Circular dichroism superlens structure based on nested double helix surface and its preparation method

Abstract

The present invention discloses a circular dichroism superlens structure based on a nested double helical surface and a preparation method thereof, comprising a substrate, a PMMA support layer fixedly arranged on the upper end of the substrate, a gold-plated layer arranged on the end face of the PMMA support layer, the gold-plated layer having the same thickness, the PMMA support layer consisting of an inner helical surface and an outer helical surface, cleaning the substrate, bonding it to a sample holder with glue after cleaning, designing a superlens using 3D modeling software, importing a direct writing system for direct writing processing, taking out the sample for development, and then drying it, and using electron beam evaporation technology to obtain a finished product. Beneficial effects of the present invention: Under the same left-handed light incident condition, the focal intensity of the circular dichroism superlens based on the inner and outer nested double helical surface structure is 10 times that of the focal intensity of the circular dichroism superlens based on the ordinary single helical surface structure, and the present invention can produce a larger circular polarization conversion by constructive interference when light is incident, effectively increasing the proportion of effective focusing energy and improving focusing efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of optical materials, and in particular to a circular dichroism superlens structure based on a nested double helix surface shape and a preparation method thereof. Background Art

[0002] When electromagnetic waves interact with matter, they mainly rely on the phase and polarization properties of the electromagnetic waves. As one of the basic properties of electromagnetic waves, polarization plays an important role in electromagnetic wave signal transmission and molecular detection. Polarization imaging technology combines traditional optical intensity imaging and polarization technology by utilizing the polarization characteristics of target radiation, reflection, scattering or transmitted light. On the basis of obtaining the target's spatial position information and intensity information, it detects the target's polarization information, greatly increasing the amount of information and effectively identifying and detecting the target in a complex environment. Therefore, polarization imaging technology has a wide range of applications in many fields such as military target identification, biomedical imaging and sensing, drug molecule detection, industrial and agricultural production monitoring, and geological survey. It has huge development potential and is an important direction for research and application at home and abroad.

[0003] The traditional multi-path polarization imaging system uses different polarization analyzers in multiple channels to obtain the intensity diagrams of linear polarization components and circular polarization components. The large number of optical subsystems leads to a large volume of the overall system, and the differences in device parameters between subsystems can cause polarization measurement errors, which in turn leads to low sensitivity of the system.

[0004] The circular dichroism lens based on metasurface materials is a new type of device that integrates circular dichroism and lens functions. It can selectively focus and image incident light with different circular polarization states. Metasurface materials are micro-nano structures composed of sub-wavelength unit structures arranged according to artificial design. They can obtain physical phenomena and functions that traditional materials cannot achieve or require a combination of multiple components to achieve. Compared with traditional materials and devices, metamaterials are flexible in design, have strong ability to regulate electromagnetic fields, are small in size, light in weight, and are easy to integrate.

[0005] At present, the focusing efficiency of circular dichroism lenses is very low. This is because the PB phase (Pancharatnam-Berry Phase) principle is adopted. The focusing energy mainly comes from the component opposite to the circular polarization of the incident light (i.e., the cross-polarization component). However, the polarization conversion efficiency of the usual structure is relatively low, which makes it difficult to extract effective light signals from background noise in actual work, limiting the application scope of circular dichroism lenses. Summary of the invention

[0006] The object of the present invention is to provide a circular dichroism metalens structure based on a nested double helix surface and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0007] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a circular dichroism superlens structure based on a nested double helical surface, comprising a substrate, a PMMA support layer is fixedly arranged on the upper end of the substrate, a gold-plated layer is arranged on the end face of the PMMA support layer, the gold-plated layer has the same thickness, and the PMMA support layer is composed of an inner helical surface and an outer helical surface.

[0008] Preferably, the thickness of the gold-plated layer is 100-200 nm.

[0009] Preferably, the inner helical surface has the same height as the outer helical surface, which is 1400 nm.

[0010] Preferably, the radius of the outer helical surface is 1000 nm, which is twice the radius of the inner helical surface.

[0011] Preferably, the azimuth angles of the inner helical surface and the outer helical surface always differ by 75°, the inner helical surface and the outer helical surface are integral, and are arranged in rotation at different azimuth angles according to the required phase.

[0012] Preferably, the inner helical surface and the outer helical surface are closely packed arrays.

[0013] Preferably, the substrate is a silicon dioxide substrate.

[0014] The preparation method of circular dichroism metalens based on nested double helix surface shape comprises the following steps:

[0015] Step 1: Place the silicon dioxide substrate in acetone solution and alcohol solution for 10 minutes in sequence to remove dirt, then wash with flowing deionized water, and finally blow dry with high-pressure nitrogen;

[0016] Step 2: Glue the cleaned silica substrate onto a dedicated sample holder with glue, apply negative photoresist on the front side of the substrate, and drop a drop of refractive index matching oil on the back side of the substrate;

[0017] Step 3: Use 3D modeling software to design a 3D spiral surface structure metalens, and then import it into a 3D laser direct writing system for direct writing processing, using a pulsed direct writing mode during the direct writing process;

[0018] Step 4: After exposure by the 3D laser direct writing system, take out the sample and soak it in an isopropanol solution for 20 minutes for development, then put it in another isopropanol solution for cleaning, and finally blow dry with high-pressure nitrogen;

[0019] Step 5: Using electron beam evaporation technology, select gold as the evaporation material, set the evaporation thickness to 100-200nm, the equipment power to 8kW, and the vacuum degree to 1×10-4Pa to obtain a superlens based on an internally and externally nested double helix surface structure.

[0020] Beneficial Effects

[0021] The circular dichroism metalens structure based on nested double helix surface shapes and the preparation method thereof provided by the present invention, under the same left-handed light incident condition, the focal intensity of the circular dichroism metalens based on the inner and outer nested double helix surface shape structure is 10 times the focal intensity of the circular dichroism metalens based on the ordinary single helix surface structure, and the inner and outer nested double helix surface shape structure can cause constructive interference when light is incident to produce a larger circular polarization conversion, effectively increasing the proportion of effective focusing energy, thereby improving focusing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the inner and outer nested double helix surface structure of the present invention;

[0023] Figure 2 It is a schematic front view of the double helix surface structure with inner and outer nesting according to the present invention;

[0024] Figure 3 It is a schematic diagram of the cross-polarization transmittance and phase of the single helical surface structure and the inner and outer nested double helical surface structure as a function of the total azimuth angle when left-handed light is incident in the present invention;

[0025] Figure 4 This is a scanning electron microscope image of a superlens based on a double helical surface structure in the present invention;

[0026] Figure 5 Schematic diagrams of focusing characteristics of a metalens based on a single helical surface structure and a metalens based on an inner-outer nested double helical surface structure when left-handed light is incident and right-handed light is incident, respectively, in the present invention.

[0027] Reference numerals

[0028] 1-gold-plated layer, 2-PMMA supporting layer, 3-substrate, 4-inner helical surface, 5-outer helical surface. DETAILED DESCRIPTION

[0029] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0030] Example

[0031] like Figure 1-5 As shown, the circular dichroism superlens structure based on the nested double helical surface includes a substrate 3, a PMMA support layer 2 is fixedly arranged on the upper end of the substrate 3, a gold-plated layer 1 is arranged on the end face of the PMMA support layer 2, the gold-plated layer 1 has the same thickness, and the PMMA support layer 2 is composed of an inner helical surface 4 and an outer helical surface 5.

[0032] Preferably, the thickness of the gold-plated layer 1 is 100-200 nm.

[0033] Preferably, the inner helical surface 4 and the outer helical surface 5 have the same height, which is 1400 nm.

[0034] Preferably, the radius of the outer helical surface 5 is 1000 nm, which is twice the radius of the inner helical surface 4 .

[0035] Preferably, the azimuth angles of the inner helical surface 4 and the outer helical surface 5 always differ by 75°, the inner helical surface 4 and the outer helical surface 5 are integral, and are arranged in rotation at different azimuth angles according to the required phase.

[0036] Preferably, the inner helical surface 4 and the outer helical surface 5 are closely packed arrays.

[0037] Preferably, the substrate 3 is a silicon dioxide substrate.

[0038] The preparation method of circular dichroism metalens based on nested double helix surface shape comprises the following steps:

[0039] Step 1: Place the silicon dioxide substrate in acetone solution and alcohol solution for 10 minutes in sequence to remove dirt, then wash with flowing deionized water, and finally blow dry with high-pressure nitrogen;

[0040] Step 2: Glue the cleaned silica substrate onto a dedicated sample holder with glue, apply negative photoresist on the front side of the substrate, and drop a drop of refractive index matching oil on the back side of the substrate;

[0041] Step 3: Use 3D modeling software to design a 3D spiral surface structure metalens, and then import it into a 3D laser direct writing system for direct writing processing, using a pulsed direct writing mode during the direct writing process;

[0042] Step 4: After exposure by the 3D laser direct writing system, take out the sample and soak it in an isopropanol solution for 20 minutes for development, then put it in another isopropanol solution for cleaning, and finally blow dry with high-pressure nitrogen;

[0043] Step 5: Using electron beam evaporation technology, select gold as the evaporation material, set the evaporation thickness to 100-200nm, the equipment power to 8kW, and the vacuum degree to 1×10-4Pa to obtain a superlens based on an internally and externally nested double helix surface structure.

[0044] When the incident light is incident on the surface of the double helix structure, due to the discontinuity of the inner and outer nested double helix surfaces, the incident light can be decomposed into two parts, the inner and outer parts, which act on the inner helix surface and the outer helix surface respectively. At the same time, the cross-polarization components of the two parts of the incident light will constructively interfere with each other, thereby improving the cross-polarization conversion efficiency. In this regard, a comparative experiment is introduced to compare the optical responses of the inner and outer nested double helix structure and the ordinary single helix structure (which can be considered as the double helix structure when the azimuth angles of the inner and outer helix surfaces always differ by 0°).

[0045] like Figure 3 As shown, Figure 3-1 is a curve of the cross-polarization transmittance of the double helix surface structure and the change with the total azimuth angle; Figure 3-2 is a curve of the phase of the double helix surface structure and the change with the total azimuth angle; Figure 3-3 is a curve of the cross-polarization transmittance of the single helix surface structure and the change with the total azimuth angle; Figure 3-4 is a curve of the phase of the single helix surface structure and the change with the total azimuth angle. Note that in the above two cases, the phase can reach a response of 0-2π, and the cross-polarization transmittance of the outer nested double helix surface structure is 10 times that of the ordinary single helix surface structure.

[0046] The focusing capabilities of the circular dichroism metalens based on the inner and outer nested double helix surface structure and the circular dichroism metalens based on the ordinary single helix surface structure are compared. Figure 5 As shown, Figure 5-1 is a cross-sectional view of the focus of the metalens based on the inner and outer nested double helix surface structure when left-handed light is incident along the X-axis; Figure 5-2 is a cross-sectional view of the focus of the metalens based on the inner and outer nested double helix surface structure when right-handed light is incident along the X-axis; Figure 5-3 is a cross-sectional view of the focus of the metalens based on the single helix surface structure when left-handed light is incident along the X-axis; Figure 5-4 is a cross-sectional view of the focus of the metalens based on the single helix surface structure when right-handed light is incident along the X-axis. It is noted that these two types of metalens have lens function only for left-handed circularly polarized incident light, and the transmittance for right-handed circularly polarized incident light is almost 0, and have typical optical characteristics of circular dichroism metalens.

[0047] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the invention content within the protection scope of the present invention.

Claims

1. A circular dichroism metalens structure based on a nested double helix surface, comprising a substrate (3), characterized in that: A PMMA support layer (2) is fixedly arranged on the upper end of the substrate (3); a gold-plated layer (1) is arranged on the end surface of the PMMA support layer (2); the gold-plated layer (1) has a uniform thickness; the PMMA support layer (2) is composed of an inner helical surface (4) and an outer helical surface (5); the inner helical surface (4) and the outer helical surface (5) have the same height; The inner helical surface (4) and the outer helical surface (5) are integral; When the incident light is incident on the surface of the nested double helical structure, the incident light is decomposed into two parts, the inner and outer parts, which act on the inner and outer helical surfaces respectively, and the cross-polarization components of the inner and outer parts of the incident light undergo constructive interference.

2. The circular dichroism superlens structure based on nested double helix surface according to claim 1, characterized in that: The thickness of the gold-plated layer (1) is 100-200 nm.

3. The circular dichroism superlens structure based on nested double helix surface according to claim 1, characterized in that: The height of the outer helical surface (5) is 1400 nm.

4. The circular dichroism superlens structure based on nested double helical surfaces according to claim 1, characterized in that: The radius of the outer helical surface (5) is 1000 nm, which is twice the radius of the inner helical surface (4).

5. The circular dichroism metalens structure based on nested double helix surface according to claim 1, characterized in that: The inner helical surface (4) and the outer helical surface (5) are in a closely packed morphology array.

6. The circular dichroism metalens structure based on nested double helical surfaces according to claim 1, characterized in that: The substrate (3) is a silicon dioxide substrate.

Images