CN116827442A - Method for realizing chiral nanometer light source, method for exciting chiral light and method for controlling chiral light signal - Google Patents
Method for realizing chiral nanometer light source, method for exciting chiral light and method for controlling chiral light signal Download PDFInfo
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Abstract
The invention provides a method for realizing chiral nanometer light source, a method for exciting chiral light and a method for controlling chiral light signals. Meanwhile, the far-field optical excitation mode is different from the traditional research chiral light source far-field optical excitation mode, different superposition states of Smith-Peser radiation in the nano optical trap structure are excited by virtue of the advantages of electron beam nanoscale beam spots, the effective control of chiral degree of the chiral nano light source is realized in the hundred-nanometer electron beam moving range, and the method has extremely strong supporting power and reference value for the future development of the chiral nano light source.
Description
Technical Field
The invention relates to a chiral nanometer light source, in particular to a method for modulating smith-Percoll radiation into the chiral nanometer light source by utilizing electron beams to be incident into a periodically stacked square light trap structure so as to excite the smith-Percoll radiation, which can analyze the excitation and the modulation of the chiral smith-Percoll radiation nanometer light source and guide the application of an optical circuit and binary information processing.
Background
Smith-pezier radiation (Smith-Purcell Radiation, SPR) is a special electron beam diffraction radiation that originates from electrons that are rapidly generated by polarization charges and oscillations in the structure during glancing incidence of the electron beam on the surface of the grating structure. Since the radiation wavelength is strongly dependent on the periodicity of the grating structure and the radiation intensity is closely related to the incident electron beam current, it is easier to design a radiation source with richer optical properties. By means of a corresponding grating structure design, it is expected to realize a nanoscale light source carrying smith-peltier radiation. Smith-pezier radiation was originally used to design high power terahertz sources, free electron lasers and other devices, and charged particle beam shaping and detection, and then to expand its optical performance to the linearly polarized and vortex light fields in order to meet the needs of more types of radiation sources. However, chirality, another important property of a smith-peltier radiation source, often needs to be achieved by coherent superposition of two beams of orthogonally polarized linear polarized smith-peltier radiation, which is difficult to achieve in a conventional single grating structure, which also presents a greater challenge for new structural designs carrying smith-peltier radiation.
Chirality is a physical property that is widely found in nature, i.e., the property that an object cannot coincide with its mirror image. Since two different circular polarization states of light correspond to two spin states (left-handed circular polarization and right-handed circular polarization, σ= ±1), the spin-related effect can be further generalized to the optical field, namely optical chirality (Optical chirality, OC), and has wide application in the fields of information processing, information storage, optical routing and the like. To measure the magnitude of the chirality of the signal, the chirality cd= (I LCP -I RCP )/(I LCP +I RCP ) Wherein I LCP And I RCP Left-hand circular polarization (CircularlyPolarized, LCP) and Right-hand circular polarization (Right-handed Circularly Polarized, RCP) photon spin components, respectively, in radiation. Since the spin angular momentum of photons can be used as a robust, high capacity information carrier, the optical chirality is predicted to enable manipulation of the information carrier in optical information processing. The characteristics of orthogonality and high dimension have wide application prospect in the aspects of information coding and information cryptography. The light source, which is the most important component in the optical circuit, determines the storage performance and information processing capability in the optical circuit. The chiral nanometer light source has high integration caused by small size and high dimension caused by photon spin, has important significance for the transmission and processing of optical information in an optical circuit, and provides a new approach for the future binary informatization processing and transmission.
With the rapid development of optical circuits and integrated photonics, many optical structures have reached nanometer dimensions, particularly metal nanostructures, microcavity structures, nanohole structures, etc., in order to obtain better optical performance or optical information processing capabilities. It is therefore becoming increasingly important to study the optical properties of nanostructures to achieve high spatial resolution excitation and detection at sub-wavelength and even deep sub-wavelength scales. The cathode fluorescence microscopic imaging technology is a non-invasive detection means based on a scanning electron microscope or a transmission electron microscope, utilizes electron beams to excite and collect cathode fluorescence signals of a sample, has the advantages of nanoscale space resolution capability and accurate excitation, and can realize fluorescence imaging with the resolution of 10nm at maximum. The method is widely applied to research of interaction of electrons and substances, nanoscale luminescence detection, nanoscale excitation regulation and control and the like. The excitation of different mode information types is realized by controlling the incidence position of the electron beam at the light path excitation end; and combining the circular polarization detection module at the light path collecting end to perform ultra-fine circular polarization detection on the nanometer scale on the emergent optical signal. In the study of smith-pezier radiation, the cathode fluorescence microscopy technology shows strong advantages, and flexible radiation wavelength regulation, circular polarization control and the like are realized.
Disclosure of Invention
The invention aims to provide a method for realizing chiral nanometer light source by utilizing electron beams, which enables electron beams without spin injection to realize chiral light emission by exciting Smith-Peltier radiation in a periodically stacked square optical trap structure.
The technical scheme of the invention is as follows:
a method for implementing chiral nano-light sources using electron beams (see fig. 1) for excitation and manipulation of smith-peltier radiation in a periodically stacked square optical trap structure. The method comprises gold/silicon dioxide (Au/SiO) 2 ) Preparation of a square nano optical trap structure in a periodically stacked photon crystal, and chiral manipulation of electron beam-excited chiral smith-peltier radiation in the optical trap structure.
Au/SiO 2 The processing preparation of the periodically stacked square optical trap structure is divided into two steps: au/SiO 2 And (3) preparing the periodically stacked photonic crystal. Au and SiO are sequentially evaporated on a silicon wafer by an electron beam evaporation coating method 2 A layer; 2. etching on Au/SiO with focused ion beam 2 And etching a square optical trap hole structure in the periodically stacked photonic crystal. Wherein, au layer and SiO 2 The layer period is 6-10 periods, and the total number of the layers is 12-20. The thickness of the Au layer is 200-220 nm, siO 2 The thickness of the layer is 250-300 nm. The square optical trap structure is a square hole structure with the side length of 600-700 nm.
Chiral Smith-Peltier radiation in the optical trap structure is generated by incidence of electron beam into hollow part of optical trap, and the side wall of optical trap is one-dimensional Au/SiO 2 The grating structure, the electron beam passes through the side wall of the optical trap, and the Smith-Peltier radiation is excited in the side wall. Since the intensity of smith-pezier radiation decays exponentially with increasing distance of the electron beam from the grating structure, we choose to strike the electron beam at the top corner from the square optical trap structure and consider only the radiation generated by the electron beam in the nearest neighboring side wall in the optical trap. In a square optical trap structure, the Smith-Peltier radiation generated in adjacent sidewalls exists in the form of a set of orthogonal polarizations, i.e., radiating linesThe polarization directions are respectively perpendicular to the respective sidewall planes. When an electron beam is incident on a geometrically asymmetric position of the optical trap structure, a difference in distance between the electron beam and an adjacent side wall causes a phase difference between polarization currents generated in the adjacent side wall, and therefore the same phase difference exists between the set of orthogonally polarized smith-pezier radiation generated by the polarization currents, and two orthogonal linearly polarized radiation with a fixed phase difference are finally combined into circularly polarized light to be emitted from the optical trap, so that the emission of specific chiral light is realized.
The excitation of optical chirality in the square nanometer optical trap radiation source is generated by the nano-scale movement of the excitation position of the electron beam, the larger the distance difference between the electron beam and the adjacent side wall is, the larger the phase difference of Smith-Percoll radiation generated by the adjacent side wall is, and when the phase difference is changed between-2/pi and 2/pi, the circular polarization state of the radiation light can be converted. The closer the phase difference is to-2/pi or 2/pi, the higher the chirality of the radiated light is, and when the phase difference is 0, the superposition principle of circularly polarized light cannot be satisfied, and the chirality is also 0. Therefore, the switching of the presence/absence of the square nanometer optical trap radiation source and the circular polarization state can be realized by moving the electron beam to change the excitation area, thereby realizing control.
The electron beam provided by the invention excites chiral radiation in the nanometer optical trap, and is a chiral nanometer light source realized by superposing two beams of Smith-Persian radiation which are excited by the electron beam at the same time. Under the condition of no spin state injection, the emission of chiral light under the sub-wavelength scale is realized by changing the phase difference of a group of orthogonal polarized linear polarization Smith-Percoll radiation, so that the use scale of the chiral light source is greatly reduced, the excitation position can be accurately changed by the simple electron beam nano-scale movement, the superposition state of linear polarization is further changed, and the sub-wavelength scale control of the radiation chirality is realized. In the research of a new generation of information carrier of nano photonics, the control of spin freedom degree is changed from traditional far-field laser excitation to excitation by utilizing Smith-Percoll radiation through mutual superposition, and the optical diffraction limit is broken through. The chiral nanometer light source can be applied to light spin and orbit coupling research and quantum information device integration, and has the characteristics of small scale, high sensitivity, high robustness and the like. On the premise of realizing the chiral light source in a large scale by commonly applying far-field optical mode at present, the invention has wide market prospect for realizing the chiral nanometer light source by utilizing the electron beam.
Drawings
FIG. 1 shows a schematic diagram of sample structure and phenomena according to an embodiment of the present invention.
Figure 2 shows a schematic diagram of an embodiment of the invention.
Figure 3 shows the mode distribution in a square optical trap structure in accordance with embodiments of the present invention.
Fig. 4 shows a plot of the phase difference between two orthogonally normalized smith-peltier radiations as a function of the electron beam incidence position for an embodiment of the present invention, each pixel representing the injection point of the electron beam.
Fig. 5 shows a plot of the relative intensity between two orthogonally normalized smith-peltier radiations as a function of the position of incidence of the electron beam, each pixel representing the injection point of the electron beam, according to an embodiment of the present invention.
Fig. 6 shows the incidence of a 30keV, 20nA electron beam at geometrically asymmetric positions of a square optical trap structure (marked in the electron microscopy), the left-hand circular polarization and right-hand circular polarization components of the obtained simulated and experimental radiation signals, and the calculated chirality.
Fig. 7 shows the chiral degree of the radiation light according to the wavelength when the electron beam is incident on each point (marked in the electron microscope) on the straight line parallel to the diagonal line according to the embodiment of the present invention.
FIG. 8 shows a simulated radiation chirality distribution graph of the present invention with respect to electron beam incidence position, with a detection wavelength of 740nm.
Fig. 9 shows the intensity of the radiation beam as a function of wavelength when the electron beam is incident at each point (marked in the electron microscope image) on the straight line of the diagonal line according to the embodiment of the present invention.
Detailed Description
The present invention is described in further detail below with reference to the drawings and detailed description so that those skilled in the art can more clearly understand the present invention.
The structure diagram of an excitation experimental sample of electron beams on chiral light in a square nanometer optical trap in the embodiment of the invention is shown in fig. 1: the structure comprises three parts, wherein the first part is a substrate part, and consists of a Si substrate and SiO 2 A spacer layer; the second part is a photonic crystal part with a total of 12 layers of 6 periods and is composed of an Au layer and SiO 2 Alternate stacking of layers wherein the uppermost layer is SiO 2 Layer, au layer and SiO 2 The layer thicknesses were 200nm and 250nm, respectively. The third part is a light trap part, the light trap is a square hole structure with the side length of 700nm, and the depth is about 3 mu m.
The preparation method of the experimental sample for exciting the chiral light experimental sample in the square nanometer optical trap by the electron beam is further provided below, and comprises the following steps:
step one, deposition of SiO on Si substrate using Plasma Enhanced Chemical Vapor Deposition (PECVD) 2 And (5) a spacer layer to obtain the SiO2/Si substrate.
Step two, for SiO 2 Ultrasonic cleaning Si substrate with organic solvent, ultrasonic cleaning with acetone (cleaning time 10-15 min), ethanol (cleaning time 10-20 min), and deionized water (cleaning time 20-30 min), and blow drying deionized water remaining on the substrate with nitrogen gun to obtain clean SiO 2 A Si substrate.
Step three, siO is subjected to evaporation coating by utilizing an electron beam 2 Sequentially depositing Au layer and SiO on Si substrate 2 A layer with a vapor deposition rate of aboutFinally obtaining Au/SiO 2 The photonic crystals are periodically stacked.
And fourthly, etching a square hole structure with the side length of 700nm in the photonic crystal by utilizing a Focused Ion Beam (FIB) etching mode, wherein the depth is about 3 mu m. Gallium (Ga) ions are selected as an etching source, the voltage of the ion source is 30kV, the beam current is about 9pA, the etching depth is 3 mu m, and finally the square nanometer optical trap structure shown in figure 1 is obtained.
The excitation of chiral light in a square nanowell by an electron beam in the present invention is based on superposition of a set of orthogonally polarized smith-peltier radiations excited by the electron beam: the electron beam is grazing incidence to the well sidewall, creating a polarization current in the sidewall, schematically shown in fig. 2, which creates smith-peltier radiation. Since the radiation intensity is strongly dependent on the distance of the electron beam from the grating surface, we only consider the case where the electron beam is incident near the top angle of the optical trap and the effect of the polarization current generated in the adjacent sidewall nearest to the electron beam. The resulting smith-pezier radiation should meet the pattern type in the optical trap structure by analyzing the eigenmodes of the optical trap and the resonance conditions with the electron beam dispersion curve, i.e. the type of smith-pezier radiation present in the optical trap when the dispersion curve intersects, which also determines the wavelength of the final light emission, see fig. 3. The optical signal radiated from the square nanowell comes from the superposition of a set of orthogonally polarized smith-pezier radiations generated by adjacent sidewalls, and when there is a fixed phase difference between the two radiations, the final superposition results in either elliptically polarized light or circularly polarized light. When an electron beam is incident on a geometrically asymmetric position of a square nano optical trap, the electron beam has a fixed distance difference from an adjacent side wall, the influence of the electron beam on polarized current has a time delay, and when the electron beam is incident on different positions, the phase difference between the polarized currents generated in the adjacent side wall is analyzed, as shown in fig. 4, the phase difference is found to be different at different geometrically asymmetric positions, and meanwhile, the phase difference distribution is symmetrical about a diagonal line, so that the condition of generating a circularly polarized signal by superposition is satisfied. On the other hand, the factor affecting the circular polarization characteristics of the radiation is the difference in intensity between the set of orthogonally polarized smith-pezier radiation, and the greater the difference in intensity, the closer the superimposed radiation is to linear polarization. We have thus simulated a profile of the relative intensity between two orthogonally normalized smith-peltier radiations with the position of incidence of the electron beam, each pixel representing the injection point of the electron beam, as shown in figure 5. It can be found that the closer to the angular bisector, i.e. the geometrically symmetric position, the smaller the intensity difference, the more advantageous the superposition to produce circularly polarized light. Finally for the purpose of measuringThe degree of chirality of a circularly polarized signal, we define the degree of chirality cd= (I) LCP -I RCP )/(I LCP +I RCP ) Wherein I LCP And I RCP Left-hand circular polarization (Left-handed Circularly Polarized, LCP) and Right-hand circular polarization (Right-handed Circularly Polarized, RCP) photon spin components, respectively, in radiation.
The measurement flow of the electron beam room temperature chiral nanometer light source excitation is given below: the electron beam room temperature chiral nanometer light source excitation is carried out in a scanning electron microscope-based cathode fluorescence microscopic imaging system, the electron beam passes through a small hole of a parabolic mirror above a sample to excite the sample, the radiated cathode fluorescence is collected by the parabolic mirror above the sample, a collecting light path is finally captured by a Photomultiplier (PMT) for short, the circularly polarized component of the cathode fluorescence of the sample is extracted through a quarter wave plate and a linear polarizer which are arranged in the collecting light path, and the long axis of the quarter wave plate forms +/-45 degrees with the polarization direction of the linear polarizer to respectively extract the left-hand circularly polarized component and the right-hand circularly polarized component. In the cathode fluorescence detection, the cathode fluorescence spectrum of the sample is collected in Pan mode.
Specific examples are as follows:
processing and preparing a square nanometer optical trap sample according to the steps as shown in figure 1, wherein the Si substrate and the SiO are from bottom to top 2 Spacer layer, 200nm thick Au and 250nm thick SiO 2 And a 700nm x 700nm square hole structure etched in the photonic crystal structure using a focused ion beam. Experimental measurements were performed in a cathodic fluorescence microscopy imaging system (Gatan MonoCL4 Plus) in a scanning electron microscope (FEI Quanta 450 FEG) using a quarter wave plate (AQWP 10M-980, THORLABS) and a linear polarizer (LPVIS 100, THORLABS) to detect sample cathodic fluorescence signals over the wavelength range 690nm to 850nm by Pan mode pair.
The sample is sent into a vacuum cavity, an electron beam with the beam current of 20nA is incident to a geometric asymmetric position of an optical trap (shown as an electron microscope chart in figure 6) at room temperature, left-hand circular polarization signals and right-hand circular polarization signals (shown as a spectrogram in figure 6) radiated in the optical trap are collected, and the calculated chirality changes along with the wavelength. In order to verify the experimental result, we obtained the result under the same excitation condition (see the spectrum b in fig. 6) by using the time domain finite difference simulation method (FDTD) numerical simulation, the spectrum peak positions are all around 740nm, and the calculated chirality is also well matched. This also verifies the authenticity of the experimental results.
Changing the injection position of the electron beam, the moving path follows the change condition of the chirality with the wavelength (marked by a spectrogram in fig. 7) at different excitation positions measured under the same excitation source voltage and beam current conditions on the perpendicular line of the angular bisector of the square nanometer optical trap (marked by the spectrogram in fig. 7), and the chiral degree is found to be increased and then reduced firstly and then to be reduced to be higher than 40% at the angular bisector position as the electron beam gradually approaches the angular bisector from the angular bisector position. As the electron beam is moved away from the angular bisector position, the chiral degree increases and decreases in opposite directions. Considering that the beam spot of the electron beam is about 10nm multiplied by 10nm, the electron beam can move from the III position to the IV position about 40nm to realize the existence of chiral phenomenon, and can move from the III position about 80nm to the VI position to realize the inversion of chiral phenomenon, thus being a chiral regulation means with high robustness and high spatial resolution. To confirm the authenticity of this experimental phenomenon, the chiral degree distribution calculated at 740nm of the radiation peak when the electron beam is incident at each point near the vertex angle of the square nano-optical trap was obtained by FDTD simulation, as shown in fig. 8. It can be found that the chirality increases and decreases first and then decreases reversely as the electron beam injection position approaches the angular bisector, thus proving the experimental result.
In addition, the correspondence between the intensity of optical radiation and the excitation position of electron beam in the square nano optical trap structure was studied. As shown in fig. 9, the radiation intensity gradually decreases as the electron beam gradually gets farther from the top corner of the square nanooptical trap. This provides guidance for future applications of nanooptical trap light sources.
According to the invention, electron beams are firstly utilized to be incident into a square nano optical trap structure to generate chiral light emission, the ultra-high spatial resolution of the electron beams breaks through the optical diffraction limit, the square optical trap structure is accurately excited to obtain a group of orthogonal polarized Smith-Peltier radiation, and chiral radiation signals are obtained through the superposition relation of fixed phase differences. Meanwhile, the far-field optical excitation mode is different from the traditional far-field optical excitation mode for researching the chiral light source, and by virtue of the advantages of the electron beam nanoscale beam spots, different superposition states of Smith-Peser radiation in the nano optical trap structure are excited, so that the chiral degree of the chiral nano light source is effectively controlled in the hundred-nanometer electron beam moving range. The invention is a novel room temperature chiral nanometer light source excitation and control method with nanometer scale, high sensitivity and strong robustness, besides the square nanometer optical trap structure with the size, the method can be expanded to other periodic optical trap structures, and can meet chiral light emission under different radiation wavelengths. The present nanometer photonics device is developed rapidly, the demand for new freedom degree for controlling the information carrier is stronger, and the present invention has strong supporting power and reference value for the development in future.
Finally, it should be noted that the examples are disclosed for the purpose of aiding in the further understanding of the present invention, and those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.
Claims (8)
1.A method for realizing chiral nanometer light source is characterized in that Au/SiO is prepared firstly 2 And periodically stacking the photonic crystals, etching square holes in the stacked photonic crystals to obtain a square nano optical trap structure, and making electron beams incident into the square nano optical trap structure to obtain the chiral nano light source.
2. The method for realizing the chiral nanometer light source according to claim 1, wherein the method for coating the film on SiO by electron beam evaporation is characterized in that 2 Sequentially depositing an Au layer and SiO on a Si substrate 2 A layer with a vapor deposition rate of aboutObtain the thickness ofAu/SiO of 3-5 μm 2 The photonic crystals are periodically stacked.
3. The method of claim 1, wherein a square hole structure is etched in the photonic crystal by means of focused ion beam etching (FIB), wherein gallium ions are selected as the etching source, the ion source voltage is 25-30 kV, and the beam current is about 7-9 pA.
4. The method for realizing the chiral nanometer light source according to claim 1, wherein the Au layer and the SiO layer 2 The layer period is 6-10 periods, and the total number of the layers is 12-20.
5. The method for realizing chiral nanometer light source of claim 4, wherein the thickness of the Au layer is 200-220 nm and SiO 2 The thickness of the layer is 250-300 nm.
6. The method for realizing the chiral nanometer light source of claim 1, wherein the square optical trap structure is a square hole structure with a side length of 600-700 nm.
7. The method for exciting chiral light is characterized in that when an electron beam is incident on a geometrically asymmetric position of a square nano optical trap structure, a difference in distance between the electron beam and an adjacent side wall causes a phase difference between polarization currents generated in the adjacent side wall, and further causes the same phase difference between the set of orthogonal polarized smith-pezier radiations generated by the polarization currents, the phase difference is between-2/pi and 2/pi, and two orthogonal linear polarized radiations with fixed phase difference are finally combined into circularly polarized light to be emitted from the square nano optical trap structure, so that chiral light emission is realized.
8. A method for controlling chiral optical signals, wherein the chiral optical signals are obtained by superposition of fixed phase differences by using the method for exciting chiral light according to claim 7, chiral optical emission is generated when an electron beam is incident on a geometrically asymmetric position of a square nano optical trap structure, chiral optical emission cannot be generated when the electron beam is incident on a geometrically symmetric position of the square nano optical trap structure, and the existence of the chiral optical signals is controlled by moving the electron beam.
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