Visible light wave band photon orbital angular momentum ultrafast light current detection system

Abstract

The invention discloses a visible light band photon orbital angular momentum ultrafast light current detection system, and relates to the technical field of optical detection, and the system comprises a light splitting device which is used for dividing incident light emitted by a femtosecond light source into pump light and detection light; the vortex wave plate is used for converting the pump light into vortex light; the quarter-wave plate is used for changing the polarization state of the vortex light to form linearly-polarized and circularly-polarized vortex light, and the linearly-polarized and circularly-polarized vortex light irradiates a sample to generate transient light current so as to generate terahertz waves; the detection crystal receives the terahertz waves and the detection light, and a terahertz wave electric field changes the refractive index of the detection crystal and changes the polarization state of the detection light; and the balance detector is used for recording terahertz time domain waveform signals. By adopting the system provided by the invention, not only can OAM photocurrent detection of femtosecond magnitude time resolution be realized, but also non-contact measurement of OAM photocurrent can be realized without applying a metal electrode.

Description

Technical Field

[0001] This application relates to the field of optical detection technology, and particularly relates to an ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band. Background Art

[0002] As an important degree of freedom of the optical field, the efficient detection and characterization of photon orbital angular momentum (OAM) are crucial for optical communication, quantum information processing, and integrated photonic devices. Traditional OAM detection relies on indirect methods such as interference or diffraction, which have problems such as complex systems and difficulty in integration. There is a theory that semiconductor absorption of OAM light can induce angular photocurrent (OPGE effect), providing a new way for direct electronic readout of OAM information. In recent years, progress has been made in the experimental detection of OAM photocurrent in the mid-infrared band for materials such as WTe2, TaIrTe4, graphene, and PdSe2.

[0003] However, it still faces the challenge of being unable to achieve picosecond-level ultrafast detection of OAM photocurrent in the visible light band. Therefore, there is an urgent need for a non-contact, ultrafast time-resolved spectroscopic technique to realize the detection technology of ultrafast OAM photocurrent. Summary of the Invention

[0004] The embodiments of this application provide an ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band to solve the problem of OAM ultrafast photocurrent detection in the prior art.

[0005] The embodiments of this application provide an ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band, including:

[0006] A beam splitting device for splitting the incident light emitted by a femtosecond light source into pump light and probe light;

[0007] A vortex wave plate disposed downstream of the pump light, and the vortex wave plate is used to convert the pump light into vortex light;

[0008] A quarter-wave plate disposed downstream of the vortex light, and the quarter-wave plate is used to change the polarization state of the vortex light to form linearly polarized and circularly polarized vortex light. The linearly polarized and circularly polarized vortex light irradiates on the sample to generate transient photocurrent, and then generates terahertz waves;

[0009] A detection crystal disposed downstream of the terahertz wave and the probe light. The detection crystal receives the terahertz wave and the probe light, and the terahertz wave electric field changes the refractive index of the detection crystal and changes the polarization state of the probe light;

[0010] A balanced detector disposed after the detection crystal, and the balanced detector records the terahertz time-domain waveform signal.

[0011] In a possible implementation, the balanced detector records the terahertz time-domain waveform signal, performs a Fourier transform on the terahertz time-domain waveform signal to obtain the corresponding frequency-domain signal, divides the frequency-domain signal by the response function of the system, and then performs an inverse Fourier transform to obtain the ultrafast photocurrent signal.

[0012] In a possible implementation, it further includes: a first parabolic mirror, disposed downstream of the sample, and the first parabolic mirror is used to reflect the terahertz wave and collimate it into parallel light; a second parabolic mirror, disposed downstream of the first parabolic mirror and the probe light, and the second parabolic mirror is used to focus the parallel terahertz wave reflected by the first parabolic mirror and reflect it to coincide with the probe light.

[0013] In a possible implementation, a through hole is provided in the center of the second parabolic mirror, and the probe light passes through the through hole and irradiates the terahertz wave on the detection crystal.

[0014] In a possible implementation, it further includes: a corner cube prism, disposed downstream of the beam splitting device, and the corner cube prism is used to reflect the probe light and, in combination with the motorized displacement stage, realize the delay of the pump light.

[0015] In a possible implementation, first reflectors are respectively provided at the incident end and the exit end of the corner cube prism. The two first reflectors reflect the probe light to the corner cube prism and then reflect the light emitted from the corner cube prism, so that the reflected exit light has the same direction as the probe light.

[0016] In a possible implementation, the cross section of the corner cube prism is an isosceles right triangle.

[0017] In a possible implementation, a second reflector is provided downstream of the pump light. The probe light and the pump light split by the beam splitting device are perpendicular to each other, and the second reflector reflects the pump light to a direction parallel to the probe light.

[0018] A visible light band photon orbital angular momentum ultrafast photocurrent detection system in this application has the following advantages:

[0019] 1. It can achieve OAM photocurrent detection with a time resolution of picosecond or sub-femtosecond order of magnitude.

[0020] 2. Without applying metal electrodes, it realizes non-contact measurement of OAM photocurrent. Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0022] Figure 1 It is a schematic diagram of the composition structure of a visible light band photon orbital angular momentum ultrafast photocurrent detection system provided by an embodiment of the present application.

[0023] Explanation of the reference numerals in the accompanying drawings: 100, beam splitter; 200, vortex wave plate; 300, quarter-wave plate; 400, sample; 500, first parabolic mirror; 600, corner cube prism; 700, second parabolic mirror; 800, detection crystal; 900, balanced detector. Specific embodiments

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0025] Figure 1 It is a schematic diagram of the structure of a visible light band photon orbital angular momentum ultrafast photocurrent detection system provided by an embodiment of the present application. An embodiment of the present application provides a visible light band photon orbital angular momentum ultrafast photocurrent detection system, including:

[0026] A beam splitter 100 for splitting the incident light emitted by a femtosecond light source into pump light and probe light;

[0027] A vortex wave plate 200 disposed downstream of the pump light, and the vortex wave plate 200 is used to convert the pump light into vortex light;

[0028] A quarter-wave plate 300 disposed downstream of the vortex light, and the quarter-wave plate 300 is used to change the polarization state of the vortex light to form linearly polarized and circularly polarized vortex light. The linearly polarized and circularly polarized vortex light irradiates on the sample 400 to generate a transient photocurrent, and then generates a terahertz wave;

[0029] A detection crystal 800 disposed downstream of the terahertz wave and the probe light. The detection crystal 800 receives the terahertz wave and the probe light. The terahertz wave electric field changes the refractive index of the detection crystal 800 and changes the polarization state of the probe light;

[0030] A balanced detector 900 is provided after the detection crystal 800, and the balanced detector 900 records the terahertz time-domain waveform signal.

[0031] Exemplarily, the femtosecond light can be visible light of any band after nonlinear frequency conversion. The vortex light formed after the pump light passes through the vortex wave plate 200 will carry angular momentum information, and the vortex light will be converted into linearly polarized and circularly polarized vortex light after passing through the quarter-wave plate 300 in the form of a rotatable quarter-wave plate.

[0032] The beam splitter device 100 can employ a semi-transparent and semi-reflective mirror, which is set at an angle of 45° with the horizontal direction. After the femtosecond light emitted by the femtosecond light source is incident on the beam splitter device in the horizontal direction, the pump light propagates in the vertically downward direction.

[0033] In an embodiment of the present application, a corner cube prism 600 is further provided downstream of the detection light generated by the beam splitter device 100. After being reflected by the corner cube prism 600, a delay of the pump light is achieved in combination with an electric displacement stage. Specifically, the corner cube prism 600 is set on a moving stage that moves along the incident direction of the detection light. When the moving stage drives the corner cube prism 600 to move in the vertical direction, the optical path of the detection light will change to achieve the effect of synchronous propagation of the detection light and the terahertz wave.

[0034] Specifically, since the detection light split by the beam splitter device 100 propagates in the horizontal direction, in order to enable it to enter the corner cube prism 600 in the vertical direction, the present application further provides first mirrors at the incident end and the exit end of the corner cube prism 600 respectively. The two first mirrors reflect the detection light to the corner cube prism 600 and then reflect the light emitted by the corner cube prism 600, so that the reflected exit light has the same direction as the detection light. After setting the two first mirrors, it can be ensured that the detection light emitted from the beam splitter device 100 and the detection light incident on the detection crystal 800 have the same direction, avoiding interference between the detection light and the pump light.

[0035] In an embodiment of the present application, the system further includes a first parabolic mirror 500 and a second parabolic mirror 700. The first parabolic mirror 500 is set downstream of the sample 400, and the first parabolic mirror 500 is used to reflect the terahertz wave and collimate it into parallel light.

[0036] The second parabolic mirror 700 is set downstream of the first parabolic mirror 500 and the detection light. The second parabolic mirror 700 is used to focus the terahertz wave reflected by the first parabolic mirror 500 and reflect it to coincide with the detection light.

[0037] Both the first parabolic mirror 500 and the second parabolic mirror 700 are parabolic reflectors. The terahertz waves emitted from the sample 400 are divergent light. After being focused by the first parabolic mirror 500, they will be converted into parallel light, which will also be changed to propagate vertically upward. The second parabolic mirror 700 refocuses the parallel light and, after changing the direction, focuses it on the detection crystal 800.

[0038] Further, a through hole is provided in the center of the second parabolic mirror 700. The probe light passes through the through hole and irradiates the detection crystal 800 together with the terahertz wave. The probe light reflected by the first mirror enters the through hole in the horizontal direction and then irradiates the same point on the detection crystal 800 together with the probe light reflected by the second parabolic mirror 700. The balanced detector 900 converts the terahertz wave into an electrical signal to obtain a terahertz time-domain waveform signal. Performing a Fourier transform on the terahertz time-domain waveform signal gives the corresponding frequency-domain signal. Dividing the frequency-domain signal by the response function of the system gives the electric field information of the frequency-domain signal. Using Ohm's law, the frequency-domain photocurrent signal can be obtained. Performing an inverse Fourier transform on the frequency-domain photocurrent signal gives the ultrafast photocurrent signal containing OAM information.

[0039] In an embodiment of the present application, a second mirror is provided downstream of the pump light. The probe light and the pump light split by the beam splitter 100 are perpendicular to each other. The second mirror reflects the pump light to a direction parallel to the probe light.

[0040] The second mirror is arranged in a direction parallel to the beam splitter 100. The vertically downward propagating pump light will be changed to propagate in the horizontal direction, that is, a direction parallel to the probe light, after being reflected by the second mirror, thus reducing the volume of the system.

[0041] Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments as well as all changes and modifications falling within the scope of the present application.

[0042] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. An ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band, characterized in that, Comprising: A beam splitting device (100) for splitting the incident light emitted by a femtosecond light source into pump light and probe light; A vortex wave plate (200) disposed downstream of the pump light, the vortex wave plate (200) being configured to convert the pump light into vortex light; A quarter-wave plate (300) disposed downstream of the vortex light, the quarter-wave plate (300) being configured to change the polarization state of the vortex light to form linearly polarized and circularly polarized vortex light, and the linearly polarized and circularly polarized vortex light irradiating on a sample (400) to generate a transient photocurrent, thereby generating terahertz waves; A detection crystal (800) disposed downstream of the terahertz wave and the probe light, the detection crystal (800) receiving the terahertz wave and the probe light, and the terahertz wave electric field changing the refractive index of the detection crystal (800) and changing the polarization state of the probe light; A balanced detector (900) disposed after the detection crystal (800), the balanced detector (900) recording the terahertz time-domain waveform signal.

2. The ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band according to claim 1, wherein The balanced detector (900) obtains the terahertz time-domain waveform signal, performs a Fourier transform on the terahertz time-domain waveform signal to obtain a corresponding frequency-domain signal, divides the frequency-domain signal by the response function of the system, and then performs an inverse Fourier transform to obtain the ultrafast photocurrent signal.

3. The ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band according to claim 1, characterized in that, Further comprising: A first parabolic mirror (500) disposed downstream of the sample (400), the first parabolic mirror (500) being configured to reflect the terahertz wave and collimate it into parallel light; A second parabolic mirror (700) disposed downstream of the first parabolic mirror (500) and the probe light, the second parabolic mirror (700) being configured to focus the parallel terahertz wave reflected by the first parabolic mirror (500) and reflect it to coincide with the probe light.

4. The ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band according to claim 3, characterized in that, A through hole is provided in the center of the second parabolic mirror (700), and the probe light passes through the through hole and irradiates on the detection crystal (800) together with the terahertz wave.

5. An ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band according to claim 1, characterized in that, Further comprising: A corner cube prism (600) disposed downstream of the beam splitting device (100), the corner cube prism (600) being configured to reflect the probe light and, in combination with an electric displacement stage, achieve a delay of the pump light.

6. The ultrafast photocurrent detection system for visible light band photon orbital angular momentum according to claim 5, wherein First reflectors are respectively provided at the incident end and the exit end of the corner cube prism (600), and the two first reflectors reflect the probe light to the corner cube prism (600) and then reflect the light emitted from the corner cube prism (600) so that the reflected exit light has the same direction as the probe light.

7. An ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band according to claim 5, characterized in that, The cross section of the corner cube prism (600) is an isosceles right triangle.

8. The ultrafast photocurrent detection system for photon orbital angular momentum in the visible light band according to claim 1, wherein A second reflector is disposed downstream of the pump light, the probe light and the pump light split by the beam splitting device (100) are perpendicular to each other, and the second reflector reflects the pump light to a direction parallel to the probe light.

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