Cascade enhanced optical input window for photoelectric cathode

Abstract

The invention provides a cascade enhanced optical input window for a photoelectric cathode, which belongs to the field of optoelectronic devices and comprises a substrate layer and a cascade structure. The cascade structure is located between the substrate layer and the photoelectric emission layer; the cascade structure is used for modulating incident light; the cascade structure sequentially comprises a nano pattern layer, a waveguide layer and a plasmon layer along the incident light direction; incident light enters from one side of the substrate layer, deflects after being modulated by the nano pattern layer, and forms a waveguide in the waveguide layer, so that the plasmon layer generates a local plasmon resonance effect to promote the photoelectric emission layer to absorb light. The quantum efficiency of the photoelectric cathode is improved, and the photoelectric response capability of a photoelectric device is further improved.

Description

Technical Field

[0001] The invention relates to the field of optoelectronic devices, in particular to a cascade enhanced optical input window for a photocathode. Background Art

[0002] Photocathodes are widely used in various vacuum photoelectric detection and imaging devices such as photomultiplier tubes and image intensifiers, playing an important role in the field of low-light detection and imaging technology. In addition, photocathodes, as vacuum electron sources capable of producing high-quality electron beams, are used in scientific devices such as accelerator light injectors and electron microscopes.

[0003] The quantum yield (QE) of the photocathode is an important indicator to measure the photoelectric response performance of the photoelectric device. It refers to the ratio of photons converted into electrons escaping through the photocathode. The traditional photocathode is usually composed of a transparent glass substrate and a photoelectric emission material, and has problems such as low quantum efficiency and narrow response spectrum. Summary of the invention

[0004] The purpose of the present invention is to provide a cascade enhanced optical input window for a photocathode, which can improve the quantum efficiency of the photocathode and thus improve the photoelectric response capability of the photoelectric device.

[0005] To achieve the above object, the present invention provides a cascade enhanced optical input window for a photocathode, comprising: a substrate layer and a cascade structure; the cascade structure is located between the substrate layer and the photoelectric emission layer; the cascade structure is used to modulate incident light;

[0006] The cascade structure is composed of a nano-pattern layer, a waveguide layer and a plasmon layer in sequence along the direction of incident light; the incident light enters from one side of the substrate layer, is modulated by the nano-pattern layer and is deflected, and a waveguide is formed in the waveguide layer, so that the plasmon layer produces a localized plasmon resonance effect, thereby prompting the photoelectric emission layer to absorb light.

[0007] Optionally, the material of the substrate layer is an optically transparent material.

[0008] Optionally, the nano pattern layer is composed of two or more materials with different refractive indices alternating according to a certain rule.

[0009] Optionally, the material of the nano pattern layer is oxide, fluoride or nitride material.

[0010] Optionally, the waveguide layer is one or more layers of oxide film, fluoride film or nitride film.

[0011] Optionally, the plasmon layer is one or more layers of negative dielectric constant material particles distributed between the waveguide layer and the photoelectric emission layer; the negative dielectric constant material particles are used to generate a localized plasmon resonance effect in a target band.

[0012] Optionally, the plasmon layer is embedded in the waveguide layer, and an upper edge of the plasmon layer is flush with an upper edge of the waveguide layer.

[0013] Optionally, the plasmon layer is embedded in the photoelectric emission layer.

[0014] Optionally, the material of the plasmon layer is metal or a metal composite material.

[0015] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: at the target wavelength, the present invention manufactures a double-layer waveguide through a cascade structure consisting of a nanopattern layer, a waveguide layer and a plasmon layer, thereby enhancing the light absorption performance of the photocathode. Compared with the single-layer structure, the present invention can more significantly improve the quantum efficiency and response wavelength range of the photoelectric emission layer, and still maintain a high enhancement effect at a position far away from the plasmon resonance band. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 A schematic diagram of the structure of a cascade enhanced optical input window for a photocathode provided by the present invention;

[0018] Figure 2 Schematic diagram of the structure of the waveguide layer, the plasmon layer and the photoelectric emission layer in Example 1;

[0019] Figure 3 Schematic diagram of the structure of the cascade enhanced optical input window for the photocathode in Example 1;

[0020] Figure 4 Schematic diagram of the structure of the waveguide layer, the plasmon layer and the photoelectric emission layer in Example 2;

[0021] Figure 5 Schematic diagram of the structure of the cascade enhanced optical input window for the photocathode in Example 2;

[0022] Figure 6 The schematic diagram of the photocathode control group without adding a cascade structure Figure 1 ;

[0023] Figure 7 The schematic diagram of the photocathode control group without adding a cascade structure Figure 2 ;

[0024] Figure 8 is a comparison diagram of the photocathode absorption rate of Example 1 and that of the photocathode without adding the cascade structure;

[0025] Fig. 9 It is a comparison chart of the photocathode absorption rate of Example 2 and that of the photocathode without adding the cascade structure.

[0026] Explanation of symbols: 1-substrate layer, 2-nano pattern layer, 3-waveguide layer, 4-plasmon layer, 5-photoelectric emission layer. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The optical structure arranged on the substrate side of the light incident end can increase the absorption rate of the photocathode by regulating the incident light field of the photocathode, so as to improve the photoelectric response ability of the photoelectric device. For example, China North Night Vision Technology Co., Ltd. discloses a method for preparing a photocathode coated with a multi-layer dielectric anti-reflection film (patent publication number CN111261489A), and a micro-nano grating structure prepared on anti-halation glass (patent publication number CN113241293A); the Xi'an Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences discloses a structural design based on plasmon gold nanoparticles (patent publication number CN115763191A), both of which can increase the absorption rate of the photocathode through micro-nano structure design, thereby improving the photoelectric response ability of the photoelectric device.

[0029] The purpose of the present invention is to provide a cascade-enhanced optical input window for a photocathode, the gain of its photoelectric response performance is jointly generated by a nano-pattern composed of a dielectric material and a localized surface plasmon cascade structure composed of a metal material, and the cascade effect between the structures is used to further enhance the photoelectric response capability of the photocathode. This structural combination can achieve an effect of 1+1>2 and has huge development potential.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1As shown, the cascade enhanced optical input window for the photocathode provided by the present invention comprises: a substrate layer 1 and a cascade structure. The cascade structure is located between the substrate layer 1 and the photoelectric emission layer 5. The cascade structure is used to modulate the incident light. The cascade structure acts as a group of optical resonators at the target wavelength.

[0032] The cascade structure is sequentially composed of a nano-pattern layer 2, a waveguide layer 3 and a plasmon layer 4 along the direction of the incident light. That is, the nano-pattern layer 2, the waveguide layer 3 and the plasmon layer 4 are sequentially arranged on the substrate layer 1 and placed on the back of the photoelectric emission layer 5. The nano-pattern layer 2, the waveguide layer 3 and the plasmon layer 4 in the cascade structure act together to modulate the incident light, thereby achieving absorption enhancement of the photocathode photoelectric emission layer 5.

[0033] The incident light of the target wavelength enters from one side of the substrate layer 1, is modulated by the nano-pattern layer 2, and is deflected, forming a waveguide in the waveguide layer 3, which is manifested as an enhancement of the light field near the interface between the waveguide layer 3 and the photoelectric emission layer 5, causing the plasmon layer 4 to produce a localized plasmon resonance effect, thereby prompting the photoelectric emission layer 5 to absorb light, thereby increasing the quantum efficiency of the photocathode. The nano-pattern layer 2 and the plasmon layer 4 work together to modulate the incident light, achieving enhanced absorption of the photocathode photoelectric emission layer 5.

[0034] Specifically, the material of the substrate layer 1 is a transparent material. A transparent material refers to a material with a transmittance close to 100% within the target wavelength range and minimal absorption and scattering losses. The material of the substrate layer 1 can generally be selected from oxides, fluorides or nitrides, including but not limited to silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, magnesium fluoride, quartz, etc.

[0035] The nano pattern layer 2 is composed of two or more materials with different refractive indexes alternately according to a certain rule. The refractive index of the material of the nano pattern layer 2 is the same as or different from the refractive index of the material of the substrate layer 1. The nano pattern layer 2 can be made of silicon oxide, hafnium oxide, zirconium oxide, titanium oxide, aluminum oxide, aluminum nitride or one or more other oxides, fluorides or nitrides.

[0036] In the present invention, the nano pattern layer 2 is located on the upper surface of the substrate layer 1, and is a nano topological structure distributed according to a certain rule. Among them, the distribution according to a certain rule refers to protrusions or depressions arranged at a certain interval; or refers to a pattern with a certain periodic distribution, including but not limited to circles, triangles, polygons, cones, spheres, hemispheres, rings, etc., and the period includes but is not limited to orthogonal periods, triangular periods and other regular periodic arrangements; the production of the pattern can be achieved by ion beam etching, laser etching, chemical etching and other technical methods.

[0037] The size and spacing of the nanopattern are adjusted according to the size of the target wavelength, and the nanopattern should be between one tenth and ten times the target wavelength. In principle, the size of the nanopattern does not exceed the spacing of the nanopattern. The substrate layer 1 and the nanopattern layer 2 are composed of at least two or more materials with different refractive indices.

[0038] The waveguide layer 3 is one or more layers of oxide film, fluoride film or nitride film. The material of the waveguide layer 3 includes but is not limited to hafnium oxide, zirconium oxide, titanium dioxide, tantalum pentoxide, lanthanum fluoride, gadolinium fluoride, etc. One or more layers of oxide film, fluoride film or nitride film are directly arranged between the nano-pattern layer 2 and the plasmon layer 4. Thin film deposition can be achieved by atomic layer deposition, sputtering, evaporation, vapor deposition and other methods. The refractive index and thickness of the material of the waveguide layer 3 match the structure of the substrate layer 1 and the nano-pattern layer 2. Specifically, the refractive index of the material of the waveguide layer 3 is the same as or different from that of the material in the nano-pattern layer 2. The waveguide layer and the nano-pattern layer work together to localize the incident light in the waveguide layer and near the surface of the surface plasmon.

[0039] The plasmon layer 4 is one or more layers of negative dielectric constant material particles distributed between the waveguide layer 3 and the photoelectric emission layer 5. The negative dielectric constant material particles are metal particles or other metal composite material particles. The negative dielectric constant material particles are used to be excited by the light intensity near the interface between the waveguide layer 3 and the photoelectric emission layer 5 to generate a localized plasmon resonance effect in the target band. The material of the plasmon layer 4 is metal or metal composite.

[0040] Specifically, the material of the plasmon layer 4 includes but is not limited to gold, silver, copper, aluminum, etc. The shape of the negative dielectric constant material particles includes but is not limited to sphere, hemisphere, ellipsoid, column, rod, ring, etc. The material, shape, size and density of the negative dielectric constant material particles are determined according to the application requirements of the target band and match the structure of the substrate layer 1, the nano-pattern layer 2 and the waveguide layer 3. The preparation of the negative dielectric constant material particles can be achieved by evaporation, sputtering, chemical method and other methods.

[0041] As a specific implementation manner, plasmon layer 4 is embedded in the waveguide layer 3 , and the upper edge of plasmon layer 4 is flush with the upper edge of waveguide layer 3 .

[0042] As another specific implementation, the plasmon layer 4 is embedded in the photoelectric emission layer 5 .

[0043] The present invention manufactures a double-layer waveguide at the target wavelength through a cascade structure composed of a nano-pattern layer 2, a waveguide layer 3 and a plasmon layer 4, enhances the light absorption performance of the photocathode, and the enhanced light field is distributed between the two layers of waveguides, so that the cascade structure obtains a more obvious purcell enhancement in a larger range. Compared with a single-layer structure, the cascade effect of the dielectric-metal double-layer structure provided by the present invention can more significantly improve the quantum efficiency of the photoelectric emission layer 5, and still maintain a high enhancement effect at a position far away from the plasmon resonance band. At the same time, the cascade structure can convert more energy into the surface plasmon resonance mode, reduce the electric dipole radiation to the surface wave mode that cannot be used for loss, and thus more effectively utilize the enhancement effect of the surface plasmon resonance.

[0044] In order to better understand the solution of the present invention, it is further described below in conjunction with specific embodiments.

[0045] Example 1

[0046] like Figure 2 and Figure 3 The structure of the cascade enhanced optical input window for the photocathode provided in this embodiment is shown. This embodiment has obvious absorption enhancement at a wavelength of 400nm to 600nm. SiO2 is selected as the substrate material. SiO2 and ZrO2 are arranged alternately as the nano-pattern layer 2. The nano-pattern is arranged in a square array and prepared by etching technology. The radius of the nano-pattern is 155nm, the duty cycle is 0.35, and the thickness is 220nm. TiO2 is deposited on the nano-pattern layer 2 as a waveguide layer 3 with a thickness of 150nm.

[0047] In order to highlight the gain of the photocathode device based on the cascade structure of the present invention, this embodiment also designed an experimental control group, such as Figure 6 and Figure 7 As shown, the photoelectric conversion device based on a common substrate is used as a control group 1, and its structure is as follows Figure 6 As shown, the photoelectric emission layer 5 of the device is directly placed on the planar substrate, without the cascade structure of the waveguide layer 3, the nanopattern layer 2 and the plasmon layer 4. The photoelectric conversion device based on only a single-layer waveguide is used as the control group 2, and its structure is as follows Figure 7 As shown in Figure 2. The planar substrate material of both is quartz.

[0048] Figure 8 The absorption spectra of the light input device of this embodiment and the control group combined with the photocathode of the same thickness, the photoelectric emission layer 5 material of the selected photocathode is S25 multi-alkali cathode, the thickness is 40nm ~ 120nm. Preferably, the diameter of the silver hemisphere of the plasmon layer 4 is 80nm, the height is 40nm, and the spherical center distance is 300nm. The thickness of the photoelectric emission layer 5 is preferably 80nm.

[0049] observe Figure 8 It can be seen that the photocathode provided in this embodiment has obvious absorption enhancement at 400nm to 600nm. In particular, the cascade structure provides a significant further improvement in absorption capacity near 550nm. The positive hemispherical structure increases the contact area between the plasmon particles and the photoelectric absorption layer, which can effectively improve the absorption efficiency of photons and enhance the photoelectric response performance of the photocathode.

[0050] Example 2

[0051] like Figure 4 and Figure 5 The structure of the cascade enhanced photocathode provided in this embodiment is shown. This embodiment has obvious absorption enhancement at a wavelength of 400nm to 750nm. SiO2 is selected as the substrate material. SiO2 and ZrO2 are arranged alternately as the nano-pattern layer 2. The nano-pattern is arranged in a hexagonal array and prepared by etching technology. The radius of the nano-pattern is 155nm, the duty cycle is 0.35, and the thickness is 240nm. TiO2 is deposited on the nano-pattern layer 2 as a waveguide layer 3 with a thickness of 150nm.

[0052] Metal hemispherical particles arranged at equal intervals are used as the plasmon layer 4. The metal particles are evenly distributed on the waveguide layer 3, and their upper edges are flush with the upper edge of the waveguide layer 3. The metal material is aluminum. First, a metal sphere is prepared by a solution method, and then the waveguide layer 3 is deposited. Then, the surface is polished by chemical mechanical polishing technology to obtain a metal hemisphere embedded in the waveguide layer 3. The diameter of the hemispherical particles is 60nm to 150nm, the distance between the sphere centers is 100nm to 600nm, and the height is 30nm to 100nm.

[0053] In order to highlight the gain of the photocathode device based on the cascade structure of the present invention, this embodiment also designed an experimental control group, such as Figure 6 and Figure 7 As shown, the photoelectric conversion device based on a common substrate is used as a control group 1, and its structure is as follows Figure 6 As shown, the photoelectric emission layer 5 of the device is directly placed on the planar substrate, without the waveguide layer 3 and the cascade structure of the nano-pattern layer 2 and the plasmon layer 4. The photoelectric conversion device based on only a single-layer waveguide is used as the control group 2, and its structure is as follows Figure 7 As shown in Figure 2, the planar substrate material of both is SiO2.

[0054] Fig. 9The absorption spectra of the light input device of this embodiment and the control group combined with the photocathode of the same thickness, the photoelectric emission layer 5 material of the selected photocathode is S25 multi-alkali cathode, the thickness is 40nm ~ 120nm. Preferably, the metal hemisphere of the plasmon layer 4 has a diameter of 60nm, a height of 40nm, and a spherical center distance of 480nm. The thickness of the photoelectric emission layer 5 is preferably 80nm.

[0055] observe Fig. 9 It can be seen that the photocathode provided in this embodiment has obvious absorption enhancement at 400nm to 750nm, and in particular, the cascade structure provides a significant further enhancement of the photocathode absorption at 650nm to 750nm. Compared with the positive hemispherical structure, the waveguide layer 3 is embedded with the plasmon layer 4 of the hemispherical structure, which reduces the contact area with the photoelectric absorption layer. However, through the mechanical polishing technology, the surface of the plasmon layer 4 can be made flat and low in roughness, which is conducive to improving the resolution of the photocathode and meeting the application of low-light imaging and the like.

[0056] In summary, the present invention controls the light field near the incident surface of the photocathode by designing a reasonable dielectric-metal joint structure, significantly increasing the light absorption performance of the photocathode in a multi-band and wide spectral range, thereby greatly improving the photoelectric response performance of the photocathode and broadening the application scenarios of the photocathode.

[0057] By manufacturing multi-layer waveguides through the cascade effect, the probability of photons being absorbed by the photocathode is increased. Compared with a single-layer structure, a more significant improvement in photoelectric performance can be achieved over a larger range. By adjusting and optimizing the material and geometric parameters of the structure, the photocathode absorption rate can be further enhanced in one or more target bands.

[0058] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0059] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A cascade-enhanced optical input window for a photocathode, characterized in that: The cascade enhanced optical input window for the photocathode comprises: a substrate layer, a cascade structure and a photoelectric emission layer; the cascade structure is located between the substrate layer and the photoelectric emission layer; the cascade structure is used to modulate the incident light; The cascade structure is composed of a nano-pattern layer, a waveguide layer and a plasmon layer in sequence along the direction of incident light; the incident light enters from one side of the substrate layer, is modulated by the nano-pattern layer and is deflected, and a waveguide is formed in the waveguide layer, so that the plasmon layer produces a localized plasmon resonance effect, thereby prompting the photoelectric emission layer to absorb light.

2. The cascade-enhanced optical input window for a photocathode according to claim 1, characterized in that: The material of the substrate layer is an optically transparent material.

3. The cascade-enhanced optical input window for a photocathode according to claim 1, characterized in that: The nano pattern layer is composed of two or more materials with different refractive indices alternately formed according to a certain rule.

4. The cascade-enhanced optical input window for a photocathode according to claim 1 or 3, characterized in that: The material of the nano pattern layer is oxide, fluoride or nitride material.

5. The cascade-enhanced optical input window for a photocathode according to claim 1, characterized in that: The waveguide layer is one or more layers of oxide film, fluoride film or nitride film.

6. The cascade-enhanced optical input window for a photocathode according to claim 1, characterized in that: The plasmon layer is one or more layers of negative dielectric constant material particles distributed between the waveguide layer and the photoelectric emission layer; the negative dielectric constant material particles are used to generate a localized plasmon resonance effect in a target band.

7. The cascade-enhanced optical input window for a photocathode according to claim 1 or 6, characterized in that: The plasmon layer is embedded in the waveguide layer, and an upper edge of the plasmon layer is flush with an upper edge of the waveguide layer.

8. The cascade-enhanced optical input window for a photocathode according to claim 1 or 6, characterized in that: The plasmon layer is embedded in the photoemissive layer.

9. The cascade-enhanced optical input window for a photocathode according to claim 1, characterized in that: The material of the plasmon layer is metal or a metal composite material.

Images