阅读说明：本技术 二维半导体材料中光生载流子的差分反射探测系统 (Differential reflection detection system for photogenerated carriers in two-dimensional semiconductor material ) 是由 姚鹏 李昱江 杨林 王浩枫 于 2021-08-17 设计创作，主要内容包括：本发明涉及一种二维半导体材料中光生载流子的差分反射探测系统,属于全光学微观探测领域。本发明二极管激光器输出连续激光,用于激发钛宝石激光器,钛宝石激光器输出脉冲激光,被分束镜分成两束,用于激发倍频晶体和光纤连续激光器,倍频晶体输出的激光被输入到机械斩波器,机械斩波器输出的泵浦激光通过显微物镜后到达样品,光纤连续激光器输出的探测激光通过机械位移平台后,通过显微物镜后到达样品,样品的反射信号通过显微物镜和滤波片后到达光电探测器,样品的反射信号中泵浦激光被光电探测器前的滤波片滤去,光电探测器连接锁相放大器,锁相放大器连接机械斩波器。本发明实现了半导体光生载流子的瞬态光学探测。(The invention relates to a differential reflection detection system for photogenerated carriers in a two-dimensional semiconductor material, belonging to the field of all-optical microscopic detection. The diode laser outputs continuous laser for exciting the titanium gem laser, the titanium gem laser outputs pulse laser which is divided into two beams by a beam splitter for exciting a frequency doubling crystal and an optical fiber continuous laser, the laser output by the frequency doubling crystal is input into a mechanical chopper, the pump laser output by the mechanical chopper reaches a sample after passing through a microscope objective, the detection laser output by the optical fiber continuous laser reaches the sample after passing through a mechanical displacement platform, the reflection signal of the sample reaches a photoelectric detector after passing through the microscope objective and a filter, the pump laser in the reflection signal of the sample is filtered by the filter in front of the photoelectric detector, the photoelectric detector is connected with a phase-locked amplifier, and the phase-locked amplifier is connected with the mechanical chopper. The invention realizes the transient optical detection of semiconductor photon-generated carriers.)

1. A differential reflection detection system for photo-generated carriers in a two-dimensional semiconductor material is characterized by comprising a diode laser, a titanium sapphire laser, an optical fiber continuous laser, a frequency doubling crystal (BBO), a mechanical chopper, a mechanical displacement platform, a microscope objective, a filter, a photoelectric detector and a phase-locked amplifier;

the diode laser is used as a pumping source to output continuous laser, the continuous laser is used for exciting the titanium sapphire laser, and the titanium sapphire laser outputs pulse laser;

the laser emitted from the titanium gem laser is divided into two beams by a beam splitter, and the two beams are respectively used for exciting a frequency doubling crystal (BBO) and an optical fiber continuous laser, and the laser generated by the frequency doubling crystal (BBO) and the optical fiber continuous laser is respectively used as pump laser and detection laser; the pump laser is used for exciting the sample to generate carriers; the frequency of the detection laser is adjusted to be consistent with the frequency corresponding to the excitonic energy of the sample;

laser output by a frequency doubling crystal (BBO) is input into a mechanical chopper, and pump laser output by the mechanical chopper reaches a sample after passing through a microscope objective;

the detection laser output by the optical fiber continuous laser changes the optical path of the detection laser through linear displacement by the mechanical displacement platform, and then reaches a sample after passing through the microscope objective;

the reflected signal of the sample reaches a photoelectric detector after passing through a microscope objective and a filter, pump laser in the reflected signal of the sample is filtered by the filter in front of the photoelectric detector, the photoelectric detector is connected with a phase-locked amplifier, the phase-locked amplifier is connected with a mechanical chopper, the phase-locked amplifier analyzes and measures the obtained detection laser reflected signal according to the frequency of the mechanical chopper, and detection laser reflected signals R and R with constant phase difference generated by the pump laser and the detection laser due to optical path difference are obtained through phase locking₀Then calculating a differential reflection signal (R-R)₀)/R₀Wherein the reflected light of the detection laser has a reflection signal R when the two-dimensional semiconductor material is not excited by the pump laser₀The reflected signal when the two-dimensional semiconductor material is excited by the pump laser is R.

2. The system of claim 1, wherein the diode laser is used as a pump source to output 532 nm continuous laser with an output power of 10 watts, the continuous laser is used to excite the Tisapphire laser, and the Tisapphire laser can output a pulse laser with an output power of about 2 watts in a range of 650nm to 950 nm.

3. The system of claim 2, wherein the ti-sapphire laser is configured to generate laser pulses with a repetition rate of 80MHz at 100fs via mode locking, the time interval between two laser pulses is 13 ns, and the bandwidth of the laser pulses is continuously adjustable.

4. The system according to claim 1, wherein the frequency doubling crystal (BBO) doubles the frequency of the input laser light to meet the requirement of experiment for a specific wavelength, and the frequency doubling crystal can be placed at any position in the experiment system according to the requirement of experiment.

5. The system for differential reflective detection of photogenerated carriers in a two-dimensional semiconductor material as claimed in claim 1 wherein the fiber-optic continuous laser is capable of producing a wide range of output wavelengths that produce laser wavelengths that vary with the excitation wavelength, ranging from 390 to 1050 nanometers.

6. The system for differential reflection detection of photogenerated carriers in a two dimensional semiconductor material as claimed in claim 1 wherein the mechanical chopper is rotated at a frequency of 2KHz and its fan blades will continuously chop the pump laser, making the pump laser intermittent.

7. The system for differential reflective detection of photogenerated carriers in a two dimensional semiconductor material as claimed in claim 1 wherein said photodetector is a silicon based photodetector and converts the detected optical signal into an electrical signal that is transmitted to a lock in amplifier.

8. The system for differential reflective detection of photogenerated carriers in a two-dimensional semiconductor material as claimed in claim 1, wherein the pump laser and the detection laser are both focused vertically on the sample surface through the microscope objective.

9. The system for differential reflection detection of photogenerated carriers in a two-dimensional semiconductor material as claimed in claim 8, wherein the system further comprises a camera for collecting the reflected light of the detection laser after being reflected by the sample and passing through the microscope objective to observe the sample and to observe whether the focal point of the laser is on the surface of the sample.

10. A system for differential reflection detection of photogenerated carriers in a two-dimensional semiconductor material as claimed in claim 9 further comprising optical devices 1-8, wherein optical devices 1-4 are half-mirrors and optical devices 5-8 are mirrors; the laser output by the titanium gem laser reaches the optical fiber continuous laser and the frequency doubling crystal through the semi-transparent semi-reflecting mirror 1, the laser output by the frequency doubling crystal reaches the mechanical chopper through the reflecting mirror 6, and the laser output by the mechanical chopper reaches the microscope objective through the reflecting mirror 7 and the semi-transparent semi-reflecting mirror 2; laser output by the optical fiber continuous laser passes through the mechanical displacement platform and then reaches the microscope objective through the reflector 5 and the semi-transparent and semi-reflective mirrors 4, 3 and 2; the reflected light of the detection laser and the pumping laser passing through the sample passes through the micro objective lens and then reaches the filter plate through the semi-transparent semi-reflective mirrors 2, 3 and 4, and the reflected light of the detection laser passing through the sample passes through the micro objective lens and then reaches the camera through the semi-transparent semi-reflective mirrors 2 and 3 and the reflector 8.

Technical Field

The invention belongs to the field of all-optical microscopic detection, and particularly relates to a differential reflection detection system for photogenerated carriers in a two-dimensional semiconductor material.

Background

Carrier kinetic processes are very important physical processes for many applications. "carrier-kinetic processes" can be generally considered as the displacement of carriers in real space, the transfer of energy or the simultaneous disappearance of electrons and holes. Because the charged carriers are generally endowed with the roles of carrying information and energy, the carrier transport process can directly influence the carrier performance of the carriers in practical application.

Since the transport process of carriers is very rapid, often occurring within a few picoseconds, the study of the transport process of carriers in non-thermodynamic equilibrium requires that the experimental system have a very high time resolution. Optical experimental methods used for the study of carrier transport processes so far include transient gratings, spatially resolved photoluminescence, and ultrafast laser pumping detection techniques. In contrast, ultrafast laser-based optical technology, because of its high temporal resolution, is considered as a standard tool for studying carrier kinetics in non-thermodynamic equilibrium.

The patent is intended to design an all-optical detection system for photo-generated carriers in a two-dimensional semiconductor material with femtosecond-nanosecond time resolution and transient response based on light reflection.

Disclosure of Invention

Technical problem to be solved

The invention aims to solve the technical problem of how to provide a differential reflection detection system for photo-generated carriers in a two-dimensional semiconductor material so as to realize the detection of the dynamics of the carriers in the two-dimensional semiconductor material under the time scale of femtosecond to picosecond.

(II) technical scheme

In order to solve the technical problem, the invention provides a differential reflection detection system for photo-generated carriers in a two-dimensional semiconductor material, which comprises a diode laser, a titanium sapphire laser, an optical fiber continuous laser, a frequency doubling crystal (BBO), a mechanical chopper, a mechanical displacement platform, a microscope objective, a filter, a photoelectric detector and a phase-locked amplifier;

the diode laser is used as a pumping source to output continuous laser, the continuous laser is used for exciting the titanium sapphire laser, and the titanium sapphire laser outputs pulse laser;

the laser emitted from the titanium gem laser is divided into two beams by a beam splitter, and the two beams are respectively used for exciting a frequency doubling crystal (BBO) and an optical fiber continuous laser, and the laser generated by the frequency doubling crystal (BBO) and the optical fiber continuous laser is respectively used as pump laser and detection laser; the pump laser is used for exciting the sample to generate carriers; the frequency of the detection laser is adjusted to be consistent with the frequency corresponding to the excitonic energy of the sample;

laser output by a frequency doubling crystal (BBO) is input into a mechanical chopper, and pump laser output by the mechanical chopper reaches a sample after passing through a microscope objective;

the detection laser output by the optical fiber continuous laser changes the optical path of the detection laser through linear displacement by the mechanical displacement platform, and then reaches a sample after passing through the microscope objective;

the reflected signal of the sample reaches a photoelectric detector after passing through a microscope objective and a filter, pump laser in the reflected signal of the sample is filtered by the filter in front of the photoelectric detector, the photoelectric detector is connected with a phase-locked amplifier, the phase-locked amplifier is connected with a mechanical chopper, the phase-locked amplifier analyzes and measures the obtained detection laser reflected signal according to the frequency of the mechanical chopper, and detection laser reflected signals R and R with constant phase difference generated by the pump laser and the detection laser due to optical path difference are obtained through phase locking₀Then calculating a differential reflection signal R-R₀)/R₀Wherein the reflected light of the detection laser has a reflection signal R when the two-dimensional semiconductor material is not excited by the pump laser₀The reflected signal when the two-dimensional semiconductor material is excited by the pump laser is R.

Further, the diode laser is used as a pumping source to output 532 nm continuous laser with output power of 10 watts, the continuous laser is used for exciting the titanium sapphire laser, the titanium sapphire laser can output pulse laser within the range of 650nm to 950nm, and the output power is about 2 watts.

Further, the titanium sapphire laser generates laser pulses with the repetition frequency of 80MHz and the frequency of 100fs through mode locking, the time interval between two laser pulses is 13 nanoseconds, and the bandwidth of the laser pulses is continuously adjustable.

Furthermore, the frequency doubling crystal (BBO) doubles the frequency of the input laser, so that the requirement of experiment on specific wavelength is met, and the frequency doubling crystal can be placed at any position in an experiment system according to the requirement of the experiment.

Further, fiber-optic continuum lasers are capable of producing a wide range of output wavelengths that produce laser wavelengths that vary as a function of excitation wavelength, ranging from 390 to 1050 nanometers.

Furthermore, the mechanical chopper rotates at the frequency of 2KHz, and the fan blades of the mechanical chopper can continuously cut off the pump laser, so that the pump laser is intermittent.

Furthermore, the photoelectric detector is a silicon-based optical detector, converts the detected optical signal into an electrical signal, and transmits the electrical signal into the phase-locked amplifier.

Further, the pump laser and the detection laser are vertically converged on the surface of the sample through the microscope objective.

Further, the system also comprises a camera, and the camera collects the reflected light of the detection laser after being reflected by the sample and passing through the microscope objective so as to observe the sample and simultaneously observe whether the focal point of the laser is on the surface of the sample.

Further, the system also comprises an optical device 1-8, wherein the optical device 1-4 is a half-transmitting half-reflecting mirror, and the optical device 5-8 is a reflecting mirror; the laser output by the titanium gem laser reaches the optical fiber continuous laser and the frequency doubling crystal through the semi-transparent semi-reflecting mirror 1, the laser output by the frequency doubling crystal reaches the mechanical chopper through the reflecting mirror 6, and the laser output by the mechanical chopper reaches the microscope objective through the reflecting mirror 7 and the semi-transparent semi-reflecting mirror 2; laser output by the optical fiber continuous laser passes through the mechanical displacement platform and then reaches the microscope objective through the reflector 5 and the semi-transparent and semi-reflective mirrors 4, 3 and 2; the reflected light of the detection laser and the pumping laser passing through the sample passes through the micro objective lens and then reaches the filter plate through the semi-transparent semi-reflective mirrors 2, 3 and 4, and the reflected light of the detection laser passing through the sample passes through the micro objective lens and then reaches the camera through the semi-transparent semi-reflective mirrors 2 and 3 and the reflector 8.

(III) advantageous effects

The invention provides a differential reflection detection system for photogenerated carriers in a two-dimensional semiconductor material, which is an effective detection system summarized through experimental verification. The method is suitable for two-dimensional semiconductor materials, and transient optical detection of semiconductor photon-generated carriers is realized by utilizing the characteristic of ultrafast laser femtosecond-level duration. The differential reflection detection system fully utilizes femtosecond-level pulse laser generated by a titanium gem laser, and realizes the detection of carrier dynamics in a two-dimensional semiconductor material under the time scale of femtosecond to picosecond; meanwhile, due to the adoption of an all-optical detection means, the differential reflection detection system has extremely strong universality and is an ideal tool for researching carrier dynamics.

Drawings

FIG. 1 is a schematic diagram of a pulsed laser light source module in a detection system according to the present invention;

FIG. 2 is a reference diagram of a differential reflection detection system of the present invention.

Detailed Description

In order to make the objects, contents and advantages of the present invention clearer, the following detailed description of the embodiments of the present invention will be made in conjunction with the accompanying drawings and examples.

In view of the above problems, the present invention is directed to an all-optical detection system for photo-generated carriers in a two-dimensional semiconductor material with femtosecond-nanosecond time resolution and timely response based on light reflection, the system comprising: diode laser, titanium gem laser, optical fiber continuous laser, frequency doubling crystal (BBO), mechanical chopper, mechanical displacement platform, microscope objective, filter, photoelectric detector and phase-locked amplifier, the system also can include camera.

The diode laser is used as a pumping source to output 532 nm continuous laser with the output power of 10 watts, the continuous laser is used for exciting the titanium sapphire laser, the titanium sapphire laser can output pulse laser within the range of 650nm to 950nm (the wavelength range of the output laser can be changed under the condition of introducing nitrogen), and the output power is about 2 watts. The titanium gem laser generates laser pulses with 100fs and the repetition frequency of 80MHz through mode locking, and the time interval between two laser pulses is about 13 nanoseconds. The bandwidth of the laser pulse is continuously adjustable, typically kept around 10nm, and the pulsed laser light source module is shown in fig. 1.

The outgoing laser of the titanium gem laser is divided into two beams by a beam splitter (1) and is respectively used for exciting a frequency doubling crystal (BBO) and an optical fiber continuous laser. The fiber continuous laser can generate a wider output wavelength range, so the fiber continuous laser is widely applied to an ultrafast laser pumping detection system, and the generated laser wavelength can change along with the change of the excitation wavelength and ranges from 390 to 1050 nanometers; the frequency doubling crystal doubles the frequency of the input laser, so that the requirement of experiment on specific wavelength is met, and the frequency doubling crystal can be placed at any position in an experiment system according to the requirement of the experiment. The laser light generated by the frequency doubling crystal (BBO) and the fiber continuum laser will be used as pump laser light and probe laser light, respectively, as shown in fig. 2. Wherein the pump laser is used for exciting the sample to generate carriers; the frequency of the detection laser is adjusted to be consistent with the frequency corresponding to the exciton energy of the sample, so that the detection signal reflected by the sample carries the 'information' of the density of the carriers in the exciton energy state.

Laser output by a frequency doubling crystal (BBO) is input into a mechanical chopper, and pump laser output by the mechanical chopper reaches a sample after passing through a microscope objective. A mechanical chopper is introduced to generate a differential reflected signal. The mechanical chopper rotates at the frequency of 2KHz, and the fan blades of the mechanical chopper can continuously chop the pump laser, so that the pump laser is intermittent; while the detection laser is always in a continuous state. At this time, the reflection signal of the reflected light of the probe laser when the two-dimensional semiconductor material is not excited by the pump laser is R₀When the pump laser excites the two-dimensional semiconductor material, the reflection signal is R, thereby forming a differential reflection signal delta R/R₀＝(R-R₀)/R₀。

The detection laser output by the optical fiber continuous laser changes the optical path of the detection laser through the mechanical displacement platform and linear displacement, so that time delay is introduced, and then the detection laser reaches a sample after passing through the microscope objective. Introducing a mechanical displacement platform into a detection laser light path: for time-resolved trend of change of carrier density in exciton energy state in detection sample, the time difference between the arrival of the pump laser and the arrival of the detection laser at the sample can be continuously changed, so that the detection laser arrives at the sample later than the arrival of the pump laser at the sample, namely, a time delay delta T exists between the detection laser and the pump laser, and as the time of arrival of the detection laser at the sample is slower and more than that of the pump laser, the detection signal reflected by the sample reflects the change of carrier density (in exciton state corresponding to the detection laser energy) with time after being excited by the pump laser.

The reflected signal of the sample reaches the photoelectric detector after passing through the microscope objective and the filter, and the pump laser in the reflected signal of the sample is filtered by the filter in front of the photoelectric detector. The photoelectric detector is connected with a phase-locked amplifier, and the phase-locked amplifier is connected with a mechanical chopper. The reflected signal of the sample is led into a silicon-based optical detector, and the detected optical signal is converted into an electric signal and transmitted into a phase-locked amplifier. Wherein, the phase-locked amplifier is connected with the mechanical chopper, the detected laser reflection signal obtained by measurement is analyzed according to the frequency (2 KHz) of the mechanical chopper, the detected laser reflection signal R with constant phase difference generated by the pump laser and the detected laser due to the optical path difference is obtained by phase locking, and then the differential reflection signal (R-R) is artificially calculated₀)/R₀. The advantage of calculating the differential reflection signal is that the signal generated by exciting the sample with the ambient light can be removed, so that the carrier density of the exciton state corresponding to the detection laser energy after the sample is excited by the laser can be obtained, that is, the pump laser can excite part of the carriers in the exciton state corresponding to the detection laser energy to the conduction band, so as to reduce the carrier density of the exciton state corresponding to the detection laser energy, and the larger the difference of the carrier densities of the exciton states corresponding to the detection laser energy, the stronger the differential reflection signal.

Further, 1) the light source used is a diode laser, which generates 532 nm continuous laser with power of 10 w; 2) the laser bandwidth generated by the titanium sapphire laser can be adjusted between 50 femtoseconds and 80 picoseconds.

Further, a frequency doubling crystal (BBO) is selectively used or not used according to a predetermined wavelength, and has no fixed position.

Further, 1) a mechanical chopper is arranged in the pump laser light path and used for generating intermittent pump pulse laser; 2) reflected signal R₀And R is a signal for measuring the reflected detection laser, and the signal of the pump laser is filtered by a filter plate in front of the detector.

Further, the displacement stage changes the optical path of the probe laser by linear displacement, thereby changing the time difference Δ T between the probe laser and the pump laser reaching the sample. In the fifth step 1), a lock-in amplifier (lock-in amplifier) is used for processing the electric signal generated by the photoelectric detector; 2) the pump laser and the detection laser are vertically converged on the surface of the sample through the microscope objective.

As shown in fig. 2, a camera is further disposed in the system, and the camera collects reflected light of the detection laser after being reflected by the sample and passing through the microscope, so as to observe the sample and observe whether the focal point of the laser is on the surface of the sample.

As shown in fig. 2, the system further includes an optical device 1-8, wherein 1-4 is a half-mirror and 5-8 is a mirror.

The laser output by the titanium gem laser reaches the optical fiber continuous laser and the frequency doubling crystal through the semi-transparent semi-reflecting mirror 1, the laser output by the frequency doubling crystal reaches the mechanical chopper through the reflecting mirror 6, and the laser output by the mechanical chopper reaches the microscope objective through the reflecting mirror 7 and the semi-transparent semi-reflecting mirror 2; laser output by the optical fiber continuous laser passes through the mechanical displacement platform and then reaches the microscope objective through the reflector 5 and the semi-transparent and semi-reflective mirrors 4, 3 and 2; the reflected light of the sample passes through the microscope, then reaches the filter plate through the half mirrors 2, 3 and 4, and then reaches the camera through the half mirrors 2 and 3 and the reflector 8.

The invention is an effective detection system summarized by experimental verification. The method is suitable for two-dimensional semiconductor materials, and transient optical detection of semiconductor photon-generated carriers is realized by utilizing the characteristic of ultrafast laser femtosecond-level duration. The differential reflection detection system fully utilizes femtosecond-level pulse laser generated by a titanium gem laser, and realizes the detection of carrier dynamics in a two-dimensional semiconductor material under the time scale of femtosecond to picosecond; meanwhile, due to the adoption of an all-optical detection means, the differential reflection detection system has extremely strong universality and is an ideal tool for researching carrier dynamics.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.