Transient broadband two-dimensional infrared spectrum system and detection method thereof

Abstract

The invention discloses a transient broadband two-dimensional infrared spectrum system and a detection method thereof, and belongs to the technical field of spectrum detection. According to the system, on the basis of a conventional two-dimensional infrared spectrum system, variable-frequency visible-near infrared pulses and broadband intermediate infrared pulses are generated through laser pulses not utilized by an optical parameter amplifier, the functions of optical pulse triggering of photochemical reaction and broadband two-dimensional infrared spectrum detection are achieved, and an observation window is expanded to 2ns. Meanwhile, for a sample capable of generating fluorescence, the fluorescence is collected and detected by using a parabolic mirror and a photodiode by changing the sequence of the action of visible-near infrared pulse and intermediate infrared pulse with the sample, and the system has the detection function of a fluorescence coded infrared spectrum at the same time, so that the detection sensitivity of the two-dimensional infrared spectrum is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral detection, and relates to a transient broadband two-dimensional infrared spectroscopy system excited by a femtosecond pulse and a detection method thereof, and specifically refers to a femtosecond time-resolved infrared spectroscopy system based on the combination of visible-near infrared and mid-infrared pulses. Background Art

[0002] Photochemical reaction is an important type of physical and chemical process. It refers to a series of complex induced reactions that occur when molecules absorb photons and then transition to electronic excited states, such as photooxidation, photosubstitution, and photocross-linking. These reactions usually involve complex kinetic processes, including molecular isomerization, intermolecular interactions, and solvation regulation. A deep understanding of the complex behavior and regulation mechanisms between molecules is the key to improving the efficiency of photochemical reactions. As an important means to study this process, two-dimensional infrared spectroscopy can directly reflect the dynamic processes of complex chemical systems, such as conformational changes, bond valence changes, and solvation, through information such as changes in characteristic infrared vibration frequencies and vibration coupling and relaxation processes. Conventional two-dimensional infrared spectroscopy systems use narrow-band mid-infrared pulses (~200cm -1 ), which is split by a wedge, beam splitter or optical pulse shaper, and a two-dimensional spectrum is generated through the third-order nonlinear effect. Its time observation window is limited by the vibrational state lifetime, which is usually in the order of picoseconds. However, photochemical reactions are electronic excited state processes that require high-frequency light pulses to induce (in the ultraviolet to near-infrared range). The characteristic infrared vibration frequencies involved are often distributed in different frequency domains and require broadband infrared pulses to detect. The simultaneous generation of visible-near-infrared light pulses, broadband infrared pulses, and narrowband infrared pulses to pump the two-dimensional spectrum requires extremely high laser power, which is difficult to achieve under normal laboratory conditions. Summary of the invention

[0003] The purpose of the present invention is to provide a transient broadband two-dimensional infrared spectroscopy system and a detection method thereof. The system generates variable-frequency visible-near infrared pulses (450-1000nm) and broadband mid-infrared pulses (1000-4000cm) through unused laser pulses of an optical parametric amplifier on the basis of a conventional two-dimensional infrared spectroscopy system. -1 ), realizing the functions of light pulse triggering of photochemical reactions and broadband two-dimensional infrared spectrum detection, and the observation window is extended to 2ns. At the same time, for samples that can produce fluorescence, by changing the order of visible-near infrared pulses and mid-infrared pulses acting on the samples, and using parabolic mirrors and photodiodes to collect and detect fluorescence, the system also has the detection function of fluorescence-coded infrared spectroscopy, which greatly improves the detection sensitivity of two-dimensional infrared spectroscopy.

[0004] The technical solution adopted by the present invention is:

[0005] A transient broadband two-dimensional infrared spectroscopy system, the system comprises an 800nm ​​femtosecond laser (50fs, 1kHz), an optical parametric amplifier TOPAS, a difference frequency generator DFG, a monochromator and a mercury cadmium telluride MCT double-row array detector, an integrator and a data acquisition card, a computer, a chopper controller, a non-collinear optical parametric amplifier NOPA, a broadband infrared generation chamber, a time-resolved pulse generation chamber and a sample chamber;

[0006] The near-infrared pulses generated by the femtosecond laser and TOPAS generate narrow-band mid-infrared pulses of the required wavelength after passing through DFG and enter the time-resolved pulse generation chamber, which is used as pump light pulses for detecting the two-dimensional infrared spectrum; the 800nm ​​pulses that are not converted by TOPAS are frequency-doubled by BBO crystals to generate 400nm pulses, which are then divided into two beams of 90% and 10% according to the energy by the beam splitter BS, and enter the broadband infrared generation chamber and NOPA respectively.

[0007] Broadband infrared generation chamber: After the two pulses with wavelengths of 400nm and 800nm ​​enter, they are first adjusted by the delay compensation plate DP to completely overlap on the time scale, and then adjusted by the half-wave plate WP to make the polarization angles completely consistent, and a 267nm pulse is generated through the BBO crystal; the three pulses are focused onto the argon gas flow column Ar through the concave reflector M to generate broadband infrared pulses, and after being collimated by two concave reflectors M, the 267nm, 400nm and 800nm ​​pulses are filtered out by the high-transmittance germanium plate Ge, and then the direction is adjusted by the reflector M to enter the time-resolved pulse generation chamber;

[0008] Non-collinear optical parametric amplifier NOPA: After the collinear 400nm and 800nm ​​pulses enter, they are first divided into two beams of 400nm and 800nm ​​by the dichroic mirror DM; the 800nm ​​pulse passes through the delay line DS3, and is focused by the lens L on the sapphire window SW to generate supercontinuum white light, and then focused on the BBO crystal through the lens L; the 400nm pulse is adjusted by the reflector M and focused on the BBO crystal, overlapping with the focus of the supercontinuum white light in the crystal space; the time overlap of the supercontinuum white light and the 400nm pulse on the BBO crystal is achieved by adjusting the delay line DS3; optical parametric amplification of different wavelengths is achieved by adjusting the angle of the BBO crystal, and the generated signal light passes through the delay line DS4, passes through the polarizer P, the chopper, and enters the sample chamber after adjusting the angle of the reflector M;

[0009] In the sample chamber, the signal light pulse from NOPA is angle-adjusted by the reflector M so that it overlaps spatially with the infrared pulse from the time-resolved pulse generation chamber on the sample pool S.

[0010] The time-resolved pulse generation chamber is used to generate the pump light (pump) and the local oscillator light LO required for two-dimensional infrared spectroscopy detection. The optical path difference between the pump light and the local oscillator light LO and the broadband infrared pulse BBIR probe light k is adjusted by the time delay line DS2 to achieve time resolution. The mid-narrowband infrared pulse MIR from the DFG entering the time-resolved pulse generation chamber is divided into three beams by the wedge mirror W and the beam splitter BS (beam splitting ratio 50:50), namely k 3 (probe), k 1 、k 2 and k LO , and the pulse energy ratio is 47:47:6. The optical pulses k 1 、k 2 pass through the time delay line DS1, and interference optical pulses are generated on the second beam splitter BS (beam splitting ratio 50:50). Half of them serve as the pump light and enter the sample chamber via the half-wave plate WP and the polarizer P, and the other half is used for phase correction and detected by the single-channel MCT detector SC. The time difference between k 1 、k 2 pulses generates one-dimensional spectral information of the two-dimensional infrared spectrum via Fourier transform. The optical pulse k LO enters the sample chamber via the mirror M and serves as the local oscillator light. The broadband infrared optical pulse k 3 enters the sample chamber via the dispersion compensation plate C and the polarizer P and serves as the probe light.

[0011] The parabolic mirror PM in the sample chamber focuses the parallel incident pump light k 1 &k 2 , the probe light k 3 and the local oscillator light k LO into the sample cell S, and then the other parabolic mirror PM collects the probe light and the local oscillator light, and converges them to the upper and lower row arrays of the monochromator and the MCT double-row array detector via the mirror M, the lens L and the polarizer P respectively. The visible-near infrared pulse from the non-collinear optical parametric amplifier used to trigger the electronic excited state process enters the sample chamber and is focused by the lens L, and irradiates the sample cell through the mirror M, overlapping completely with the spot spaces of k 1 、k 2 and k 3 three beams of pulses, and the generated fluorescence is focused onto the photodiode PD by the concave mirror M.

[0012] Furthermore, the broadband infrared generation chamber, the time-resolved pulse generation chamber and the sample chamber are covered by a box body made of 5-mm-thick acrylic board. The box body is connected to the dry air generator via the air valve and the tetrafluoroethylene tube to control the humidity inside the box body below 5%.

[0013] Furthermore, the sample pool is a "sandwich" structure, that is, the liquid sample is sandwiched between two calcium fluoride windows coated with FEP film, and the sample thickness is adjusted by a polytetrafluoroethylene gasket (usually 50 microns). The "sandwich" structure is fixed in a copper module and the temperature is controlled by a water bath circulation pump.

[0014] Furthermore, the integrator is triggered by the electronic pulse signal input by the chopper to integrate the signal input by the MCT detector (the integration time is usually set to 2000ns), and the data acquisition card collects the external channel signals fed back by the chopper controllers CH1 and CH2, which respectively reflect the visible-near infrared pulse and k 2 The state of whether the pulse is blocked or not divides the data into four columns: “on-on”, “on-off”, “off-on” and “off-off”. The single-channel MCT detector and photodiode PD in the same period are also recorded by the external channel of the integrator, which are used for phase correction of two-dimensional spectrum and analysis of fluorescence coded infrared spectrum respectively.

[0015] A detection method based on a transient broadband two-dimensional infrared spectroscopy system comprises the following steps:

[0016] 1) The time difference τ between the visible-near infrared pulse and the mid-infrared pulse is set by the time delay line DS4: when the visible-near infrared pulse reaches the sample pool position before the mid-infrared pulse, that is, τ>0; otherwise, that is, τ<0, it is the fluorescence coded two-dimensional infrared spectrum acquisition mode.

[0017] 2) In transient broadband 2D spectroscopy acquisition mode, k 3 and k LO The intensity changes of the MCT double-row array detectors are recorded by the upper and lower rows, respectively, corresponding to the chopper controller CH1 (responsible for the switch of visible-near infrared pulses) and the chopper controller CH2 (responsible for k 2 The state of the pulse switch is divided into four groups: 1-"on-on", 2-"on-off", 3-"off-on" and 4-"off-off". Among them, the difference between 1 and 2 is stored as the excited state signal, that is, the signal when the visible-near infrared pulse is not blocked; the difference between 3 and 4 is stored as the ground state signal, that is, the signal when the visible-near infrared pulse is blocked by the chopper;

[0018] 3) Set k through time delay line DS2 3 and k 2 The relative time delay t 2 , set the pump light k through the time delay line DS1 1 and k 2 Relative time delay t 1The range of ts and te, and the moving step length dt; when DS1 moves from the ts position to the te position, each time it moves the distance dt, the excited state signal and the ground state signal are recorded according to the method 1-2, 3-4 in step 2). The data is recorded in the upper array data (signal light) of the MCT double-row array detector minus the lower array data (background light).

[0019] 4) According to the above acquisition method, a p*(2q+3) matrix is ​​obtained. Among them, p is the total number of positions moved by DS1, q is the total number of channels of the MCT single-row array, and the excited state signal and the ground state signal occupy a p*q matrix respectively. The first column of the matrix is ​​the time delay t set by DS1 1 , and the last two columns are the light intensity information recorded by the MCT single channel (SC) and the photodiode (PD), respectively.

[0020] 5) The matrix recorded in step 4) can be used to obtain two two-dimensional spectral data by conventional methods. The difference between the two is the transient two-dimensional infrared spectrum at the corresponding time τ. The corresponding two frequencies are ω directly recorded by the MCT array. 3 and time delay t 1 ω converted by Fourier transform 1 .

[0021] 6) In the fluorescence coded two-dimensional spectral acquisition mode, the MCT double-row array detector is used to record the pump light k 1 and k 2 interference signal.

[0022] The present invention provides a transient broadband two-dimensional infrared spectroscopy system and a detection method thereof, which generates broadband mid-infrared pulses (1000-4000cm -1 ) and visible-near-infrared pulses (450-1000nm), and the time sequence of the visible-near-infrared pulses and mid-infrared pulses acting on the sample is adjusted by a time delay line to achieve two detection modes: transient broadband two-dimensional infrared spectroscopy and fluorescence coded two-dimensional infrared spectroscopy.

[0023] Beneficial effects of the present invention:

[0024] 1. Transient broadband two-dimensional infrared spectrum acquisition mode:

[0025] (1) Variable frequency visible-near infrared pulses: For photochemical processes with different excitation wavelengths, the generation of pulses with different wavelengths in the visible-near infrared range can be achieved by adjusting the angle of the BBO crystal.

[0026] (2) Broadband mid-infrared pulse detection: conventional detection light is 200cm -1Narrowband optical pulses, whose energy is limited by the wedge-shaped light splitting ratio, can only capture limited characteristic vibrational relaxation and coupling dynamic information. -1 ) detection, the frequency domain range is 15 times that of conventional means, and the energy adjustable range is wide, which improves the detection sensitivity.

[0027] 2. Fluorescence coded two-dimensional infrared spectrum acquisition mode:

[0028] (1) For samples that can generate fluorescence, the present invention changes the order in which visible-near infrared pulses and mid-infrared pulses act on the samples, and uses parabolic mirrors and photodiodes to collect and detect fluorescence. The system also has the function of detecting fluorescence-coded infrared spectra.

[0029] (2) Compared with conventional two-dimensional infrared spectroscopy systems, the vibrational state information of molecules is directly reflected in the fluorescence intensity, and the detection efficiency is higher. Therefore, the detection sensitivity of two-dimensional infrared spectroscopy can be greatly improved, which can meet the detection needs of low-concentration samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the optical path diagram of the present invention.

[0031] Figure 2 This is an optical path diagram of the broadband pulse generation chamber and the non-collinear optical parametric amplifier of the present invention.

[0032] Figure 3 This is a light path diagram of the time-resolved pulse generation chamber and the sample chamber of the present invention.

[0033] Figure 4 Schematic diagram of the time sequence of light pulses in two different signal acquisition modes of the present invention.

[0034] In the figure: 1-femtosecond laser; 2-optical parametric amplifier (TOPAS); 3-difference frequency generator (DFG); 4-time-resolved pulse generation chamber; 5-broadband infrared generation chamber; 6-non-collinear optical parametric amplifier (NOPA); 7-sample chamber; 8-monochromator and mercury cadmium telluride MCT double-row array detector; 9-integrator and data acquisition card; 10-computer; 11-chopper controller A; 12-chopper controller B. DETAILED DESCRIPTION

[0035] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0036] like Figure 1As shown, the spectral system of the present invention includes: a femtosecond laser (50fs, 800nm, 1kHz) 1, an optical parametric amplifier (TOPAS) 2, a difference frequency generator (DFG) 3, a time-resolved pulse generation chamber 4, a broadband infrared generation chamber 5, a non-collinear optical parametric amplifier (NOPA) 6, a sample chamber 7, a monochromator and a mercury cadmium telluride MCT double-row array detector 8, an integrator and a data acquisition card 9, a computer 10, a chopper controller A11 and a chopper controller B12.

[0037] The present invention comprises an 800nm ​​wavelength light source generated by a femtosecond laser 1, outputting near infrared (NIR) pulses and residual 800nm ​​pulses via an optical parametric amplifier (TOPAS) 2, the near infrared is used to pump a difference frequency generator (DFG) 3 to generate narrowband mid-infrared pulses (MIR), and the residual 800nm ​​pulses are used to generate broadband infrared pulses (BBIR) and visible-near infrared pulses. The specific implementation of these parts is further described below in conjunction with the accompanying drawings.

[0038] Generation of broadband infrared pulses and visible-near infrared pulses: The residual 800nm ​​pulse is frequency-doubled by the BBO crystal to generate a 400nm pulse, which is then transformed into two beams of 90% and 10% by the beam splitter BS, and enters the broadband infrared generation chamber 5 and the non-collinear optical parametric amplifier (NOPA) 6 respectively ( Figure 2 ). In the broadband infrared generation chamber 5, the time difference between the 400nm and 800nm ​​pulses is corrected by the delay compensation plate DP. The polarization direction of the 800nm ​​pulse is adjusted by the half-wave plate WP to make it completely consistent with the 400nm pulse, and then it is tripled by the BBO crystal to generate a 266nm pulse. The three beams of 266nm, 400nm, and 800nm ​​pulses are focused on the argon gas flow column Ar through the concave reflector M to generate broadband mid-infrared pulses, and then collimated by two concave reflectors M, and the visible light pulses are filtered out by the high-transmittance germanium plate Ge, and the direction is adjusted by the plane reflector M to enter the time-resolved generation chamber 4. In the non-collinear optical parametric amplifier (NOPA) 6, the collinear 400nm and 800nm ​​pulses are split by the dichroic mirror DM, and the 400nm light is focused to the center of the BBO crystal through the plane and concave reflectors M. The 800nm ​​light is adjusted to have a time difference with the 400nm pulse through the time delay line DS3, and is collected on the sapphire window SW through the lens L to produce supercontinuum white light, which is then focused to the center of the BBO crystal by the lens L, and completely overlaps with the 400nm pulse in the crystal, producing an adjustable pulse in the visible-near infrared range (the wavelength is related to the BBO angle). After the pulse is collimated by the lens L, the direction is adjusted by the reflector M, the relative time delay with the mid-infrared pulse is adjusted by the delay line DS4, and the polarizer P is selected before entering the sample chamber 7.

[0039] Two-dimensional infrared spectrum detection part: Femtosecond laser 1 generates light pulses with a wavelength of 800nm ​​and a repetition frequency of 1kHz. After the two mirrors M adjust the angle, the light pulses are incident on the optical parametric amplifier (TOPAS) 2 and the difference frequency generator (DFG) 3. The software of TOPAS and DFG controls the corresponding parameters to generate narrow-band mid-infrared pulses (MIR) of the required wavelength, and then enter the time-resolved pulse generation chamber 4 ( Figure 3 ) is generated by k 1 &k 2 The interference of pump light and background light k LO , and broadband mid-infrared pulse k 3 The parabolic reflector PM in the sample chamber 7 converts the parallel incident pump light (k 1 &k 2 ), detection light (k 3 ) and background light (k LO ) is focused into the sample pool S, and then the detection light and background light are collected by another parabolic reflector PM, adjusted by the reflector M, converged by the lens L, and selected by the polarizer P, and finally enter the slit of the monochromator 8 and irradiate the upper and lower rows of the MCT double-row array detector. The polarization direction of the polarizer P should be completely consistent with the detection light, the purpose is to filter the signal interference caused by sample scattering. The 1kHz electronic pulse signal generated by the femtosecond laser controller is input to the integrator and the chopper controller B12 respectively. The chopper controller B12 has a built-in frequency divider that converts 1kHz into a 500Hz electronic pulse signal, which is output to the chopper controller A11 for controlling the rotation frequency of the choppers CH1 and CH2. The monochromator and the MCT double-row array detector 8 are connected to the integrator through a data line. After the integrator is triggered by the 1kHz electronic pulse signal input by the femtosecond laser 1, the signals input by the MCT double-row array detector 8, the single-channel detector SC and the photodiode PD are integrated (the integration time is usually set to 2000ns), and then the data are divided into four groups of 1-"on-on", 2-"on-off", 3-"off-on" and 4-"off-off" according to the electronic pulse signals of the chopper controller A11 and the chopper controller B12, and the data are recorded by the data acquisition card and sent to the computer 10 to generate a data file. The sample pool S adopts a "sandwich" structure, that is, the liquid sample is sandwiched between two calcium fluoride windows coated with FEP film, and the sample thickness (usually 50 microns) is adjusted by a polytetrafluoroethylene gasket. The "sandwich" structure is fixed in a copper module and the temperature is controlled by a water bath circulation pump.

[0040] In this embodiment, the detection mode is transient broadband two-dimensional infrared spectroscopy, the delay line DS4 is fixed at 1ps, the delay line DS2 is fixed at 100fs, and the delay line DS1 ( Figure 3 ) has a scan range of -300fs to 2500fs with a step size of 4fs.

[0041] The scanning detection method of this embodiment based on the transient broadband two-dimensional infrared spectroscopy system includes the following steps:

[0042] 1) Set the time delay of delay line DS4 to 1ps and set the delay time of delay line DS2 to 100fs.

[0043] 2) Set the start and end positions of the delay line DS1 to -300fs and 2500fs, with a step size of 4fs.

[0044] 3) The delay line moves from the starting position to the ending position (forward movement) and is stored as a 701*131 matrix M1.

[0045] 4) The 1st to 129th columns in the data file can be used to obtain two two-dimensional spectral data by conventional methods. After phase correction is completed by the 130th column data, the difference spectrum between the two is the transient two-dimensional infrared spectrum of the photoinduced reaction at 1ps time.

Claims

1. A transient broadband two-dimensional infrared spectroscopy system, characterized in that: The system includes 800nm ​​femtosecond laser, optical parametric amplifier TOPAS, difference frequency generator DFG, monochromator and mercury cadmium telluride MCT double-row array detector, integrator and data acquisition card, computer, chopper controller, non-collinear optical parametric amplifier NOPA, broadband infrared generation chamber, time-resolved pulse generation chamber and sample chamber; The near-infrared pulses generated by the femtosecond laser and TOPAS are passed through DFG to generate narrow-band mid-infrared pulses of the required wavelength and enter the time-resolved pulse generation chamber, which is used as pump light pulses for detecting two-dimensional infrared spectra. The 800nm ​​pulses not converted by TOPAS are frequency-doubled by BBO crystals to generate 400nm pulses, which are then divided into two beams of 90% and 10% by energy by the beam splitter BS, and enter the broadband infrared generation chamber and NOPA respectively. Broadband infrared generation chamber: After the two pulses with wavelengths of 400nm and 800nm ​​enter, they are first adjusted by the delay compensation plate DP to completely overlap on the time scale, and then adjusted by the half-wave plate WP to make the polarization angles completely consistent, and a 267nm pulse is generated through the BBO crystal; the three pulses are focused onto the argon gas flow column Ar through the concave reflector M to generate broadband infrared pulses, and after being collimated by two concave reflectors M, the 267nm, 400nm and 800nm ​​pulses are filtered out by the high-transmittance germanium plate Ge, and then the direction is adjusted by the reflector M to enter the time-resolved pulse generation chamber; Non-collinear optical parametric amplifier NOPA: After the collinear 400nm and 800nm ​​pulses enter, they are first divided into two beams of 400nm and 800nm ​​by the dichroic mirror DM; the 800nm ​​pulse passes through the delay line DS3, and is focused by the lens L on the sapphire window SW to generate supercontinuum white light, and then focused on the BBO crystal through the lens L; the 400nm pulse is adjusted by the reflector M and focused on the BBO crystal, overlapping with the focus of the supercontinuum white light in the crystal space; the time overlap of the supercontinuum white light and the 400nm pulse on the BBO crystal is achieved by adjusting the delay line DS3; optical parametric amplification of different wavelengths is achieved by adjusting the angle of the BBO crystal, and the generated signal light passes through the delay line DS4, passes through the polarizer P, the chopper, and enters the sample chamber after adjusting the angle of the reflector M; In the sample chamber, the signal light pulse from NOPA is angle-adjusted by the reflector M so that it overlaps spatially with the infrared pulse from the time-resolved pulse generation chamber on the sample cell S; The time-resolved pulse generation chamber is used to generate the pump light and background light LO required for two-dimensional infrared spectrum detection. The optical path difference between the pump light and background light LO and the broadband infrared pulse BBIR detection light k3 is adjusted by the time delay line DS2 to achieve time resolution. The medium-narrowband infrared pulse MIR from DFG entering the time-resolved pulse generation chamber is divided into k1, k2 and k3 by the wedge mirror W and the beam splitter BS. LO Three beams, with a pulse energy ratio of 47:47:6; light pulses k1 and k2 pass through the time delay line DS1, and generate interference light pulses on the second beam splitter BS, half of which is used as pump light to enter the sample chamber through the half-wave plate WP and the polarizer P, and the other half is used for phase correction and detected by the single-channel MCT detector SC; the time difference between k1 and k2 pulses is transformed into one-dimensional spectrum information of the two-dimensional infrared spectrum through Fourier transformation; light pulse k LO Enters the sample chamber through the reflector M and is used as background light; The broadband infrared light pulse k3 enters the sample chamber through the dispersion compensation plate C and the polarizer P and is used as the detection light; The parabolic reflector PM in the sample chamber reflects the parallel incident pump light k1&k2, detection light k3 and background light k LO Focused into the sample pool S, the detection light and background light are collected by another parabolic reflector PM, and converged to the upper and lower rows of the monochromator and the MCT double-row array detector respectively through the reflector M, lens L and polarizer P; The visible-near infrared pulse from the non-collinear optical parametric amplifier used to trigger the electronic excited state process enters the sample chamber and is focused by lens L. It is irradiated to the sample pool through mirror M, and the light spot space of the three pulses k1, k2 and k3 completely overlaps. The generated fluorescence is focused onto the photodiode PD through concave mirror M.

2. A transient broadband two-dimensional infrared spectroscopy system according to claim 1, characterized in that: The broadband infrared generation chamber, time-resolved pulse generation chamber and sample chamber are covered by a box made of 5mm thick acrylic plate. The box is connected to a dry air generator via an air valve and a PTFE tube to control the humidity in the box below 5%.

3. A transient broadband two-dimensional infrared spectroscopy system according to claim 1, characterized in that: The sample pool has a "sandwich" structure, that is, the liquid sample is sandwiched between two calcium fluoride windows coated with FEP film, and the sample thickness is adjusted by a polytetrafluoroethylene gasket; the "sandwich" structure is fixed in a copper module and the temperature is controlled by a water bath circulation pump.

4. A transient broadband two-dimensional infrared spectroscopy system according to claim 1, characterized in that: The integrator is triggered by the electronic pulse signal input by the chopper and integrates the signal input by the MCT detector. The data acquisition card collects the external channel signals fed back by the chopper controllers CH1 and CH2, which respectively reflect whether the visible-near infrared pulse and k2 pulse are blocked, and divides the data into four columns: "on-on", "on-off", "off-on" and "off-off". The single-channel MCT detector and photodiode PD in the same period are also recorded by the external channel of the integrator, which are used for phase correction of two-dimensional spectrum and analysis of fluorescence coded infrared spectrum respectively.

5. A detection method using a transient broadband two-dimensional infrared spectroscopy system according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) The time difference τ between the visible-near infrared pulse and the mid-infrared pulse is set by the time delay line DS4: when the visible-near infrared pulse reaches the sample pool position before the mid-infrared pulse, that is, τ>0, it is; otherwise, that is, τ<0, it is the fluorescence encoding two-dimensional infrared spectrum acquisition mode; 2) In transient broadband 2D spectroscopy acquisition mode, k3 and k LO The intensity changes are recorded by the upper and lower rows of the MCT double-row array detectors, respectively, corresponding to the states of the chopper controllers CH1 and CH2, and are divided into four groups: 1-"on-on", 2-"on-off", 3-"off-on" and 4-"off-off"; among them, the difference between 1 and 2 is stored as the excited state signal, that is, the signal when the visible-near-infrared pulse is not blocked; the difference between 3 and 4 is stored as the ground state signal, that is, the signal when the visible-near-infrared pulse is blocked by the chopper; 3) Setting the relative time delay t2 of k3 and k2 through the time delay line DS2, setting the range ts and te of the relative time delay t1 of the pump light k1 and k2 through the time delay line DS1, and the moving step dt; during the process of DS1 moving from the ts position to the te position, each time it moves a distance of dt, recording the excited state signal and the ground state signal according to the methods 1-2, 3-4 in step 2); the data is recorded in the manner of subtracting the lower row array data from the upper row array data of the MCT double-row array detector; 4) According to the above acquisition method, a p*(2q+3) matrix is ​​obtained; wherein p is the total number of positions moved by DS1, q is the total number of channels of the MCT single-row array, and the excited state signal and the ground state signal occupy a p*q matrix respectively; the first column of the matrix is ​​the time delay t1 set by DS1, and the last two columns are the light intensity information recorded by the MCT single channel and the photodiode respectively; 5) The matrix recorded in step 4) can be used to obtain two two-dimensional spectral data by conventional methods, and the difference between the two is the transient two-dimensional infrared spectrum at the corresponding time τ, and the corresponding two frequencies are ω3 directly recorded by the MCT array and ω1 converted by Fourier transform with time delay t1; 6) In the fluorescence coded two-dimensional spectral acquisition mode, the MCT double-row array detector is used to record the interference signal of the pump light k1 and k2.

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