CN109596576B - Nano-optical field spin-orbit interaction measurement system and method - Google Patents

Abstract

A probe heterodyne interference device for rotation resolution, a nanometer optical field spin-orbit interaction measurement system and a method are provided. The probe heterodyne interference device comprises: the single-beam laser is divided into original measuring light and original reference light through the light splitting module; the difference frequency generating device carries out frequency modulation on the original measuring light and the original reference light and outputs the measuring light and the reference light with a preset frequency difference; the measuring light polarization control device is arranged in the transmission direction of the measuring light; the focusing and scanning device is arranged in the output direction of the reference light of the measuring light polarization control device to output the illumination light; the illumination light excites a sample to generate a nanometer light field, and the aperture type scanning near-field optical microscope device detects and collects the nanometer light field in a near field and outputs sample information light; the reference light polarization compensation device is arranged in the transmission direction of the reference light, and the reference light enters the reference light polarization compensation device to output polarization compensation light; the sample information light and the polarization compensation light are transmitted to the coupling device to generate interference to generate heterodyne interference light.

Description

Nano-optical field spin-orbit interaction measurement system and method

technical field

The invention relates to the field of nano-optics and nano-photonics measurement, in particular to a spin-resolved probe heterodyne interference device, a nano-optical field spin-orbit interaction measurement method and system.

Background technique

When light propagates in the medium, there are two kinds of rotations around the optical axis at the same time. One is the spin rotation in time due to the chirality and helicity of the photon. This rotation is based on the polarization of the photon. Has spin angular momentum. The other is derived from the rotation of the spatial distribution of light intensity and phase, and this rotation based on the spatial distribution of light has orbital angular momentum. When a photon or light propagates in a non-homogeneous optical medium or is refracted or reflected on an optical surface, the spin angular momentum and orbital angular momentum of the photon will be coupled and transformed with each other, resulting in a photon spin-orbit interaction.

The photon spin-orbit interaction in traditional geometrical optics is very weak and difficult to observe. Metasurface devices in nano-optics can serve as a class of effective functional device platforms to enhance photonic spin-orbit interactions for observation. In the traditional technology, the scanning near-field optical microscope based on the probe heterodyne interference technology can realize the near-field measurement of the phase-resolved super-diffractive optical resolution, but it is difficult to directly realize the near-field measurement of the rotational resolution, so it is impossible to directly realize the near-field measurement. Measurements of spin-orbit interactions in nano-optical fields are carried out in the near field.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a probe heterodyne interference device, a nano-optical field spin-orbit interaction measurement system and method.

The present invention provides a rotationally resolved probe heterodyne interference device, comprising:

A spectroscopic module, through which a single laser beam is divided into the original measurement light and the original reference light;

The difference frequency generating device is arranged in the transmission direction of the original measurement light and the original reference light, performs frequency modulation on the original measurement light and the original reference light, outputs the measurement light and the reference light, and makes the measurement light and the reference light the light produces a predetermined frequency difference;

a measurement light polarization control device, which is arranged in the transmission direction of the measurement light, and adjusts the polarization state of the measurement light after the measurement light is incident on the measurement light polarization control device;

The focusing and scanning device is arranged in the output direction of the reference light of the measurement light polarization control device, focuses the measurement light after passing through the measurement light polarization control device to output illumination light, and fine-tunes the illumination light relative to the sample. excitation position;

Aperture-type scanning near-field optical microscope device, wherein the illumination light excites the sample to generate a nano-optical field, and the aperture-type scanning near-field optical microscope device collects the nano-optical field in near-field detection and outputs sample information light;

a reference light polarization compensation device, arranged in the transmission direction of the reference light, and the reference light is incident on the reference light polarization compensation device to output polarization compensation light;

a coupling device, the sample information light and the polarization compensation light incident on the coupling device interfere to generate heterodyne interference light.

In one embodiment, the difference frequency generating apparatus includes:

The first frequency shifter and the first diaphragm are arranged in sequence along the propagation direction of the original measurement light;

The second frequency shifter and the second diaphragm are arranged in sequence along the propagation direction of the original reference light;

The first frequency shifter and the second frequency shifter are acousto-optic frequency shifters or acousto-optic modulators.

In one embodiment, the measurement light polarization control device includes a polarizer, a quarter-wave plate or a spatial light modulator, which are arranged in sequence along the propagation direction of the measurement light.

In one embodiment, the focus scanning device includes:

a focusing element, the measuring light is incident on the focusing element after passing through the measuring light polarization control device, and outputs weakly focused illumination light;

A scanning element that fine-tunes the excitation position of the weakly focused illumination light relative to the sample.

In one embodiment, the aperture scanning near-field optical microscope device comprises:

a scanning stage, used for placing the sample, a light-passing hole passing through the scanning stage is opened in the center of the scanning stage;

a scanning head, arranged opposite to the sample;

an optical fiber probe, arranged in linkage with the scanning head and connected with the coupling device, the needle tip of the optical fiber probe detects the nano-optical field of the sample in the near field and transmits the sample through the optical fiber of the optical fiber probe information light to said coupling means;

a scanning near-field optical microscope controller, connected with the scanning head and the scanning stage, and used for synchronously controlling the scanning head and the scanning stage to achieve three-dimensional displacement with micron-level and nano-level precision;

A video microscope and a CCD camera, the video microscope is arranged opposite to the sample carried on the scanning stage, and the CCD camera is fixed to the video microscope for assisting imaging and feeding back the relative position of the fiber probe and the sample .

In one embodiment, the optical fiber probe is an uncoated bare optical fiber probe or a metal-coated aperture probe, or a functional probe with metal nanoparticles attached to the tip or a function of etching helical chiral nanostructures probe.

In one embodiment, the reference light polarization compensation device includes:

An electric half-wave plate and an electric quarter-wave plate, the electric half-wave plate and the quarter-wave plate are used for electronically controlling and compensating the polarization state of the reference light, along the propagation direction of the reference light Set in sequence;

an optical fiber polarization controller, connected to the coupling device, the optical fiber polarization controller adjusts the polarization state in the optical fiber of the optical fiber polarization controller and transmits the polarization compensation light to the coupling device;

an optical fiber collimating coupler, the optical fiber collimating coupler is placed between the motorized quarter-wave plate and the optical fiber polarization controller.

In one embodiment, the fiber collimating coupler is a low numerical aperture objective or a graded index lens for coupling spatial light into the fiber of the fiber polarization controller.

In one embodiment, the coupling device comprises a non-polarization maintaining fiber optic coupler.

In one embodiment, the probe heterodyne interference device further comprises:

In one embodiment, the light splitting module includes a polarization beam splitter and a reflection mirror, and the reflection mirror is arranged in a light exit direction of the polarization beam splitter.

The present invention also provides a nano-optical field spin-orbit interaction measurement method for measuring the nano-optical field spin-orbit interaction on a mesoscopic scale, including:

By referring to the light polarization compensation device and the coupling device, using the rotation resolution detection method, the heterodyne interference light is generated and the selected rotation or convolution is obtained for resolution;

Ultra-optical diffraction-limited imaging and phase-resolved performance were obtained by probe heterodyne interferometry.

In one embodiment, the rotationally resolved detection method comprises:

The orthogonal polarization calibration method is used to obtain circularly polarized compensation light, and the circularly polarized compensation light and the sample information light interfere in the coupling device to generate the heterodyne interference light;

By adjusting the reference light polarization compensation device to control and switch the rotation of the circular polarization compensation light, the rotation resolution detection of the nano-optical field of the sample is realized.

In one embodiment, the orthogonal polarization calibration method includes:

Use standard left- or right-circularly polarized illumination light to be incident on the unstructured area of the sample, adjust the reference light polarization compensation device to make the heterodyne interference light output by the coupling device reach an extinction state, so as to obtain a right- or left-handed circular Polarization Compensated Light.

In one embodiment, the probe heterodyne interference method comprises:

The optical fiber probe collects the near-field high spatial frequency information of the nano-optical field of the sample and transmits it to the far-field to realize ultra-optical diffraction limit measurement;

The original reference light and the original measurement light pass through the difference frequency generating device, and the generated reference light and the measurement light have a predetermined frequency difference;

Demodulation of the heterodyne interference light can realize the relative phase measurement of the nano-optical field at the position of the optical fiber probe.

The present invention also provides a nano-optical field spin-orbit interaction measurement system, comprising:

A laser generating device for outputting the original measuring light and the original reference light;

a probe heterodyne interference device, arranged in the light output direction of the laser generating device, using the aforementioned probe heterodyne interference device to generate heterodyne interference light;

The data receiving and processing device is arranged in the output direction of the heterodyne interference light, and is used for receiving the heterodyne interference light and analyzing the heterodyne interference information.

In one embodiment, the laser generating device includes:

a laser, the laser outputs a single longitudinal mode laser with good coherence;

A shaping unit, the single longitudinal mode laser outputs single longitudinal mode and single transverse mode laser light through the shaping unit.

In one embodiment, the shaping unit includes:

A beam expanding device, a shaping device, a collimating device, and an optical filtering device are arranged in sequence along the light output transmission direction of the laser.

In one embodiment, the data receiving and processing apparatus includes:

a photodetector, where the heterodyne interference light is incident on the photodetector and outputs an alternating current signal;

a lock-in amplifier, electrically connected to the photodetector;

A reference signal mixing module, electrically connected to the lock-in amplifier, the reference signal mixing module provides a reference frequency signal for the lock-in amplifier, and the lock-in amplifier phase-locks and demodulates the AC signal Output phase-locked demodulation signal;

A data acquisition module, electrically connected to the lock-in amplifier, is used for collecting the lock-in demodulation signal.

In one embodiment, the system further includes a computing control terminal, which is electrically connected to the aperture probe heterodyne interference scanning near-field optical microscope device and the data receiving and processing device, respectively.

Rotationally resolved probe heterodyne interference device, nano-optical field spin-orbit interaction measurement method and system, using probe heterodyne interference device, orthogonal polarization calibration method and rotation resolution detection method are adopted in the method And the probe heterodyne interferometry method, realizes the near-field measurement of super-diffractive optics diffraction-limited rotational resolution and phase-resolved. The ultra-diffractive optical limit measurement can realize the characterization at the mesoscopic scale, the rotational resolution measurement can realize the characterization of the spin angular momentum of the nano-optical field, and the phase-resolved measurement can realize the characterization of the orbital angular momentum of the nano-optical field, so the present invention The near-field direct measurement of photon spin-orbit interactions in samples can finally be realized at the mesoscopic scale.

Description of drawings

1 is a schematic structural diagram of a rotationally resolved heterodyne probe interference device according to an embodiment;

2 is a structural diagram of a difference frequency generating device of a rotationally resolved heterodyne probe interference device according to another embodiment;

3 is a schematic structural diagram of a rotationally resolved heterodyne probe interference device according to an embodiment;

4 is a schematic structural diagram of a nano-optical field spin-orbit interaction measurement system according to an embodiment;

5 is a schematic structural diagram of a nano-optical field spin-orbit interaction measurement system according to another embodiment;

6 is a structural diagram of a surface unit in a metasurface device in which the sample is in one embodiment;

Fig. 7 is the electron microscope photograph that the sample described in one embodiment is metasurface device;

8 is a schematic diagram of the actual structure of a nano-optical field spin-orbit interaction measurement system according to an embodiment;

FIG. 9 is a schematic diagram of rotational resolution detection in one embodiment;

Fig. 10 is the measurement result of the nano-optical field spin-orbit interaction measurement system of one embodiment;

FIG. 11 is a three-dimensional measurement result of a nano-optical field spin-orbit interaction measurement system according to an embodiment.

Description of main component symbols

Spin-Orbit Interaction Measurement System 10

Laser generator 100

Laser 110

Shaping unit 120

Probe Heterodyne Interference Device 200

Splitter module 210

Polarizing Beamsplitters and Mirrors 211

difference frequency generator 220

first frequency shifter 221

first aperture 222

Second frequency shifter 223

Second diaphragm 224

Measuring light polarization control device 230

Polarizer 231

Quarter-Wave Plate or Spatial Light Modulator 232

Focus Scanning Unit 240

Focusing element 241

Scanning element 242

Aperture Scanning Near Field Optical Microscope Unit 250

Scanning table 251

Scan head 252

Fiber Probes 253

Scanning Near Field Optical Microscope Controller 254

Video Microscope 255

CCD camera reference light polarization compensation device 256

Reference light polarization compensation device 260

Electric Half-Wave Plate 261

Motorized Quarter Wave Plate 262

Fiber Collimation Couplers 263

Fiber Polarization Controller 264

Coupling device 270

Non-PM Fiber Couplers 271

Data receiving and processing device 300

Photodetector 310

Lock-in Amplifier 320

Reference Signal Mixing Module 330

Data Acquisition Module 340

Computing Control Terminal 400

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Referring to FIG. 1 , the present embodiment provides a probe heterodyne interference device 200 for rotational resolution, including: a light splitting module 210 , a difference frequency generating device 220 , a measuring light polarization control device 230 , a focusing scanning device 240 , an aperture type Scanning near-field optical microscope device 250 , reference light polarization compensation device 260 and coupling device 270 . The single beam of laser light of the light splitting module 210 is divided into the original measurement light and the original reference light through the light splitting module 210 . The difference frequency generating device 220 performs frequency modulation on the original measurement light and the original reference light, and outputs the measurement light and the reference light with a predetermined frequency difference. The predetermined frequency difference may be Δω. The measurement light polarization control device is arranged in the transmission direction of the measurement light. The focus scanning device 240 is arranged in the output direction of the reference light of the measurement light polarization control device 230 . After the measurement light is incident on the measurement light polarization control device 230 , the polarization state of the measurement light is adjusted, and then the focusing and scanning device 240 is focused to output the illumination light. The illumination light excites the sample to generate a nanometer light field, and the aperture scanning near-field optical microscope device 250 collects the nanometer light field in near-field detection and outputs sample information light. The reference light polarization compensation device 260 is arranged in the transmission direction of the reference light. The reference light is incident on the reference light polarization compensation device 260 to output polarization compensation light. The sample information light and the polarization compensation light are transmitted to the coupling device 270 and interfere to generate heterodyne interference light.

The probe heterodyne interference device provided by the invention has rotational resolution, and adopts the orthogonal polarization calibration method, the rotational resolution detection method and the probe heterodyne interference method. The near-field measurement of superdiffractive optics diffraction-limited rotational resolution and phase-resolved is realized. The ultra-diffractive optical limit measurement can realize the characterization at the mesoscopic scale, the rotational resolution measurement can realize the characterization of the spin angular momentum of the nano-optical field, and the phase-resolved measurement can realize the characterization of the orbital angular momentum of the nano-optical field, so the present invention The near-field direct measurement of photon spin-orbit interactions in samples can finally be realized at the mesoscopic scale.

In one embodiment, the light splitting module 210 includes a polarization beam splitter and a reflection mirror 211 , and the reflection mirror is arranged in the light exit direction of the polarization beam splitter.

Referring to FIG. 2, in one embodiment, the difference frequency generating device 220 includes: a first frequency shifter 221 and a first aperture 222, which are arranged in sequence along the propagation direction of the measurement light; a second frequency shifter 223 and the second aperture 224, which are arranged in sequence along the propagation direction of the reference light. The first frequency shifter 221 and the second frequency shifter 223 are acousto-optic frequency shifters or acousto-optic modulators.

Referring to FIG. 3, in one embodiment, the measurement light polarization control device 230 includes a polarizer 231, a quarter-wave plate or a spatial light modulator 232, which are arranged in sequence along the propagation direction of the measurement light.

Wherein, in one embodiment, the focusing and scanning device 240 includes a focusing element 241 and a scanning element 242 . After the measurement light is weakly focused by the focusing element 241, it illuminates the sample through the scanning element 242 and performs focus scanning and sample alignment.

The focusing element 241 can be a low numerical aperture objective lens or a long focal length lens, which can achieve weak focusing of incident light and maintain its polarization state unchanged in the application of approximately normal incidence. The scanning element 242 includes a mirror and a mechanical control unit. The scanning element 242 may be integrated or separate. When the scanning element 242 is an integrated type, it may be a scanning galvanometer that integrates the reflecting mirror and the mechanical control. When the scanning element 242 is of a separate type, the mechanical control unit can be separated from the mirror. It can be in the form of loading the focusing element 241 on a two-dimensional motorized stage and then passing through a separate mirror. The focusing scanning device 240 can realize the scanning adjustment of the focusing illumination focus relative to the sample plane and the light field plane within the range of 100 microns, so as to facilitate the selection of the sample illumination area or the nano-optical field measurement area.

In one embodiment, the aperture-type scanning near-field optical microscope device 250 includes a scanning stage 251 , a scanning head 252 , a fiber probe 253 , a scanning near-field optical microscope controller 254 , a video microscope 255 and a CCD camera 256 . The scanning stage 251 is provided with a light-passing hole passing through the scanning stage 251 for placing the sample. The scanning head 252 is disposed opposite to the sample. The fiber probe 253 is linked with the scan head 252 and connected to the coupling device 270 . During measurement, the scanning head 252 controls the optical fiber probe 253 to be suspended at a position of several nanometers to several tens of nanometers above the sample, and the nano-optical field detected in the near field is transmitted to the optical fiber probe 253 through the conducting fiber. The coupling device 270 . The scanning near-field optical microscope controller 254 is electrically connected with the scanning stage 251 and the scanning head 252 , and is used for controlling the scanning stage 251 and the scanning head 252 to move. The video microscope 255 is disposed opposite to the sample carried on the scanning stage 251 . The CCD camera 256 is fixed on the video microscope 255 . A video microscope 255 and a CCD camera 256 are used for real-time observation and monitoring of the measurement field of view.

The scanning stage 251 may be a three-dimensional micro-scale scanning stage based on a stepping motor, or a three-dimensional nano-scale scanning stage based on piezoelectric ceramics. The center of the scanning table 251 needs to pass light to realize the transmission illumination mode (the fiber probe 253 is used as a near-field nano-light source) or the transmission collection mode (the fiber probe 253 is used as a near-field detector), so as to realize the 3D scanning measurement of the nano-optical field of the sample. The scan head 252 may be a scan head of a scanning near-field optical microscope. The scanning head 252 can be synchronized with the scanning near-field optical microscope controller 254 to realize the head scanning function with precise control of the tip-sample distance and three-dimensional nanometer precision. The scan head 252 can realize nanoscale tip-sample spacing control in shear mode or tapping mode. The scan head 252 can carry various types of fiber probes 253 . The fiber probe 253 may be a coated fiber aperture probe, a bare fiber probe, or a nano-antenna modified functional probe. The optical fiber probe 253 is an uncoated bare optical fiber probe or a metal-coated aperture probe, or a functional probe with metal nanoparticles attached to the tip or a functional probe with etched helical chiral nanostructures. The tip dimension of the fiber optic probe 243 is on the order of one tenth of a wavelength.

Wherein, in one embodiment, the reference light polarization compensation device 260 includes a motorized half-wave plate 261, a motorized quarter-wave plate 262, a fiber collimator/coupler 263 and a fiber polarization controller 264. The transmission directions of the light are set sequentially. The electric half-wave plate 261 and the electric quarter-wave plate 262 can precisely and electrically adjust the polarization state of the polarization compensation light. The optical fiber polarization controller 264 generates birefringence by applying stress to the optical fiber, so as to control the polarization state of the optical field mode in the optical fiber of the reference optical path. The optical fiber polarization controller 264 is in a manual control mode, which can statically and rapidly adjust the polarization state before the probe heterodyne interference device 200 is stabilized. The fiber collimation coupler 263 couples spatial light into the fiber polarization controller 264 . In one embodiment, the fiber collimating coupler 263 may be a low numerical aperture objective or a graded index lens for coupling spatial light into the fiber of the fiber polarization controller.

The electric half-wave plate 261 and the electric quarter-wave plate 262 are driven by a hollow rotating motor with a controllable rotation angle, and the probe heterodyne interference device 200 is compensated by fine-tuning the polarization state of the reference light in the space light Variation in the mode polarization state in the conducting fiber. During the measurement process, the electric half-wave plate 261 and the electric quarter-wave plate 262 can perform real-time rotation adjustment and compensation for polarization state changes through a feedback mechanism according to the contrast of the interference signal, and always keep the interference signal in the best contrast.

Wherein, in one embodiment, the coupling device 270 includes a non-polarization maintaining fiber coupler 271 . The sample information light in the measurement optical path and the polarization compensation light in the reference optical path are overlapped at the non-polarization-maintaining fiber coupler 271 to generate heterodyne interference light.

The invention also provides a method for measuring the spin-orbit interaction of the nano-optical field, which is used to realize the spin-orbit interaction of the nano-optical field on the mesoscopic scale, including:

By referring to the light polarization compensation device and the coupling device, using the rotation resolution detection method, the heterodyne interference light is generated and the selected rotation or convolution is obtained for resolution;

Ultra-optical diffraction-limited imaging and phase-resolved performance were obtained by probe heterodyne interferometry.

In one embodiment, the rotationally resolved detection method comprises:

The orthogonal polarization calibration method is used to obtain circularly polarized compensation light, and the circularly polarized compensation light and the sample information light interfere in the coupling device to generate the heterodyne interference light;

By adjusting the reference light polarization compensation device to control and switch the rotation of the circular polarization compensation light, the rotation resolution detection of the nano-optical field of the sample is realized.

In one embodiment, the orthogonal polarization calibration method includes:

Use standard left- or right-circularly polarized illumination light to be incident on the unstructured area of the sample, adjust the reference light polarization compensation device to make the heterodyne interference light output by the coupling device reach an extinction state, so as to obtain a right- or left-handed circular Polarization Compensated Light.

In one embodiment, the probe heterodyne interference method comprises:

The optical fiber probe collects the near-field high spatial frequency information of the nano-optical field of the sample and transmits it to the far-field to realize ultra-optical diffraction limit measurement;

The original reference light and the original measurement light pass through the difference frequency generating device to generate a predetermined frequency difference between the reference light and the measurement light;

Demodulation of the heterodyne interference light can realize the relative phase measurement of the nano-optical field at the position of the optical fiber probe.

Referring to FIG. 4 , an embodiment of the present invention provides a nano-optical field spin-orbit interaction measurement system 10 . The nano-optical field spin-orbit interaction measurement system 10 includes: a laser generating device 100 , a probe heterodyne interference device 200 and a data receiving and processing device 300 . The laser generating device 100 is used for outputting the original measurement light and the original reference light. The probe heterodyne interference device 200 is arranged in the light output direction of the laser generating device 100 . The probe heterodyne interference device 200 adopts the aforementioned probe heterodyne interference device 200 . The laser light is incident on the rotationally resolved probe heterodyne interference device 200 for generating heterodyne interference light by interference. The data receiving and processing device 300 is arranged in the output direction of the heterodyne interference light, and is used for receiving and demodulating the heterodyne interference light.

Referring to FIG. 5 , in one embodiment, the laser generating device 100 includes a laser 110 and a shaping unit 120 . The laser 110 outputs single longitudinal mode laser light with good coherence. The single longitudinal mode laser passes through the shaping unit 120 to output single longitudinal mode and single transverse mode laser light.

In one embodiment, the laser 110 is a frequency-stabilized single longitudinal mode laser. The frequency-stabilized laser may be a gas or solid-state laser. In one embodiment, the shaping unit 120 includes: a beam expanding device, a shaping device, a collimating device, and an optical filtering device, the beam expanding device, the shaping device, the collimating device, and the optical filtering device They are arranged in sequence along the transmission direction of the laser output from the laser 110 .

In one embodiment, the data receiving and processing apparatus 300 includes: a photodetector 310 , a lock-in amplifier 320 , a reference signal mixing module 330 and a data acquisition module 340 . The photodetector 310 can convert the weak optical signal from the optical fiber coupler 271 into the alternating current signal and perform pre-amplification. The photodetector 310 may be a photomultiplier tube or an avalanche diode. The lock-in amplifier 320 is electrically connected to the photodetector 310 . The reference signal mixing module 330 is electrically connected to the lock-in amplifier 320 . The reference signal mixing module 330 provides a reference frequency signal for the lock-in amplifier 320 . The lock-in amplifier 320 performs phase-locking and demodulation on the AC signal and outputs a phase-locked demodulation signal. The data acquisition module 340 is electrically connected to the lock-in amplifier 320 for collecting the phase-lock demodulation signal.

In one embodiment, the nano-optical field spin-orbit interaction measurement system 10 may further include a computing control terminal 400 . The computing control terminal 400 is electrically connected to the aperture scanning near-field optical microscope device 250 and the data receiving and processing device 300 respectively. The computing control terminal 400 can control the scanning head 252 through the near-field optical microscope controller 254 to perform needle advancing and retracting and three-dimensional scanning of the optical fiber probe 253 . The phase-locked demodulation signal collected by the data collection module 340 may be processed by the calculation control terminal 400 to obtain spatially distributed synchronization data of phase, amplitude and shape.

In one embodiment, the sample may be a Matesurface device. The metasurface device is a circular polarization sensitive structure based on geometric phase. By designing the structural parameters of the metasurface device, it can realize the spin-vortex conversion of the optical field, and then generate a vortex optical field with a topological charge of 3 under circularly polarized light illumination.

The design of the cell structure in the metasurface device is shown in FIG. 6 . The unit structure adopts the geometric form of gold nanorod pairs. The geometric form can improve the filling factor of the unit structure design, thereby increasing the scattering cross section of the metasurface device and improving the conversion efficiency of the metasurface device. By arranging the orientation angles of each of the unit structures in the metasurface device according to the following rules, a vortex light field with a topological charge of 3 can be generated under circularly polarized light illumination.

可单独调控相位，

为第i个单元的中心坐标，且满足

，p为超构表面器件的像元尺寸。图7为利用电子束刻蚀工艺加工出的超构表面器件的电镜照片。所述超构表面器件的大小为7μm×7μm。图5左上角插图为金纳米棒对的加工结构，其长度标尺为100nm。Among them, the unit orientation angle

The phase can be adjusted individually,

is the center coordinate of the i-th unit and satisfies

, p is the pixel size of the metasurface device. FIG. 7 is an electron microscope photograph of a metasurface device processed by an electron beam etching process. The size of the metasurface device is 7 μm×7 μm. The inset in the upper left corner of Fig. 5 is the processed structure of the gold nanorod pair, and its length scale is 100 nm.

FIG. 8 is a schematic diagram of the spin-resolved detection principle of the spin-orbit interaction measurement system 10 . In one embodiment, two light fields are generated after irradiating the metasurface device with left-handed circularly polarized measurement light: a left-handed circularly polarized plane wave and a right-handed vortex light with a topological charge of 3. The left-handed polarized light and the right-handed vortex light then undergo heterodyne interference with the circularly polarized reference light, so by controlling the handedness of the reference light, the handedness resolution detection of the left-handed polarized light and the right-handed vortex light can be realized . When the reference light is right-handed circularly polarized light, the right-handed reference light is orthogonal to the left-handed polarized light, and heterodyne interference cannot be generated; the right-handed reference light and the right-handed vortex light produce heterodyne interference, which can be used The spin-orbit interaction measurement system measures the complex amplitude distribution of the near-field right-handed component, and at this time, obtains the 6π vortex phase distribution generated by the spin-vortex conversion. When the reference light is left-handed circularly polarized light, the left-handed reference light is orthogonal to the right-handed vortex light, and heterodyne interference cannot be generated; The spin-orbit interaction measurement system 10 measures the complex amplitude distribution of the near-field left-handed component, and at this time obtains the plane wavefront distribution with the same phase.

In one embodiment, the key for the spin-orbit interaction measurement system 10 to achieve rotationally resolved detection is to use an orthogonal polarization calibration method to generate circularly polarized compensation light. In the orthogonal polarization calibration method, the reference light polarization compensation device 260 is adjusted based on the heterodyne interference light intensity of the coupling device 270, and the reference light is circularly polarized compensation light by means of orthogonal extinction. Adjust the polarizer 231 and the quarter-wave plate 232 in the measurement light polarization control device 230 so that the measurement light is left-handed or right-handed circularly polarized light, and then incident on the unstructured area or transparent blank of the sample area, finely adjust the electric half-wave plate 261 and the electric quarter-wave plate 262 in the reference light polarization compensation device 260, so that the heterodyne interference light of the optical fiber coupler 271 reaches extinction, then a right-handed or left-handed Circularly polarized compensated light.

The working process of the spin-orbit interaction measurement system 10 will be described below by taking FIG. 9 as an example. The laser 110 emits laser light and is incident on the shaping unit 120 . The shaping unit 120 shapes the laser light and then enters the polarization beam splitter and the reflection mirror 211 into two laser beams, a measurement optical path and a reference optical path. The measuring optical path laser is incident on the first frequency shifter 221 , the first diaphragm 222 , the polarizer 231 , and the quarter-wave plate 232 in sequence. The polarizer 231 and the quarter-wave plate 232 adjust the polarization state of the measurement light according to the application situation, and then pass through the focusing element 241 for weak focusing, and then enter the scanning element 242. The clear aperture of stage 251 illuminates the sample and performs focus scanning and sample alignment. Here, the samples are metasurface devices. The video microscope 255 and the CCD camera 256 observe and monitor the measurement field of view in real time, and transmit the observation data to the computing control terminal 400 . The computer control terminal 400 is a computer. The computer issues an instruction to the scanning near-field optical microscope controller 254 to control the scanning head 252 to move with three-dimensional nanometer precision. As the scanning head 252 moves, the tip of the optical fiber probe 253 detects the near-field nano-optical field of the sample, and the sample information light is obtained through the optical fiber transmission of the optical fiber probe 253 . The optical fiber probe 253 is an aperture type probe with good circular symmetry, so it has the ability to maintain the rotation of the circularly polarized light measured in the near field. At the same time, the reference optical path laser passes through the second frequency shifter 223, the second diaphragm 224, the electric half-wave plate 261, the electric quarter-wave plate 262, and the fiber collimation/coupling in sequence. The optical fiber polarization controller 263 and the optical fiber polarization controller 264 obtain polarization-compensated light. Using the orthogonal polarization calibration method, finely adjusting the electric half-wave plate 261 and the electric quarter-wave plate 262 can obtain left-handed or right-handed circularly polarized compensation light, which is used to achieve near-field rotational resolution detection. Finally, the near-field information light and the circularly polarized compensating light with a specific handedness generate heterodyne interference light in the fiber coupler 271 . The heterodyne interference light is incident on the photodetector 310 and then outputs an alternating current signal. The reference signal mixing module 330 provides a reference frequency signal for the lock-in amplifier 320, and performs phase-lock demodulation on the AC signal to obtain a phase-lock demodulation signal. The data acquisition module 340 collects the phase-locked demodulation signal and processes it by the computer 400 to obtain synchronization data of the phase, amplitude and shape of the near-field three-dimensional spatial distribution.

As shown in FIG. 10 , the spin-orbit interaction measurement system 10 proposed by the present invention can realize near-field measurement with rotational resolution and phase resolution. Based on the orthogonal polarization calibration method, even when the conversion efficiency of the metasurface device is low, measurement results with high signal-to-noise ratio and contrast can still be obtained. The optical fiber probe performs two-dimensional scanning measurement in the near field of the metasurface device. By controlling the rotation of the circularly polarized compensation light in the reference optical path, the amplitude and phase of the specific rotation component of the nano-optical field can be obtained point by point. The near-field distribution data were obtained to obtain the geometric phase distribution generated by the photon spin-orbit interaction in the metasurface device.

As shown in FIG. 11 , the spin-orbit interaction measurement system 10 proposed by the present invention can realize the near-field three-dimensional tomography measurement with rotational resolution and phase resolution. By precisely controlling the distance between the optical fiber probe 253 and the sample with nanometer precision, the three-dimensional spatial cross-section measurement function along the optical axis can be realized, and the three-dimensional amplitude and phase of the near-field nano-optical field can be obtained point by point in real time Distribution information, and then simultaneously obtain the geometric phase distribution generated by the photon spin-orbit interaction in the metasurface device and the dynamic phase distribution of the rotation change obtained by the optical field propagation.

The present invention is also suitable for measuring and characterizing other types of transmissive metasurface devices. As for the metasurface structure device, the present invention can be extended to all other circular polarization-sensitive metasurface structures based on geometric phase modulation. Metasurface structure device unit geometry design can include nanorods, nanostars, nanodisk aggregates, etc. The device material may include metal materials such as gold, silver, and aluminum, and may also include dielectric materials with higher refractive index such as silicon and titanium dioxide. Device functions can include vortex light generation and conversion, photonic spin-Hall effect devices, holographic multiplexing, etc.

The above-mentioned embodiments only represent several embodiments of the present invention, and are more specific and detailed along with the description, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (19)

1. A probe heterodyne interference device for rotation resolution is characterized by comprising:

the single-beam laser is divided into original measuring light and original reference light through the light splitting module;

a difference frequency generating device, arranged in the transmission direction of the original measuring light and the original reference light, for performing frequency modulation on the original measuring light and the original reference light, outputting the measuring light and the reference light, and generating a predetermined frequency difference between the measuring light and the reference light;

the measurement light polarization control device is arranged in the transmission direction of the measurement light, and the polarization state of the measurement light is adjusted after the measurement light enters the measurement light polarization control device;

a focusing and scanning device which is arranged in the output direction of the reference light of the measuring light polarization control device, focuses the measuring light passing through the measuring light polarization control device to output illumination light, and finely adjusts the excitation position of the illumination light relative to the sample;

the aperture type scanning near-field optical microscope device excites the sample to generate a nanometer optical field, and the aperture type scanning near-field optical microscope device detects and collects the nanometer optical field in a near field and outputs sample information light;

the reference light polarization compensation device is arranged in the transmission direction of the reference light, and the reference light is incident to the reference light polarization compensation device and then outputs polarization compensation light;

and the sample information light and the polarization compensation light enter the coupling device to generate interference to generate heterodyne interference light.

2. The rotationally resolved probe heterodyne interference apparatus of claim 1, wherein the difference frequency generating means includes:

the first frequency shifter and the first diaphragm are sequentially arranged along the propagation direction of the original measuring light;

the second frequency shifter and the second diaphragm are sequentially arranged along the propagation direction of the original reference light;

the first frequency shifter and the second frequency shifter are acousto-optic frequency shifters or acousto-optic modulators.

3. The rotationally resolved probe heterodyne interference apparatus of claim 1, wherein the measurement light polarization control apparatus includes a polarizer and a quarter-wave plate or a spatial light modulator, which are sequentially arranged along a propagation direction of the measurement light.

4. The rotationally resolved probe heterodyne interferometry apparatus of claim 1, wherein the focus scanning apparatus comprises:

the measuring light enters the focusing element to output weakly focused illuminating light after passing through the measuring light polarization control device;

a scanning element that fine-tunes an excitation position of the weakly focused illumination light relative to the sample.

5. The gyresolventizing probe heterodyne interferometry device of claim 1, wherein the aperture-type scanning near-field optical microscope device comprises:

the scanning platform is used for placing a sample, and the center of the scanning platform is provided with a light through hole penetrating through the scanning platform;

a scanning head disposed opposite the sample;

the optical fiber probe is linked with the scanning head and is connected with the coupling device, the nano optical field of the sample is detected by the near field of the needle point of the optical fiber probe, and the sample information light is transmitted to the coupling device through the optical fiber of the optical fiber probe;

the scanning near-field optical microscope controller is connected with the scanning head and the scanning platform and is used for synchronously controlling the scanning head and the scanning platform to realize micron-scale and nano-scale precision three-dimensional displacement;

the device comprises a video microscope and a CCD camera, wherein the video microscope is opposite to a sample carried by the scanning platform, and the CCD camera is fixed on the video microscope and used for assisting in imaging and feeding back the relative position of the optical fiber probe and the sample.

6. The rotational resolution probe heterodyne interference apparatus of claim 5, wherein the optical fiber probe is a bare optical fiber probe without coating film or a metal-coated aperture probe or a functional probe with a tip adhered with metal nanoparticles or a functional probe with etched helical chiral nanostructure.

7. The rotation-resolving probe heterodyne interference apparatus of claim 1, wherein the reference light polarization compensation apparatus includes:

the electric half-wave plate and the electric quarter-wave plate are used for electrically controlling and compensating the polarization state of the reference light and are sequentially arranged along the propagation direction of the reference light;

the optical fiber polarization controller is connected with the coupling device and used for adjusting the polarization state in the optical fiber of the optical fiber polarization controller and transmitting the polarization compensation light to the coupling device;

the optical fiber collimating coupler is arranged between the electric quarter-wave plate and the optical fiber polarization controller.

8. The rotationally resolved probe heterodyne interference apparatus of claim 7, wherein the fiber collimating coupler is a low numerical aperture objective lens or a graded index lens for coupling spatial light into the fiber of the fiber polarization controller.

9. The rotation-resolving probe heterodyne interferometry apparatus of claim 1, wherein the coupling apparatus comprises a non-polarization-maintaining fiber coupler.

10. The rotational resolution probe heterodyne interference apparatus of claim 1, wherein the optical splitting module includes a polarizing beam splitter and a mirror disposed in a light exiting direction of the polarizing beam splitter.

11. A method for measuring nanometer optical field spin-orbit interaction, which adopts the gyrodynamic resolution probe heterodyne interference apparatus of any one of claims 1 to 10, and is used for measuring nanometer optical field spin-orbit interaction on mesoscopic scale, and is characterized by comprising the following steps:

by a reference light polarization compensation device and a coupling device, heterodyne interference light is generated and selective rotation or opposite rotation is obtained for resolution by a rotation resolution detection method;

and the performance of super-optical diffraction limit imaging and phase resolution is obtained by adopting a probe heterodyne interference method.

12. The method of claim 11, wherein the spin-resolved detection method comprises:

obtaining circular polarization compensation light by adopting an orthogonal polarization calibration method, wherein the circular polarization compensation light and the sample information light interfere in the coupling device to generate heterodyne interference light;

and the rotation resolution detection of the nanometer optical field of the sample is realized by adjusting the reference light polarization compensation device to control and switch the rotation of the circular polarization compensation light.

13. The method of claim 12, wherein the orthogonal polarization calibration method comprises:

and standard left-handed or right-handed circularly polarized illumination light is incident to a non-structural area of the sample, and the reference light polarization compensation device is adjusted to enable heterodyne interference light output by the coupling device to reach an extinction state so as to obtain right-handed or left-handed circularly polarized compensation light.

14. The method of claim 11, wherein the probe heterodyne interferometry comprises:

the optical fiber probe collects near-field high spatial frequency information of a nanometer optical field of a sample and transmits the information to a far field so as to realize ultra-optical diffraction limit measurement;

the original reference light and the original measuring light pass through a difference frequency generating device, and the generated reference light and the measuring light have a preset frequency difference;

and the heterodyne interference light demodulation can realize the relative phase measurement of the nanometer optical field at the position of the optical fiber probe.

15. A nano-optic field spin-orbit interaction measurement system, comprising:

the laser generating device is used for outputting the original measuring light and the original reference light;

the probe heterodyne interference device for rotational resolution is arranged in the light output direction of the laser generation device, and is used for generating heterodyne interference light by adopting the probe heterodyne interference device for rotational resolution of any one of claims 1 to 10;

and the data receiving and processing device is arranged in the output direction of the heterodyne interference light and is used for receiving the heterodyne interference light and analyzing heterodyne interference information.

16. The nano-optic field spin-orbit interaction measurement system of claim 15, wherein the laser generation device comprises:

the laser outputs single longitudinal mode laser with good coherence;

and the single longitudinal mode laser passes through the shaping unit to output laser of a single longitudinal mode and a single transverse mode.

17. The nano-optic field spin-orbit interaction measurement system of claim 16, wherein the shaping unit comprises:

the laser comprises a beam expanding device, a shaping device, a collimating device and a filtering device, wherein the beam expanding device, the shaping device, the collimating device and the filtering device are sequentially arranged along the light output transmission direction of the laser.

18. The nano-optic field spin-orbit interaction measurement system according to claim 15, wherein the data receiving and processing means comprises:

the heterodyne interference light is incident to the photoelectric detector and then outputs an alternating current signal;

the phase-locked amplifier is electrically connected with the photoelectric detector;

the reference signal mixing module is electrically connected with the phase-locked amplifier and provides a reference frequency signal for the phase-locked amplifier, and the phase-locked amplifier performs phase locking and demodulation on the alternating current signal and outputs a phase-locked demodulation signal;

and the data acquisition module is electrically connected with the phase-locked amplifier and is used for acquiring the phase-locked demodulation signal.

19. The nanoscopic optical field spin-orbit interaction measurement system of claim 15, wherein the system further comprises a computational control terminal electrically connected to the aperture type scanning near-field optical microscope device and the data receiving and processing device, respectively.

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