A transient fluorescence detection system with sub-arcminute pulse width resolution

Abstract

The application provides a transient fluorescence detection system with sub-gate pulse width time resolution, comprising: a gate pulse generation system configured to generate gate pulses required for transient fluorescence detection based on first fundamental frequency light input thereto; an ultrashort pulse generation system configured to generate a few-cycle magnitude femtosecond pulse based on second fundamental frequency light input thereto; a fluorescence generation system located downstream of the ultrashort pulse generation system and configured to use the few-cycle magnitude femtosecond pulse as fluorescence excitation light to excite a sample to generate fluorescence; and an optical parametric fluorescence amplification system located downstream of the gate pulse and the fluorescence and configured to amplify the part of the fluorescence that is coincident in time and space with the gate pulse through optical parametric amplification, thereby realizing transient fluorescence detection. When the ultrashort pulse is used as an excitation light source, the optimal time resolution of the transient fluorescence detection can reach 60 femtoseconds, the time resolution limit of optical parametric transient fluorescence detection can be broken through, and sub-gate pulse width time resolution less than the gate pulse width can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrum measurement, in particular to a transient fluorescence detection system with sub-threshold pulse width time resolution. Background Art

[0002] Ultrafast time-resolved fluorescence spectroscopy can directly reveal the dynamics of excited states of matter. Its simple spectral composition makes it an important tool for studying physicochemical processes such as excited-state relaxation, energy transfer, and charge transfer in various condensed matter systems. It has been widely used in research fields such as photophysics, photochemistry, and optoelectronic materials. Time-resolved fluorescence measurement techniques can be primarily categorized into electrical and optical methods. Limited by the timescale of electronic response, electrical measurement methods such as single-photon counting and streak cameras generally struggle to achieve temporal resolution exceeding picoseconds. With the advancement of ultrafast laser technology, pulse widths have gradually shortened and peak powers have steadily increased. Techniques such as optical Kerr switching and fluorescence upconversion, based on nonlinear optical effects, utilize ultrashort pulses as optical gate pulses, making it relatively easy to achieve femtosecond time resolution for transient fluorescence detection. These techniques have been successfully applied to studying ultrafast fluorescence dynamics in excited states of systems such as dye molecules.

[0003] Three factors primarily limit the temporal resolution of transient fluorescence detection: the pulse width of the fluorescence excitation light, the gate pulse width, and the group velocity dispersion of the nonlinear crystal. For optical detection methods such as fluorescence upconversion and optical Kerr gates, the signal conversion efficiency is approximately proportional to the gate pulse intensity. Without considering dispersion, the temporal resolution depends primarily on the time-domain convolution of the excitation pulse and gate pulse widths. Therefore, the gate pulse width becomes the primary factor limiting the temporal resolution of these techniques.

[0004] Optical parametric fluorescence amplification technology is a new optical measurement method. It uses the fluorescent seed light radiated by the sample as the signal light and performs non-collinear optical parametric amplification on it in a parametric crystal. It has a high sensitivity of up to 10 6 The optical gain is high, with both wide-spectrum detection and femtosecond time resolution. Existing optical parametric fluorescence amplification technology can achieve a time resolution of 100 fs when the gate pulse width for fluorescence detection is approximately 70 fs, which is greater than the gate pulse width.

[0005] A temporal resolution of 100 fs is sufficient for most ultrafast experimental applications. However, for processes such as intramolecular vibrational relaxation, internal conversion, electron transfer, and resonant energy transfer in complex molecular systems, the time scale is less than 100 fs, and the temporal resolution of transient fluorescence detection needs to be further improved. Therefore, it is urgent to develop a transient fluorescence detection scheme with a temporal resolution smaller than the gate pulse width. Summary of the Invention

[0006] In view of the above problems, the present invention proposes a transient fluorescence detection system with sub-threshold pulse width time resolution, which overcomes the above problems or at least partially solves the above problems.

[0007] One object of the present invention is to improve the temporal resolution of transient fluorescence detection by using femtosecond pulses of a small cycle magnitude as a fluorescence excitation light source to obtain a temporal resolution of sub-gate pulse width.

[0008] Another object of the present invention is to utilize non-collinear optical parametric amplification technology supplemented by pulse compression means to obtain femtosecond pulses of a small cycle order.

[0009] In particular, the present invention provides a transient fluorescence detection system with sub-hierarchical pulse width time resolution, comprising:

[0010] a gate pulse generating system configured to generate a gate pulse required for transient fluorescence detection based on the first fundamental frequency light input thereto;

[0011] An ultrashort pulse generation system configured to generate a femtosecond pulse of a few cycles based on a second fundamental frequency light input thereto;

[0012] a fluorescence generating system, located downstream of the ultrashort pulse generating system, configured to use a few-cycle femtosecond pulse as fluorescence excitation light to excite the sample to generate fluorescence; and

[0013] The optical parametric fluorescence amplification system is located downstream of the gate pulse and the fluorescence and is configured to amplify the portion of the fluorescence that overlaps with the gate pulse in time and space through optical parametric amplification, thereby realizing transient fluorescence detection.

[0014] Optionally, the pulse width of the few-cycle femtosecond pulse is less than or equal to 20 fs;

[0015] The ultrashort pulse generation system includes:

[0016] a supercontinuum white light generating unit configured to generate supercontinuum broadband white light based on the first light beam from the second fundamental frequency light;

[0017] a pump light generating unit configured to generate pump light required for non-collinear optical parametric amplification based on a second light beam from the second fundamental frequency light;

[0018] a non-collinear optical parametric amplification unit, located downstream of the supercontinuum broadband white light and the pump light, configured to perform non-collinear optical parametric amplification on the portion of the supercontinuum broadband white light and the pump light that overlaps in time and space to obtain a broadband pulse; and

[0019] The pulse compression unit is located downstream of the non-collinear optical parametric amplifier unit and is configured to perform dispersion compensation on the wide-spectrum pulse to obtain a femtosecond pulse of a small cycle level.

[0020] Optionally, the non-collinear optical parametric amplification unit includes:

[0021] a time delay unit, located downstream of the pump light generating unit, configured to change the time delay of the pump light relative to the supercontinuum broadband white light;

[0022] a first optical parametric crystal configured to perform non-collinear optical parametric amplification on portions of the supercontinuum broadband white light and the pump light that overlap in time and space;

[0023] a first focusing optical element, located upstream of the first optical parametric crystal and downstream of the supercontinuum white light generating unit, configured to focus the supercontinuum broadband white light onto the first optical parametric crystal; and

[0024] The second focusing optical element, located upstream of the first optical parametric crystal and downstream of the time delay unit, is configured to focus the pump light onto the first optical parametric crystal.

[0025] Optionally, the pulse compression unit includes at least one of a chirped mirror, a prism pair, a grating pair, and a pulse shaper.

[0026] Optionally, the ultrashort pulse generation system further includes:

[0027] a half-wave plate, located upstream of the supercontinuum white light generating unit and the pump light generating unit, configured to rotate the polarization of the second fundamental frequency light by 90°;

[0028] a first beam splitter, located upstream of the supercontinuum white light generating unit and the pump light generating unit and downstream of the half-wave plate, configured to split the polarization-rotated second fundamental frequency light into a first light beam and a second light beam at a specified splitting ratio; and

[0029] The beam collimating element is located downstream of the non-collinear optical parametric amplifier unit and upstream of the pulse compression unit, and is configured to collimate the wide-spectrum pulse beam amplified by the non-collinear optical parametric amplifier unit.

[0030] Optionally, the transient fluorescence detection system further includes:

[0031] a pulse characterization system, located downstream of the ultrashort pulse generation system, configured to measure characteristics of a few-cycle femtosecond pulse generated by the ultrashort pulse generation system, the characteristics including pulse width and phase information; and

[0032] The pulse repetition frequency modulation system is located downstream of the pulse characterization system and upstream of the fluorescence generation system, and is configured to periodically modulate a few-cycle femtosecond pulse to provide a modulation frequency for the fluorescence excitation light of the fluorescence generation system.

[0033] Optionally, the fluorescence generating system comprises:

[0034] Sample rack, used to place samples;

[0035] a fluorescence excitation unit, located downstream of the ultrashort pulse generation system and upstream of the sample holder, configured to adjust the polarization and intensity of the fluorescence excitation light and focus it onto the sample surface to excite the sample to radiate fluorescence; and

[0036] The fluorescence collection unit is located downstream of the sample holder and is configured to collect fluorescence radiated by the sample.

[0037] Optionally, the optical parametric fluorescence amplification system includes:

[0038] a second optical parametric crystal configured to perform optical parametric amplification on a portion of the fluorescence that overlaps with the gate pulse in time and space;

[0039] a third focusing optical element, located upstream of the second optical parametric crystal and downstream of the gate pulse generation system, configured to focus the gate pulse on the second optical parametric crystal; and

[0040] The fluorescence focusing unit is located upstream of the second optical parametric crystal and downstream of the fluorescence generating system, and is configured to focus the fluorescence on the second optical parametric crystal.

[0041] Optionally, the transient fluorescence detection system further includes:

[0042] a femtosecond laser light source configured to generate laser pulses;

[0043] a second beam splitter, located downstream of the femtosecond laser light source and upstream of the gate pulse generation system and the ultrashort pulse generation system, configured to split the laser pulse into a first fundamental frequency light and a second fundamental frequency light; and

[0044] The optical path delay system is located upstream of the gate pulse generating system and downstream of the second beam splitter, and is configured to change the time delay between the fluorescence as the seed light and the gate pulse as the pump light in the optical parametric fluorescence amplification system by changing the optical path of the first fundamental frequency light.

[0045] Optionally, the transient fluorescence detection system further includes:

[0046] a fluorescence coupling system, located downstream of the optical parametric fluorescence amplification system, configured to couple the fluorescence signal amplified by the optical parametric fluorescence amplification system into the data acquisition system; and

[0047] a data acquisition system, located downstream of the fluorescence coupling system, for acquiring the amplified fluorescence signal to obtain a transient fluorescence signal;

[0048] Among them, the data acquisition system includes a grating polychromator and a spectral detector.

[0049] The transient fluorescence detection system provided by the present invention is based on optical parametric fluorescence amplification technology. By using femtosecond pulses of a few cycles generated by an ultrashort pulse generation system as a fluorescence excitation light source to excite the sample to generate fluorescence as the seed light for optical parametric fluorescence amplification, and using gate pulses generated by a gate pulse generation system as the pump light for optical parametric fluorescence amplification, a transient fluorescence detection time resolution of sub-gate pulse width is achieved.

[0050] Furthermore, the transient fluorescence detection system provided by the present invention utilizes a non-collinear optical parametric amplification unit to obtain a wide-spectrum signal light in the visible light band, supplemented by pulse compression means for dispersion compensation, to obtain femtosecond pulses of a small cycle order, thereby ensuring the time resolution of sub-gate pulse width in the optical parametric fluorescence amplification system.

[0051] Furthermore, the transient fluorescence detection system provided by the present invention utilizes a pulse characterization system to measure the characteristics (including pulse width, phase information, power, etc.) of the few-cycle femtosecond pulses generated by the ultrashort pulse generation system, thereby better monitoring the quality of the few-cycle femtosecond pulses to further ensure the time resolution of the sub-gate pulse width.

[0052] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are specifically listed below.

[0053] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference numerals in the accompanying drawings designate the same or similar components or parts. It should be understood by those skilled in the art that the drawings are not necessarily drawn to scale. In the accompanying drawings:

[0055] Figure 1 This is a diagram of the working principle of optical parametric fluorescence amplification;

[0056] Figure 2 is a schematic structural block diagram of a transient fluorescence detection system with sub-gate pulse width time resolution according to an embodiment of the present invention;

[0057] Figure 3 1 is a schematic diagram of the optical path structure of a transient fluorescence detection system with sub-threshold pulse width time resolution according to another embodiment of the present invention;

[0058] Figure 4 1 is a schematic diagram of the optical path structure of a pulse characterization system in a transient fluorescence detection system with subthreshold pulse width time resolution according to an embodiment of the present invention;

[0059] Figure 5 is a spectrum diagram of the spectrum tuning result of the wide-spectrum signal light output by the non-collinear optical parametric amplifier unit according to one embodiment of the present invention;

[0060] Figure 6a and Figure 6b This is a spectrum of characteristic measurement results of a femtosecond pulse of a few cycles generated by an ultrashort pulse generation system using a dispersion scanning method by a pulse characterization system according to one embodiment of the present invention;

[0061] Figure 6c and Figure 6d They are respectively a measured dispersion scanning two-dimensional spectrum according to an embodiment of the present invention and a dispersion scanning two-dimensional spectrum reconstructed by an inversion algorithm;

[0062] Figure 7 FIG. 4 is a graph showing the test results of the time resolution of an optical parametric fluorescence amplification system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0063] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0064] The inventors of this application have been dedicated to the development of optical parametric fluorescence amplification technology. Through research, they discovered that, for large-signal optical parametric fluorescence amplification, the gain is related to the gate pulse intensity, with the intensity's influence manifesting in an exponential term. This means that the amplification efficiency of signals temporally coinciding with the gate pulse peak is significantly higher than that of signals on either side of the gate pulse. This principle analysis demonstrates that, compared to optical detection methods such as fluorescence upconversion and optical Kerr gates, optical parametric fluorescence amplification offers the potential to achieve a temporal resolution for transient fluorescence detection that is smaller than the gate pulse width.

[0065] Figure 1A diagram of the operating principle of optical parametric fluorescence amplification (OPF) is presented. Generally, a femtosecond pulse (800nm, 70fs) output by a Ti:Sapphire femtosecond laser source serves as a pump source and is split into two paths. One path, after frequency doubling through a β-phase barium metaborate crystal (θ = 29.2°, φ = 0°) in a gate pulse generation system, serves as the pump light for the OPA, i.e., the gate pulse for fluorescence detection (with a pulse width of approximately 70fs). The other path pumps an ultrashort pulse device, serving as the excitation light for the fluorescence generation system. The ultrashort pulse device typically uses a commercially available tunable frequency conversion device. Its principle is essentially collinear optical parametric amplification to generate signal and idler light in the near-infrared range. Through nonlinear frequency conversion methods such as frequency doubling, sum frequency conversion, and difference frequency conversion, continuously tunable femtosecond laser pulses from the ultraviolet to the near-infrared range are generated. The central wavelength of the excitation light is set to 650nm, and the kinetic curve of the scattered light after parametric amplification is recorded, i.e., the instrument response function. Gaussian fitting of the curve yields a half-maximum width of 100fs, with a temporal resolution greater than the gate pulse width. This is because the collinear configuration gain bandwidth of commercial tunable frequency conversion devices is narrow and they are not equipped with dispersion compensation function. The pulse width of their output is generally 1.25 to 1.5 times that of the femtosecond laser light source. Therefore, the excitation light pulse width becomes the main factor limiting the improvement of time resolution.

[0066] As mentioned earlier, the gain of optical parametric fluorescence amplification technology is exponentially dependent on the gate pulse intensity. Therefore, if the pulse width of the excitation light output by the ultrashort pulse device can be made much smaller than the gate pulse width, there is hope of breaking through the limitation of the gate pulse width and achieving a time resolution smaller than the gate pulse width (i.e., sub-gate pulse width).

[0067] Based on the above research and findings, the present invention proposes a transient fluorescence detection system 100 with sub-threshold pulse width time resolution.

[0068] Figure 2 FIG is a schematic structural block diagram of a transient fluorescence detection system 100 with sub-threshold pulse width time resolution according to an embodiment of the present invention. Figure 2As shown, the transient fluorescence detection system 100 generally includes a gate pulse generation system 110, an ultrashort pulse generation system 120, a fluorescence generation system 130, and an optical parametric fluorescence amplification system 140. The gate pulse generation system 110 is configured to generate the gate pulse required for transient fluorescence detection based on a first fundamental frequency light input thereto. The ultrashort pulse generation system 120 is configured to generate a few-cycle femtosecond pulses based on a second fundamental frequency light input thereto. The fluorescence generation system 130 is located downstream of the ultrashort pulse generation system 120 and is configured to use the few-cycle femtosecond pulses as fluorescence excitation light to excite the sample to produce fluorescence. The optical parametric fluorescence amplification system 140 is located downstream of the gate pulses generated by the gate pulse generation system 110 and the fluorescence generated by the fluorescence generation system 130 and is configured to amplify the portion of the fluorescence that overlaps in time and space with the gate pulse through optical parametric amplification, thereby achieving transient fluorescence detection.

[0069] For example, the first fundamental frequency light and the second fundamental frequency light are both 800 nm fundamental frequency light.

[0070] The transient fluorescence detection system 100 provided in an embodiment of the present invention is based on optical parametric fluorescence amplification technology. By using a femtosecond pulse of a few cycles generated by an ultrashort pulse generation system 120 as a fluorescence excitation light source to excite the sample to generate fluorescence as the seed light for optical parametric fluorescence amplification, and using the gate pulse generated by the gate pulse generation system 110 as the pump light for optical parametric fluorescence amplification, a transient fluorescence detection time resolution of sub-gate pulse width is obtained.

[0071] The gate pulse generation system 110 is used to frequency-convert the first fundamental frequency light into the pump light (i.e., gate pulse) required by the optical parametric fluorescence amplification system 140. In some specific embodiments, the 800nm ​​fundamental frequency light is frequency-doubled through a 2mm-thick β-phase barium metaborate crystal (θ = 29.2°, φ = 0°) to produce a 400nm pump light. Limited by the group velocity mismatch and phase matching bandwidth during the frequency-doubled frequency process, the gate pulse generated by the gate pulse generation system 110 has a pulse width slightly greater than the pulse width of the 800nm ​​fundamental frequency light (70 fs). For example, by selecting an appropriate frequency-doubled crystal, the gate pulse generated by the gate pulse generation system 110 can have a pulse width between 70 and 80 fs.

[0072] In some optional embodiments, the pulse width of the short-cycle femtosecond pulses generated by the ultrashort pulse generation system 120 is less than or equal to 20 fs. Preferably, the pulse width of the short-cycle femtosecond pulses is in the range of 10 fs to 20 fs. This ensures that the pulse width of the excitation light output by the ultrashort pulse generation system 120 is much smaller than the gate pulse width, thereby better achieving sub-gate pulse width temporal resolution.

[0073] Figure 3FIG. 1 is a schematic diagram of the optical path structure of a transient fluorescence detection system 100 with subthreshold pulse width time resolution according to another embodiment of the present invention.

[0074] See also Figure 3 As shown, in some embodiments, the ultrashort pulse generation system 120 may include: a supercontinuum white light generation unit 6, configured to generate supercontinuum broadband white light based on a first light beam from a second fundamental frequency light; a pump light generation unit 8, configured to generate pump light required for non-collinear optical parametric amplification based on a second light beam from the second fundamental frequency light; a non-collinear optical parametric amplification unit 121, located downstream of the supercontinuum broadband white light and the pump light, configured to perform non-collinear optical parametric amplification on a portion of the supercontinuum broadband white light and the pump light that overlaps in time and space to obtain a broadband pulse; and a pulse compression unit 16, located downstream of the non-collinear optical parametric amplification unit 121, configured to perform dispersion compensation on the broadband pulse to obtain a femtosecond pulse of a few cycles.

[0075] In the embodiment of the present invention, a non-collinear optical parametric amplifier unit 121 is used to obtain a wide-spectrum signal light in the visible light band, and pulse compression is used to compensate for dispersion, thereby obtaining a femtosecond pulse of a small cycle order, thereby ensuring the time resolution of the sub-gate pulse width in the optical parametric fluorescence amplification system 140.

[0076] The supercontinuum white light generating unit 6 is used to generate broadband white light in the visible light band, which serves as the signal light for the non-collinear optical parametric amplifier unit 121. In some specific embodiments, 800nm ​​fundamental frequency light is focused onto a 3mm thick sapphire crystal, resulting in nonlinear frequency expansion and a broadband light source with good coherence. The supercontinuum white light generated by the sapphire crystal covers the spectral range from the visible light to the near-infrared region. For ultraviolet supercontinuum white light generation, calcium fluoride crystals can be used instead.

[0077] The pump light generation unit 8 is used to convert the second fundamental frequency light into the pump light required by the non-collinear optical parametric amplifier unit 121. In some specific embodiments, the 800nm ​​fundamental frequency light is frequency-doubled by passing it through a 2mm-thick β-phase barium metaborate crystal (θ = 29.2°, φ = 0°) to generate a 400nm pump light. The 400nm pump light is then pulse-stretched by passing it through a 3cm-thick quartz block to better temporally overlap with the supercontinuum broadband white light signal light of different frequency components.

[0078] Continue to see Figure 3 In some embodiments, the non-collinear optical parametric amplification unit 121 may include a time delay unit 10 , a first optical parametric crystal 13 , a first focusing optical element 7 , and a second focusing optical element 11 .

[0079] The first focusing optical element 7 is located upstream of the first optical parametric crystal 13 and downstream of the supercontinuum white light generating unit 6, and is configured to focus the supercontinuum broadband white light on the first optical parametric crystal 13. Specifically, the first focusing optical element 7 can be a converging reflector, such as a concave reflector.

[0080] The time delay unit 10, located downstream of the pump light generating unit 8, is configured to vary the time delay of the pump light relative to the supercontinuum broadband white light. Specifically, the time delay unit 10 may comprise a linear translation stage and a pair of 400nm mirrors positioned at a 90° angle, one of which may be positioned on the linear translation stage. By manually moving the linear translation stage to change the distance between the two mirrors, the optical path length of the 400nm pump light is continuously varied, thereby adjusting the relative time delay between the pump light and the supercontinuum broadband white light signal.

[0081] The second focusing optical element 11 is located upstream of the first optical parametric crystal 13 and downstream of the time delay unit 10, and is configured to focus the pump light on the first optical parametric crystal 13. Specifically, the second focusing optical element 11 can be an ultraviolet plano-convex lens for focusing the 400 nm pump light on the first optical parametric crystal 13.

[0082] The first optical parametric crystal 13 is configured to perform non-collinear optical parametric amplification on the temporally and spatially overlapping portions of the supercontinuum broadband white light and the pump light. Specifically, the first optical parametric crystal 13 has a large second-order nonlinear optical coefficient. After being cut at a specific angle (e.g., θ = 31.5°, φ = 0°), the first optical parametric crystal 13 can achieve phase matching over a wide spectral range when the pump light is incident nearly parallel to the surface normal. In some specific embodiments, the first optical parametric crystal 13 can be made of β-phase barium metaborate.

[0083] In some embodiments, a reflector 12 may be further provided in the optical path between the second focusing optical element 11 and the first optical parametric crystal 13. The pump light passing through the time delay unit 10 is focused by the second focusing optical element 11 and then reflected by the reflector 12 into the first optical parametric crystal 13. The reflector 12 may be a 400 nm reflector, which can obtain a wavelength of less than 20 fs near the central wavelength of 400 nm. 2 The reflectivity for p-polarization is greater than 99%.

[0084] Those skilled in the art will appreciate that the pump light and signal light must overlap in time and space within the first optical parametric crystal 13 to achieve non-collinear optical parametric amplification. Spectral tuning can be achieved by adjusting the relative delay between the pump light and signal light and the angle (non-collinear angle) between the two beams.

[0085] Optionally, a reflector 9 may be provided in the optical path between the pump light generating unit 8 and the non-collinear optical parametric amplifier unit 121 to reflect the pump light generated by the pump light generating unit 8 and guide it into the non-collinear optical parametric amplifier unit 121. Specifically, the reflector 9 may be provided between the pump light generating unit 8 and the time delay unit 10. The reflector 9 may be a 400 nm reflector, which may obtain a wavelength of less than 20 fs near the central wavelength of 400 nm. 2 The reflectivity for p-polarization is greater than 99%.

[0086] The pulse compression unit 16 is used to compensate for the dispersion of the broadband pulses generated by non-collinear optical parametric amplification, achieving a relatively flat time-domain phase and generating femtosecond pulses with a low cycle count. In some embodiments, the pulse compression unit 16 can utilize dispersive elements such as chirped mirrors, prism pairs, and grating pairs to flexibly control the dispersion and offset dispersion introduced in the optical path. In other embodiments, the pulse compression unit 16 can also utilize a pulse shaper to achieve pulse compression.

[0087] Continue to see Figure 3 In some embodiments, the ultrashort pulse generation system 120 may further include a half-wave plate 4, located upstream of the supercontinuum white light generation unit 6 and the pump light generation unit 8, configured to rotate the polarization (e.g., p-polarization) of the second fundamental frequency light (e.g., 800 nm fundamental frequency light) by 90°; and a first beam splitter 5, located upstream of the supercontinuum white light generation unit 6 and the pump light generation unit 8 and downstream of the half-wave plate 4, configured to split the polarization-rotated second fundamental frequency light into a first light beam and a second light beam at a specified splitting ratio. Specifically, the first beam splitter 55 has a p-polarization splitting ratio of 98%:2% (transmission:reflection).

[0088] In some embodiments, the ultrashort pulse generation system 120 may further include a beam collimating element 14, located downstream of the non-collinear optical parametric amplifier 121 and upstream of the pulse compression unit 16, and configured to collimate the broad-spectrum pulse beam amplified by the non-collinear optical parametric amplifier 121. Specifically, the beam collimating element 14 may be a concave mirror.

[0089] Optionally, a reflector 15 may be provided in the optical path between the beam collimating element 14 and the pulse compression unit 16. After being amplified by the first optical parametric crystal 13, the broad-spectrum signal beam is collimated by the beam collimating element 14 and then reflected by the reflector 15 before entering the pulse compression unit 16. Specifically, the reflector 15 may be a plane reflector with a silver-plated surface having a reflectivity greater than 95% in the visible light band.

[0090] Continue to see Figure 3In some embodiments, the transient fluorescence detection system 100 may further include a pulse characterization system 17. The pulse characterization system 17 is located downstream of the ultrashort pulse generation system 120 and is configured to measure the characteristics of the femtosecond pulses of the few-cycle order generated by the ultrashort pulse generation system 120. The characteristics include pulse width, phase information, power, intensity, etc.

[0091] The embodiment of the present invention utilizes the pulse characterization system 17 to measure the characteristics (including pulse width, phase information, power, etc.) of the few-cycle femtosecond pulses generated by the ultrashort pulse generation system 120, so as to better monitor the quality of the few-cycle femtosecond pulses and further ensure the time resolution of the sub-gate pulse width.

[0092] Pulse characterization methods can include pulse autocorrelation, frequency-resolved optical switching, spectral interferometry, or dispersion scanning.

[0093] In one specific embodiment, dispersion scanning is used for pulse characterization. The pulse characterization system 17 may include a pair of antiparallel optical wedges and a 10μm-thick β-phase barium metaborate crystal placed downstream of the pair of wedges. After passing through the pair of wedges, the compressed pulse is focused in the β-phase barium metaborate crystal. By continuously varying the amount of wedge insertion, a dispersion scanning trajectory can be obtained, and an inversion algorithm can be used to obtain the pulse's time domain information, thereby achieving pulse characterization. Characterization using dispersion scanning eliminates the need for beam splitting to generate reference pulses, allowing direct measurement of individual pulses, simplifying the structure of the pulse characterization system 17.

[0094] Figure 4 FIG. 1 is a schematic diagram of the optical path structure of the pulse characterization system 17 in the transient fluorescence detection system 100 with subthreshold pulse width time resolution according to an embodiment of the present invention. Figure 4 As shown, in one specific embodiment, the pulse characterization system 17 includes a pair of antiparallel optical wedges 171, an off-axis parabolic mirror 172, a β-phase barium borate (BBO) crystal 173 (specifically, 10 μm thick) arranged along the optical path from upstream to downstream, a fundamental frequency light collimator 174 (specifically, a fused silica lens), another optical wedge 175, a filter 176 (specifically, a UV filter), a focusing element 177 (such as a fused silica lens), and a data acquisition system 178. The data acquisition system 178 can be the same system as the data acquisition system 32 of the transient fluorescence detection system 100, which will be described later. This reduces the number of components and lowers the cost of the transient fluorescence detection system 100. Of course, the data acquisition system 177 can also be independent of the data acquisition system 32.

[0095] Optionally, reflectors 179 and 180 may be further provided in the optical path between the optical wedge 171 and the off-axis parabolic mirror 172 for reflecting and directing the pulses into the off-axis parabolic mirror 172 .

[0096] In a specific dispersion scanning example, the dispersion-compensated femtosecond pulse output by the pulse compression unit 16 passes through a pair of antiparallel quartz wedges 171 and is focused by an off-axis parabolic mirror 172 into a 10-μm-thick β-phase barium metaborate crystal 173 downstream of the pair of wedges for frequency doubling. A fused silica lens 174 downstream of the barium metaborate crystal 173 collimates the frequency-doubled light and the residual transmitted fundamental frequency light, which are then incident on a quartz wedge 175 at the Brewster angle, resulting in polarization-selective reflection of the frequency-doubled signal. The frequency-doubled signal is further filtered out by an ultraviolet filter 176 downstream of the quartz wedge 175 to remove the remaining fundamental frequency signal. The signal is then focused and coupled into an optical fiber by a fused silica lens 177, where a data acquisition system 178 records the spectrum and intensity of the frequency-doubled signal. By continuously varying the insertion distance of one of the wedges 171, a dispersion scanning trajectory can be obtained. Using an inversion algorithm, the time-domain information of the pulse is obtained, enabling measurement of the pulse width output by the pulse compression unit 16.

[0097] In some embodiments, the transient fluorescence detection system 100 may further include a pulse repetition frequency modulation system 18, which is located downstream of the pulse characterization system 17 and upstream of the fluorescence generation system 130, and is configured to periodically modulate femtosecond pulses of a few cycles to provide a modulation frequency for the fluorescence excitation light of the fluorescence generation system 130.

[0098] Optionally, the pulse repetition frequency modulation system 18 can use a chopper or an electro-optical modulator to periodically modulate the excitation light, and the modulation frequency is determined according to the data acquisition scheme. In a specific embodiment, the pulse repetition frequency modulation system 18 uses a chopper.

[0099] Optionally, a reflector 19 can be placed in the optical path between the pulse repetition frequency modulation system 18 and the fluorescence generation system 130. The ultrashort pulses after pulse characterization are modulated by the pulse repetition frequency modulation system 18 and reflected by the reflector 19 as fluorescence excitation light. The reflector 19 can be a flat reflector with a silver-plated surface and a reflectivity greater than 95% in the visible light band.

[0100] Continue to see Figure 3 In some embodiments, the fluorescence generation system 130 may include a fluorescence excitation unit 20, a sample holder 21, and a fluorescence collection unit 22. The sample holder 21 is used to place a sample thereon. The fluorescence excitation unit 20 is located downstream of the ultrashort pulse generation system 120 and upstream of the sample holder 21 and is configured to adjust the polarization and intensity of the fluorescence excitation light and focus it onto the sample surface to excite the sample to emit fluorescence.

[0101] In one specific embodiment, the fluorescence excitation unit 20 includes a half-wave plate, a polarizer, a neutral density attenuator, a short-wave pass filter, and a lens or off-axis parabolic mirror positioned on a manual linear translation stage. This structure is well known to those skilled in the art and will not be described in detail herein to avoid obscuring or obscuring the improvements of the present invention.

[0102] Optionally, the sample holder 21 is located on a manual linear translation stage, which can fine-tune the spot size of the excitation light on the sample surface. In addition, the sample holder 21 can also be equipped with a magnetic stirring device to achieve uniform stirring of the liquid sample in the contrast dish.

[0103] The fluorescence collection unit 22 is located downstream of the sample holder 21 and is configured to collect fluorescence emitted by the sample. Fluorescence collection unit 22 can utilize forward, backward, or sideways collection. For example, a lens, off-axis parabolic mirror, or Cassegrain objective can be used to collect the fluorescence beam emitted by the sample cell. A longpass filter (e.g., inserted behind the sample holder 21) can be used to filter out transmitted excitation light.

[0104] In a specific embodiment, the fluorescence collecting unit 22 is a one-inch plano-convex lens, which can collimate the fluorescence into a parallel beam with a diameter of about 20 mm.

[0105] Continue to see Figure 3 In some embodiments, the optical parametric fluorescence amplification system 140 may include a third focusing optical element 28 , a fluorescence focusing unit 24 , and a second optical parametric crystal 30 .

[0106] The third focusing optical element 28 is located upstream of the second optical parametric crystal 30 and downstream of the gate pulse generation system 110, and is configured to focus the gate pulse on the second optical parametric crystal 30. Specifically, the third focusing optical element 28 can be an ultraviolet plano-convex lens, which is used to focus the 400 nm gate pulse generated by the gate pulse generation system 110 on the second optical parametric crystal 30.

[0107] The fluorescence focusing unit 24 is located upstream of the second optical parametric crystal 30 and downstream of the fluorescence generating system 130, and is configured to focus the fluorescence on the second optical parametric crystal 30. The fluorescence focusing unit 24 can use a lens, an off-axis parabolic mirror, etc. for focusing.

[0108] In a specific embodiment, the fluorescence focusing unit 24 includes a manual linear stage and a lens located on the stage. By operating the manual linear stage to change the position of the lens, the size of the fluorescence spot focused on the surface of the second optical parametric crystal 30 can be precisely controlled.

[0109] The second optical parametric crystal 30 is configured to perform optical parametric amplification on the portion of the fluorescence that overlaps with the gate pulse in time and space. Specifically, the second optical parametric crystal 30 can adopt the same configuration as the first optical parametric crystal 13.

[0110] Optionally, a reflector 29 may be further provided in the optical path between the third focusing optical element 28 and the second optical parametric crystal 30 .

[0111] Specifically, the reflector 29 may be a 400 nm reflector, which can obtain a wavelength of less than 20 fs near the center wavelength of 400 nm. 2 The 400nm pump light generated by gate pulse generation system 110 passes through third focusing optical element 28 and is then reflected by reflector 29 and focused into second optical parametric crystal 30. By adjusting the beam angle between the gate pulse and the fluorescence seed light and changing the phase matching condition, transient fluorescence detection within a specific wavelength range can be achieved.

[0112] Optionally, a reflector 23 may be provided in the optical path between the fluorescence collecting unit 22 and the fluorescence focusing unit 24 to guide the collected fluorescence reflection into the fluorescence focusing unit 24. Specifically, the reflector 23 may be a plane reflector with a silver-plated surface, a reflectivity greater than 95% in the visible light band, and a diameter of 38 mm.

[0113] Continue to see Figure 3 In some embodiments, the transient fluorescence detection system 100 may further include an optical path delay system 25. The optical path delay system 25 is located upstream of the gate pulse generation system 110 and is configured to change the time delay between the fluorescence as the seed light and the gate pulse as the pump light in the optical parametric fluorescence amplification system 140 by changing the optical path length of the first fundamental frequency light.

[0114] In one specific embodiment, the optical path delay system 25 comprises a high-precision electronically controlled translation stage and a hollow angle mirror mounted on the stage. The hollow angle mirror is gold-plated, providing a reflectivity greater than 90% in the near-infrared spectral region. A program-controlled movement of the translation stage back and forth drives the hollow angle mirror, thereby changing the optical path of the gate pulse and obtaining a kinetic curve of the amplified fluorescence. The stage has a minimum step size of 0.1 μm, corresponding to a time accuracy of 0.67 fs, and a maximum range of 300 mm, corresponding to a kinetic time scan range of 2 ns.

[0115] Optionally, a reflector 26 may be provided in the optical path between the optical path delay system 25 and the gate pulse generating system 110. Specifically, the reflector 26 is an 800 nm reflector, which can obtain a wavelength of less than 20 fs near the central wavelength of 800 nm. 2 The reflectivity for p-polarization is greater than 99%.

[0116] In some other alternative embodiments, the optical path delay system 25 can also be set between the ultrashort pulse generation system 120 and the fluorescence generation system 130, rather than upstream of the gate pulse generation system 110, for example, it can be set between the pulse characterization system 17 and the fluorescence excitation unit 20, and the time delay between the fluorescence seed light and the gate pulse can be adjusted by changing the optical path of the pulse generated by the ultrashort pulse generation system 120.

[0117] Continue to see Figure 3 In some embodiments, the transient fluorescence detection system 100 may further include a femtosecond laser light source 1 configured to generate laser pulses; and a second beam splitter 2 located downstream of the femtosecond laser light source 1 and upstream of the gate pulse generation system 110 and the ultrashort pulse generation system 120, configured to split the laser pulses into a first fundamental frequency light and a second fundamental frequency light.

[0118] In a specific embodiment, the femtosecond laser light source 1 can be based on a titanium sapphire laser amplification system, and output laser pulses with a pulse width of 70 fs, a central wavelength of 800 nm, and a repetition frequency of 5 kHz.

[0119] The second beam splitter 2 splits the laser pulse output by the femtosecond laser light source 1 into two paths. The reflected part acts as the second fundamental frequency light to the ultrashort pulse generation system 120 , and the transmitted part acts as the first fundamental frequency light to the gate pulse generation system 110 .

[0120] Optionally, a reflector 3 may be provided between the second beam splitter 2 and the ultrashort pulse generating system 120. Part of the laser pulse (i.e., the second fundamental frequency light) reflected by the second beam splitter 2 is reflected by the reflector 3 and acts on the ultrashort pulse generating system 120. Specifically, the reflector 3 is an 800nm ​​reflector, which can obtain a wavelength of less than 20 fs near the center wavelength of 800nm. 2 The reflectivity for p-polarization is greater than 99%.

[0121] In some embodiments, the transient fluorescence detection system 100 may further include a data acquisition system 32 , which is located downstream of the optical parametric fluorescence amplification system 140 and is configured to acquire the fluorescence signal after optical parametric amplification to obtain a transient fluorescence signal.

[0122] In a specific embodiment, the data acquisition system 32 may include a grating polychromator and a spectral detector. The grating polychromator receives the fluorescence signal transmitted from the optical parametric fluorescence amplification system 140. The blazed grating inside the polychromator performs spectroscopic analysis, which is then collected by a linear array spectral detector at the back end. The spectral detector can be a high-speed detector based on CMOS (Complementary Metal-Oxide Semiconductor) or a multi-channel lock-in amplifier. Data acquisition requires the use of a chopper in the pulse repetition frequency modulation system 18. For the acquisition scheme of the CMOS detector, the chopper needs to be adjusted to continuously block and release the excitation light pulse sequence, and the intensity of the collected pulses is subtracted in real time to deduct the parametric fluorescence background of the second optical parametric crystal 30 to obtain the transient fluorescence signal. For the data acquisition scheme of the multi-channel lock-in amplifier, a suitable modulation frequency is applied to the excitation light through the chopper to extract the amplified transient fluorescence signal from the parametric fluorescence background noise. The principle of multi-channel lock-in amplifier data acquisition has been described in the relevant prior art in this field and should be known to those skilled in the art, so it will not be further described here.

[0123] In some embodiments, the transient fluorescence detection system 100 may further include a fluorescence coupling system 31, which is located downstream of the optical parametric fluorescence amplification system 140 and upstream of the data acquisition system 32, and is configured to couple the fluorescence signal amplified by the optical parametric fluorescence amplification system 140 into the data acquisition system 32.

[0124] In one specific embodiment, the fluorescence coupling system 31 may include a set of doublet lenses and an optical fiber connected thereto. The doublet lens collimates and focuses the amplified fluorescence beam into the optical fiber, which then connects to the data acquisition system 32. The optical fiber can be directly coupled to the fluorescence receiving component of the data acquisition system 32 (e.g., a grating polychromator) via an optical fiber adapter.

[0125] It should be noted that upstream and downstream in this application are based on the transmission direction of light in the system.

[0126] The above describes the transient fluorescence detection system 100 with sub-threshold pulse width time resolution and the structures of its components. The following describes the time resolution test principle and experimental results of transient fluorescence detection through a specific embodiment.

[0127] The structure of the transient fluorescence detection system 100 in this embodiment is as follows. Figure 3 As shown, the pulse characterization system 17 adopts Figure 4The structure shown performs dispersion scanning. During fluorescence parametric amplification, the 400nm pump light generated by the gate pulse generation system 110 and the fluorescence seed light emitted by the sample act together on the second optical parametric crystal 30. When the two coincide in time and space and meet specific phase matching conditions, the fluorescence signal at a specific moment is amplified. Therefore, the pump light, also known as the gate pulse, affects the temporal resolution of the transient fluorescence detection process.

[0128] When testing the temporal resolution of the optical parametric fluorescence amplification system 140, the sample at the sample holder 21 is replaced with 1 mm thick frosted glass to scatter the excitation light. After the scattered light passes through the fluorescence collection unit 22 and the fluorescence focusing unit 24, it is optically parametrically amplified with a 400 nm gate pulse in the second optical parametric crystal 30. The electrically controlled translation stage in the optical path delay system 25 performs high-precision scanning using a time step of 5 fs. The data acquisition system 32 records the corresponding kinetic curve, and the full width at half maximum obtained by fitting is the temporal resolution of the system. When using the wide-spectrum pulse output by the non-collinear optical parametric amplification unit 121 as the excitation light, it is necessary to compensate for the dispersion of the supercontinuum white light generation unit 6, including the dispersion introduced by the transmission element in the subsequent optical path, through the pulse compression unit 16. Then, the pulse characterization system 17 is used to perform in-situ measurement of the excitation light pulse width at the sample position of the sample holder 21.

[0129] The experimental results show that the broadband signal light output by the non-collinear optical parametric amplifier unit 121 is continuously adjustable in the visible spectrum region. The spectrum tuning results are as follows: Figure 5 As shown. By changing the relative delay of the pump light and the signal light and the phase matching conditions, the signal light spectrum is continuously adjustable in the range of 500-750nm, the spectral bandwidth is greater than 150nm, and the supported Fourier transform limit pulse width is less than 10fs. In the pulse compression unit 16, a pair of chirped mirrors and prisms are used to compensate for dispersion. The dispersion scanning device in the pulse characterization system 17 tests the wide-spectrum signal light, and the results are shown in Figures 6a to 6d As shown. The dispersion scanning two-dimensional spectrum reconstructed by the inversion algorithm ( Figure 6d ) and the measured results ( Figure 6c ) has good consistency, and the reliable results of pulse width of about 10fs are obtained (such as Figure 6b It is a femtosecond pulse with a few cycles.

[0130] The temporal resolution of the optical parametric fluorescence amplification system 140 was tested by using a few-cycle femtosecond pulse as the excitation light. The results are as follows: Figure 7 As shown in Figure 2, Gaussian fitting of the kinetic curve of parametrically amplified scattered light from the excitation light yields a corresponding full width at half maximum of approximately 60 fs, which is smaller than the gate pulse width (70-80 fs). Under the same experimental conditions, using a commercial frequency conversion device as the excitation light, the measured temporal resolution of the system is approximately 100 fs, significantly larger than the gate pulse width.

[0131] In summary, for optical parametric fluorescence amplification technology, there is an exponential dependence between the parametric gain and the gate pulse intensity, and the amplification efficiency at the gate pulse peak is significantly greater than on both sides. Based on this principle, the present invention performs pulse compression and pulse characterization on the wide-spectrum signal light output by the non-collinear optical parametric amplifier unit 121, and uses the resulting femtosecond pulses of a few cycles as fluorescence excitation light, achieving a time resolution less than the gate pulse width, i.e., a sub-gate pulse width time scale. The solution of the present invention can overcome the limitations of optical gate pulses, significantly improving the temporal resolution capability of transient fluorescence detection, and providing excellent technical support for transient spectroscopy research of ultrafast processes within the time scale of hundreds of femtoseconds.

[0132] In the description provided herein, numerous specific details are described. However, it is understood that embodiments of the present invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques are not shown in detail so as not to obscure the understanding of this description.

[0133] At this point, those skilled in the art will recognize that, although a number of exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications consistent with the principles of the present invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A transient fluorescence detection system with sub-hilar pulse width time resolution, comprising: a gate pulse generating system configured to generate a gate pulse required for transient fluorescence detection based on the first fundamental frequency light input thereto; An ultrashort pulse generation system configured to generate a femtosecond pulse of a few cycles based on a second fundamental frequency light input thereto; a fluorescence generating system, located downstream of the ultrashort pulse generating system, configured to use the few-cycle femtosecond pulses as fluorescence excitation light to excite the sample to generate fluorescence; as well as The optical parametric fluorescence amplification system is located downstream of the gate pulse and the fluorescence and is configured to amplify the portion of the fluorescence that overlaps with the gate pulse in time and space through optical parametric amplification, thereby realizing transient fluorescence detection.

2. The transient fluorescence detection system according to claim 1, wherein: The pulse width of the short-cycle femtosecond pulse is less than or equal to 20 fs; The ultrashort pulse generation system comprises: a supercontinuum white light generating unit, configured to generate supercontinuum broadband white light based on the first light beam from the second fundamental frequency light; a pump light generating unit configured to generate pump light required for non-collinear optical parametric amplification based on a second light beam from the second fundamental frequency light; a non-collinear optical parametric amplification unit, located downstream of the supercontinuum broadband white light and the pump light, configured to perform non-collinear optical parametric amplification on a portion of the supercontinuum broadband white light and the pump light that overlaps in time and space to obtain a broadband pulse; and The pulse compression unit is located downstream of the non-collinear optical parametric amplifier unit and is configured to perform dispersion compensation on the wide-spectrum pulse to obtain the few-cycle-level femtosecond pulse.

3. The transient fluorescence detection system according to claim 2, wherein: The non-collinear optical parametric amplification unit includes: a time delay unit, located downstream of the pump light generating unit, configured to change the time delay of the pump light relative to the supercontinuum broadband white light; a first optical parametric crystal configured to perform non-collinear optical parametric amplification on a portion of the supercontinuum broadband white light and the pump light that overlaps in time and space; a first focusing optical element, located upstream of the first optical parametric crystal and downstream of the supercontinuum white light generating unit, configured to focus the supercontinuum broadband white light on the first optical parametric crystal; and A second focusing optical element, located upstream of the first optical parametric crystal and downstream of the time delay unit, is configured to focus the pump light on the first optical parametric crystal.

4. The transient fluorescence detection system according to claim 2, wherein: The pulse compression unit includes at least one of a chirped mirror, a prism pair, a grating pair, and a pulse shaper.

5. The transient fluorescence detection system according to claim 2, wherein: The ultrashort pulse generation system further comprises: a half-wave plate, located upstream of the supercontinuum white light generating unit and the pump light generating unit, configured to rotate the polarization of the second fundamental frequency light by 90°; a first beam splitter, located upstream of the supercontinuum white light generating unit and the pump light generating unit and downstream of the half-wave plate, configured to split the polarization-rotated second fundamental frequency light into the first light beam and the second light beam at a specified splitting ratio; and The beam collimating element is located downstream of the non-collinear optical parametric amplifier unit and upstream of the pulse compression unit, and is configured to collimate the wide-spectrum pulse beam amplified by the non-collinear optical parametric amplifier unit.

6. The transient fluorescence detection system according to claim 1, further comprising: a pulse characterization system, located downstream of the ultrashort pulse generation system, configured to measure characteristics of the few-cycle femtosecond pulses generated by the ultrashort pulse generation system, the characteristics including pulse width and phase information; as well as A pulse repetition frequency modulation system, located downstream of the pulse characterization system and upstream of the fluorescence generation system, is configured to periodically modulate the few-cycle femtosecond pulses to provide a modulation frequency for the fluorescence excitation light of the fluorescence generation system.

7. The transient fluorescence detection system according to claim 1, wherein: The fluorescence generating system comprises: Sample rack, used to place samples; a fluorescence excitation unit, located downstream of the ultrashort pulse generation system and upstream of the sample holder, configured to adjust the polarization and intensity of the fluorescence excitation light and focus it onto the sample surface to excite the sample to radiate fluorescence; and The fluorescence collecting unit is located downstream of the sample holder and is configured to collect the fluorescence radiated by the sample.

8. The transient fluorescence detection system according to claim 1, wherein: The optical parametric fluorescence amplification system comprises: a second optical parametric crystal configured to perform optical parametric amplification on a portion of the fluorescence that overlaps with the gate pulse in time and space; a third focusing optical element, located upstream of the second optical parametric crystal and downstream of the gate pulse generation system, configured to focus the gate pulse on the second optical parametric crystal; and The fluorescence focusing unit is located upstream of the second optical parametric crystal and downstream of the fluorescence generating system, and is configured to focus the fluorescence on the second optical parametric crystal.

9. The transient fluorescence detection system according to claim 1 , further comprising: a femtosecond laser light source configured to generate laser pulses; a second beam splitter, located downstream of the femtosecond laser light source and upstream of the gate pulse generation system and the ultrashort pulse generation system, configured to split the laser pulse into the first fundamental frequency light and the second fundamental frequency light; as well as An optical path delay system is located upstream of the gate pulse generating system and downstream of the second beam splitter, and is configured to change the time delay between the fluorescence serving as the seed light and the gate pulse serving as the pump light in the optical parametric fluorescence amplification system by changing the optical path of the first fundamental frequency light.

10. The transient fluorescence detection system according to claim 1, further comprising: a fluorescence coupling system, located downstream of the optical parametric fluorescence amplification system, configured to couple the fluorescence signal amplified by the optical parametric fluorescence amplification system into a data acquisition system; as well as The data acquisition system is located downstream of the fluorescence coupling system and is used to acquire the amplified fluorescence signal to obtain a transient fluorescence signal; Wherein, the data acquisition system includes a grating polychromator and a spectrum detector.

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