Cascade-enhanced optical input window for photocathode

Abstract

The present application belongs to the field of optoelectronic devices. Provided is a cascade-enhanced optical input window for a photocathode. The cascade-enhanced optical input window for a photocathode comprises: a substrate layer (1), a cascaded structure, and a photoemissive layer (5), wherein the cascaded structure is located between the substrate layer (1) and the photoemissive layer (5); the cascaded structure is used for modulating incident light; the cascaded structure sequentially comprises a nano-pattern layer (2), a waveguide layer (3) and a plasmonic layer (4) in the direction of the incident light; and the incident light enters from one side of the substrate layer (1), and is deflected after being modulated by the nano-pattern layer (2), and then a waveguide is formed in the waveguide layer (3), such that the plasmonic layer (4) generates a localized plasmon resonance effect, thereby promoting light absorption of the photoemissive layer (5).

Description

A cascade-enhanced optical input window for a photocathode

[0001] This application claims priority to the Chinese patent application No. 202411355504.5, filed on September 26, 2024, and entitled "A Cascade-Enhanced Optical Input Window for a Photocathode", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of optoelectronic devices, and in particular to a cascade-enhanced optical input window for a photocathode. BACKGROUND

[0003] Photocathodes are widely used in various types of vacuum photodetectors and imaging devices such as photomultiplier tubes, image intensifiers, etc., and play an important role in the field of low-light detection and imaging technology. In addition, as a vacuum electron source capable of generating high-quality electron beams, photocathodes are used in scientific devices such as accelerator light injectors and electron microscopes.

[0004] The quantum efficiency (QE) of a photocathode is an important indicator for measuring the photoelectric response performance of a photoelectric device, which refers to the ratio of photons converted into electron emission by a photocathode. Traditional photocathodes are usually composed of a transparent glass substrate and a photoemission material, which have the problems of low quantum efficiency and narrow response spectrum. SUMMARY

[0005] The present application provides a cascade-enhanced optical input window for a photocathode, comprising: a substrate layer, a cascade structure, and a photoemission layer; the cascade structure is located between the substrate layer and the photoemission layer; the cascade structure is used for modulating incident light;

[0006] The cascade structure comprises, in sequence along the direction of incident light, a nano-pattern layer, a waveguide layer, and a plasmonic layer; incident light enters from one side of the substrate layer, is deflected after being modulated by the nano-pattern layer, forms a waveguide in the waveguide layer, and causes the plasmonic layer to produce a localized plasmonic resonance effect to promote light absorption by the photoemission layer. BRIEF DESCRIPTION OF DRAWINGS

[0007] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0008] FIG. 1 is a structural schematic diagram of a cascade-enhanced optical input window for a photocathode according to one or more embodiments.

[0009] Fig. 2 is a schematic diagram of the structure of the waveguide layer, plasmonic layer and photoemission layer in Example 1;

[0010] Fig. 3 is a schematic diagram of the structure of the cascade enhanced optical input window for the photocathode in Example 1;

[0011] Fig. 4 is a schematic diagram of the structure of the waveguide layer, plasmonic layer and photoemission layer in Example 2;

[0012] Fig. 5 is a schematic diagram of the structure of the cascade enhanced optical input window for the photocathode in Example 2;

[0013] Fig. 6 is a schematic diagram of the structure of the photocathode control group without adding a cascade structure;

[0014] Fig. 7 is a schematic diagram of the structure of the photocathode control group without adding a cascade structure;

[0015] Fig. 8 is a comparison chart of the absorption rates of the photocathode in Example 1 and the photocathode without adding a cascade structure;

[0016] Fig. 9 is a comparison chart of the absorption rates of the photocathode in Example 2 and the photocathode without adding a cascade structure.

[0017] Reference signs: 1 - substrate layer, 2 - nanometer pattern layer, 3 - waveguide layer, 4 - plasmonic layer, 5 - photoemission layer. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0019] 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 capability of the photoelectric device. For example, a photocathode prepared by coating a multilayer dielectric antireflection film (patent publication number CN111261489A) and a micro-nano grating structure prepared on an anti-halo glass (patent publication number CN113241293A) disclosed by China North Night Vision Technology Co., Ltd. can increase the absorption rate of the photocathode through micro-nano structure design, thereby improving the photoelectric response capability of the photoelectric device.

[0020] The purpose of the present application is to provide a cascade enhanced optical input window for a photocathode, the gain of the photoelectric response performance of which is jointly generated by a nano-pattern composed of a dielectric material and a localized surface plasmon cascade structure composed of a metal material, the further enhancement of the photoelectric response capability of the photocathode is realized by using the cascade effect between the structures, the combination of the structures can achieve the effect of 1+1>2, has great development potential, can improve the quantum efficiency of the photocathode, and improve the photoelectric response capability of the photoelectric device.

[0021] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below in combination with the drawings and specific embodiments.

[0022] As shown in FIG. 1, the cascade enhanced optical input window for a photocathode provided by the present application comprises a substrate layer 1 and a cascade structure. The cascade enhanced optical input window for a photocathode further comprises a photoemission layer 5. The cascade structure is located between the substrate layer 1 and the photoemission layer 5. The cascade structure is used for modulating incident light. The cascade structure functions as a group of optical resonators at a target wavelength.

[0023] The cascade structure is in turn a nano-pattern layer 2, a waveguide layer 3 and a plasmon layer 4 along the direction of 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 photoemission layer 5. Through the joint action of the nano-pattern layer 2, the waveguide layer 3 and the plasmon layer 4 in the cascade structure on the modulation of incident light, the absorption enhancement of the photoemission layer 5 of the photocathode is realized.

[0024] The incident light of the target wavelength enters from one side of the substrate layer 1, is deflected after being modulated by the nano-pattern layer 2, forms a waveguide in the waveguide layer 3, and exhibits light field enhancement near the interface between the waveguide layer 3 and the photoemission layer 5, so as to make the plasmon layer 4 produce localized plasmon resonance effect, so as to promote the light absorption of the photoemission layer 5, thereby increasing the quantum efficiency of the photocathode. The nano-pattern layer 2 and the plasmon layer 4 jointly act on the modulation of incident light, and realize the absorption enhancement of the photoemission layer 5 of the photocathode.

[0025] In one or more embodiments, the material of the substrate layer 1 is a transparent material. That is, the material of the substrate layer 1 is an optically transparent material. The transparent material refers to a transmittance close to 100% and very small absorption and scattering loss in the target wavelength range. 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 and the like.

[0026] The nano-pattern layer 2 is composed of two or more than two materials with different refractive indexes arranged alternately. 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 selected from silicon oxide, hafnium oxide, zirconium oxide, titanium oxide, aluminum oxide, aluminum nitride or other one or more oxide, fluoride or nitride materials.

[0027] In the present application, the nano-pattern layer 2 is located on the upper surface of the substrate layer 1 and is a nano-topology arranged regularly. The regular arrangement refers to the arrangement of protrusions or recesses with a certain interval, or refers to a pattern with a certain periodicity, including but not limited to a circle, a triangle, a polygon, a cone, a sphere, a hemisphere, a ring, etc. The period includes but is not limited to an orthogonal period, a triangular period and other regular periodic arrangements. The pattern can be made by ion beam etching, laser etching, chemical etching and other technical methods.

[0028] The size and pitch of the nano-pattern are adjusted according to the size of the target wavelength, and the nano-pattern should be between one-tenth and ten times of the target wavelength. The size of the nano-pattern is not more than the pitch of the nano-pattern in principle. The substrate layer 1 and the nano-pattern layer 2 are composed of at least two or more than two materials with different refractive indexes.

[0029] The waveguide layer 3 is one or more oxide films, fluoride films or nitride films. 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. The one or more oxide films, fluoride films or nitride films are directly arranged between the nano-pattern layer 2 and the plasmonic layer 4. The film deposition can be realized by atomic layer deposition, sputtering, evaporation, vapor deposition and other methods. The refractive index and thickness of the material of the waveguide layer 3 are matched with 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 nano-pattern layer 2. The waveguide layer 3 and the nano-pattern layer 2 work together to localize the incident light in the waveguide layer 3 and near the surface plasmon surface.

[0030] The plasmonic layer 4 is one or more 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 excited by the light intensity near the interface between the waveguide layer 3 and the photoelectric emission layer 5 to produce a localized plasmon resonance effect in the target waveband. The material of the plasmonic layer 4 is a metal or a metal composite. That is, the material of the plasmonic layer 4 is a metal or a metal composite material.

[0031] In one or more embodiments, the material of the plasmonic 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, spherical, semi-spherical, ellipsoidal, cylindrical, rod-shaped, ring-shaped, etc. The material, shape, size and density of the negative dielectric constant material particles are determined according to the application requirements of the target waveband, and are matched with the structures 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 realized by evaporation, sputtering, chemical method, etc.

[0032] As a specific embodiment, the plasmonic layer 4 is embedded in the waveguide layer 3, and the upper edge of the plasmonic layer 4 is flush with the upper edge of the waveguide layer 3.

[0033] As another specific embodiment, the plasmonic layer 4 is embedded in the photoelectric emission layer 5.

[0034] The present application manufactures a double-layer waveguide at the target wavelength through the cascade structure composed of the nano-pattern layer 2, the waveguide layer 3 and the plasmonic layer 4, enhances the light absorption performance of the photoelectric cathode, and the enhanced light field is distributed between the two-layer waveguides, so that the cascade structure obtains more obvious purcell enhancement in a larger range. Compared with the single-layer structure, the cascade effect of the dielectric-metal double-layer structure provided by the present application 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 plasmonic resonance waveband. At the same time, the cascade structure can convert more energy to the surface plasmon resonance mode, reduce the electric dipole radiation to the surface wave mode which cannot be utilized, and thus more effectively utilize the enhancement effect of the surface plasmonic resonance.

[0035] In order to better understand the scheme of the present application, the following further illustrates the specific embodiments.

[0036] Embodiment 1

[0037] As shown in FIG. 2 and FIG. 3, the structure of the cascade enhanced optical input window for the photoelectric cathode provided by the present embodiment has obvious absorption enhancement at the wavelength of 400nm-600nm. SiO2 is selected as the substrate material. SiO2 and ZrO2 arranged alternately are used as the nano-pattern layer 2, and the nano-patterns are arranged in a square array and prepared by etching technology. The radius of the nano-patterns is 155nm, the duty cycle is 0.35, and the thickness is 220nm. TiO2 is deposited on the nano-pattern layer 2 as the waveguide layer 3, and the thickness is 150nm.

[0038] In order to highlight the gain of the photocathode device based on the cascade structure of the present application, an experimental control group is designed simultaneously, as shown in FIG. 6 and FIG. 7. The photoelectric conversion device based on a common substrate is taken as control group 1, and its structure is shown in FIG. 6. The photoemission layer 5 of the device is directly placed on the plane substrate without the cascade structure of the waveguide layer 3, the nano-pattern layer 2 and the plasmonic layer 4. The photoelectric conversion device based on only a single waveguide layer is taken as control group 2, and its structure is shown in FIG. 7. The plane substrate materials of the two are both quartz.

[0039] FIG. 8 is the absorption spectrum of the light input device of the present embodiment and the control group respectively combined with the same thickness of the photocathode. The photoemission layer 5 material of the selected photocathode is S25 multialkali cathode, and the thickness is 40 nm-120 nm. Preferably, the silver hemisphere diameter of the plasmonic layer 4 is 80 nm, the height is 40 nm, and the sphere center distance is 300 nm. The thickness of the photoemission layer 5 is preferably 80 nm.

[0040] As can be seen from FIG. 8, the photocathode provided by the present embodiment has obvious absorption enhancement at 400 nm-600 nm. In particular, the cascade structure provides further improvement of the absorption capacity near 550 nm. By adopting the positive hemisphere structure, the contact area of the plasmonic particles and the photoelectric absorption layer is increased, which can effectively improve the absorption efficiency of the photons and improve the photoelectric response performance of the photocathode.

[0041] Embodiment 2

[0042] The structures of the cascade enhanced photocathode provided by the present embodiment are shown in FIG. 4 and FIG. 5. The present embodiment has obvious absorption enhancement at 400 nm-750 nm wavelength. SiO2 is selected as the substrate material. SiO2 and ZrO2 are alternately arranged as the nano-pattern layer 2, and the nano-pattern is arranged in a hexagonal array and prepared by etching technology. The radius of the nano-pattern is 155 nm, the duty cycle is 0.35, and the thickness is 240 nm. TiO2 is deposited on the nano-pattern layer 2 as the waveguide layer 3, and the thickness is 150 nm.

[0043] Metal hemisphere particles arranged at equal intervals are used as the plasmonic layer 4, and the metal particles are uniformly distributed on the waveguide layer 3, with the upper edge of the metal particles flush with the upper edge of the waveguide layer 3. The metal material is selected as aluminum. First, the metal spheres are prepared by using the solution method, then the waveguide layer 3 is deposited, and then the surface is polished by using the chemical mechanical polishing technology to obtain the metal hemisphere inlaid in the waveguide layer 3. The diameter of the hemisphere particles is 60 nm-150 nm, the sphere center distance is 100 nm-600 nm, and the height is 30 nm-100 nm.

[0044] In order to highlight the gain of the photocathode device based on the cascade structure of the present application, the experimental control group is designed at the same time, as shown in Figures 6 and 7. The photoelectric conversion device based on a common substrate is taken as control group 1, and its structure is shown in Figure 6. The photoelectric emission layer 5 of the device is directly placed on the plane substrate without the cascade structure of the waveguide layer 3 and the nano-pattern layer 2 and the plasmonic layer 4. The photoelectric conversion device based on only a single layer of waveguide is taken as control group 2, and its structure is shown in Figure 7. The plane substrate materials of the two are both SiO2.

[0045] Figure 9 is the absorption spectrum of the light input device of the present embodiment and the control group combined with the same thickness of the photocathode, respectively. The photoelectric emission layer 5 material of the selected photocathode is S25 multialkali photocathode, and the thickness is 40 nm-120 nm. Preferably, the diameter of the metal hemisphere of the plasmonic layer 4 is 60 nm, the height is 40 nm, and the distance between the centers of the spheres is 480 nm. The thickness of the photoelectric emission layer 5 is preferably 80 nm.

[0046] As can be seen from Figure 9, the photocathode provided by the present embodiment has obvious absorption enhancement at 400 nm-750 nm. In particular, the cascade structure provides significant further enhancement of the photocathode absorption at 650 nm-750 nm. Compared with the positive hemisphere structure, the plasmonic layer 4 with the waveguide layer 3 inlaid hemisphere structure reduces the contact area with the photoelectric absorption layer, but through the mechanical polishing technology, the surface of the plasmonic layer 4 can be made flat with low roughness, which is beneficial to improve the resolution of the photocathode and meet the application of micro-light imaging and the like.

[0047] In summary, by designing a reasonable medium-metal combined structure, the present application regulates the light field near the incident surface of the photocathode, significantly increases the light absorption performance of the photocathode in a multi-band and wide spectral range, thereby greatly improves the photoelectric response performance of the photocathode and broadens the application scenarios of the photocathode.

[0048] Through the cascade effect, the multi-layer waveguide is manufactured to increase the probability of photon absorption by the photocathode. Compared with the single-layer structure, more significant improvement of the photoelectric performance can be obtained in a larger range. Through the adjustment and optimization of the structure of the material and geometric parameters, further enhancement of the absorption rate of the photocathode in one or more target wavebands can be realized.

[0049] According to the specific embodiments provided by the present application, the following technical effects are disclosed: the present application manufactures a double-layer waveguide through the cascade structure of the nano-pattern layer 2, the waveguide layer 3 and the plasmonic layer 4 at the target wavelength, enhances the light absorption performance of the photocathode, and compared with the single-layer structure, the present application can more significantly improve the quantum efficiency and response wavelength range of the photoelectric emission layer 5, and still maintain a high enhancement effect at a position far away from the plasmonic resonance waveband.

[0050] The various embodiments described in this specification are intended to be exemplary only. The various embodiments were chosen and described in order to best explain the principles of the application and the practical application thereof. The methods and apparatuses disclosed herein are therefore to be considered in all respects as illustrative and not restrictive.

[0051] The principles and implementations of the present application are described in the specific examples herein, and the above descriptions of the examples are only used to help understand the method and core idea of the present application. Meanwhile, for those skilled in the art, the specific implementation and application range will be changed according to the idea of the present application. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A cascaded enhancement optical input window for a photocathode, characterized by, The photocathode uses a cascade enhanced optical input window, which comprises a substrate layer (1), a cascade structure and a photoemission layer (5); the cascade structure is located between the substrate layer (1) and the photoemission layer (5); the cascade structure is used for modulating incident light; The cascade structure is in sequence of a nano-pattern layer (2), a waveguide layer (3) and a plasmonic layer (4) along the direction of incident light; incident light enters from one side of the substrate layer (1), is deflected after being modulated by the nano-pattern layer (2), forms a waveguide in the waveguide layer (3), and makes the plasmonic layer (4) produce a localized plasmonic resonance effect to promote the photoemission layer (5) 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 (1) is an optically transparent material.

3. The cascade enhanced optical input window for a photocathode of claim 1, wherein, The nano-pattern layer (2) is composed of two or more than two materials with different refractive indexes alternately 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 (2) is an oxide, fluoride or nitride material.

5. The cascade enhanced optical input window for a photocathode of claim 1, wherein, The waveguide layer (3) is one or more layers of oxide film, fluoride film or nitride film.

6. The cascade enhanced optical input window for a photocathode of claim 1, wherein, The plasmonic layer (4) is one or more layers of negative dielectric constant material particles distributed between the waveguide layer (3) and the photoemission layer (5); the negative dielectric constant material particles are used for producing a localized plasmonic resonance effect in a target waveband.

7. The cascade enhanced optical input window for a photocathode according to claim 1 or 6, characterized in that, The plasmonic layer (4) is embedded in the waveguide layer (3), and the upper edge of the plasmonic layer (4) is flush with the upper edge of the waveguide layer (3).

8. The cascade enhanced optical input window for a photocathode according to claim 1 or 6, characterized in that, The plasmonic layer (4) is embedded in the photoemission layer (5).

9. The cascade enhanced optical input window for a photocathode of claim 1, wherein, The material of the plasmonic layer (4) is a metal or a metal composite material.

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