CN109709630B - Sub-wavelength vortex light beam array generation method based on metal nano super surface - Google Patents
Sub-wavelength vortex light beam array generation method based on metal nano super surface Download PDFInfo
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Abstract
The invention provides a method for generating a sub-wavelength vortex light beam array based on a metal nano super surface, which comprises the steps of firstly preparing a specific metal nano super surface structure formed by a metal nano rod array, then vertically irradiating the specific metal nano super surface structure by circularly polarized light, thereby converting the circularly polarized light into a vortex beam array with a sub-wavelength scale, and preparing the specific metal nano super surface structure capable of generating the sub-wavelength vortex light beam array by reasonably designing the size and the arrangement of the metal nano rods, compared with other vortex light beam generating modes, the method has the advantages of simple structure, easy integration, uniform light intensity distribution and the like, and the vortex light beam array generated by the method not only can enhance the information safety and the capacity in the information transmission and storage, but also can capture a large number of particles in the particle capture at one time, and the motion characteristics of different objects can be detected simultaneously, and the application field of the vortex light beam is expanded.
Description
Technical Field
The invention relates to the field of novel optical field regulation in micro-nano optics, in particular to a method for generating a sub-wavelength vortex light beam array based on a metal nano super-surface.
Background
Vortex beam, also known as optical vortex, is an optical field with isolated singularities, in which the wave vector carrying the phase singularity, called phase vortex beam (OAM), has an azimuthal term and rotates around the vortex center in the optical expression μ0(r,θ,z)＝μ0The phase factor exp (il theta) exists in (r, z) exp (il theta) exp (-ikz), where r is the displacement vector from the origin, mu0Representing amplitude, theta azimuth, z propagation distance, l its topological charge, k wave number, and magnitude
λ represents the wavelength of incident light. Orbital angular momentum carried by each photon due to different topological charge numbers
Different. The center of the vortex light beam is a micron-sized dark spot, and no heat loss effect exists when the micro-nano particles are controlled, so that the vortex light beam has wide application in the field of micro-nano control, and meanwhile, when the vortex light beam traps the particles, the particles can rotate through orbital angular momentum, so that the vortex light beam is also called as an optical wrench. The vortex light beams have strong stability in long-distance transmission and theoretically have an infinite orthogonal state, the vortex light beams with different azimuth angles in coaxial transmission are orthogonal to each other, and crosstalk between the light beams is minimum, so that the light beams can be effectively multiplexed and demultiplexed, and the vortex light beams have huge application prospects in the field of secret communication. In addition, the vortex beam has huge application potential in the fields of biomedicine, micromechanics, astronomy, quantum information processing and the like.
The current method for generating vortex beams mainly comprises the following steps: spiral phase plate method, geometric mode conversion method, spatial light modulator method, computer generated hologram method, and the like. The spiral phase plate method adds a spiral phase to light during the period with the spiral phase, the change of geometric mode is the mode of changing incident light through an optical device, the essence of the two methods is that the optical path of the incident light is modulated, so that different positions have different phases, but the accumulation of the optical path makes the device have certain physical size, which also becomes an important factor limiting the development of miniaturization and integration; the spatial light modulator method and the computer generated hologram method reproduce vortex beams by the holographic principle, which can generate a plurality of vortex beams, but the light energy distribution of the beams is not uniform, and the beams of different orders overlap with each other, so that the vortex beams with single topological charge number are difficult to separate from the beams. Although there are several methods of generating a vortex beam, there are some drawbacks and limited application scenarios. Therefore, the vortex light beam array generator capable of generating uniform light energy distribution and without high-order diffraction influence is researched, and the vortex light beam array generator with the sub-wavelength scale has important significance in the field of micro-nano optics.
In 1984, the british professor Berry first proposed the concept of geometric phase. Berry studies have found that when an adiabatic Physical system evolves from an initial state through a cycle along a path (in a parameter space or state space) and back to the initial state, the final state is not equivalent to the initial state, and an additional phase factor needs to be added (quantitative phase factors of the radial Society A: Physical, Physical and Engineering Sciences, Vol.392, No.1802, pages 45-57, 08March 1984); in 1956, the Indian Raman institute, professor Pancharatam, developed that the electromagnetic wave generated an extra phase during the polarization transformation (Generalized the interference and its applications, Pancharatam S., Proc edings of the Indian Academy of Sciences-Section A, Vol.44, No.5, pages 247-. The electromagnetic wave in a certain polarization state evolves along a certain path on the surface of the Poincare sphere and returns to the initial state, the final state and the initial state of the electromagnetic wave are different by a phase factor, and the value of the phase factor is equal to half of a closed loop solid angle enclosed by the geodesic of the evolution path. Based on these theories, related researchers have proposed the concept of geometric phase type super surfaces. The phase parameters of the electromagnetic waves are regulated and controlled through the geometric curvature of the sub-wavelength metal or medium structure on a two-dimensional plane, so that a desired wave front is constructed, and a series of complex plane optical devices including a plane imaging lens, a directional surface wave coupler, a super-oscillation lens, a vortex optical beam generator and a vortex optical beam splitter are obtained. The invention obtains a sub-wavelength vortex light beam array generation method based on the geometric phase type super surface research.
In the above background art, the vortex beam generation methods such as the spiral phase plate method, the geometric mode conversion method, the spatial light modulator method, and the computer generated hologram method all have some defects, and the application scenarios are limited. The invention researches and designs a sub-wavelength vortex light beam array generation method based on a metal nano super surface, which not only can enhance information safety and capacity in information transmission and storage, simultaneously captures and controls a large number of particles in micro-nano control, but also can simultaneously detect the motion characteristics of different objects, and expands the application field of vortex light beams.
Disclosure of Invention
The invention aims to convert the amplitude and the phase of a vortex light beam array into the size and the rotation angle of a metal nanorod, simultaneously regulate and control the amplitude and the phase of an incident light beam by reasonably designing the size and the rotation angle of the metal nanorod, and prepare the metal nanorod array in periodic distribution by adopting an electron beam etching method, so that a metal nano super-surface structure is formed, and a transmission area formed by the metal nano super-surface structure generates a sub-wavelength vortex light beam array with uniform light energy distribution under the condition that circularly polarized light is normally incident from the bottom of the metal nano super-surface structure, so as to solve the problems in the background technology. Compared with other vortex light beam generation methods, the sub-wavelength vortex light beam array generation method based on the metal nano super surface has the advantages of simple structure, easiness in integration and the like.
The invention discloses a method for generating a sub-wavelength vortex light beam array based on a metal nano super surface, which comprises the following steps: firstly, preparing a specific metal nano super-surface structure which is formed by a metal nanorod array and a quartz glass substrate and is integrally in a cuboid shape, wherein the metal nanorod array comprises n metal nanorods, n is a positive integer and is greater than 4, the metal nanorods are periodically distributed on the upper surface of the quartz glass substrate, any point in a plane where the upper surface of the metal nanorod array is located is taken as an origin, the specific metal nano super-surface structure is emitted from the origin, the length and width directions of the specific metal nano super-surface structure are respectively an X axis and a Y axis, and the opposite direction of the thickness of the specific metal nano super-surface structure is a Z axis; then, circularly polarized light with the wavelength of 532nm is vertically irradiated to a specific metal nano super-surface structure from a region with the Z being less than 0, after the circularly polarized light acts with any one metal nanorod, a phase factor 2 theta is added to the light wave phase, wherein theta is the included angle between the long axis of any one metal nanorod and the X axis, as the included angle theta between the long axis of each metal nanorod and the X axis is different, the circularly polarized light transmitted from the XY plane with the Z being 0 presents different phases at different positions of a transmission region with the Z being greater than 0, 4 adjacent metal nanorods in the two directions of the X axis and the Y axis generate a vortex light beam, the diameter of the vortex light beam is 180nm, and due to the action of the metal nanorod array, a vortex light beam array with the sub-wavelength scale with uniform light energy distribution and spiral phase distribution is generated in the transmission region with the Z being greater than 0.
The specific method for preparing the specific metal nano super surface structure comprises the following steps:
s1) spin-coating photoresist on a quartz glass substrate
S11) cleaning the silica glass substrate
Placing an original quartz glass substrate in a cuboid shape in HCl solution with the concentration of 0.5mol/L and the temperature of 35-50 ℃, standing for 10 minutes, placing the quartz glass substrate in pure water with the temperature of about 50 ℃ for soaking for 5 minutes, taking out the quartz glass substrate, and then carrying out secondary cleaning by using the pure water with the temperature of about 50 ℃ to complete the chemical cleaning of the quartz glass substrate;
s12) drying the quartz glass substrate
Placing the quartz glass substrate treated in the step S11) on a cleaning basket, introducing high-clean air or nitrogen at the temperature of about 80 ℃ into the cleaning basket for 10-20 minutes, and drying the quartz glass substrate after the quartz glass substrate and the cleaning basket are fully dried;
s13) spin-on resist
Adsorbing the quartz glass substrate treated in the step S12) on a vacuum chuck, adjusting the rotating speed of the vacuum chuck to 500rpm, dripping photoresist into the center of the upper surface of the quartz glass substrate, and after 5 seconds, increasing the rotating speed of the vacuum chuck to 3000-7000 rpm, and spinning the photoresist for 30 seconds to form a photoresist coating with the thickness of 140 nm;
s14) soft baking of quartz glass substrate after glue homogenizing
After the photoresist is uniformly coated on the upper surface of the quartz glass substrate, placing the quartz glass substrate treated in the step S13) on a vacuum hot plate at 80 ℃ for soft baking for 2-5 minutes;
s2) exposing with electron beam to obtain pattern
S21) focused electron beam exposure
Accelerating voltage of 30KV, light spot size of 30nm, and exposure dose of 25 μ c/cm2Exposing the quartz glass substrate processed in the step S1), and controlling the electron beam vector exposure machine by using a preset program to obtain a photoresist nanorod array pattern with the length of each nanorod being 90nm, the width of each nanorod being 30nm and the thickness of each nanorod being 140-150 nm on the upper surface of the quartz glass substrate, wherein the photoresist nanorods of each row and each column in the photoresist nanorod array pattern are respectively arranged at intervals at an included angle of 45 degrees to 45 degrees with the X axis, and the distance between the geometric centers of any two adjacent photoresist nanorods is 180 nm;
s22) baking the quartz glass substrate after exposure
Placing the quartz glass substrate treated in the step S21) in an oven at 150-170 ℃, baking for 90 minutes, and standing and cooling for 30 minutes in a normal temperature environment;
s3) development
S31) developing and fixing
Immersing the quartz glass substrate processed in the step S2) in a developing solution at the temperature of 21 +/-0.2 ℃ for 60-120 seconds, and then putting the quartz glass substrate in an isopropanol solution for 30-40 seconds to complete fixation, so as to obtain a nanorod array pattern on the upper surface of the quartz glass substrate;
s32) post-fixing baking substrate
Taking out the quartz glass substrate treated in the step S31), and placing the quartz glass substrate on a vacuum hot plate at 80 ℃ for soft drying for 2-5 minutes to obtain a dried nanorod array pattern on the upper surface of the quartz glass substrate;
s33) pattern inspection, evaporating the metal film
Inspecting the dried nanorod array pattern on the upper surface of the quartz glass substrate treated in the step S32) by using a scanning electron microscopy observation technology, and evaporating metal gold (Au) on the quartz glass substrate by using a thermal evaporation table after determining that the dried nanorod array pattern is qualified, wherein the thickness of the gold (Au) is 20-30 nm;
s34) removing the photoresist to obtain a metal pattern
And (2) stripping the quartz glass substrate treated in the step S33) with acetone to remove residual electron beam photoresist and metal gold, and obtaining a gold nanorod array on the upper surface of the quartz glass substrate, wherein the sizes of the gold nanorods in the gold nanorod array are all 90nm long, 30nm wide and 25nm thick, every 1 row and every 1 column of the gold nanorods in the gold nanorod array are respectively arranged at intervals with an included angle of 45 degrees to 45 degrees with the X axis, and the distance between the geometric centers of any two adjacent gold nanorods is 180nm, so that the specific metal nano super-surface structure is obtained.
The invention prepares the periodic metal nanorod super-surface capable of generating the sub-wavelength vortex beam array by reasonably designing the size and the arrangement of the metal nanorods and utilizing a mature micro-nano processing method of electron beam etching. Compared with other vortex light beam generation modes, the method has the advantages of simple structure, easiness in integration, uniform light intensity distribution and the like. The vortex light beam array generated by the method can enhance the information safety and capacity in information transmission and storage, capture a large number of particles in particle capture at one time, detect the motion characteristics of different objects simultaneously and expand the application field of vortex light beams.
Drawings
FIG. 1 is a schematic view of the metallic nano-super surface structure of the present invention
FIG. 2 is a single vortex light beam phase distribution diagram of a transmission area (an area with Z being more than 0) obtained by finite difference simulation of time domain at a distance of 100nm from a gold nanorod array along a Z axis;
FIG. 3 is a simulation result obtained by finite difference in time domain: (a) the light intensity distribution diagram of the transmission area (the area with the Z more than 0) at the position 100nm away from the gold nanorod array along the Z axis; (b) phase distribution diagram of transmission region (region with Z > 0) at a distance of 100nm from gold nanorod array along Z axis
FIG. 4 is a scanning electron microscope photograph of gold nanorod array obtained by electron beam etching
Detailed Description
The present invention is described in further detail below with reference to the attached drawings.
The invention relates to a method for generating a sub-wavelength vortex light beam array based on a metal nano super surface, which comprises the steps of firstly preparing a specific metal nano super surface structure, wherein a cuboid-shaped high-transmission quartz glass is used as a substrate, preparing a gold nanorod array which is periodically arranged on the upper surface of the substrate by using an electron beam etching process, the gold nanorod array comprises n gold nanorods, wherein n is a positive integer and is more than 4, the gold nanorod array emits light from an original point which is any point in a plane where the upper surface of the gold nanorod array is located, the length and the width directions of the specific metal nano super surface structure are respectively an X axis and a Y axis, the reverse direction of the thickness of the specific metal nano super surface structure is a Z axis, namely the upper surface of the gold nanorod array is located on an XY plane where Z is 0, the sizes of the gold nanorods are respectively 90nm multiplied by 30nm by 25nm, and the specific metal nano surface structure light is transversely distributed on the X axis and Y axis, The longitudinal direction and the X axis are respectively arranged in a 45 degree and 45 degree included angle staggered mode, namely the gold nanorods are arranged at intervals of 360nm +/-10 nm, as the gold nanorods are arranged at intervals of 180nm in every 1 row and every 1 column of the gold nanorod array, and are respectively arranged at intervals of 45 degree and 45 degree included angles with the X axis, 360nm is arranged between the gold nanorods arranged at an included angle of 45 degree with the X axis and the next gold nanorods arranged at an included angle of 45 degree with the X axis in the row or the next gold nanorods on the column, and an allowable error range is added, therefore, the gold nanorods in the gold nanorod array are called to be arranged at intervals of 360nm +/-10 nm; then, circularly polarized light with the wavelength of 532nm is vertically irradiated to a specific metal nano super-surface structure from a region with Z less than 0, after the circularly polarized light acts with any one gold nanorod, the phase of the light wave is added with a phase factor 2 theta, wherein theta is the included angle between the long axis of any gold nanorod and the X axis, as the included angle theta between the long axis of each gold nanorod and the X axis is different, circularly polarized light transmitted from an XY plane at the position where Z is 0 presents different phases at different positions of a transmission area where Z is greater than 0, 4 gold nanorods adjacent in the two directions of the X axis and the Y axis generate a vortex light beam, the diameter of the vortex light beam is 180nm, namely, the diameter of the vortex light beam is smaller than the wavelength of the incident circular polarized light, so under the action of the gold nanorod array, and a sub-wavelength vortex beam array with uniform optical energy distribution and spiral phase distribution is generated in the transmission area with Z & gt 0.
The specific method for preparing the specific metal nano super surface structure comprises the following steps:
s1) spin-coating photoresist on a quartz glass substrate
S11) cleaning the silica glass substrate
Placing a high-purity quartz glass substrate with the refractive index of 90 percent, the highest temperature resistance of 1500 ℃, the thickness of 3mm and the length and width of 800nm in an HCl solution with the concentration of 0.5mol/L and the temperature of 45 ℃, standing for 10 minutes, then placing the quartz glass substrate in pure water with the temperature of about 50 ℃ for soaking for 5 minutes, taking out the quartz glass substrate, and then carrying out secondary cleaning by using the pure water with the temperature of about 50 ℃ to finish the chemical cleaning of the quartz glass substrate;
s12) drying the quartz glass substrate
Placing the quartz glass substrate treated in the step S11) on a cleaning basket, introducing high-clean air or nitrogen at the temperature of about 80 ℃ into the cleaning basket for 10-20 minutes, and drying the quartz glass substrate after the quartz glass substrate and the cleaning basket are fully dried;
s13) spin-on resist
Adsorbing the quartz glass substrate processed in the step S12) on a vacuum chuck, adjusting the rotating speed of the vacuum chuck to be 500rpm, dripping 5% polymethyl Methacrylate (PMMA) photoresist into the center of the upper surface of the quartz glass substrate, and after 5 seconds, increasing the rotating speed of the vacuum chuck to 3000-7000 rpm, and spinning the photoresist for 30 seconds to form a photoresist coating with the thickness of 140 nm;
s14) soft baking of quartz glass substrate after glue homogenizing
After the photoresist is uniformly coated on the upper surface of the quartz glass substrate, placing the quartz glass substrate treated in the step S13) on a vacuum hot plate at 80 ℃ for soft baking for 2-5 minutes;
s2) exposing with electron beam to obtain pattern
S21) focused electron beam exposure
The size of the light spot is 30nm, the accelerating voltage is 30KV, and the exposure dose is 25 mu c/cm2Model No. Raith 150 an electron beam vector exposure machine vectors the quartz glass substrate processed in step S1)And exposing, namely controlling an electron beam vector exposure machine by utilizing a preset program to obtain a photoresist nanorod array graph with the rod length of 90nm, the rod width of 30nm and the thickness of 150nm on the upper surface of the quartz glass substrate, wherein 1 row and 1 column of photoresist nanorods in the photoresist nanorod array graph are respectively arranged at intervals at an included angle of 45 degrees and 45 degrees with the X axis, and the distance between the geometric centers of any two adjacent photoresist nanorods is 180 nm.
S22) baking the quartz glass substrate after exposure
Placing the quartz glass substrate treated in the step S21) in an oven at 170 ℃, baking for 90 minutes, and standing and cooling for 30 minutes in a normal temperature environment;
s3) development
S31) developing and fixing
Immersing the quartz glass substrate processed in the step S2) in a developing solution in which tetramethylcyclopentanone (MIBK) and Isopropanol (IPA) with the temperature of 21 +/-0.2 ℃ are mixed in a ratio of 1:3 for 100 seconds, and then putting the developing solution in an isopropanol solution for 40 seconds to complete fixation, so as to obtain a nanorod array pattern on the upper surface of the quartz glass substrate;
s32) post-fixing baking substrate
Taking out the quartz glass substrate treated in the step S31), and placing the quartz glass substrate on a vacuum hot plate at 80 ℃ for soft drying for 2-5 minutes to obtain a dried nanorod array pattern on the upper surface of the quartz glass substrate;
s33) pattern inspection, evaporating the metal film
Inspecting the dried nanorod array pattern on the upper surface of the quartz glass substrate treated in the step S32) by using a Scanning Electron Microscope (SEM) observation technology, and evaporating 1 layer of 25 nm-thick metal gold (Au) on the quartz glass substrate by using a thermal evaporation table after determining that the dried nanorod array pattern is qualified;
s34) removing the photoresist to obtain a metal pattern
And (2) stripping the quartz glass substrate treated in the step S33) with acetone to remove residual electron beam photoresist and metal gold, and obtaining a gold nanorod array on the upper surface of the quartz glass substrate, wherein the sizes of the gold nanorods in the gold nanorod array are all 90nm long, 30nm wide and 25nm thick, every 1 row and every 1 column of the gold nanorods in the gold nanorod array are respectively arranged at intervals with an included angle of 45 degrees to 45 degrees with the X axis, and the distance between the geometric centers of any two adjacent gold nanorods is 180nm, so that the specific metal nano super-surface structure is obtained. Fig. 4 is a Scanning Electron Microscope (SEM) photograph thereof, and 100nm in fig. 4 is used only as a scale.
Fig. 2 to 3 show the effect of generating the sub-wavelength periodic vortex beam of the specific metal nano super-surface structure composed of the metal nanorod array by using a finite difference time domain method:
firstly, 25 gold nanorod arrays which are respectively arranged at intervals of 45 degrees and 45 degrees in the transverse direction and the longitudinal direction and form an included angle of 45 degrees and 45 degrees with an X axis respectively and are arranged at intervals of 360nm period are arranged, as shown in figure 1, wherein the length of each of the 25 gold nanorods is 90nm, the width of each of the gold nanorods is 30nm, and the thickness of each of the gold nanorods is 25nm, as shown in figure 1; then setting the simulation area to be 400nm multiplied by 2000nm, and setting the left-handed circularly polarized light with the wavelength of 532nm to vertically irradiate the gold nanorod array of the specific metal nano super-surface structure from the bottom of the specific metal nano super-surface structure; then, respectively arranging a field monitor at the positions of 20nm, 50nm, 100nm, 500nm, 1000nm and 2000nm away from the upper surface of the gold nanorod array along the Z axis in a transmission area (an area with the Z more than 0) so as to respectively monitor the electric field, the magnetic field and the like at the position of each monitor; and finally, obtaining the electric field intensity distribution, the field vector phase distribution and the like of each position of the transmission area through simulation calculation. FIG. 3(a) shows the distribution of the electric field intensity in the transmission region of the specific metal nano-super-surface structure at a distance of 100nm from the nanorod array along the Z-axis, with the light energy being concentrated and periodically distributed; FIG. 3(b) shows the phase distribution of the transmission region of the specific metal nano-sized super-surface structure at a distance of 100nm from the nanorod array along the Z-axis, and it can be seen that the phase distribution is-pi spiral with the phase centered at the center of each spiral (i.e., the strongest point of light intensity) of FIG. 3 (a). The simulation result shows that after a beam of circularly polarized light vertically irradiates the specific metal nano super-surface structure prepared by the invention, the circularly polarized light transmitted from the XY plane with Z being 0 is converted into a sub-wavelength vortex light beam array; FIG. 2 is a result of extracting data of a single vortex beam of FIG. 3(b) alone and redrawing the data to obtain a more pronounced spiral effect.
The invention prepares the periodic metal nanorod super-surface capable of generating the sub-wavelength vortex beam array by reasonably designing the size and the arrangement of the metal nanorods and utilizing a mature micro-nano processing method of electron beam etching. Compared with other vortex light beam generation modes, the method has the advantages of simple structure, easiness in integration, uniform light intensity distribution and the like. The vortex light beam array generated by the method can enhance the information safety and capacity in information transmission and storage, capture a large number of particles in particle capture at one time, detect the motion characteristics of different objects simultaneously and expand the application field of vortex light beams.
While the foregoing describes illustrative embodiments of the invention to facilitate understanding thereof by those skilled in the art, it will be clear that the invention is not limited in scope to a specific real-time approach. Such variations are obvious and all the inventions utilizing the concepts of the present invention are intended to be protected.
Claims (9)
1. A method for generating a sub-wavelength vortex beam array based on a metal nano super surface is characterized by comprising the steps of firstly preparing a specific metal nano super surface structure which is formed by a metal nanorod array and a quartz glass substrate and is integrally in a cuboid shape, wherein the metal nanorod array comprises n metal nanorods, n is a positive integer and is greater than 4, the metal nanorods are periodically distributed on the upper surface of the quartz glass substrate, the specific metal nano super surface structure is emitted from an original point which is any point in a plane where the upper surface of the metal nanorod array is located, the length and width directions of the specific metal nano super surface structure are respectively an X axis and a Y axis, and the reverse direction of the thickness of the specific metal nano super surface structure is a Z axis; then, circularly polarized light with the wavelength of 532nm is vertically irradiated to the specific metal nano super-surface structure from a region with the Z being less than 0, after the circularly polarized light acts with any one metal nanorod, a phase factor 2 theta is added to the light wave phase, wherein theta is the included angle between the long axis of any one metal nanorod and the X axis, because the included angle theta between the long axis of each metal nanorod and the X axis is different, the circularly polarized light transmitted from the XY plane at the position with the Z being 0 presents different phases at different positions of a transmission region with the Z being more than 0, 4 metal nanorods adjacent in the two directions of the X axis and the Y axis generate a vortex light beam, the diameter of the vortex light beam is 180nm, and due to the action of the metal nanorod array, a vortex light beam array with the sub-wavelength scale with uniform light energy distribution and spiral phase distribution is generated in the transmission region with the Z being more than;
wherein, the preparation method of the specific metal nano super surface structure comprises the following steps:
s1) spin-coating photoresist on a quartz glass substrate
S11) cleaning the silica glass substrate
Placing an original quartz glass substrate in a cuboid shape in HCl solution with the concentration of 0.5mol/L and the temperature of 35-50 ℃, standing for 10 minutes, placing the quartz glass substrate in pure water with the temperature of about 50 ℃ for soaking for 5 minutes, taking out the quartz glass substrate, and then carrying out secondary cleaning by using the pure water with the temperature of about 50 ℃ to complete the chemical cleaning of the quartz glass substrate;
s12) drying the quartz glass substrate
Placing the quartz glass substrate treated in the step S11) on a cleaning basket, introducing high-clean air or nitrogen at the temperature of about 80 ℃ into the cleaning basket for 10-20 minutes, and drying the quartz glass substrate after the quartz glass substrate and the cleaning basket are fully dried;
s13) spin-on resist
Adsorbing the quartz glass substrate treated in the step S12) on a vacuum chuck, adjusting the rotating speed of the vacuum chuck to 500rpm, dripping photoresist into the center of the upper surface of the quartz glass substrate, and after 5 seconds, increasing the rotating speed of the vacuum chuck to 3000-7000 rpm, and spinning the photoresist for 30 seconds to form a photoresist coating with the thickness of 140 nm;
s14) soft baking of quartz glass substrate after glue homogenizing
After the photoresist is uniformly coated on the upper surface of the quartz glass substrate, placing the quartz glass substrate treated in the step S13) on a vacuum hot plate at 80 ℃ for soft baking for 2-5 minutes;
s2) exposing with electron beam to obtain pattern
S21) focused electron beam exposure
Accelerating voltage of 30KV, light spot size of 30nm, and exposure dose of 25 μ c/cm2Exposing the quartz glass substrate processed in the step S1), and controlling the electron beam vector exposure machine by using a preset program to obtain a photoresist nanorod array pattern with the length of each nanorod being 90nm, the width of each nanorod being 30nm and the thickness of each nanorod being 140-150 nm on the upper surface of the quartz glass substrate, wherein the photoresist nanorods of each row and each column in the photoresist nanorod array pattern are respectively arranged at intervals at an included angle of 45 degrees to 45 degrees with the X axis, and the distance between the geometric centers of any two adjacent photoresist nanorods is 180 nm;
s22) baking the quartz glass substrate after exposure
Placing the quartz glass substrate treated in the step S21) in an oven at 150-170 ℃, baking for 90 minutes, and standing and cooling for 30 minutes in a normal temperature environment;
s3) development
S31) developing and fixing
Immersing the quartz glass substrate processed in the step S2) in a developing solution at the temperature of 21 +/-0.2 ℃ for 60-120 seconds, and then putting the quartz glass substrate in an isopropanol solution for 30-40 seconds to complete fixation, so as to obtain a nanorod array pattern on the upper surface of the quartz glass substrate;
s32) post-fixing baking substrate
Taking out the quartz glass substrate treated in the step S31), and placing the quartz glass substrate on a vacuum hot plate at 80 ℃ for soft drying for 2-5 minutes to obtain a dried nanorod array pattern on the upper surface of the quartz glass substrate;
s33) pattern inspection, evaporating the metal film
Inspecting the dried nanorod array pattern on the upper surface of the quartz glass substrate treated in the step S32) by using a scanning electron microscopy observation technology, and evaporating metal gold (Au) on the quartz glass substrate by using a thermal evaporation table after determining that the dried nanorod array pattern is qualified, wherein the thickness of the gold (Au) is 20-30 nm;
s34) removing the photoresist to obtain a metal pattern
And (2) stripping the quartz glass substrate treated in the step S33) with acetone to remove residual electron beam photoresist and metal gold, and obtaining a gold nanorod array on the upper surface of the quartz glass substrate, wherein the sizes of the gold nanorods in the gold nanorod array are all 90nm long, 30nm wide and 25nm thick, every 1 row and every 1 column of the gold nanorods in the gold nanorod array are respectively arranged at intervals with an included angle of 45 degrees to 45 degrees with the X axis, and the distance between the geometric centers of any two adjacent gold nanorods is 180nm, so that the specific metal nano super-surface structure is obtained.
2. The method for generating a sub-wavelength vortex beam array based on metal nano-super surface according to claim 1, wherein the original quartz glass substrate in the step S11) is high-purity quartz glass with a thickness of 3mm, a length and a width of 800nm, a light transmittance of more than 90% and a maximum temperature resistance of 1500 ℃.
3. The method for generating the sub-wavelength vortex beam array based on the metal nano-super surface according to claim 2, wherein the photoresist in the step S13) is polymethyl methacrylate (PMMA) with a concentration of 5%.
4. The method as claimed in claim 3, wherein the developing solution of step S31) is a mixture of tetramethylcyclopentanone (MIBK) and isopropyl alcohol (IPA) at a ratio of 1: 3.
5. The method for generating the sub-wavelength vortex beam array based on the metal nano-super surface according to claim 3, wherein the temperature of the HCl solution in the step S11) is 45 ℃.
6. The method for generating the sub-wavelength vortex beam array based on the metal nano-super surface according to claim 4, wherein the oven temperature in the step S22) is 170 ℃.
7. The method for generating the sub-wavelength vortex beam array based on the metal nano-super surface according to claim 5, wherein the quartz glass substrate is immersed in the developing solution for 100 seconds and placed in the isopropanol solution for 40 seconds in the step S31).
8. The method for generating the sub-wavelength vortex beam array based on the metal nano-super surface according to claim 5, wherein the thickness of the gold (Au) in the step S33) is 25 nm.
9. The method for generating the sub-wavelength vortex beam array based on the metal nano-super surface according to any one of claims 1 to 8, wherein the circularly polarized light is left-handed circularly polarized light.
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