Femtosecond transient absorption and nanosecond transient absorption integrated system and test method thereof

Abstract

According to the femtosecond transient absorption and nanosecond transient absorption integrated system and the test method thereof provided by the invention, femtosecond transient absorption and nanosecond transient absorption are coupled together to work, and a first optical chopper and a second optical chopper are introduced to modulate repetition frequencies of a femtosecond laser and a nanosecond laser; the time range of the nanosecond transient absorption test is shortened or prolonged, the measurement of fs-TA and ns-TA can be completed at one time, and the measurement from femtosecond level to millisecond level is fully covered.

Description

Background Art

[0002] The statements in this section only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Transient absorption technology is an ultrafast spectroscopy technique used to study the electron, exciton, and vibrational dynamics processes of materials after photoexcitation, and can reveal ultrafast processes such as the relaxation of the excited state, charge transfer, energy transfer, and charge separation. According to the different laser pulse widths and time resolutions, transient absorption technology can be divided into femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA). Among them, femtosecond transient absorption has extremely high time resolution and is mainly used to study the ultrafast processes from femtoseconds to picoseconds in the initial stage of the excited state; while the time resolution of nanosecond transient absorption is relatively low, and it is mainly used to study the slower dynamic processes from nanoseconds to microseconds in the later stage of the excited state. The two are highly complementary in the time scale, and their combined use can cover the complete dynamic process of the material from photoexcitation to the restoration of the ground state.

[0004] However, in practical applications, due to the differences in the laser types and delay adjustment methods of femtosecond transient absorption and nanosecond transient absorption devices, usually two independent devices are required for separate tests, and continuous tests from femtoseconds to microseconds time scale cannot be achieved. This not only leads to low test efficiency but also makes it difficult to coherently integrate experimental data. In addition, limited by the laser repetition frequency, traditional nanosecond transient absorption can usually only measure the dynamic process of hundreds of microseconds and cannot fully characterize the long-delay process at the millisecond level.

[0005] Therefore, developing a system that can achieve long-delay nanosecond transient absorption testing and integrate femtosecond transient absorption with long-delay nanosecond transient absorption to achieve continuous testing from femtoseconds to milliseconds time scale is an urgent problem to be solved at present. Summary of the Invention

[0006] To overcome the deficiencies of the above-mentioned prior art, the present invention provides an integrated system for femtosecond transient absorption and nanosecond transient absorption and its testing method, which couples femtosecond transient absorption and nanosecond transient absorption to work together, introduces an optical chopper to adjust the repetition frequencies of the femtosecond laser and the nanosecond laser, shortens or extends the time range of nanosecond transient absorption testing, and can complete the measurements of fs-TA and ns-TA at one time, comprehensively covering the measurements from femtoseconds to milliseconds.

[0007] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides an integrated system for femtosecond transient absorption and nanosecond transient absorption, comprising: a femtosecond transient absorption test system, a nanosecond transient absorption system, and a timing control module; The femtosecond transient absorption test system and the nanosecond transient absorption system perform optical path switching on the probe light of femtosecond transient absorption and the probe light of nanosecond transient absorption through a detachable mirror, and the pump light generated by the femtosecond transient absorption test system serves as the pump light for both femtosecond transient absorption and nanosecond transient absorption; The femtosecond transient absorption test system includes at least a femtosecond laser, a first signal delay generator, and a first optical chopper; The nanosecond transient absorption system includes at least a nanosecond laser, a second signal delay generator, and a second optical chopper; The first optical chopper and the second optical chopper are used to adjust the laser pulse repetition frequency, shorten or extend the nanosecond transient absorption test time, and achieve continuous testing in the time range from femtoseconds to milliseconds; The first signal delay generator and the second signal delay generator are used to synchronize the laser pulses of the femtosecond laser and the nanosecond laser and perform delay adjustment.

[0008] In a second aspect, the present invention provides a test method for an integrated system of femtosecond transient absorption and nanosecond transient absorption, comprising: Turn on the first signal delay generator, and output signals from the first signal delay generator to the femtosecond laser and the second signal delay generator; Use the femtosecond transient absorption test system to perform tests in the initial stage of transient absorption; Alternately collect the probe light passing through the test material in the pump-on state and the pump-off state through an optical fiber spectrometer to obtain the differential absorption spectrogram of femtosecond transient absorption; After the femtosecond transient absorption test is completed, install the detachable mirror and perform transient absorption tests through the nanosecond transient absorption system; Adjust the delay of the pump light and the probe light of nanosecond transient absorption through the second signal delay generator; Alternately collect the probe light passing through the test material in the pump-on state and the pump-off state through an optical fiber spectrometer to obtain the differential absorption spectrogram of nanosecond transient absorption; Merge the differential absorption spectrogram of femtosecond transient absorption and the differential absorption spectrogram of nanosecond transient absorption to obtain the final differential absorption spectrogram.

[0009] The above one or more technical solutions have the following beneficial effects: In the present invention, femtosecond transient absorption and nanosecond transient absorption are coupled to work together. The first optical chopper and the second optical chopper are introduced to modulate the repetition frequencies of the femtosecond laser and the nanosecond laser, shortening or extending the time range of the nanosecond transient absorption test. The measurements of fs-TA and ns-TA can be completed at one time, comprehensively covering the measurement from femtosecond to millisecond level.

[0010] Advantages of additional aspects of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The schematic diagrams in the specification forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0012] Figure 1 It is a schematic diagram of a femtosecond transient absorption - nanosecond transient absorption integrated system in an embodiment of the present invention; Figure 2 It is a schematic diagram of a zero - point calibration optical path in an embodiment of the present invention; Figure 3 It is a schematic diagram of the timing connection of a femtosecond transient absorption - nanosecond transient absorption system in an embodiment of the present invention; Figure 4(a) is a schematic diagram of the frequency relationship of the pump light, probe light, and chopper in femtosecond transient absorption in an embodiment of the present invention; Figure 4(b) is a schematic diagram of the frequency relationship of the pump light, probe light, and chopper in nanosecond transient absorption in an embodiment of the present invention, and the maximum delay time is 1 ms; Figure 4(c) is a schematic diagram of the frequency relationship of the pump light, probe light, and chopper in nanosecond transient absorption in an embodiment of the present invention, and the maximum delay time is 2 ms; Figure 5 It is a flowchart of the implementation process of femtosecond - nanosecond transient absorption test in an embodiment of the present invention; Among them, 1. femtosecond laser, 2. first beam splitter, 3. optical delay line, 4. first mirror, 5. optical parametric amplifier, 6. white light generation crystal, 7. first attenuation filter, 8. first parabolic mirror, 9. sample cell, 10. plano-convex lens, 11. fiber optic spectrometer, 12. computer, 13. first optical chopper, 14. second attenuation filter, 15. second parabolic mirror, 16. aperture, 17. nanosecond laser, 18. third attenuation filter, 19. second optical chopper, 20. third parabolic mirror, 21. removable mirror, 22. first signal delay generator, 23. second signal delay generator, 24. first signal generator, 25. second signal generator, 26. first photodetector, 27. second photodetector, 28. frequency counter, 29. filter, 30. second beam splitter. Detailed implementation manners

[0013] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. technical field of the present invention.

[0014] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present invention.

[0015] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0016] Embodiment 1 This embodiment discloses an integrated system for femtosecond transient absorption and nanosecond transient absorption, including: a femtosecond transient absorption test system, a nanosecond transient absorption system, and a timing control module; The femtosecond transient absorption test system and the nanosecond transient absorption system perform optical path switching on the probe light of femtosecond transient absorption and the probe light of nanosecond transient absorption through a removable mirror, and the pump light generated by the femtosecond transient absorption test system serves as the pump light for both femtosecond transient absorption and nanosecond transient absorption; The femtosecond transient absorption test system includes at least a femtosecond laser, a first signal delay generator, and a first optical chopper; The nanosecond transient absorption system includes at least a nanosecond laser, a second signal delay generator, and a second optical chopper; The first optical chopper and the second optical chopper are used to adjust the laser pulse repetition frequency, shorten or extend the nanosecond transient absorption test time, and achieve continuous testing in the time range from femtoseconds to milliseconds; The first signal delay generator and the second signal delay generator are used to synchronize the laser pulses of the femtosecond laser and the nanosecond laser and perform delay adjustment.

[0017] In this embodiment, the femtosecond transient absorption test system consists of a femtosecond laser, an optical parametric amplifier (OPA), a first optical chopper, an optical delay line, a white light generation crystal, and corresponding optical paths. The nanosecond transient absorption system consists of a nanosecond supercontinuum laser, a second optical chopper, and corresponding optical paths.

[0018] It should be noted that the femtosecond transient absorption device and the nanosecond transient absorption device are existing devices. The appearance of the above devices is to illustrate the integration method and technical principle of fs-TA and ns-TA.

[0019] The following combines Figure 1 to elaborate in detail on the integrated system of femtosecond transient absorption and nanosecond transient absorption in this embodiment. Among them, Module 1 is the optical path module of the femtosecond transient absorption test system, and Module 2 is the optical path module of the nanosecond transient absorption system: The optical path of Module 1 is as follows: The femtosecond laser 1 emits femtosecond laser pulses with a wavelength of 800 nm. After passing through the first beam splitter 2, 40% of the light energy enters the optical delay line 3, and 60% of the light energy passes through the first beam splitter 2 and enters the optical parametric amplifier 5 through the first mirror 4; The femtosecond laser pulses passing through the optical delay line 3 enter the white light generation crystal 6 to generate continuous white light. Here, the white light serves as the probe light for femtosecond transient absorption, namely probe1. Probe1 adjusts the intensity through the first attenuation sheet 7, and after being reflected by the first parabolic mirror 8, it is vertically focused on the surface of the sample. The focal plane of the first parabolic mirror 8 is located at the position of the sample cell 9; After passing through the sample, probe1 enters the fiber optic spectrometer 11 through the plano-convex lens 10, and the fiber optic spectrometer 11 collects data and transmits the collected data to the computer 12.

[0020] The femtosecond laser pulses pass through the first mirror 4 and enter the optical parametric amplifier 5. After passing through the optical parametric amplifier 5, monochromatic wavelength laser pulses in the range of 260 nm - 2600 nm can be obtained, which serve as the pump light, namely pump light; The pump light sequentially passes through the first optical chopper 13, namely chopper1, and the second attenuation sheet 14, and finally is reflected by the second parabolic mirror 15 and focused on the surface of the sample.

[0021] The optical path of Module 2 is as follows: The continuous white light emitted by the nanosecond laser 17, namely probe2, then probe2 sequentially passes through the third attenuation sheet 18, the second optical chopper 19, namely chopper2, the third parabolic mirror 20, and the removable mirror 21, and then is vertically focused on the surface of the sample; After passing through the sample, probe2 enters the fiber optic spectrometer 11 through the plano-convex lens 10.

[0022] It should be noted that before performing the ns-TA (nanosecond transient absorption) test, the aperture 16 should be closed first. The aperture 16 is used to block the femtosecond probe light, namely probe1.

[0023] The switching process of fs-TA (femtosecond transient absorption) and ns-TA (nanosecond transient absorption): fs-TA can achieve an optical delay of 8 ns through the optical delay line 3, that is, Figure 1 completed by Module 1 in []. The initial test of the 0 - 8 ns kinetic process of the transient absorption test is completed by femtosecond transient absorption. The excitation light is the pump light provided by the femtosecond laser 1, and the probe light is probe1. The test after 8 ns of the kinetic process of the transient absorption test is completed by ns-TA, that is, Figure 1 implemented by Module 2 in [].

[0024] The optical path switching between fs-TA and ns-TA is achieved through the removable mirror 21. After the fs-TA test is completed, the aperture 16 is closed to block probe1, and at the same time, the removable mirror 21 is installed to reflect the nanosecond continuous white light, that is, probe2, onto the sample surface.

[0025] Among them, the femtosecond transient absorption test system and the nanosecond transient absorption system share the sample cell 9, the plano-convex lens 10, and the fiber spectrometer 11.

[0026] In addition, the pump lights of fs-TA and ns-TA are both provided by the femtosecond laser 1, that is, the monochromatic laser pulse in the range of 260 nm - 2600 nm provided by the optical parametric amplifier 5 is used as the pump light.

[0027] This embodiment sets up a zero-point calibration optical path for time calibration. As shown in Figure 2 , the zero-point calibration optical path is located in the part from the sample cell 9 to the fiber spectrometer 11. The time calibration of fs-TA and ns-TA is completed by two photodetectors (Thorlabs, PDA10A2), that is, the first photodetector 26 and the second photodetector 27, and the frequency counter 28 (Pendulum, CNT90).

[0028] On the side of the sample cell 9 close to the fiber spectrometer 11, along the propagation directions of the pump light (i.e., the pump beam) and the probe light (i.e., the probe beam), a filter 29 and a second beam splitter 30 are respectively placed. The second beam splitter 30 reflects 5% of the probe light to the first photodetector 26, and the remaining probe light enters the fiber spectrometer 11 through the plano-convex lens 10. The pump light enters the second photodetector 27 through the filter 29. The optical paths of the two detectors, that is, the first photodetector 26 and the second photodetector 27, to the sample cell 9 are the same, ensuring no time difference. Signal Processing and Real-time Monitoring: The signal output terminals of the two photodetectors are respectively connected to the A port and B port of the frequency counter 28, namely Input A and Input B. The frequency counter 28 adopts the time difference measurement mode (time interval), calculates the time difference between the two photodetectors in real time, and reads the delay time of the pump light and probe light in real time through the connected computer 12.

[0029] Zero Point Calibration and Delay Adjustment: The fs-TA adjusts the optical delay line according to the time difference between the A port and B port of the frequency counter 28, so that the time difference between the pump light and probe light reaching the sample cell is zero. Due to the chirp effect, fine adjustment is also required according to the differential spectrogram before the test. Usually, the start point of the test is taken as the point when the differential spectrogram begins to change, and it is initialized as the zero point of the fs-TA in the program. The ns-TA adjusts the delay between the second signal delay generator 23, i.e., SDG2, and the first signal generator 24, i.e., SG1, according to the time difference between the A port and B port of the frequency counter 28, so that the time difference between the pump light and probe light is zero. It is initialized as the zero moment of the ns-TA in the program. This method can not only calibrate the zero point, but also monitor the delay of the pump light and probe light in real time. The femtosecond laser 1 uses a titanium sapphire laser, and the repetition frequency is adjustable from 1 - 1000 Hz. In this embodiment, 1000 Hz is taken as an example for illustration. The optical parametric amplifier 5, i.e., OPA, can provide laser pulses with a single-color wavelength range of 260 nm - 2600 nm.

[0030] The schematic diagram of the timing connection of the femtosecond-nanosecond transient absorption system is as Figure 3 shown. The first signal delay generator 22, i.e., SDG1, can be the timing control module built in the femtosecond laser 1. The CH3 port and CH4 port of the first signal delay generator SDG1 control the femtosecond laser and the first optical chopper chopper1 to work synchronously with a signal of 1000 Hz, and there is no delay between the CH3 port and CH4 port.

[0031] The chopping blade of the first optical chopper (Thorlab, MC2000B) can be selected according to the frequency of the femtosecond laser and the required output frequency. In this embodiment, MC1F10A is selected, and the duty cycle is adjustable from 0 - 50%.

[0032] Preferably, the following settings are adopted in this embodiment: Blade: (MC1F10A), Ref. In: EXT-INNER, Phase: 45°, duty cycle: 50%, Harm N: 1, Harm D: 2.

[0033] According to the frequency division formula of chopper1: , where represents the external input frequency, which is also 1000 Hz of SDG1. The numerator N represents Harm N, and the denominator D represents Harm D; represents the repetition frequency of the laser pulse after passing through the chopping plate. This means that the operating frequency after passing through Blade will be 1 / 2 of the reference signal frequency, which also means that the output frequency of the femtosecond laser pulse changes from 1000 Hz to 500 Hz. The CH5 port of SDG1 triggers the second signal delay generator 23, i.e., SDG2, as a synchronous signal. There is no delay between the CH3 port, CH4 port, and CH5 port of the first signal delay generator SDG1. There is no delay between the first signal delay generator SDG1 and the second signal delay generator SDG2.

[0034] The second signal delay generator SDG2 (SRS, DG645) can provide a delay signal with an accuracy of 5 ps and a delay range of 0 - 2000 ms. The channel delay between the CH1 - CH4 ports of the second signal delay generator SDG2 can be independently set. A pulse with a TTL amplitude is generated by a high-precision circuit and digitally controlled. The CH1 port of SDG2 is connected to the second optical chopper, i.e., chopper2. The CH2 port of the second signal delay generator SDG2 is connected to the EXT port of the first signal generator SG1 as the external trigger source of the first signal generator SG1. The first signal generator SG1 and the second signal generator SG2 are the control modules of the nanosecond laser. In this embodiment, the nanosecond laser is a white light laser with a pulse width of 0.8 ns, a wavelength range of 340 nm - 2150 nm, and a repetition frequency of 2000 Hz. The first signal generator SG1 provides a modulation signal for the nanosecond laser, and the second signal generator SG2 provides a laser emission control signal for the nanosecond laser. The first signal generator SG1 is triggered by the rising edge. The CH1 port is connected to the Trigger Modulation input port of the nanosecond laser. The pulse width of the CH1 port is 260 μs, the duty cycle is 52%, the frequency is 2000 Hz, and the delay time is 0. The CH1 port of the first signal generator SG1 simultaneously provides a trigger signal for the second signal generator SG2. The second signal generator SG2 is used to provide a laser emission control signal for the Trigger signal input port of the nanosecond laser. The second signal generator SG2 is also in the external trigger mode and is triggered by the falling edge. The pulse width of the CH1 port of the second signal generator SG2 is 250 μs, the duty cycle is 50%, the frequency is 2000 Hz, and the delay time is 0.

[0035] Under the coordinated operation of the first signal generator SG1 and the second signal generator SG2, the nanosecond laser can emit laser pulses at 2000 Hz. By changing the delay time between the second signal delay generator SDG2 and the first signal generator SG1, the delay time between the pump light emitted by the femtosecond laser and the probe2 light emitted by the nanosecond laser can be changed.

[0036] The frequency relationship among the pump light, probe1 light of fs-TA, and the first optical chopper is shown in Figure 4(a). The second optical chopper, i.e., chopper2, is used to change the frequency of the nanosecond laser pulse, i.e., probe2 light. Since the frequency of the femtosecond laser pulse, i.e., pump light, is 500 Hz after passing through chopper1, the frequency of probe1 light should be twice that of the pump light, which is 1000 Hz.

[0037] Correspondingly, the second optical chopper chopper2 of ns-TA is set as follows: Blade: (MC1F10A), Ref.In: EXT-INNER, Phase: 45°, Harm N: 1, Harm D: 2, duty cycle: 50%.

[0038] According to the frequency division formula , after the probe2 light passes through the second optical chopper chopper2, the repetition frequency of the probe2 light is 1000 Hz. Under this setting, the probe2 light collected by the fiber spectrometer can achieve alternating changes between the pump-on and pump-off states. In this case, the maximum delay can reach 1 ms. In this embodiment, the maximum delay time of ns-TA is 1 ms, and the frequency relationship among the pump light, probe2 light, and the second optical chopper is shown in Figure 4(b).

[0039] For example: If a longer delay time is required, the frequency division of the first optical chopper chopper1 and the second optical chopper chopper2 can be adjusted, and the repetition frequencies of the pump light and the probe2 light can be reduced according to the frequency division formula. It should be noted that the repetition frequency of the probe2 light should be twice that of the pump light. For example, when the Harm N of the first optical chopper chopper1 is 1, Harm D is 4, and the duty cycle is 25%, the repetition frequency of the pump light is 250 Hz; when the Harm N of the second optical chopper chopper2 is 1, Harm D is 4, and the duty cycle is 25%, the repetition frequency of the probe2 light is 500 Hz. Theoretically, the maximum delay of the pump light and the probe2 light can reach 2 ms. That is, the maximum value of the delay time is the period of chopper2. In this embodiment, the maximum delay time of ns-TA is 2 ms, and the frequency relationship among the pump light, the probe2 light, and the second optical chopper is shown in Fig. 4(c).

[0040] The output port of the first optical chopper chopper1 is connected to the EXT port of the fiber optic spectrometer to control the working time of the fiber optic spectrometer. Under this setting, the working frequency of the fiber optic spectrometer is the same as that of the probe light, and the probe light passing through the material in the pump-on and pump-off states can be collected. Moreover, the fiber optic spectrometer is controlled by chopper2 and is not affected by the delay between the second signal delay generator SDG2 and the first signal generator SG1.

[0041] Optionally, the fiber optic spectrometer is an AvaSpec-ULS2048CL-EVO spectrometer, and the integration time is 9 μs - 59 s.

[0042] Preferably, the integration time of the fiber optic spectrometer is set to 100 μs.

[0043] In this embodiment, the repetition frequencies of the femtosecond laser and the nanosecond laser are modulated by an optical chopper in combination with a timing control module, and the femtosecond transient absorption (fs-TA) and the nanosecond transient absorption (ns-TA) are coupled to work together to realize the alternating detection of the excited state spectrum (pump-on-probe) and the non-excited state spectrum (pump-off-probe); and the differential absorption spectrum (ΔA) is calculated based on the differential spectrum formula, and finally the three-dimensional data within the delay range from femtoseconds to milliseconds is obtained.

[0044] Embodiment 2 This embodiment proposes a test method for a femtosecond transient absorption and nanosecond transient absorption integrated system, including: Turn on the first signal delay generator, and output a signal from the first signal delay generator to the femtosecond laser and the second signal delay generator; Use a femtosecond transient absorption test system to perform tests in the initial stage of transient absorption; Alternately collect the probe light passing through the test material in the pump-on state and the pump-off state by means of an optical fiber spectrometer to obtain a differential absorption spectrogram of femtosecond transient absorption; After the femtosecond transient absorption test is completed, install a removable mirror and perform a transient absorption test using a nanosecond transient absorption system; Adjust the delay of the pump light and the probe light of the nanosecond transient absorption through the second signal delay generator; Alternately collect the probe light passing through the test material in the pump-on state and the pump-off state by means of an optical fiber spectrometer to obtain a differential absorption spectrogram of nanosecond transient absorption; Merge the differential absorption spectrogram of femtosecond transient absorption and the differential absorption spectrogram of nanosecond transient absorption to obtain the final differential absorption spectrogram.

[0045] The following combines Figure 5 Taking a material with a kinetic process tested up to a long delay time of 1.5 ms as an example, the implementation process of femtosecond-nanosecond transient absorption testing is described in detail: Step 1: Turn on SDG1 and output a 1 kHz signal to the femtosecond laser and SDG2.

[0046] After receiving the trigger signal, SDG2 sends out a 1 kHz pulse signal to the first signal generator SG1. The first signal generator SG1 generates a modulation signal with a frequency of 2 kHz and a pulse width of 260 μs, which is connected to the TriggerModulation input port of the nanosecond laser. At the same time, the first signal generator SG1 sends out a 2 kHz signal to trigger the second signal generator SG2. The two-signal generator SG2 uses a falling-edge trigger to generate a square wave signal with a frequency of 2 kHz and a pulse width of 250 μs to provide a laser emission control signal for the Trigger signal input of the nanosecond laser. Thus, the femtosecond laser and the nanosecond laser respectively emit laser pulses of 1 kHz and 2 kHz.

[0047] Step 2: In the initial stage of the transient absorption test, use a femtosecond transient absorption system for testing.

[0048] The femtosecond laser emits femtosecond pulses at 1 kHz, 60% of which enters the optical parametric amplifier to generate laser pulses with a monochromatic wavelength in the range of 260 nm - 2600 nm as the pump light. After the pump light passes through the first optical chopper chopper1, the pulse frequency becomes 500 Hz. 40% of the light enters the optical delay line, providing an optical delay of 0 - 8 ns with a time resolution of 0.1 ps. The laser pulse passing through the optical delay line enters the white light generation crystal to generate continuous white light, namely probe1, as the probe light for femtosecond transient absorption, with a repetition frequency of 1 kHz.

[0049] Step 3: The first optical chopper chopper1 synchronously outputs a trigger signal to trigger the fiber spectrometer to continuously collect data twice.

[0050] The sampling period of the fiber spectrometer is 1 ms, the sampling rate is 1 kHz, and the integration time is set to 100 μs. Under this design, the fiber spectrometer can alternately record the probe light in the pump-on and pump-off states. The fiber spectrometer collects the spectrum according to the Ref output signal of the first optical chopper chopper1. In two consecutive collections, the first is the probe light in the pump-on state, and the second is the probe light in the pump-off state. To improve the signal-to-noise ratio, 10 data points are collected and averaged at each delay time as the spectral data at that delay time.

[0051] The differential absorption spectrum is calculated by the following formula:

[0052] where, is the transmitted light in the pump-on state, is the transmitted light in the pump-off state.

[0053] Step 4: By controlling the stepping of the optical delay line through a program, a differential absorption spectrum diagram with a delay time of 0 - 8 ns can be obtained, and finally three-dimensional data is generated . The distribution of the delay times is controlled by the program and can be set in a linear uniform distribution or an exponential distribution within 8 ns.

[0054] After the femtosecond transient absorption test is completed, the program pauses to wait for the switching of the nanosecond transient absorption.

[0055] A removable mirror is placed to reflect the nanosecond continuous white light, namely probe2, onto the sample surface, and the parameter settings of the first optical chopper chopper1 and the second optical chopper chopper2 are adjusted according to the requirements of the delay time.

[0056] Taking the delay time of 1.5 ms as an example, the parameter settings of the first optical chopper chopper1 and the second optical chopper chopper2 are adjusted through the program: Harm N: 1, Harm D: 4, dutycycle: 25% for the first optical chopper chopper1; Harm N: 1, Harm D: 4, duty cycle: 25% for the second optical chopper chopper2. Under this setting, the repetition frequency of the pump light is 250 Hz, and the repetition frequency of the probe2 is 500 Hz, that is, the time interval of the probe2 light between pump-on and pump-off is 2 ms, which can meet the delay requirement of 1.5 ms. In this embodiment, the frequency relationship among the pump light, the probe2 light and the second optical chopper of the ns-TA is shown in Fig. 4(c).

[0057] Step 6: The delay of the femtosecond laser pump and the nanosecond continuous white light probe2 is controlled by the second signal delay generator SDG2.

[0058] The timing signal schematic diagram of the femtosecond-nanosecond transient absorption system is as Figure 3 shown. The second signal delay generator SDG2 can provide a delay signal with an accuracy of 5 ps and a delay range of 0 - 2000 ms.

[0059] Step 7: After the excitation light (pump-on) passes through the first optical chopper chopper1, the pulse frequency becomes 250 Hz, that is, the period is 4 ms. The data acquisition process is the same as that of the femtosecond transient absorption. The first optical chopper chopper1 synchronously outputs a trigger signal to trigger the fiber optic spectrometer to continuously collect 2 times. The sampling period of the fiber optic spectrometer is 2 ms, the sampling rate is 500 Hz, and the integration time is set to 100 μs. Under this design, the fiber optic spectrometer can alternately record the probe light in the pump-on and pump-off states.

[0060] Step 8: The fiber optic spectrometer collects the spectrum according to the Ref output signal of the first optical chopper chopper1. In the two consecutive acquisitions, the first time is the probe light in the pump-on state, and the second time is the probe light in the pump-off state.

[0061] To improve the signal-to-noise ratio, 10 sets of data are collected at each delay time and averaged as the spectral data at this delay time. The differential absorption spectrum is calculated by the following formula:

[0062] where is the transmitted light in the pump-on state, Is the transmitted light in the pump-off state.

[0063] Step 9: By controlling the step of the second signal delay generator SDG2 through the program, differential absorption spectra within the delay range of 8 ns to 1.5 ms can be obtained, and finally three-dimensional data is generated. . The distribution of the delay moments is controlled by the program and can be set according to linear uniform distribution or exponential distribution.

[0064] Step 10: Combine the three-dimensional data of the differential spectra of femtosecond transient absorption from 0 to 8 ns with the three-dimensional data of the differential spectra of nanosecond transient absorption from 8 ns to 1.5 ms and save them as a single file.

[0065] Among them, the fs-TA test is Steps 1 - 4, and the ns-TA test is Steps 5 - 10.

[0066] In this embodiment, through signal control and optical path design, fs-TA and ns-TA are integrated together to complete the full-process test of femtosecond-nanosecond transient absorption at one time. By modulating the pulse frequencies of the femtosecond laser and the nanosecond laser with an optical chopper, the ns-TA delay time can be adjusted to achieve long-delay transient absorption tests at the millisecond level.

[0067] The solution of this embodiment can adjust the maximum delay time of nanosecond transient absorption according to the material kinetic lifetime to meet the test requirements of long-delay transient absorption at the millisecond level.

[0068] Although the specific implementation manners of the present invention are described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made without creative efforts by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A femtosecond transient absorption and nanosecond transient absorption integrated system, characterized in that: include: Femtosecond transient absorption test system, nanosecond transient absorption system and timing control module; The femtosecond transient absorption test system and the nanosecond transient absorption system switch the optical paths of the detection light of femtosecond transient absorption and the detection light of nanosecond transient absorption through a detachable reflector, and the pump light generated by the femtosecond transient absorption test system is used as the pump light of femtosecond transient absorption and nanosecond transient absorption respectively; The femtosecond transient absorption test system at least includes a femtosecond laser, a first signal delay generator and a first optical chopper; The nanosecond transient absorption system at least includes a nanosecond laser, a second signal delay generator and a second optical chopper; The first optical chopper and the second optical chopper are used to adjust the laser pulse repetition frequency, shorten or extend the nanosecond transient absorption test time, and realize continuous testing in the femtosecond to millisecond time range; The first signal delay generator and the second signal delay generator are used to synchronize the laser pulses of the femtosecond laser and the nanosecond laser and to perform delay adjustment.

2. The femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 1, characterized in that: The femtosecond transient absorption test system and the nanosecond transient absorption system share a sample cell and a fiber optic spectrometer, and a zero point calibration optical path is arranged between the sample cell and the fiber optic spectrometer for time calibration.

3. The femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 2, characterized in that: The zero point calibration optical path includes a first photodetector, a second photodetector, a second beam splitter, a filter, a plano-convex lens and a frequency counter; Wherein, the second beam splitter is used to split the detection light into two beams, one of which is reflected to the first photodetector, and the other enters the fiber optic spectrometer after passing through the plano-convex lens; The pump light enters the second photodetector after being filtered by the filter; The frequency counter is used to calculate the time difference between the first photodetector and the second photodetector, and then obtain the delay time of the detection light and the pump light.

4. The femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 1, characterized in that: The first signal delay generator synchronously sends signals to the femtosecond laser, the first photoelectric chopper and the second signal delay generator, so that the femtosecond laser, the first photoelectric chopper and the second signal delay generator work synchronously.

5. A femtosecond transient absorption and nanosecond transient absorption integrated system as claimed in claim 1 or 4, characterized in that: The second signal delay generator is connected to the second photoelectric chopper and the first signal generator respectively; the first signal generator provides a modulation signal for the nanosecond laser, and the delay time between the femtosecond laser and the nanosecond laser can be changed by changing the delay time between the second signal delay generator and the first signal generator.

6. The femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 2, characterized in that: The fiber optic spectrometer is used to collect the probe light passing through the test material in the pump-on state and the pump-off state, calculate the differential absorption spectrum, and generate three-dimensional data in the femtosecond to millisecond time range.

7. The femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 1, characterized in that: The first optical chopper and the second optical chopper are used to adjust the laser pulse repetition frequency so that the detection light repetition frequency is twice that of the pump light.

8. The femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 1, characterized in that: The femtosecond transient absorption test system is used to complete the excited state initial dynamics test in the time range of 0 to 8 ns; the nanosecond transient absorption system is used to complete the dynamic process test in the time range of 8 ns to a preset delay time.

9. A method for testing an integrated system of femtosecond transient absorption and nanosecond transient absorption, characterized in that: include: Turning on the first signal delay generator, outputting a signal to the femtosecond laser and the second signal delay generator through the first signal delay generator; The femtosecond transient absorption test system is used to test the initial stage of transient absorption; The fiber optic spectrometer is used to alternately collect the probe light passing through the test material in the pump-on state and the pump-off state to obtain the differential absorption spectrum of the femtosecond transient absorption; After the femtosecond transient absorption test is completed, a detachable reflector is installed and a transient absorption test is performed using a nanosecond transient absorption system; The delay of the pump light and the detection light of the nanosecond transient absorption is adjusted by the second signal delay generator; The fiber optic spectrometer is used to alternately collect the probe light passing through the test material in the pump-on state and the pump-off state to obtain the differential absorption spectrum of nanosecond transient absorption; The differential absorption spectrum of the femtosecond transient absorption and the differential absorption spectrum of the nanosecond transient absorption are combined to obtain a final differential absorption spectrum.

10. The method for testing a femtosecond transient absorption and nanosecond transient absorption integrated system according to claim 9, characterized in that: According to the delay time requirement, the parameter settings of the first optical chopper and the second optical chopper are adjusted.

Images