阅读说明：本技术 一种实现原子尺度激光泵浦探测的方法和装置 (Method and device for realizing atomic scale laser pumping detection ) 是由 江颖 郭钞宇 于 2020-05-14 设计创作，主要内容包括：本发明公开了一种实现原子尺度激光泵浦探测的方法和装置,该方法包括：调节第一激光器发射的第一激光脉冲和第二激光器发射的第二激光脉冲之间的延迟时间；基于预设调制频率调制所述延迟时间；合束准直所述第一激光脉冲和所述第二激光脉冲并照射待探测物；探测被照射的所述待探测物的隧穿电流信号；基于所述预设调制频率提取所述隧穿电流信号中的与所述延迟时间相关的信号。本发明在实现信号调制的同时保证了单位时间内激光平均功率恒定,因此可以消除热效应对扫描隧道显微镜的影响,实现了激光泵浦探测技术和扫描隧道显微镜技术的结合,能够同时获得原子级别的空间分辨率和纳秒尺度的时间分辨率。(The invention discloses a method and a device for realizing atomic scale laser pumping detection, wherein the method comprises the following steps: adjusting a delay time between a first laser pulse emitted by a first laser and a second laser pulse emitted by a second laser; modulating the delay time based on a preset modulation frequency; the combined beam collimates the first laser pulse and the second laser pulse and irradiates an object to be detected; detecting a tunneling current signal of the irradiated object to be detected; and extracting a signal related to the delay time in the tunneling current signal based on the preset modulation frequency. The invention ensures that the average power of the laser is constant in unit time while realizing signal modulation, thereby eliminating the influence of thermal effect on the scanning tunnel microscope, realizing the combination of laser pumping detection technology and scanning tunnel microscope technology, and simultaneously obtaining the spatial resolution of atomic level and the time resolution of nanosecond scale.)

1. A method of implementing atomic scale laser pumping detection, the method comprising:

adjusting a delay time between a first laser pulse emitted by a first laser and a second laser pulse emitted by a second laser;

modulating the delay time based on a preset modulation frequency;

the combined beam collimates the first laser pulse and the second laser pulse and irradiates an object to be detected;

detecting a tunneling current signal of the irradiated object to be detected;

and extracting a signal related to the delay time in the tunneling current signal based on the preset modulation frequency.

2. The method for realizing atomic scale laser pumping detection according to claim 1,

said adjusting a delay time between a first laser pulse emitted by a first laser and a second laser pulse emitted by a second laser, said delay time being modulated based on a preset modulation frequency,

the method specifically comprises the following steps: triggering the first laser based on a first electrical pulse of a pulse delay, triggering the second laser based on a second electrical pulse of the waveform generator, modulating the delay time based on a preset modulation frequency of the waveform generator.

3. The method for realizing atomic scale laser pumping detection according to claim 2,

the delay time is modulated based on a preset modulation frequency of a waveform generator,

specifically, a square wave with a preset frequency modulation range F is applied to modulate the frequency of the second electric pulse based on the repetition frequency F of the first electric pulse and the second electric pulse, the repetition frequency of the second electric pulse after frequency modulation is changed between F + F and F-F, wherein F >1000F, and the switching frequency of the square wave is F0.

4. The method for realizing atomic scale laser pumping detection according to claim 3,

the minimum value and the maximum value of the time of the second electric pulse deviating from the normal sequence after the frequency modulation are respectively delta t_dAnd n Δ t_dWherein n-F/F0, the time of the second electrical pulse from the normal sequence varies linearly, the delay time varies based on an odd harmonic function F (t), the odd harmonic function F (t) and Δ t_dAnd (4) correlating.

5. The method for realizing atomic scale laser pumping detection according to claim 4,

the extracting a signal related to the delay time from the tunneling current signal based on the preset modulation frequency,

specifically, the tunneling current is obtained based on a scanning tunneling microscope, the tunneling current is used as a source signal, a phase-locked amplifier refers to the switching frequency F0 of the square wave, and a component F (t) which is identical to the waveform of the square wave and only contains odd harmonics in the odd harmonic function F (t) is extracted_od(t) for said odd harmonic-only component f_od(t) successively carrying out a first order approximation,And after Taylor formula expansion and integration processing, acquiring a current signal containing a carrier kinetic signal.

6. The method for realizing atomic scale laser pumping detection according to any of claims 1 to 5,

the first laser comprises a Q-switch laser, the second laser comprises a Q-switch laser, and a Q-switch modulator is arranged in a resonant cavity of the Q-switch laser.

7. The method for realizing atomic scale laser pumping detection according to claim 6,

the first laser and the second laser comprise nanosecond lasers or picosecond lasers.

8. A device for realizing atomic scale laser pumping detection is characterized by comprising

The delay time adjusting module is used for adjusting the delay time between a first laser pulse emitted by the first laser and a second laser pulse emitted by the second laser;

the delay time modulation module is used for modulating the delay time based on a preset modulation frequency;

the beam combination collimation module is used for combining and collimating the first laser pulse and the second laser pulse and irradiating an object to be detected;

the tunneling current signal detection module is used for detecting the tunneling current signal of the irradiated object to be detected;

and the signal extraction module is used for extracting a signal related to the delay time in the tunneling current signal based on the preset modulation frequency.

9. The apparatus for realizing atomic scale laser pumping detection according to claim 8,

the delay time adjusting module comprises a pulse delayer;

the delay time modulation module comprises a waveform generator;

triggering the first laser based on a first electrical pulse of a pulse delay, triggering the second laser based on a second electrical pulse of the waveform generator, modulating the delay time based on a preset modulation frequency of the waveform generator.

10. The apparatus for realizing atomic scale laser pumping detection according to claim 9,

the beam combination collimation module comprises a polarizer, a beam splitter, a filter, a half-wave plate and a prism which are connected in a preset sequence;

the tunneling current signal detection module comprises a scanning tunneling microscope, and the scanning tunneling microscope acquires the tunneling current;

the signal extraction module takes the tunneling current as a source signal, the phase-locked amplifier refers to the switching frequency F0 of the square wave, and extracts a component F (t) which is identical to the waveform of the square wave and only contains odd harmonics_od(t) for said odd harmonic-only component f_odAnd (t) sequentially carrying out first-order approximation, Taylor formula expansion and integration treatment to obtain a current signal containing a carrier kinetic signal.

Technical Field

The present specification relates to the field of detection, and in particular, to a method and apparatus for implementing atomic scale laser pumping detection.

Background

The Scanning Tunneling Microscope (STM) utilizes the principle of quantum Tunneling, and can obtain spatial resolution of atomic scale through Tunneling current, thereby having great significance and wide application prospect in research in the fields of surface science, material science, life science and the like. However, because the signal source (tunneling current) of the STM needs to be extracted after passing through the electrical amplifier, the time resolution of the STM is limited by the bandwidth of an external circuit, and can only reach microsecond level at present.

The time resolution of pump-probe technology in optics depends on the laser pulse width, and ultra-high time resolution can be achieved by using ultra-short laser pulses, but the spatial resolution of the technology depends on the spot diameter, and the technology is far from reaching the atomic level due to the limit of diffraction limit. By combining the laser pump-probe technology with the STM, carrier kinetic signals are extracted from tunneling currents, the time resolution of the STM can be greatly improved in principle, and the atomic-level spatial resolution and the nanosecond-scale time resolution can be obtained in real time. However, the thermal effect of the laser can greatly interfere with the tunneling current, which is the biggest challenge of combining the two technologies, and in addition, the laser-induced tunneling current is high-order and small compared with the background current, and the signal-to-noise ratio needs to be improved by means of a weak signal extraction method.

Disclosure of Invention

An object of the embodiments of the present disclosure is to provide a method and an apparatus for implementing atomic scale laser pumping detection, so as to eliminate the influence of thermal effect on the scanning tunneling microscope technology, implement the combination of the laser pumping detection technology and the scanning tunneling microscope technology, obtain the spatial resolution at the atomic level and the temporal resolution at the nanosecond level at the same time, and greatly improve the signal-to-noise ratio of the laser-induced tunneling current by using the lock-in amplification technology.

To achieve the above object, in one aspect, an embodiment of the present specification provides a method for implementing atomic scale laser pumping detection, including:

adjusting a delay time between a first laser pulse emitted by a first laser and a second laser pulse emitted by a second laser;

modulating the delay time based on a preset modulation frequency;

the combined beam collimates the first laser pulse and the second laser pulse and irradiates an object to be detected;

detecting a tunneling current signal of the irradiated object to be detected;

and extracting a weak signal related to the delay time in the tunneling current signal based on the preset modulation frequency.

On the other hand, this specification embodiment also provides an apparatus for implementing atomic scale laser pumping detection, including:

the delay time adjusting module is used for adjusting the delay time between a first laser pulse emitted by the first laser and a second laser pulse emitted by the second laser;

the delay time modulation module is used for modulating the delay time based on a preset modulation frequency;

the beam combination collimation module is used for combining and collimating the first laser pulse and the second laser pulse and irradiating an object to be detected;

the tunneling current signal detection module is used for detecting the tunneling current signal of the irradiated object to be detected;

and the signal extraction module is used for extracting a weak signal related to the delay time in the tunneling current signal based on the preset modulation frequency.

As can be seen from the technical solutions provided by the embodiments of the present specification, the embodiments of the present specification can ensure that the average power of laser is constant in unit time while realizing signal modulation, so that the influence of thermal effect on the scanning tunneling microscope can be eliminated, the combination of the laser pumping detection technology and the scanning tunneling microscope technology is realized, the spatial resolution at the atomic level and the temporal resolution at the nanosecond scale can be obtained simultaneously, and the signal-to-noise ratio of the laser induced tunneling current can be greatly improved by using the phase-locked amplification technology.

Drawings

FIG. 1 is a flow diagram of a method of implementing atomic scale laser pump detection in accordance with some embodiments of the present disclosure.

Fig. 2 is a block diagram of an apparatus for implementing atomic scale laser pumping detection according to some embodiments of the present disclosure.

FIG. 3 is a graph of validation results for some embodiments of the present description.

Fig. 4 is an exploded view of delay time modulation according to some embodiments of the present disclosure.

Fig. 5 is a schematic diagram of an apparatus for implementing atomic scale laser pump detection in accordance with some embodiments of the present disclosure.

Detailed Description

In order to make those skilled in the art better understand the technical solutions in the present specification, the technical solutions in the embodiments of the present specification will be clearly and completely described below with reference to the drawings in the embodiments of the present specification, and it is obvious that the described embodiments are only a part of the embodiments of the present specification, and not all of the embodiments. All other embodiments obtained by a person skilled in the art based on the embodiments in the present specification without any inventive step should fall within the scope of protection of the present specification.

As shown in fig. 1, some embodiments of the present description provide a method for implementing atomic scale laser pumping detection, the method comprising the steps of:

s102, adjusting the delay time between a first laser pulse emitted by a first laser and a second laser pulse emitted by a second laser;

s104, modulating delay time based on preset modulation frequency;

s106, combining the beams, collimating the first laser pulse and the second laser pulse and irradiating an object to be detected;

s108, detecting a tunneling current signal of the irradiated object to be detected;

and S110, extracting a weak signal related to delay time in the tunneling current signal based on a preset modulation frequency.

In some embodiments of the present description, the first laser is triggered based on a first electrical pulse of a pulse delay, the second laser is triggered based on a second electrical pulse of a waveform generator, and the delay time is modulated based on a preset modulation frequency of the waveform generator, wherein the pulse delay is synchronized with the waveform generator, i.e. both are in the same reference clock. It should be noted that there are many ways in which the delay can be implemented in addition to the pulse delay, and the pulse delay circuit is a circuit that can delay the pulse signal for a certain time. The pulse signal can be delayed by a plurality of methods, and besides the method can be realized by an electronic circuit, a cable, an artificial line, an ultrasonic delay line, a charge coupled device and the like can also be used for delaying the pulse signal. The modulation of the delay time by the waveform generator is to trigger the laser by outputting a specific electric pulse waveform sequence, so that the laser pulse delay time has modulation of specific frequency.

In some embodiments of the present disclosure, the second electrical pulse is frequency modulated by applying a square wave with a preset frequency modulation range F based on the repetition frequency F of the first electrical pulse and the second electrical pulse, the frequency modulated repetition frequency of the second electrical pulse is changed between F + F and F-F, wherein F >1000F, and the switching frequency of the square wave is F0. The delay time is gradually accumulated due to the frequency variation.

In some embodiments of the present disclosure, in conjunction with fig. 4, the minimum and maximum values of the time at which the frequency modulated second electrical pulse deviates from the normal sequence are Δ t_dAnd n Δ t_dWhere n is F/F0, the time at which the second electrical pulse deviates from the normal sequence varies linearly, the delay time varying based on the odd harmonic function F (t). Further explanation is as follows: the minimum time of deviation of the pulse from the normal sequence due to frequency modulation is 1/F-1/(F + F) and 1/(F-F) -1/F, where F>>Under the premise of f, the absolute values of the two parts are approximately equal and are recorded as delta t_d. The maximum time of deviation of the pulse from the normal sequence caused by frequency modulation is n Delta t_dAnd n is F/F0. Within a half-cycle, the time for which the frequency modulation causes the pulse to deviate from the normal sequence varies linearly between 0 and a maximum. The variation in delay time appears as an odd harmonic function, denoted as f (t). Odd harmonic functions f (t) and Δ t_dAnd (4) correlating.

In some embodiments, with reference to fig. 4, the tunneling current is obtained based on the scanning tunneling microscope, the tunneling current is used as a source signal, the lock-in amplifier is referenced to the switching frequency F0 of the square wave, and the odd harmonic function F (t) and the square wave are extractedHas a component f containing only odd harmonics and having the same waveform_od(t) for component f containing only odd harmonics_od(t) after sequentially carrying out first-order approximation, Taylor formula expansion and integration processing, acquiring a current signal containing a carrier kinetic signal, wherein the specific explanation is as follows: the odd harmonic function f (t) can be decomposed into an odd function f_od(t), even function f_ev(t), the change function f (t) of the delay time is reflected in the tunneling current, and the laser reaching the sample at different moments has the difference of excitation efficiency, so that the size of the tunneling current is influenced, the tunneling current is used as a source signal, and the frequency referenced by the lock-in amplifier is just the square wave modulated by the delay time. The square wave and the odd function fod (t) component in f (t) have the same waveform, and the fod (t) component can be extracted by a lock-in amplifier. Odd harmonic functions f (t) and Δ t_dAnd (4) correlating. Let Δ t be n Δ t_dAnd setting delta t → 0, performing first-order approximation, developing according to a Taylor formula, outputting dIph/dt by a lock-in amplifier, and integrating to obtain Iph (t) containing a carrier dynamic signal. As shown in fig. 3, the image of the tunneling current provides spatial information on an atomic scale (as shown in fig. 3 (a)), and the curve dI with delay time in the tunneling current obtained by this embodiment_phThe I/dt (shown in FIG. 3 (b)) is integrated to obtain I containing a carrier kinetic signal_ph(t) of (d). From the test result, the technology solves the interference of laser thermal effect, can realize nanosecond dynamic process detection on atomic scale, and has high signal-to-noise ratio by means of the phase-locked amplification technology.

In some embodiments of the present description, the first laser comprises a Q-switched laser and the second laser comprises a Q-switched laser having a Q-switched modulator disposed within a resonant cavity of the Q-switched laser. The first laser and the second laser comprise nanosecond lasers or picosecond lasers. Q-switched nanosecond laser adds a Q-switch modulator within the resonator to store energy in the resonator and release it when needed, thereby generating pulses in excess of the input current power. Therefore, compared with a laser with an external modulator, the Q-switch laser has higher efficiency and obtains larger single pulse energy. In addition, in some other embodiments, based on the scheme of the embodiment of the invention, the nanosecond laser is only required to be replaced by the picosecond laser, and thus the picosecond-level time resolution can be obtained.

As shown in fig. 2, some embodiments of the present disclosure further provide an apparatus for implementing atomic scale laser pumping detection, the apparatus including:

a delay time adjusting module 201, configured to adjust a delay time between a first laser pulse emitted by a first laser and a second laser pulse emitted by a second laser;

a delay time modulation module 202, configured to modulate the delay time based on a preset modulation frequency;

a beam combination collimation module 203, configured to combine and collimate the first laser pulse and the second laser pulse and irradiate an object to be detected;

a tunneling current signal detection module 204, configured to detect a tunneling current signal of the irradiated object to be detected;

and a signal extraction module 205, configured to extract a weak signal related to the delay time from the tunneling current signal based on a preset modulation frequency.

In some embodiments of the present description, the delay time adjustment module includes a pulse delayer; a delay time modulation module including a waveform generator; the first laser is triggered based on a first electrical pulse of the pulse delay, the second laser is triggered based on a second electrical pulse of the waveform generator, and the delay time is modulated based on a preset modulation frequency of the waveform generator. The beam combination collimation module comprises a polarizer, a beam splitter, a filter, a half-wave plate and a prism which are connected in a preset order;

the tunneling current signal detection module comprises a scanning tunneling microscope, and the scanning tunneling microscope acquires tunneling current;

the signal extraction module takes the tunneling current as a source signal, the phase-locked amplifier refers to the switching frequency F0 of the square wave, and extracts a component F (t) which is identical to the waveform of the square wave and only contains odd harmonics_od(t) for component f containing only odd harmonics_od(t) carrying out first order approximation, Taylor formula development and integration treatment in sequence to obtain the carrier-containing materialCurrent signal of kinetic signal.

In an actual application environment, the hardware configuration of the embodiment of the present invention mainly includes three parts, as shown in fig. 5, a laser unit (the laser unit includes two nanosecond pulse lasers and their electrical trigger units, one pulse delay device responsible for adjusting delay time, and the other waveform generator for modulating delay time, and the pulse delay device and the waveform generator are synchronous, that is, they are in the same reference clock), an STM unit (the scanning tunneling microscope unit includes all functional units for detecting tunneling current), and a signal extraction unit (the signal extraction unit includes a lock-in amplifier and a data acquisition card). After being collimated by the light path combined beam, the two laser pulses irradiate the part of the sample which can be detected by the STM needle point. The phase-locked amplifier extracts a signal related to the laser delay time in the tunneling current according to the frequency modulated by the waveform generator. Due to the adoption of the delay time modulation mode, the thermal effect interference of laser on the STM detection system is eliminated, and weak signals are extracted from a large current and a noise background by virtue of a phase-locked amplifier. The current serving as a signal source ensures the spatial resolution, and the laser pulse width determines the time resolution, so that the technology can realize the detection of the atomic-level nanosecond time scale dynamic process.

While the process flows described above include operations that occur in a particular order, it should be appreciated that the processes may include more or less operations that are performed sequentially or in parallel (e.g., using parallel processors or a multi-threaded environment). The present invention is described with reference to flowchart illustrations and/or block diagrams of methods according to embodiments of the invention.

It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method or device comprising the element.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, as for the method embodiment, since it is substantially similar to the apparatus embodiment, the description is simple, and the relevant points can be referred to the partial description of the apparatus embodiment. The above description is only an example of the present specification, and is not intended to limit the present specification. Various modifications and alterations to this description will become apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present specification should be included in the scope of the claims of the present specification.