Non-scattering transient absorption spectrum system

Abstract

The invention discloses a non-scattering transient absorption spectrum system, and relates to the technical field of laser spectroscopy. The system comprises a phase cycle modulator, a double-beam amplitude modulator, a pumping detection light path device and a spectrum detector, femtosecond laser is divided into pump light and probe light through a beam splitter, and the pump light is subjected to periodic phase modulation through a phase cycle modulator, so that the optical path of the pump light in two adjacent measurements is changed by odd times of half wavelength; the pump light and the probe light enter a double-beam amplitude modulator at the same time for amplitude modulation, so that the repetition frequency proportion of the pump light and the probe light is two times or a half; the pump light and the probe light are incident on a sample after passing through the pump probe light path device; and detecting the probe light passing through the sample by using a spectrum detector, and calculating to obtain a transient absorption spectrum signal without scattering noise. According to the invention, scattering signals in the transient absorption spectrum system can be completely removed under the conditions of low operation cost and low technical difficulty.

Description

Technical Field

[0001] This application relates to the technical field of laser spectroscopy, and particularly to a non-scattering transient absorption spectroscopy system. Background Art

[0002] Ultrafast time-resolved spectroscopy is an advanced detection method in the field of spectroscopy that can detect chemical reactions, molecular dynamics, and fine structures on the femtosecond ultrafast time scale. The currently widely used time-resolved spectroscopy technique is transient absorption spectroscopy, which uses a pump-probe configuration. A strong pump light is used to excite the sample motion, and after a certain time delay, a weaker probe light is used to detect the changes in the sample molecules. However, when detecting heterogeneous samples such as solid powders, colloids in high-temperature molten salts, suspended particles, high-temperature molten salts, etc., the strong scattering noise generated by the pump light on the sample will seriously interfere with the probe light, resulting in distorted collected signals and affecting the experimental quality. The strong scattering noise brought by the pump light can be divided into two parts: (1) Incoherent scattering: This part of the scattering noise is generated by the linear superposition of the pump scattered light onto the probe light and exists throughout the detection process; (2) Coherent scattering: This part of the scattering noise is caused by the optical interference between the pump scattered light and the probe light, which will cause spectral and kinetic deformations within the coherence time.

[0003] Currently, there are mainly two methods to solve the problem of strong scattering noise in the transient absorption spectroscopy system. One is to use intensity modulation to remove incoherent scattering. By placing a phase-locked mechanical chopper in the pump light and the probe light respectively, the incoherent scattering noise generated by a single pump pulse light is collected and then deducted from the collected results. Its disadvantage is that it cannot remove the coherent scattering noise of the pump light. The other method is to add a pulse shaper in the optical path to control the laser intensity and phase in real time, thereby achieving the removal of intensity scattering and phase scattering. The problem with this method is that the pulse shaper is expensive, and the cost of a single pulse shaper is already comparable to the value of a set of transient absorption spectroscopy systems, and the operation technical difficulty is relatively large. Therefore, the current transient absorption spectroscopy system still faces problems such as being unable to effectively measure strongly scattering samples, incomplete removal of scattering noise, high cost of removing scattering noise, and large operation difficulty. Summary of the Invention

[0004] The purpose of this application is to provide a non-scattering transient absorption spectroscopy system that can completely remove the scattering signal in the transient absorption spectroscopy system at low operating cost and low technical difficulty.

[0005] To achieve the above purpose, this application provides the following solutions:

[0006] The present application provides a non-scattering transient absorption spectroscopy system, comprising: a phase cycling modulator, a dual-beam amplitude modulator, a pump-probe optical path device, and a spectral detector. The pump light is subjected to periodic phase modulation by the phase cycling modulator, such that the optical path of the pump light changes by an odd multiple of half a wavelength in two adjacent measurements, corresponding to a change in phase by an integer multiple of π; the phase-modulated pump light and the probe light simultaneously enter the dual-beam amplitude modulator for amplitude modulation, such that the repetition frequency ratio of the amplitude-modulated pump light and the amplitude-modulated probe light is two times or one-half; the amplitude-modulated pump light and the amplitude-modulated probe light are introduced into the pump-probe optical path device, and after time delay, are incident on the sample; the spectral detector is used to detect the probe light that has passed through the sample, and then by collecting the probe light under different modulation conditions, a transient absorption spectral signal without scattering noise is obtained by calculation according to the time sequence.

[0007] According to the specific embodiments provided by the present application, the present application has the following technical effects:

[0008] The present application provides a non-scattering transient absorption spectroscopy system. The pump light is subjected to periodic phase modulation by the phase cycling modulator, such that the optical path of the pump light changes by an odd multiple of half a wavelength in two adjacent measurements, corresponding to a change in phase by an integer multiple of π, so that the interference signal between the pump light and the probe light in two adjacent measurements can be completely cancelled, achieving complete removal of the coherent scattering noise of the pump light; the dual-beam amplitude modulator performs amplitude modulation on the simultaneously entering pump light and probe light, such that the repetition frequency ratio of the amplitude-modulated pump light and the amplitude-modulated probe light is two times or one-half, and the incoherent scattering noise generated by the linear superposition of the pump scattered light onto the probe light is eliminated by background subtraction. The present application can simultaneously and completely remove the coherent and incoherent scattering noises existing in the transient absorption spectroscopy system through the phase cycling modulator and the dual-beam amplitude modulator, reducing the operating cost and the technical difficulty of noise removal. Description of the Drawings

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0010] Figure 1 It is a schematic structural diagram of a non-scattering transient absorption spectroscopy system in an embodiment of the present application;

[0011] Figure 2 It is a schematic diagram of the chopper blade design of the dual-beam amplitude modulator provided by the example of the present application;

[0012] Figure 3Schematic diagram of the optical path of the non-scattering transient absorption spectroscopy system provided in the first example of this application;

[0013] Figure 4 Schematic diagram of the timing control provided in the first example of this application;

[0014] Figure 5 Schematic diagram of the optical path of the non-scattering transient absorption spectroscopy system provided in the second example of this application;

[0015] Figure 6 Schematic diagram of the modulation of the dual-beam amplitude modulator provided in the second example of this application;

[0016] Figure 7 Schematic diagram of the timing control provided in the second example of this application.

[0017] Reference numerals: femtosecond laser - 1, beam splitter - 2, delay line displacement stage - 3, phase cycling modulator - 4, dual-beam amplitude modulator - 5, plano-convex lens - 6, sample - 7, first concave mirror - 8, second concave mirror - 9, spatial light filter - 10, spectral detector - 11, achromatic half-wave plate - 12, polarizer - 13, polarization beam splitter - 14, photodetector - 15, first semi-transparent and semi-reflective mirror - 16, second semi-transparent and semi-reflective mirror - 17, objective lens - 18, polarization filter - 19, third concave mirror - 20, first reflector - 21, second reflector - 22, third reflector - 23, fourth reflector - 24, fifth reflector - 25, sixth reflector - 26, seventh reflector - 27, eighth reflector - 28, ninth reflector - 29, tenth reflector - 30, eleventh reflector - 31, twelfth reflector - 32, thirteenth reflector - 33. Detailed implementation manners

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0019] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0020] To solve the problems that the system cannot measure strongly scattering samples, the scattering removal is incomplete, the solution is too expensive, and the technical difficulty is relatively large, in an exemplary embodiment, as Figure 1As shown, a non-scattering transient absorption spectroscopy system is provided. The non-scattering transient absorption spectroscopy system includes: a beam splitter 2, a phase cycling modulator 4, a dual-beam amplitude modulator 5, a pump-probe optical path device, and a spectral detector 11. The femtosecond laser is split into a pump beam and a probe beam by the beam splitter 2. The pump beam is subjected to periodic phase modulation by the phase cycling modulator 4, such that the optical path of the pump beam changes by an odd multiple of half a wavelength in adjacent two measurements, corresponding to an integer multiple of π in phase change. The phase-modulated pump beam and the probe beam enter the dual-beam amplitude modulator 5 simultaneously for amplitude modulation, such that the repetition frequency ratio of the amplitude-modulated pump beam and the amplitude-modulated probe beam is two times or one-half. The amplitude-modulated pump beam and the amplitude-modulated probe beam are introduced into the pump-probe optical path device and are incident on the sample 7 after time delay. The spectral detector 11 is used to detect the probe beam after passing through the sample 7 to obtain a non-scattering noise transient absorption spectroscopy signal.

[0021] A non-scattering transient absorption spectroscopy system of the present application can be used in ultrafast time-resolved spectroscopy experiments. By using the phase cycling modulator 4 and the dual-beam amplitude modulator 5, the coherent and incoherent scattering noises existing in the transient absorption spectroscopy system can be completely removed simultaneously, reducing the technical difficulty of noise removal. The system includes a self-designed phase cycling modulator 4 and a dual-beam amplitude modulator 5, which perform logical periodic modulation on the pulse phase and pulse frequency of the excitation beam respectively, and use a special timing sequence for signal acquisition and signal processing to achieve the complete removal of coherent and incoherent scattering noises in the transient absorption spectroscopy system. The present application solves the problems existing in the traditional transient absorption spectroscopy system, such as the inability to measure strongly scattering samples, the complex, expensive, and technically difficult scattering noise removal device, and the incomplete removal of scattering noise, and realizes the complete removal of scattering noise in the transient absorption spectroscopy system.

[0022] In another exemplary embodiment of the present application, the phase cycling modulator 4 performs periodic phase modulation of 0 phase and π phase on the pump beam.

[0023] In another exemplary embodiment of the present application, the phase cycling modulator 4 includes: a birefringent crystal and a rotating displacement stage. The birefringent crystal is disposed on the rotating displacement stage; the rotating displacement stage is used to drive the birefringent crystal to perform periodic rotation, so that the pump beam periodically aligns with the fast axis and the slow axis of the birefringent crystal, and is transmitted through the birefringent crystal for periodic phase modulation.

[0024] The birefringent crystal is a uniaxial crystal. The birefringence effect of the uniaxial crystal is used to cause an optical path difference, and by periodically aligning the fast axis and the slow axis on the rotating displacement stage, the periodic cycle of 0 phase and π phase is realized. Among them, the fast axis and the slow axis refer to two directions with different light propagation speeds in the birefringent crystal. When light propagates along these two directions, no birefringence occurs, but the propagation speeds are different. The direction with a faster propagation speed is called the fast axis, and the slower one is called the slow axis.

[0025] The phase cycling modulator 4 can create an optical path difference of nλ + λ / 2 between adjacent pulses through a uniaxial crystal; the optical path difference can be accurately up to only λ / 2, achieving zero-order (n = 0) phase modulation. Here, n = 0, 1, 2, 3, …. When n = 0, that is, the optical path difference between the o-ray and the e-ray is only half a wavelength, so as to achieve the effect of single-cycle accurate phase delay.

[0026] In another exemplary embodiment of the present application, dispersion can be eliminated by optical coating design of the used uniaxial crystal, realizing multi-pump wavelength phase cycling modulation in a wide spectral range.

[0027] In another exemplary embodiment of the present application, the thickness of the birefringent crystal is determined by the pump light wavelength used and the refractive index of the birefringent crystal. The specific thickness should meet the requirements of the following formula:

[0028]

[0029] where η o and η e respectively represent the refractive indices of the o-ray and the e-ray of the birefringent crystal, l represents the thickness of the birefringent crystal, λ represents the central wavelength of the pump light, and n is an integer, n = 0, 1, 2, 3, ….

[0030] In another exemplary embodiment of the present application, the birefringent crystal is an achromatic zero-order half-wave plate corresponding to the pump light wavelength. Using an achromatic zero-order half-wave plate can achieve system adaptation in a wide wavelength range and increase the applicability of the system.

[0031] The phase cycling modulator 4 can use a zero-order or true zero-order half-wave plate to achieve precise delay and improve temperature stability at the same time.

[0032] In another exemplary embodiment of the present application, the rotary displacement stage needs to have a signal synchronization device and a phase locking device to ensure synchronization with the laser electrical signal. The signal synchronization device means that the rotary displacement stage is controlled by a motor and needs to be driven by a pulsed electrical signal to control the rotation of the rotary displacement stage and then control the angle of the crystal, and then control the optical phase change. The synchronization device uses the trigger signal of the laser as a reference to generate the drive pulse signal of the motor, thus realizing the synchronization of the electrical signals. Phase locking is an ancillary function of signal synchronization. Ensure that the signal synchronization device can perform phase control of the electrical signal after receiving an external trigger signal. To ensure that there will be no phase drift between electrical signals over a long time.

[0033] In another exemplary embodiment of the present application, the operating mode can be selected according to the repetition frequency of the laser pulse, while being compatible with both low-repetition-frequency and high-repetition-frequency lasers. When using a low-repetition-frequency light source, complete scatter removal at the single-pulse level can be achieved. At low repetition frequencies, such as a pulse signal of 1 KHz, the system can modulate each pulse, and the state of each pulse can be different, which is usually referred to as single-pulse scatter removal. At high repetition frequencies, such as 1 MHz, since the modulation speed of the system cannot keep up with the frequency of the laser pulse, modulation of a group of pulses is achieved. The states of each group of pulses are different, but the states of the pulses within the group are the same, which is called multi-pulse scatter removal.

[0034] In another exemplary embodiment of the present application, for the phase cycle modulator 4, its rotating displacement stage is synchronized and phase-locked with the laser electrical signal, thereby achieving precise phase cycle modulation of the laser pulse.

[0035] In another exemplary embodiment of the present application, the dual-beam amplitude modulator 5 can simultaneously achieve amplitude modulation of the pump light and the probe light in one modulator, as Figure 2 shown, the dual-beam amplitude modulator 5 includes: an inner ring blade and an outer ring blade; the centers of the inner ring blade and the outer ring blade are at the same position, and the inner ring blade and the outer ring blade form a complete circle; a plurality of slits are provided on both the inner ring blade and the outer ring blade, and the ratio of the number of slits of the inner ring blade to the outer ring blade is 1:2.

[0036] The dual-beam amplitude modulator 5 can select the beam to be modulated by the inner ring and the outer ring according to the actual pulse sequence situation; it only needs to ensure that the pump light and the probe light pass through different rings respectively, that is, the pump light and the probe light are amplitude-modulated in different rings.

[0037] Exemplarily, the dual-beam amplitude modulator 5 is composed of an optical chopper, and the blade used in the chopper is composed of two parts, an inner ring and an outer ring. The inner ring is used to modulate the probe light, and the outer ring is used to modulate the pump light. The chopper blades of the inner ring and the outer ring should maintain phase synchronization, and the ratio of the number of slits is 1:2; that is, the central angles corresponding to the inner and outer ring blades should be in a 2-fold relationship.

[0038] The dual-beam amplitude modulator 5 can customize the blade according to the existing commercial chopper and use the same blade as the commercial chopper. It only needs to change the number of inner or outer slits of the blade so that the ratio of the number of slits is inner:outer = 1:2. The blade customized in this way can be directly integrated into the existing chopping device.

[0039] In another exemplary embodiment of the present application, the phase cycle modulator 4 and the dual-beam amplitude modulator 5 should achieve pulse-to-pulse synchronous modulation with the laser signal to minimize the influence brought by laser power fluctuations.

[0040] In another exemplary embodiment of the present application, in the pump optical path, a half-wave plate and a polarizer 13 are sequentially arranged in front of the phase cycling modulator 4 to form a polarization filtering system to purify the polarization state of the pump light. An analyzer is arranged behind the phase cycling modulator 4 to ensure the consistent polarization of the output pump light. A beam sampling mirror is arranged behind the phase cycling modulator 4 to collect a part of the pump light, and a photodiode probe is used to monitor the intensity change of the pump light to ensure the correct phase locking of the phase cycling modulator 4. As Figure 3 shown, the non-scattering transient absorption spectroscopy system further includes: a delay line displacement stage 3, an achromatic half-wave plate 12, a polarizer 13, a polarization beam splitter 14, and a photodetector 15. Between the beam splitter 2 and the phase cycling modulator 4, the delay line displacement stage 3, the achromatic half-wave plate 12, and the polarizer 13 are sequentially arranged along the propagation direction of the pump light optical path; the polarization beam splitter 14 and the photodetector 15 are arranged on the optical path of the pump light in the pump-probe optical path device. After the time delay of the pump light is adjusted by the delay line displacement stage 3, the pump light sequentially passes through the achromatic half-wave plate 12 and the polarizer 13 to obtain the adjusted pump light; the adjusted pump light is linearly polarized light and the polarization direction is vertical. The adjusted pump light sequentially passes through the phase cycling modulator 4 for periodic phase modulation and the double-beam amplitude modulator 5 for amplitude modulation. The amplitude-modulated pump light is split by the polarization beam splitter 14. The polarization beam splitter 14 transmits vertically polarized light and reflects horizontally polarized light. The vertically polarized light transmitted by the polarization beam splitter 14 is incident on the sample 7. The photodetector 15 is used to collect the optical signal of the horizontally polarized light. If the horizontally polarized light is collected, a high level is output; if the horizontally polarized light is not collected, a low level is output; the high level or low level output by the photodetector 15 is used as the basis for judging whether the phase cycling modulator 4 is working properly.

[0041] The polarization beam splitter 14 and the photodetector 15 constitute a feedback loop for phase modulation. A feedback loop for phase modulation is arranged in the pump beam, and a photodetector is used to detect the intensity of the sampled light to judge the phase modulation state in real time.

[0042] As Figure 1 shown, the delay line displacement stage 3 includes two mirrors: the twelfth mirror 32 and the thirteenth mirror 33. The time delay of the pump light is achieved through the two mirrors.

[0043] In another exemplary embodiment of the present application, as Figure 3As shown in the figure, the pump-probe optical path device includes: a first mirror 21, a second mirror 22, a third mirror 23, a fourth mirror 24, a fifth mirror 25, a sixth mirror 26, a plano-convex lens 6, a first concave mirror 8, a second concave mirror 9, and a spatial light filter 10. The amplitude-modulated pump light sequentially passes through the first mirror 21 and the second mirror 22 and is reflected to the plano-convex lens 6; the plano-convex lens 6 focuses the reflected pump light onto the sample 7 to excite the movement of the sample 7. The pump light passing through the sample 7 is collected by the first concave mirror 8 and then spatially filtered by the spatial light filter 10 to block the pump light. The amplitude-modulated probe light sequentially passes through the third mirror 23, the fourth mirror 24, the fifth mirror 25, and the sixth mirror 26 and is reflected to the plano-convex lens 6; the plano-convex lens 6 focuses the reflected probe light onto the sample 7. The pump light passing through the sample 7 is collected by the first concave mirror 8 and then focused by the second concave mirror 9 into the spectral detector 11.

[0044] In another exemplary embodiment of the present application, as Figure 5 shown, the pump-probe optical path device includes: a seventh mirror 27, an eighth mirror 28, a ninth mirror 29, a tenth mirror 30, an eleventh mirror 31, a first semi-transmissive and semi-reflective mirror 16, a second semi-transmissive and semi-reflective mirror 17, an objective lens 18, a polarization filter 19, and a third concave mirror 20. The amplitude-modulated pump light sequentially passes through the seventh mirror 27 and the eighth mirror 28 and is reflected to the first semi-transmissive and semi-reflective mirror 16; the amplitude-modulated probe light sequentially passes through the ninth mirror 29, the tenth mirror 30, and the eleventh mirror 31 and is reflected to the first semi-transmissive and semi-reflective mirror 16. The reflected pump light and the reflected probe light are combined by the first semi-transmissive and semi-reflective mirror 16, and the combined light is transmitted through the second semi-transmissive and semi-reflective mirror 17 and focused onto the sample 7 via the objective lens 18. The pump light reflected by the sample 7 is reflected by the second semi-transmissive and semi-reflective mirror 17 and undergoes polarization filtering at the polarization filter 19 to block the pump light from entering the spectral detector 11. The probe light reflected by the sample 7 is reflected by the second semi-transmissive and semi-reflective mirror 17, passes through the polarization filter 19, and is focused by the third concave mirror 20 into the spectral detector 11.

[0045] In another exemplary embodiment of the present application, it can be used in a microscopic transient absorption spectroscopy system to achieve filtering of the pump beam.

[0046] In another exemplary embodiment of the present application, the non-scattering transient absorption spectroscopy system includes: a computer. The computer is respectively connected to a phase cycling modulator 4, a dual-beam amplitude modulator 5, and a spectral detector 11; the computer is used to control the synchronization and phase locking of the phase cycling modulator 4 with the femtosecond laser; the computer is further used to receive the working states of the phase cycling modulator and the dual-beam amplitude modulator; the computer is further used to receive the transient absorption spectroscopy signal collected by the spectral detector 11, and perform calculations according to the acquisition timing sequence of the transient absorption spectroscopy signal to determine the non-scattering signal.

[0047] On the computer, software programming based on the LabView environment is used to control the operation of the system and the synchronization between devices, realizing functions such as automated data acquisition, running of the scattering removal algorithm, and acquisition logic control. The intelligent control system programmed based on the LabView software environment (the software programming control system based on the LabView environment) can realize the automated control and full-process monitoring of the entire experimental process, including the real-time display and data storage of experimental data and key system parameters (such as the delay time).

[0048] The non-scattering transient absorption spectroscopy system of the present application is a transient absorption spectroscopy system that can completely remove the pump scattering noise. The present application can successfully achieve the following functions: complete removal of coherent and incoherent scattering noise; the scattering removal module is low-cost and easy to operate; it has a wide range of applicability and can be perfectly integrated into the existing transient absorption spectroscopy acquisition system without additional complex operations. By using the non-scattering transient absorption spectroscopy system described in the present application, problems existing in the traditional transient absorption spectroscopy system, such as the inability to accurately measure strongly scattering samples, the inability to achieve complete scattering removal, the complex operation of the scattering removal device, and high costs, can be effectively solved.

[0049] Based on the above description of the structure of the non-scattering transient absorption spectroscopy system, the following Figures 2 to 7 gives two examples to describe in detail two non-scattering transient absorption spectroscopy systems with different structures.

[0050] Example 1: Figure 3 The non-scattering transient absorption spectroscopy system shown.

[0051] 1. Use the femtosecond laser generated by the femtosecond laser 1, which is divided into two parts by a beam splitter 2. Approximately one percent of the transmitted light is used as the probe light, which is amplitude-modulated by the inner blade of the dual-beam amplitude modulator 5 (such as Figure 2After the light path is compensated by a mirror as shown, it is then focused onto the sample 7 using a plano-convex lens 6. The detection light passing through the sample 7 is collected by a first concave mirror 8 and then focused by a second concave mirror 9 into a spectral detector 11 for spectral acquisition. The spectral detector 11 uses the pulse signal from the femtosecond laser 1 as a pulse source for external trigger acquisition, thereby achieving synchronization between the laser frequency and the acquisition frequency.

[0052] 2. The pump light reflected by the beam splitter 2 is adjusted for time delay by the delay line displacement stage 3 and then passes through an achromatic half-wave plate 12 and a polarizer 13 in sequence to ensure that the output pulse is linearly polarized light with a vertical polarization direction. Then, the pump light is adjusted for phase by the phase cycling modulator 4, and the modulated pump pulse is intensity-modulated by the outer blade of the dual-beam amplitude modulator 5 (as Figure 2 shown). The phase-modulated pump light is split by a polarization beam splitter 14. The polarization beam splitter 14 transmits vertically polarized light and reflects horizontally polarized light. The vertically polarized light transmitted by the polarization beam splitter 14 is then focused onto the sample 7 by a plano-convex lens 6. The pump beam passing through the sample 7 is recollected by the first concave mirror 8 and then spatially filtered by a spatial light filter 10 to block the pump light.

[0053] 3. The pump light reflected by the polarization beam splitter 14 is then introduced into a photodetector 15 for optical signal acquisition. The signal collected by the photodetector 15 is used as a basis for judging whether the phase cycling modulator 4 is working properly. A high level indicates the presence of reflected light, that is, the phase cycling modulator 4 is not working properly, and vice versa.

[0054] 4. The drive pulse signal of the phase cycling modulator 4 can be synchronized with the pulse signal of the femtosecond laser 1 to achieve phase-locked rotation. At the same time, the judgment level of the photodetector 15 is connected as a feedback signal to form a feedback loop for phase locking. The output of the photodetector 15 is high and low levels, which can be converted into logic signals 0 or 1 and input to a computer as a judgment signal. An output high level indicates the presence of reflected light, meaning that the phase modulator has not correctly modulated the phase, indicating that the phase is not synchronously locked. An output low level means that the phase has been locked. The logic judgment signal can, on the one hand, enable the computer to judge the state of data acquisition, and on the other hand, help monitor the working state of the device.

[0055] 5. After achieving signal synchronization among the femtosecond laser 1, the dual-beam amplitude modulator 5, the phase cycling modulator 4, and the spectral detector 11, the collected spectral signals are input to a computer for processing using a program.

[0056] According to the above steps and Figure 4 the pulse timing in, a set of complete spectral signals collected is shown in Table 1. 0 and π in Table 1 represent that the optical phase has turned 0° and 180° respectively.

[0057] Spectral signals of Example 1 in Table 1

[0058]

[0059]

[0060] After collecting the above signals using a computer, the following calculations are performed on the collected signals to obtain the complete scatter-free signal:

[0061]

[0062] Example 2: Figure 5 The scatter-free transient absorption spectroscopy system shown

[0063] 1. Use the femtosecond laser generated by the femtosecond laser 1. After passing through a beam splitter 2, it is divided into two parts. Approximately 1% of the transmitted light is used as the probe light, which is amplitude-modulated by the outer blade of the double-beam amplitude modulator 5 (as Figure 6 shown). After compensating the optical path through a mirror, it is then combined with the pump light using the first semi-transparent semi-reflective mirror 16, transmitted through the second semi-transparent semi-reflective mirror 17, and focused onto the sample 7 via the objective lens 18. The reflected probe light is reflected by the second semi-transparent semi-reflective mirror 17, passes through the polarization filter 19, and is focused into the spectral detector 11 using the first concave mirror 8 for spectral acquisition.

[0064] 2. The pump light reflected by the beam splitter 2 is adjusted for time delay through the delay line displacement stage 3, and then passes through the achromatic half-wave plate 12 and the polarizer 13 in sequence to ensure that the output pulse is linearly polarized light with a vertical polarization direction. Then, the pump light is phase-modulated through the phase cycling modulator 4 and intensity-modulated by the inner blade of the double-beam amplitude modulator 5 (as Figure 6 shown). The phase-modulated pump light is split by the polarization beam splitter 14. The polarization beam splitter 14 transmits vertically polarized light and reflects horizontally polarized light. The vertically polarized light transmitted by the polarization beam splitter 14 is combined with the probe light using the first semi-transparent semi-reflective mirror 16, transmitted through the second semi-transparent semi-reflective mirror 17, and focused onto the sample 7 via the objective lens 18. The reflected pump light is reflected by the second semi-transparent semi-reflective mirror 17 and undergoes polarization filtering at the polarization filter 19 to block the pump light from entering the detector.

[0065] 3. The pump light reflected by the polarization beam splitter 14 is then introduced into the photodetector 15 for optical signal acquisition. The signal collected by the photodetector 15 is used as the basis for judging whether the phase cycling modulator 4 is working properly. A high level indicates the presence of reflected light, that is, the phase cycling modulator 4 is not working properly, and vice versa.

[0066] 4. The drive pulse signal of the phase cycle modulator 4 can be synchronized with the pulse signal of the femtosecond laser 1 to achieve phase-locked rotation. At the same time, the judgment level of the photodetector 15 is connected as a feedback signal to implement a phase-locked feedback loop.

[0067] 5. After synchronizing the signals among the femtosecond laser 1, the dual-beam amplitude modulator 5, the phase cycle modulator 4, and the spectral detector 11, the collected spectral signals are input into a computer for processing using a program.

[0068] According to the above steps and Figure 7 the pulse timing in, a set of complete spectral signals collected is shown in Table 2.

[0069] Table 2 Spectral signals of Example 2

[0070] Signal number Probe light amplitude Pump light amplitude Pump light phase S1 on on π S2 off on π S3 on off π S4 off off π S5 on on 0 S6 off on 0 S7 on off 0 S8 off off 0

[0071] After using a computer to collect the above signals, the following calculations are performed on the collected signals to obtain a complete non-scattered signal:

[0072]

[0073] A non-scattered transient absorption spectroscopy system proposed in this application can completely remove the scattered signals in the transient absorption spectroscopy system at low instrument setup and operation costs and low technical difficulties.

[0074] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0075] Specific examples are used in this article to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A non-scattering transient absorption spectroscopy system, characterized in that, The non-scattering transient absorption spectroscopy system includes: a phase cycling modulator, a dual-beam amplitude modulator, a pump-probe optical path device, and a spectroscopic detector; The pump light is subjected to periodic phase modulation by the phase cycling modulator, such that the optical path of the pump light changes by an odd multiple of half a wavelength in two adjacent measurements, corresponding to an integer multiple of π in phase change; The phase-modulated pump light and the probe light enter the dual-beam amplitude modulator simultaneously for amplitude modulation, such that the repetition frequency ratio of the amplitude-modulated pump light and the amplitude-modulated probe light is two times or one-half; The amplitude-modulated pump light and the amplitude-modulated probe light are introduced into the pump-probe optical path device and are incident on the sample after time delay; The spectroscopic detector is used to detect the probe light after passing through the sample. Then, by collecting the probe light under different modulation conditions, a transient absorption spectral signal without scattering noise is obtained through timing calculation.

2. The non-scattering transient absorption spectroscopy system according to claim 1, wherein The phase cycling modulator performs periodic phase modulation of 0 phase and π phase on the pump light.

3. The non-scattering transient absorption spectroscopy system according to claim 1, wherein The phase cycling modulator includes: a birefringent crystal and a rotating displacement stage; The birefringent crystal is disposed on the rotating displacement stage; The rotating displacement stage is used to drive the birefringent crystal to rotate periodically, so that the pump light is periodically aligned with the fast axis and the slow axis of the birefringent crystal, and is transmitted through the birefringent crystal for periodic phase modulation.

4. The non-scattering transient absorption spectroscopy system according to claim 3, wherein The thickness calculation formula of the birefringent crystal is: where η o and η e represent the refractive indices of the ordinary light and extraordinary light in the birefringent crystal respectively, l represents the thickness of the birefringent crystal, λ represents the central wavelength of the pump light, n is an integer, n = 0, 1, 2, 3,....

5. The non-scattering transient absorption spectroscopy system according to claim 3, wherein The birefringent crystal is an achromatic zero-order half-wave plate corresponding to the wavelength of the pump light.

6. The non-scattering transient absorption spectroscopy system according to claim 1, wherein The dual-beam amplitude modulator includes: an inner ring blade and an outer ring blade; The center positions of the inner ring blade and the outer ring blade are the same, and the inner ring blade and the outer ring blade form a complete circle; A plurality of slits are provided on both the inner ring blade and the outer ring blade, and the number ratio of the slits of the inner ring blade and the outer ring blade is 1:2 or 2:

1.

7. The non-scattering transient absorption spectroscopy system according to claim 1, characterized in that, The non-scattering transient absorption spectroscopy system further includes: a delay line displacement stage, an achromatic half-wave plate, a polarizer, a polarization beam splitter, and a photodetector; Between the beam splitter and the phase cycling modulator, a delay line displacement stage, an achromatic half-wave plate, and a polarizer are sequentially arranged along the propagation direction of the pump light optical path; the polarization beam splitter and the photodetector are arranged on the optical path of the pump light in the pump-probe optical path device; After the pump light is adjusted for time delay by the delay line displacement stage, it sequentially passes through the achromatic half-wave plate and the polarizer to obtain the adjusted pump light; the adjusted pump light is linearly polarized light and the polarization direction is vertical; The adjusted pump light sequentially passes through the phase cycling modulator for periodic phase modulation and the dual-beam amplitude modulator for amplitude modulation. The amplitude-modulated pump light is split by the polarization beam splitter. The polarization beam splitter transmits vertically polarized light and reflects horizontally polarized light. The vertically polarized light transmitted by the polarization beam splitter is incident on the sample; The photodetector is used to collect the optical signal of the horizontally polarized light. If horizontally polarized light is collected, a high level is output; if horizontally polarized light is not collected, a low level is output; the high level or low level output by the photodetector is used as the basis for judging whether the phase cycling modulator is working properly.

8. The non-scattering transient absorption spectroscopy system according to claim 1, characterized in that, The non-scattering transient absorption spectroscopy system further includes: a computer; The computer is respectively connected to the phase cycling modulator, the dual-beam amplitude modulator, and the spectroscopic detector; The computer is used to control the phase cycling modulator to synchronize and phase-lock with the femtosecond laser; The computer is further used to receive the working states of the phase cycling modulator and the dual-beam amplitude modulator; The computer is further used to receive the transient absorption spectrum signals collected by the spectral detector, and perform calculations according to the acquisition timing sequence of the transient absorption spectrum signals to determine the non-scattered signals.

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