Broadband transient absorption spatio-temporal evolution detection system

Abstract

The invention discloses a broadband transient absorption spatio-temporal evolution detection system, relates to the field of ultrafast spectral imaging, and is suitable for multi-band response and spatial information combined measurement under a femtosecond pumping-detection structure. The system comprises a grating, a first group of achromatic cylindrical lenses, a first beam splitter, a second group of achromatic cylindrical lenses, a second beam splitter, a high NA microscope objective, a sample and an sCMOS camera which are arranged in sequence, the probe light is spread in the x direction after being dispersed by the grating, is compressed by the cylindrical lens, is combined with the pump light, is irradiated to a sample after being shaped in the y direction by the second cylindrical lens, and is reflected by the sample to be recovered to the camera. Through a space-wavelength mapping relation, the system realizes transient response parallel measurement of a sample at a plurality of wavelengths and spatial positions under single exposure, and constructs a delta A (y, lambda, t) three-dimensional data set. The system has high time resolution, wavelength resolution and spatial analysis capability, and is suitable for multi-dimensional observation of a material microdynamics process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultrafast spectroscopy and microscopic imaging technology, in particular to a broadband transient absorption spatiotemporal evolution detection system, belonging to the application technology category of femtosecond laser pumping-detection technology, transient absorption imaging, ultrafast dynamics measurement and microscopic spectrum combined detection. BACKGROUND

[0002] The femtosecond pumping-detection microscopic imaging system (Transient Absorption Microscopy, TAM) is a multi-dimensional detection platform combining ultrafast laser technology and microscopic imaging means, which can realize spatial imaging detection of energy state evolution process, carrier dynamics behavior and photo-induced structure phase transition of micro area of the sample within femtosecond to picosecond time scale. The technology is widely used in ultrafast process research of non-equilibrium systems such as two-dimensional materials, strongly correlated electron systems, semiconductor devices and biological samples.

[0003] At present, the commonly used TAM system mainly includes the following two technical implementation paths:

[0004] 1. Galvanometer scanning imaging method: This method uses a double-axis galvanometer system controlled by a computer to realize spatial scanning in the sample plane (x-y direction) by moving the laser focus position. In each measurement, the pump and probe beams are focused on a single point of the sample, and the transient absorption signal ΔA(λ,t) at different delay times of the point is recorded by changing the delay time of the probe light. Repeating this process can obtain the transient response image of the entire two-dimensional plane point by point. This method can realize high spectral resolution measurement of multiple wavelengths (supercontinuum white light), and can provide rich time and energy dimension information, but its measurement efficiency is low, the scanning process takes a long time, and the stability and positioning accuracy of the galvanometer system are extremely high.

[0005] 2. High-speed camera imaging method: This method uses a high-speed scientific CMOS camera (scientific Complementary Metal-Oxide Semiconductor, sCMOS) and other area array detectors to record the reflection or transmission changes of the sample in the entire field of view, and obtains the transient absorption image ΔA(x,y,t) by image difference, which has high time resolution and fast measurement advantage, and is suitable for high-throughput dynamic imaging. However, since the camera cannot distinguish different wavelength signals, this scheme can usually only perform single-wavelength imaging, lacks complete spectral dimension information, and is difficult to reflect the complex dynamics behavior of multiple excited states or energy channels in the material.

[0006] In summary, the existing TAM system has the following limitations: the galvanometer scanning system has high spectral resolution, but the measurement speed is slow and the structure is complex, which is difficult to meet the requirement of fast two-dimensional imaging; while the camera imaging system is fast and efficient, but only single-wavelength image can be obtained, and parallel spectral imaging of multiple wavelengths cannot be performed.

[0007] In order to overcome the above technical bottlenecks, a new pump-probe system with high-speed detection capability and wideband spectral information is needed to study the spatiotemporal evolution process in material systems. SUMMARY

[0008] The application provides a wideband transient absorption spatiotemporal evolution detection system, and specifically belongs to the field of ultrafast spectral imaging, and particularly relates to a femtosecond pump-probe system based on grating dispersion and double-column lens structure compression, which has high time resolution, wavelength resolution and single-dimensional spatial detection capability.

[0009] Technical scheme

[0010] Since the system adopts a dispersion mode to expand different wavelengths along the x direction, the sample needs to have uniformity of optical response in the x direction to ensure the accuracy of the signals corresponding to each wavelength; the y direction corresponds to the spatial variation under a specific wavelength, thereby constructing the spatiotemporal evolution process of the sample under the specific wavelength. The system is not a traditional two-dimensional imaging structure, but a wideband transient absorption response detection method integrating the time dimension, the wavelength dimension and the single-dimensional space.

[0011] The application provides a broadband transient absorption space-time evolution detection system, which comprises the following structure: a grating element (1) is used for horizontally dispersing broadband detection light (such as 400-700 nm) so that different wavelengths are separated along the x direction; a first group of achromatic cylindrical lenses (2) is located behind the grating and is used for compressing and shaping the detection light dispersed by the grating element (1) in the x direction; a first beam splitter (3) is located behind the first group of achromatic cylindrical lenses (2), and there is pump light behind the first beam splitter (3), which is used for combining the pump light (single wavelength) with the detection light compressed by the first group of achromatic cylindrical lenses (2) so that the two light beams are spatially overlapped; a second group of achromatic cylindrical lenses (4) is located behind the first beam splitter (3) and is used for compressing and shaping the light beam combined by the first beam splitter (3) in the y direction; a second beam splitter (5) is located behind the second group of achromatic cylindrical lenses (4) and is used for guiding the pump light and the detection light behind the second group of achromatic cylindrical lenses (4) to be focused by a high numerical aperture microscope objective (6) and then irradiated to a sample (7) together, and guiding the sample (7) reflection signal to a camera (8); the high numerical aperture microscope objective (6) is located behind the second beam splitter (5) and focuses the composite light beam output by the second beam splitter (5) on the surface of the sample (8) with high precision; the sample (7) is a sample to be detected and is located behind the high numerical aperture microscope objective (6), and can be a two-dimensional material, a phase change material, a photocatalytic material or other micro-nano structure sample with ultrafast response characteristics; and the sCMOS camera (8) is located on the other side of the second beam splitter (5) and is used for receiving the sample reflection signal, so that the transient absorption image corresponding to the position of different wavelengths is collected through the plane array parallel detection of light.

[0012] Further, the first group of achromatic cylindrical lenses (2) is located behind the grating element (1), the half cylinder of the first group of achromatic cylindrical lenses (2) faces the grating element (1), and the axis length direction of the first group of achromatic cylindrical lenses (2) is parallel to the grating of the grating element (1);

[0013] The second group of achromatic cylindrical lenses (4) is located behind the first beam splitter (3), the half cylinder of the second group of achromatic cylindrical lenses (4) faces the first beam splitter (3), and the axis length direction of the second group of achromatic cylindrical lenses (4) is perpendicular to the axis length direction of the first group of achromatic cylindrical lenses (2).

[0014] The grating is a reflection type blazed grating and is suitable for dispersing the detection light in a wide band range.

[0015] The sCMOS camera (8) is a plane array detector and is used for recording three-dimensional dynamic data in the format of ΔA(y, λ, t) and analyzing the transient absorption response of the material at different wavelengths and spatial positions.

[0016] The microscope objective is a high-resolution objective with a numerical aperture NA greater than 0.65 and is used for realizing sub-micron level spatial focusing

[0017] Through the above structure, the probe light has completed dispersion and spatial compression before entering the sample, and through the spatial-wavelength mapping relationship on the camera imaging surface, the spatial distribution of the sample at a specific wavelength and the transient response at multiple wavelengths are obtained by one-time exposure, combined with different times, so that a three-dimensional dynamic data set of Delta A(y, lambda, t) is constructed.

[0018] The pump light is single-wavelength pulse light output by a femtosecond laser, and a mechanical delay line is used to control the time delay between the pump light and the probe light.

[0019] The sample is a two-dimensional material, a phase change material, a nanostructure, a thin film device or other materials with femtosecond-level transient optical response.

[0020] Advantages

[0021] The present application has the following technical advantages:

[0022] 1. Wideband spectrum combined detection based on a camera is realized, and the problem that a large amount of time is consumed to replace the measurement position or replace the detection wavelength to obtain the spatial distribution and the multi-wavelength transient effect of the sample in the existing TAM system is overcome.

[0023] 2. Fast and efficient, the spatial distribution and the transient response of the sample at different wavelengths can be obtained by one-time exposure.

[0024] 3. The system structure is compact, a double-achromatic column lens is used in cooperation with a double-beam splitter scheme, and the optical path is stable and easy to adjust.

[0025] 4. The sCMOS high-speed area array detector is used, fast and high-throughput multi-wavelength ultrafast response recording can be realized, and the present application is suitable for researches on diffusion, carrier transport and phase change dynamics in materials.

[0026] 5. The present application has good platform compatibility, is suitable for integration with an existing pump-probe experimental system, and is convenient for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FIG. 1 is a structural schematic diagram of the broadband transient absorption spatiotemporal evolution detection system.

[0028] In the figure, the numbers represent the following:

[0029] 1 - grating element: used for dispersion of the supercontinuum probe light in the horizontal direction (x direction);

[0030] 2 - first set of achromatic column lenses: located behind the grating, used for compression and focusing of the dispersed probe light in the x direction;

[0031] 3 - First beam splitter: for spatial path merging of pump light and probe light;

[0032] 4 - Second group of achromatic cylindrical lenses: for further compression of the combined light in the vertical direction (y direction);

[0033] 5 - Second beam splitter: for guiding the composite light beam to the sample, while guiding the sample reflection signal to the imaging detector;

[0034] 6 - High numerical aperture microscope objective: for focusing the composite light beam to the sample surface;

[0035] 7 - Sample: a micro-nano structure sample to be measured, which can have a femtosecond scale optical response;

[0036] 8 - sCMOS camera: a high-speed area array imaging detector, used to collect sample reflection light signals, and realize wideband transient image acquisition. DETAILED DESCRIPTION

[0037] The application will be further described below in conjunction with examples, but the application is not limited to the following examples.

[0038] Example 1

[0039] Reference Figure 1 The wideband transient absorption spatiotemporal evolution detection system of the application specifically includes the following components and their connection methods:

[0040] The wideband light (such as 400-700 nm) emitted by the probe light source is first incident on the grating (1), and is dispersed into different wavelength probe beams along the x direction. Subsequently, the first group of achromatic cylindrical lenses (2) compress and shape the dispersed probe light in the x direction, forming a beam with compact wavelength distribution and balanced energy density along the x direction.

[0041] The probe light is combined with the pump light (single wavelength, femtosecond pulse) by the first beam splitter (3), and the two are accurately aligned in space, and together pass through the second group of achromatic cylindrical lenses (4) to complete the compression and shaping in the y direction, so that the entire composite light beam has good spatial control and focusing ability in the x and y directions.

[0042] The shaped pump and probe light pass through the second beam splitter (5) and enter the high-NA microscope objective (6), and are focused to irradiate the surface of the sample (7) to be measured. The objective not only provides sub-micron spatial resolution, but also improves the light flux collection efficiency of the system, enhances the signal-to-noise ratio, and ensures accurate acquisition of the transient response.

[0043] After the sample absorbs the pump light, the transient absorption change will be reflected in the reflection signal, which is propagated back through the original light path, and then recorded by a high-speed sCMOS camera (8) after passing through the beam splitter (5) again. Since the incident probe light has achieved dispersion and wavelength mapping in the x direction, the x-axis position in the recorded image corresponds to different wavelengths; at the same time, the y-axis corresponds to the spatial distribution of the sample at a specific wavelength.

[0044] By gradually scanning the time delay of the pump light and the probe light through the delay line, the system can obtain ΔA(y, λ) images at each time point, and finally construct a complete ΔA(y, λ, t) three-dimensional dynamic data set. This structure has the following implementation advantages:

[0045] 1. High time resolution: The system uses a femtosecond laser as the pump source, combined with mechanical or optical delay line control, to achieve a time delay accuracy of <100 fs; combined with the sCMOS camera, it can achieve μs-level fast acquisition,

[0046] Effectively capture extremely short-lived excited states and ultrafast energy processes in material systems.

[0047] 2. Multi-band parallel detection capability: The grating dispersion structure combined with the area array detector breaks through the traditional single-wavelength imaging limit and realizes the synchronous recording of dozens of wavebands in the 400-700 nm range.

[0048] 3. Spatial-wavelength joint analysis: Through the compression of the cylindrical lens and the focusing of the microscope objective, the system maintains good spatial resolution while ensuring wavelength resolution, suitable for the spatial heterogeneity dynamics research of micron-scale materials.

[0049] 4. Simple optical alignment: All optical devices are symmetrical in structure, short in path, and few in components, which is convenient for experimental setup and stable operation, and suitable for standard optical platform integration.

[0050] The entire system structure is compact, the optical elements are arranged reasonably, and it is easy to adjust and integrate, which can be widely used in ultrafast dynamics measurement tasks in the fields of material science, biophotonics, two-dimensional material physics, and semiconductor device research.

Claims

1. A broadband transient absorption spatiotemporal evolution detection system, characterized in that: The invention comprises the following structures: a grating element (1): used for horizontally dispersing a wide-spectrum detection light (such as 400-700 nm) so that different wavelengths are separated along the x-direction; a first group of achromatic cylindrical lenses (2): located behind the grating, used for compressing and shaping the detection light dispersed by the grating element (1) in the x-direction; a first beam splitter (3): located behind the first group of achromatic cylindrical lenses (2), and having a pump light behind the first beam splitter (3), used for combining the pump light (single wavelength) with the detection light compressed by the first group of achromatic cylindrical lenses (2), so that the two paths of light are spatially overlapped; a second group of achromatic cylindrical lenses (4): located behind the first beam splitter (3), and compressing and shaping the light beam combined by the first beam splitter (3) in the y-direction; a second beam splitter (5): located behind the first beam splitter (3), and used for compressing and shaping the light beam combined by the first beam splitter (3) in the y-direction; a second beam splitter (6): located behind the first beam splitter (3), and used for compressing and shaping the light beam combined by the first beam splitter (3) in the y-direction. A beam splitter (5) is located behind the second group of achromatic cylindrical lenses (4) and is used to guide the pump light and the detection light after the second group of achromatic cylindrical lenses (4) to be focused by a high numerical aperture microscope objective lens (6) and then irradiated to the sample (7) together, and at the same time guide the sample (7) reflection signal to the camera (8); a high numerical aperture microscope objective lens (6) is located behind the second beam splitter (5) and is used to focus the composite light beam output by the second beam splitter (5) on the surface of the sample (8) to be measured with high precision; a sample (7) is located behind the high numerical aperture microscope objective lens (6); an sCMOS camera (8) is located on the other side of the second beam splitter (5) and is used to receive the sample reflection signal and realize the acquisition of transient absorption images corresponding to positions of different wavelengths through the parallel detection of the light array.

2. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The first group of achromatic cylindrical lenses (2) is located behind the grating element (1), the semi-cylindrical surface of the first group of achromatic cylindrical lenses (2) faces the grating element (1), and the axial length direction of the first group of achromatic cylindrical lenses (2) is parallel to the grating of the grating element (1).

3. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The second group of achromatic cylindrical lenses (4) is located behind the first beam splitter (3), the semi-cylindrical surface of the second group of achromatic cylindrical lenses (4) faces the first beam splitter (3), and the axial length direction of the second group of achromatic cylindrical lenses (4) is perpendicular to the axial length direction of the first group of achromatic cylindrical lenses (2).

4. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The grating is a reflective blazed grating, which is suitable for the dispersion of detection light in a broadband range.

5. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The sCMOS camera (8) is a planar array detector used to record three-dimensional dynamic data in the ΔA(y,λ,t) format for analyzing the transient absorption response of materials at different wavelengths and spatial positions.

6. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The microscope objective lens is a high-resolution objective lens with a numerical aperture NA greater than 0.65, and is used to achieve submicron-level spatial focusing.

7. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The pump light is a single-wavelength pulse light output by a femtosecond laser, and the time delay between the pump light and the detection light is controlled by a mechanical delay line.

8. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The sample is a two-dimensional material, a phase change material, a nanostructure, a thin film device or other material with a femtosecond transient optical response.

9. A broadband transient absorption spatiotemporal evolution detection system according to claim 1, characterized in that: The detection light has completed dispersion and spatial compression before entering the sample. At the same time, through the space-wavelength mapping relationship on the camera imaging surface, the spatial distribution of the sample at a specific wavelength and the transient response at multiple wavelengths can be obtained in a single exposure. Combined with different times, a three-dimensional dynamic data set of ΔA(y,λ,t) is constructed.

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