversion spectral resolution. Its resolution, sensitivity, and spectral generation speed are orders of magnitude higher than those of traditional mid-infrared spectrometers.

[0063] The contents not described in detail in the above embodiments belong 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, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-wavelength pumped mid-infrared upconversion spectroscopy detection method, characterized in that, This method employs a multi-wavelength single-frequency narrowband laser as the pump light and uses a multi-period nonlinear frequency up-conversion medium to achieve broadband mid-infrared coverage and efficient mid-infrared frequency up-conversion. It utilizes high-performance near-infrared dispersion and detection elements to achieve wide-band, high-resolution, and ultra-sensitive mid-infrared spectral detection. Specifically, it includes the following steps: Step 1: Illuminate the sample to be tested with a broadband mid-infrared light source to obtain the broadband mid-infrared light absorption spectrum information of the sample; Step 2: Use multi-wavelength pump light beam combiner to form a multi-color pump field, and use a dichroic mirror to spatially combine the multi-wavelength pump light with the mid-infrared signal light. Step 3: Broadband frequency up-conversion is performed using a multi-period nonlinear medium under the action of a multi-wavelength pump field to convert the infrared signal to the visible / near-infrared band; Step 4: Use a visible / near-infrared dispersive element to spectrate and a visible / near-infrared detector array to obtain the spectrum. Divide the spectral intensity of the sample with the sample without the sample with ...

2. The method for mid-infrared upconversion spectroscopy detection using multi-wavelength pumping according to claim 1, characterized in that, The wavelength selection of the multicolor pump field should ensure that the upconversion spectra do not overlap under each pumping condition.

3. The method for mid-infrared upconversion spectroscopy detection using multi-wavelength pumping according to claim 1, characterized in that, The multi-wavelength pump light uses a single-frequency narrowband laser, so that the wavelength after nonlinear conversion corresponds one-to-one with the wavelength of the mid-infrared signal, thus preserving the spectral information of the mid-infrared signal.

4. The method for mid-infrared upconversion spectroscopy detection using multi-wavelength pumping according to claim 1, characterized in that, The multi-periodic nonlinear medium references the quasi-phase periodic extrema corresponding to the nonlinear conversion under different pump wavelengths, and designs a periodically discrete crystal or waveguide structure to obtain a broadband phase-matching window that covers the required mid-infrared spectral range.

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