A near-field optical super-resolution carrier dynamics imaging system

Abstract

The present application relates to a kind of near-field optical super-resolution carrier dynamics imaging system, wherein probe light is shot into near-field optical scanning microscope system by probe beam expander component and probe attenuator component, pump light is sequentially shot into near-field optical scanning microscope system by pump beam expander component, pump attenuator component, pump light delay component and acoustooptic modulator component, near-field optical scanning microscope system includes upper objective lens, scanning probe, sample support, lower objective lens, near-field beam splitter, near-field filter component and convex lens in the direction of probe light path in turn, pump light is focused on sample after being reflected by near-field beam splitter and forming the path direction opposite to probe light and being shot into lower objective lens, probe light is shot out by convex lens and input into lock-in amplifier by fiber coupler and photomultiplier tube.The present application combines near-field optical super-resolution imaging technology with femtosecond transient absorption spectroscopy technology, and realizes the high space-time resolution visual detection of microcosmic carrier dynamics.

Description

Technical Field

[0001] This invention relates to the field of microscopic imaging technology, specifically to a near-field optical super-resolution carrier dynamics imaging system. Background Technology

[0002] Spectrodynamic microscopy has matured and been applied to study the excited-state dynamics of photoelectric conversion materials. However, existing ultrafast time-resolution techniques, such as femtosecond transient absorption spectroscopy, while improving temporal resolution, are limited by the diffraction limit in terms of spatial resolution, making it impossible to characterize nanoscale microstructures in detail. This is particularly evident in the application of nanomaterials such as polycrystalline semiconductor thin films and quantum dots. Especially for single-photon sources (such as quantum dots, nanocrystals, and fluorescent molecules) that are widely used in quantum information and photoelectric conversion devices, existing techniques are unable to detect ultrafast dynamic processes at the single-particle scale, thus severely restricting the further development and application of these materials and devices.

[0003] To address the aforementioned issues, near-field optical scanning microscopy (NFC) offers a novel approach to overcoming the optical diffraction limit and achieving super-resolution imaging of nanostructures. NFC utilizes the probe of an atomic force microscope to locally excite and detect optical signals. Its spatial resolution no longer depends on the wavelength of light but rather on the size of the probe, thus enabling it to overcome the diffraction limit and achieve nanoscale resolution. However, traditional NFC is primarily used for detecting steady-state optical signals. Combining it with ultrafast spectral dynamics techniques for high spatiotemporal resolution excited-state dynamics research remains a current technological bottleneck.

[0004] Patent CN113251916B discloses a femtosecond interferometric scattering microscopy imaging system and measurement method. The device uses a femtosecond laser to generate femtosecond laser pulses, which are split into a reflected beam and a transmitted beam by a first beam splitter. The reflected beam, after passing through an excitation module, generates a wide-field pump spot on the sample at the sample stage, exciting the sample within the pump region. The transmitted beam, after passing through a detection module and a second beam splitter, generates a wide-field detection spot on the sample at the sample stage, detecting the signal of the excited-state sample. This signal is then processed by an imaging module to form an image. Furthermore, both the pump beam and the detection beam are focused onto the same objective lens's back focal plane. The transmitted beam, after being reflected by a total reflection mirror, passes sequentially through an optical delay line, a second variable aperture, a second intensity modulator, and a second half-wave plate. A supercontinuum white light generator then generates supercontinuum white light as the detection beam. This detection beam then passes through a third intensity modulator, is converged by a second convex lens, and after partial reflection by a second beam splitter, is focused onto the objective lens's back focal plane, generating a wide-field detection spot on the sample at the sample stage to detect the signal of the excited-state sample. Summary of the Invention

[0005] The purpose of this invention is to provide a near-field optical super-resolution carrier dynamics imaging system, which combines near-field optical super-resolution imaging technology with femtosecond transient absorption spectroscopy technology, breaks through the optical diffraction limit, and realizes high spatiotemporal resolution visualization detection of microscopic carrier dynamics, providing a brand-new research tool for in-depth study of excited-state dynamics in microstructures.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A near-field optical super-resolution carrier dynamics imaging system includes a femtosecond laser and a near-field optical scanning microscope system. The laser emitted from the femtosecond laser is split into a probe beam and a pump beam by a beam splitter. The probe beam sequentially passes through a probe beam expander and a probe attenuator before entering the near-field optical scanning microscope system. The pump beam sequentially passes through a pump beam expander, a pump attenuator, a pump beam delay assembly, and an acousto-optic modulator before entering the near-field optical scanning microscope system. The near-field optical scanning microscope system includes... The upper objective, scanning probe, sample stage, lower objective, near-field beam splitter, near-field filter assembly, and convex lens are arranged sequentially along the probe light path. The upper and lower objective lenses are symmetrically arranged. The scanning probe has nanopores for the probe light to pass through. The pump light is reflected by the near-field beam splitter to form a path direction opposite to the probe light and finally enters the lower objective lens and is focused on the sample on the sample stage. The probe light is emitted from the convex lens and passes through an optical fiber coupler and a photomultiplier tube before being input into a lock-in amplifier.

[0008] The laser emitted by the femtosecond laser is split into two laser beams by a beam splitter. One laser beam is converted into a wavelength-tunable probe beam by a first optical parametric amplifier, and the other laser beam is converted into a wavelength-tunable pump beam by a second optical parametric amplifier.

[0009] A first detection aperture is provided between the detection beam expander assembly and the detection attenuator assembly, and a second detection aperture is provided on the side of the detection attenuator assembly away from the detection beam expander assembly.

[0010] The probe light emitted from the second probe aperture enters a probe light path limiting component, which includes multiple optical path reflectors. The probe light is reflected sequentially by each optical path reflector before entering the near-field optical scanning microscope system.

[0011] The pump light delay assembly includes a movable right-angle retroreflector and multiple delay mirrors, wherein the probe light is reflected by the delay mirror on one side and then enters the right-angle retroreflector, while the probe light emitted from the right-angle retroreflector is reflected by the delay mirror on the other side and then emitted.

[0012] The acousto-optic modulator assembly includes an input aperture, an input lens, an acousto-optic modulator, and an output lens arranged sequentially along the pump light path, and the pulse frequency of the pump light is modulated by the acousto-optic modulator assembly to half of the output frequency of the femtosecond laser.

[0013] Pump light is emitted from the acousto-optic modulator assembly and then enters the near-field optical scanning microscope system via a second path limiting assembly, the second path limiting assembly including a plurality of second pump mirrors.

[0014] The near-field optical scanning microscope system includes multiple near-field mirrors. The probe light is reflected by the first near-field mirror and enters the upper objective lens. After passing through the scanning probe, sample stage, and lower objective lens in sequence, it is reflected by the second and third near-field mirrors in sequence and enters the near-field beam splitter. The probe light passes through the near-field beam splitter and near-field filter assembly in sequence and is reflected by the fourth near-field mirror and enters the convex lens. The pump light is reflected by the near-field beam splitter, the third near-field mirror, and the second near-field mirror in sequence and enters the lower objective lens.

[0015] The sample support stage is a piezoelectric moving stage.

[0016] The lock-in amplifier obtains the amplitude and phase of the transient absorption signal based on the electrical signal output by the photomultiplier tube, and transmits the amplitude to the industrial control computer in the form of a voltage signal. The repetition frequency signal of the femtosecond laser is transmitted to a timing module, and after being down-frequency processed by the timing module, it is transmitted to the acousto-optic modulator of the acousto-optic modulator assembly and the lock-in amplifier, respectively.

[0017] The advantages and positive effects of this invention are as follows:

[0018] 1. This invention, for the first time, combines near-field optical super-resolution imaging technology with femtosecond transient absorption spectroscopy, breaking through the optical diffraction limit and achieving high spatiotemporal resolution visualization of microscopic carrier dynamics. This provides a novel research tool for in-depth study of excited-state dynamics in microstructures. By developing this super-resolution carrier dynamics imaging platform, it is possible to detect carrier dynamics behavior in complex nanostructures (such as polycrystalline semiconductor films and monodisperse nanocrystals) with high precision and in multiple dimensions, filling the spatial and temporal resolution limitations of existing technologies.

[0019] 2. The present invention places the laser delay component on the pump light path, which can avoid the influence on the probe light, thereby ensuring that the probe light coupled into the nanopore of the scanning probe has sufficiently high stability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention.

[0021] Figure 2 for Figure 1 A schematic diagram of a mid-to-near field optical scanning microscope system.

[0022] Figure 3 This is a schematic diagram of a bright-field image of a monolayer MoS2 isolated grain.

[0023] Figure 4 Super-resolution carrier dynamics images of isolated monolayer MoS2 grains.

[0024] Figure 5 for Figure 4 Enlarged view of area A in the image.

[0025] Figure 6 for Figure 4 Enlarged view of region A at another time delay.

[0026] Figure 7 for Figure 4 A magnified view of region A under another time delay.

[0027] In this design, 1 is a femtosecond laser, 101 is a beam splitter, 2 is a probe beam, 201 is a first probe mirror, 202 is a first optical parametric amplifier, 203 is a second probe mirror, 204 is a probe beam expander assembly, 205 is a first probe aperture, 206 is a probe attenuator assembly, 207 is a second probe aperture, 208 is a probe beam path limiting assembly, 2081 is an optical path mirror, 3 is a pump beam, 301 is a second optical parametric amplifier, 302 is a first path limiting assembly, 3021 is a first pump mirror, 304 is an acousto-optic modulator assembly, 3041 is an input aperture, 3042 is an input lens, 3043 is an acousto-optic modulator, 3044 is an output lens, 3045 is a second steering mirror, and 305 is a pump beam expander. The components are as follows: 306 is the pump attenuator assembly, 3061 is the first steering mirror, 307 is the pump light delay assembly, 3071 is the delay mirror, 3072 is the right-angle retroreflector, 308 is the second path limiting assembly, 3081 is the second pump mirror, 4 is the near-field optical scanning microscope system, 401 is the first near-field mirror, 402 is the upper objective lens, 403 is the scanning probe, 404 is the sample stage, 405 is the lower objective lens, 406 is the second near-field mirror, 407 is the third near-field mirror, 408 is the near-field beam splitter, 409 is the near-field filter assembly, 410 is the fourth near-field mirror, 411 is the convex lens, 5 is the industrial control computer, 6 is the fiber optic coupler, 7 is the photomultiplier tube, 8 is the timing module, and 9 is the lock-in amplifier. Detailed Implementation

[0028] The invention will now be described in further detail with reference to the accompanying drawings.

[0029] like Figures 1-2 As shown, the present invention includes a femtosecond laser 1 and a near-field optical scanning microscope system 4. The laser emitted by the femtosecond laser 1 is split into two beams by a beam splitter 101. One beam is amplified by a first optical parametric amplifier 202 to form a wavelength-tunable probe beam 2, and the other beam is amplified by a second optical parametric amplifier 301 to form a wavelength-tunable pump beam 3. The probe beam 2 passes sequentially through a probe beam expander assembly 204 and a probe attenuator assembly 206 before entering the near-field optical scanning microscope system 4. The pump beam 3 passes sequentially through a pump beam expander assembly 305, a pump attenuator assembly 306, a pump beam delay assembly 307, and an acousto-optic modulator assembly 304 before entering the near-field optical scanning microscope system 4. Figure 2 As shown, the near-field optical scanning microscope system 4 includes an upper objective lens 402, a scanning probe 403, a sample stage 404, a lower objective lens 405, a near-field beam splitter 408, a near-field filter assembly 409, and a convex lens 411 arranged sequentially along the path of the probe light 2. The upper objective lens 402 and the lower objective lens 405 are symmetrically arranged. The scanning probe 403 is provided with nanopores for the probe light 2 to pass through. The pump light 3 is reflected by the near-field beam splitter 408 to form a path direction opposite to that of the probe light 2, and finally enters the lower objective lens 405 and is focused on the sample on the sample stage 404 to excite the sample. The probe light 2 is emitted from the convex lens 411 and passes through the fiber coupler 6 and the photomultiplier tube 7 in sequence before being input into the lock-in amplifier 9. The lock-in amplifier 9 obtains the amplitude and phase of the transient absorption signal according to the electrical signal output by the photomultiplier tube 7, and transmits the amplitude to the industrial control computer 5 in the form of a voltage signal. The industrial control computer 5 then transmits the signal to the display device for imaging.

[0030] like Figure 1 As shown, in this embodiment, the femtosecond laser 1 is used to output pulsed light with a pulse width of 230 fs, while the probe light 2 and pump light 3, after being amplified by the first optical parametric amplifier 202 and the second optical parametric amplifier 301, have wavelengths ranging from 300 to 3000 nm. The optical parametric amplifiers are well-known in the art and are commercially available products.

[0031] like Figure 1 As shown, in this embodiment, a laser beam emitted by the femtosecond laser 1 is reflected by the first detector mirror 201 and then enters the first optical parametric amplifier 202 to form a detector beam 2. The detector beam 2 is reflected by the second detector mirror 203 and then passes sequentially through the detector beam expander assembly 204 and the detector attenuator assembly 206. The detector beam expander assembly 204 is used to expand and collimate the detector beam 2, and the detector attenuator assembly 206 is used to adjust the intensity of the detector beam 2 to meet experimental requirements. In this embodiment, the detector beam expander assembly 204 includes multiple beam expander lenses, and the detector attenuator assembly 206 includes multiple attenuators.

[0032] like Figure 1 As shown, in this embodiment, a first detection aperture 205 is provided between the detection beam expander component 204 and the detection attenuator component 206, and a second detection aperture 207 is provided on the side of the detection attenuator component 206 away from the detection beam expander component 204. The first detection aperture 205 and the second detection aperture 207 are used to optimize the shape of the detection beam 2 and improve the beam quality.

[0033] like Figure 1 As shown, in this embodiment, the probe light 2 passes through a probe light path limiting component 208 before entering the near-field optical scanning microscope system 4. In this embodiment, the probe light path limiting component 208 includes multiple optical path reflectors 2081. The probe light 2 is reflected sequentially by each optical path reflector 2081 and finally enters the near-field optical scanning microscope system 4 to detect the transient absorption signal of the sample.

[0034] like Figure 1 As shown, in this embodiment, another laser beam emitted by the femtosecond laser 1 is amplified by the second optical parametric amplifier 301 to form pump light 3, and the pump light 3 is input into the pump beam expander 305 after passing through the first path limiting component 302. In this embodiment, the first path limiting component 302 includes two first pump reflectors 3021, and the pump light 3 is reflected sequentially by the two first pump reflectors 3021 before entering the pump beam expander 305.

[0035] like Figure 1 As shown, in this embodiment, the pump beam expander assembly 305 includes multiple beam expander lenses to expand and collimate the pump light 3, thereby ensuring that the pump light 3 can effectively cover the sample under test. The pump attenuator assembly 306 includes multiple attenuators to adjust the intensity of the pump light to meet the experimental requirements.

[0036] like Figure 1 As shown, in this embodiment, the pump light 3 is emitted from the pump attenuator assembly 306 and reflected by the first steering mirror 3061 before entering the pump light delay assembly 307. In this embodiment, the pump light delay assembly 307 includes a right-angle retroreflector 3072 and multiple delay mirrors 3071. The probe light 2 is reflected by one delay mirror 3071 and enters the right-angle retroreflector 3072, while the probe light 2 emitted from the right-angle retroreflector 3072 is reflected by the other delay mirror 3071 and exits. The pump light delay assembly 307 is used to adjust the optical path difference between the pump light 3 and the probe light 2 to measure transient absorption signals under different time delay conditions. The present invention achieves precise optical path control by controlling the precise displacement of the right-angle retroreflector 3072.

[0037] like Figure 1 As shown, in this embodiment, the pump light 3 is emitted from the pump light delay component 307, reflected by the second deflecting mirror 3045, and then enters the acousto-optic modulator component 304. In this embodiment, the acousto-optic modulator component 304 includes an input aperture 3041, an input lens 3042, an acousto-optic modulator 3043, and an output lens 3044, arranged sequentially along the path of the pump light 3. The acousto-optic modulator component 304 is used to modulate the pulse frequency of the pump light 3 to half the output frequency of the femtosecond laser 1.

[0038] like Figure 1 As shown, in this embodiment, the pump light 3 is emitted from the acousto-optic modulator assembly 304 and then enters the near-field optical scanning microscope system 4 via the second path limiting assembly 308. In this embodiment, the second path limiting assembly 308 includes a plurality of second pump reflectors 3081, and the pump light 3 is reflected sequentially by each of the second pump reflectors 3081 before entering the near-field optical scanning microscope system 4.

[0039] like Figure 2 As shown, in this embodiment, the near-field optical scanning microscope system 4 further includes multiple near-field mirrors. The probe light 2 is reflected by the first near-field mirror 401 and enters the upper objective lens 402. After passing through the scanning probe 403, the sample stage 404, and the lower objective lens 405 in sequence, it is reflected by the second near-field mirror 406 and the third near-field mirror 407 in sequence and enters the near-field beam splitter 408. The probe light 2 passes through the near-field beam splitter 408 and the near-field filter assembly 409 in sequence and is reflected by the fourth near-field mirror 410 and enters the convex lens 411. The pump light 3 is reflected by the near-field beam splitter 408, the third near-field mirror 407, and the second near-field mirror 406 in sequence and enters the lower objective lens 405.

[0040] The scanning probe 403 is provided with nanopores through which the probe light 2 passes, and the spatial resolution of the present invention depends on the size of the nanopores. The diameter of the nanopores is between 60 and 150 nm, which is selected according to experimental requirements. Common specifications are 60 nm, 90 nm or 150 nm.

[0041] In addition, the reason why the pump light delay component 307 is placed on the pump light 3 path is that the probe light 2 coupled into the scanning probe 403 needs to have extremely high stability. Placing the laser delay component on the pump light 3 path can avoid its influence on the stability of the probe light 2.

[0042] like Figure 2As shown, in this embodiment, the sample support stage 404 is a piezoelectric displacement stage. This piezoelectric displacement stage can be used to precisely control the minute displacement of the sample to ensure scanning imaging at different positions. The piezoelectric displacement stage is a technology known in the art.

[0043] like Figure 1 As shown, the present invention also includes a timing module 8. The repetition rate signal of the femtosecond laser 1 is transmitted to the timing module 8, and the output repetition rate is reduced to half of the laser repetition rate by the repetition rate output control software in the timing module 8. Then, it is transmitted to the acousto-optic modulator 3043 of the acousto-optic modulator assembly 304 and the lock-in amplifier 9 respectively to achieve timing synchronization. The industrial control computer 5, fiber optic coupler 6, photomultiplier tube 7, timing module 8, lock-in amplifier 9, and acousto-optic modulator 3043 are all technologies known in the art and are commercially available products.

[0044] The working principle of this invention is as follows:

[0045] like Figure 1 As shown, during operation, the laser emitted by the femtosecond laser 1 is split into two laser beams by the beam splitter 101. These two beams are then amplified by the first optical parametric amplifier 202 and the second optical parametric amplifier 301, respectively, to form a probe beam 2 and a pump beam 3 with adjustable output wavelengths. The probe beam 2 is expanded and collimated by the probe beam expander 204 and its intensity is adjusted by the probe attenuator 206 before entering the near-field optical scanning microscope system 4. The pump beam 3 is first expanded and collimated by the pump beam expander 305 and its intensity is adjusted by the pump attenuator 306 before entering the pump beam delay component 307. The pump beam delay component 307 is used to adjust the wavelength of the pump beam 3 relative to the probe beam 2. The optical path difference of light 2 is used to measure transient absorption signals under different time delay conditions. Since the probe light 2 of this invention needs to irradiate the sample through the nanopores on the scanning probe 403 after entering the near-field optical scanning microscope system 4, the probe light 2 requires extremely high stability. Therefore, this invention places a laser delay component on the path of the pump light 3 to ensure the stability of the probe light 2. Then, the pump light 3 passes through the acousto-optic modulator component 304 and the second path limiting component 308 before entering the near-field optical scanning microscope system 4. The acousto-optic modulator component 304 is used to modulate the pulse frequency of the pump light 3 to half the output frequency of the femtosecond laser 1.

[0046] And such Figure 2As shown, after the pump light 3 enters the near-field optical scanning microscope system 4, it is first reflected by the near-field beam splitter 408 to form a path opposite to that of the probe light 2. It is then reflected sequentially by the third near-field mirror 407 and the second near-field mirror 406 before entering the lower objective lens 405 and focusing on the sample on the sample stage 404 to excite the sample. The probe light 2, after entering the near-field optical scanning microscope system 4, sequentially passes through the upper objective lens 402, scanning probe 403, sample stage 404, lower objective lens 405, near-field beam splitter 408, near-field filter assembly 409, and convex lens 411. After exiting the convex lens 411, the probe light 2 sequentially passes through the fiber coupler 6 and photomultiplier tube 7 before being input into the lock-in amplifier 9. The lock-in amplifier 9 obtains the amplitude and phase of the transient absorption signal based on the electrical signal output by the photomultiplier tube 7 and converts the amplitude into voltage. The signal is transmitted to the industrial control computer 5, which then transmits the signal to the display device for imaging. During the above process, the nanopores on the scanning probe 403 couple the probe light 2 to a local area on the sample surface to achieve nanoscale spatial resolution. At the same time, the sample support stage 404 is a piezoelectric potential moving stage that can be used to precisely control the tiny displacement of the sample to ensure scanning imaging at different positions. The near-field filter assembly 409 is used to filter stray light from the pump light 3 or other unnecessary light signals mixed in with the probe light 2 to ensure the purity of the probe light 2. In addition, the repetition rate signal of the femtosecond laser 1 is transmitted to the timing module 8, and the repetition rate output control software in the timing module 8 reduces the output repetition rate to half of the laser repetition rate. Then, it is transmitted to the acousto-optic modulator 3043 of the acousto-optic modulator assembly 304 and the lock-in amplifier 9 to achieve timing synchronization.

[0047] This invention combines near-field optical super-resolution imaging technology with femtosecond transient absorption spectroscopy, breaking through the optical diffraction limit and achieving high spatiotemporal resolution visualization of microscopic carrier dynamics. This provides a novel research tool for in-depth study of excited-state dynamics in microstructures. By developing this super-resolution carrier dynamics imaging platform, it is possible to detect carrier dynamics behavior in complex nanostructures (such as semiconductor polycrystalline thin films and monodisperse nanocrystals) with high precision and multiple dimensions, filling the spatial and temporal resolution limitations of existing technologies.

[0048] The following application example further illustrates the working principle of the present invention.

[0049] Application Example 1:

[0050] This application example uses a monolayer MoS2 isolated grain as an example. The specific process is as follows:

[0051] 1. Sample Preparation: The experimental sample consisted of isolated monolayer molybdenum disulfide (MoS2) grains, prepared on a sapphire substrate by chemical vapor deposition (CVD) and then transferred to a 0.15 mm thick glass slide. MoS2 is a two-dimensional semiconductor material with excellent photoelectric properties, suitable for research in photoelectric conversion and transistor fields. Its bright-field image is shown below. Figure 3 As shown.

[0052] 2. Light Source Setup: A femtosecond laser 1 generates laser pulses with a pulse width of 230 fs, which are then modulated by an optical parametric amplifier into tunable wavelength pump light 3 and probe light 2. Pump light 3 is used to excite charge carriers in the MoS2 grains, and probe light 2 is used to detect the kinetic response in the sample.

[0053] 3. Excitation process: The pump light 3 first passes through the pump light delay component 307 in the system, and then is modulated to half the frequency of the femtosecond laser by the acousto-optic modulator component 304 before entering the near-field optical scanning microscope system 4. Finally, it is focused onto the MoS2 grains on the sample through the lower objective lens 405 to excite the charge carriers in the grains.

[0054] 4. Detection Process: The probe light 2 passes through the nanopores on the tip of the upper objective lens 402 and the scanning probe 403, performing super-resolution imaging of the sample surface under near-field conditions. In this way, carrier dynamics information of isolated MoS2 grains can be obtained at the nanoscale.

[0055] 5. Data Acquisition and Processing: The probe light 2 is output from the near-field optical scanning microscope system 4 and transmitted to the photomultiplier tube 7 via the fiber optic coupler 6. After gain amplification, the signal is transmitted to the lock-in amplifier 9 to obtain the amplitude and phase of the transient absorption signal. The delay time can be changed by the pump light delay component 307 to obtain the transient absorption signal at different time points and to plot the carrier dynamic decay curve. The delay time is selected for imaging.

[0056] 6. Synchronous Imaging: The piezoelectric displacement stage is controlled to scan the sample, and the transient absorption voltage signal acquired by the lock-in amplifier 9 is synchronized with the atomic force microscope imaging, ultimately obtaining ultra-high time and spatial resolution carrier dynamics images of the MoS2 grains. The measured ultra-resolution carrier dynamics images at different delay times are shown below. Figures 4-7 As shown, where Figure 5 , Figure 6 and Figure 7 for Figure 4 A magnified view of region A in the middle.

[0057] This application example successfully utilizes the near-field optical super-resolution imaging system of the present invention to reveal the carrier dynamics characteristics in isolated monolayer MoS2 grains, verifying the effectiveness of the system in nanomaterial research, and providing an important reference for further optimizing the photoelectric properties of two-dimensional semiconductor materials.

Claims

1. A near-field optical super-resolution carrier dynamics imaging system, characterized in that: The system includes a femtosecond laser (1) and a near-field optical scanning microscope system (4). The laser emitted by the femtosecond laser (1) is split into a probe beam (2) and a pump beam (3) by a beam splitter (101). The probe beam (2) passes through a probe beam expander assembly (204) and a probe attenuator assembly (206) in sequence before entering the near-field optical scanning microscope system (4). The pump beam (3) passes through a pump beam expander assembly (305), a pump attenuator assembly (306), a pump beam delay assembly (307), and an acousto-optic modulator assembly (304) in sequence before entering the near-field optical scanning microscope system (4). The near-field optical scanning microscope system (4) includes an upper objective lens (402) arranged sequentially along the path of the probe beam (2). The system includes a scanning probe (403), a sample stage (404), a lower objective lens (405), a near-field beam splitter (408), a near-field filter assembly (409), and a convex lens (411). The upper objective lens (402) and the lower objective lens (405) are symmetrically arranged. The scanning probe (403) has a nanopore for the probe light (2) to pass through. The pump light (3) is reflected by the near-field beam splitter (408) to form a path direction opposite to that of the probe light (2), and finally enters the lower objective lens (405) and is focused on the sample on the sample stage (404). The probe light (2) is emitted from the convex lens (411) and passes through the fiber coupler (6) and the photomultiplier tube (7) in sequence before being input into the lock-in amplifier (9).

2. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: The laser emitted by the femtosecond laser (1) is split into two laser beams by a beam splitter (101). One laser beam is converted into a wavelength-tunable probe beam (2) by a first optical parametric amplifier (202), and the other laser beam is converted into a wavelength-tunable pump beam (3) by a second optical parametric amplifier (301).

3. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: A first detection aperture (205) is provided between the detection beam expander assembly (204) and the detection attenuator assembly (206), and a second detection aperture (207) is provided on the side of the detection attenuator assembly (206) away from the detection beam expander assembly (204).

4. The near-field optical super-resolution carrier dynamics imaging system according to claim 3, characterized in that: The probe light (2) emitted from the second probe aperture (207) enters a probe light path limiting component (208), which includes multiple optical path reflectors (2081). The probe light (2) is reflected by each optical path reflector (2081) in sequence and then enters the near-field optical scanning microscope system (4).

5. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: The pump light delay assembly (307) includes a movable right-angle retroreflector (3072) and a plurality of delay mirrors (3071), wherein the probe light (2) is reflected by the delay mirror (3071) on one side and then enters the right-angle retroreflector (3072), while the probe light (2) emitted from the right-angle retroreflector (3072) is reflected by the delay mirror (3071) on the other side and then emitted.

6. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: The acousto-optic modulator assembly (304) includes an input aperture (3041), an input lens (3042), an acousto-optic modulator (3043), and an output lens (3044) arranged sequentially along the path of the pump light (3), and the pulse frequency of the pump light (3) is modulated by the acousto-optic modulator assembly (304) to half of the output frequency of the femtosecond laser (1).

7. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: Pump light (3) is emitted from the acousto-optic modulator assembly (304) and then enters the near-field optical scanning microscope system (4) through the second path limiting assembly (308), the second path limiting assembly (308) including a plurality of second pump mirrors (3081).

8. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: The near-field optical scanning microscope system (4) includes multiple near-field mirrors. The probe light (2) is reflected by the first near-field mirror (401) and enters the upper objective lens (402). It then passes through the scanning probe (403), the sample stage (404), and the lower objective lens (405) in sequence. After passing through the second near-field mirror (406) and the third near-field mirror (407), it enters the near-field beam splitter (408). The probe light (2) passes through the near-field beam splitter (408) and the near-field filter assembly (409) in sequence and is reflected by the fourth near-field mirror (410) into the convex lens (411). The pump light (3) is reflected by the near-field beam splitter (408), the third near-field mirror (407), and the second near-field mirror (406) in sequence and enters the lower objective lens (405).

9. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: The sample support stage (404) is a piezoelectric moving stage.

10. The near-field optical super-resolution carrier dynamics imaging system according to claim 1, characterized in that: The lock-in amplifier (9) obtains the amplitude and phase of the transient absorption signal based on the electrical signal output by the photomultiplier tube (7), and transmits the amplitude to the industrial control computer (5) in the form of a voltage signal. The repetition frequency signal of the femtosecond laser (1) is transmitted to a timing module (8), and after being down-frequency processed by the timing module (8), it is transmitted to the acousto-optic modulator (3043) of the acousto-optic modulator assembly (304) and the lock-in amplifier (9).

Images