A cascaded enhancement optical input window for a photocathode

Abstract

The application provides a kind of optical input window of cascade enhancement type for photocathode, belong to the field of optoelectronic devices, optical input window of cascade enhancement type for photocathode includes: substrate layer and cascade structure;Cascade structure is located between substrate layer and photoemissive layer;Cascade structure is used to modulate incident light;Cascade structure is in turn nano pattern layer, waveguide layer and plasmonic layer along the direction of incident light;Incident light enters from one side of substrate layer, is deflected after being modulated by nano pattern layer, forms waveguide in waveguide layer, so that plasmonic layer produces localized plasmon resonance effect, to promote photoemissive layer to carry out photoabsorption.The application improves the quantum efficiency of photocathode, and further improves the photoelectric response capability of photoelectric device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic devices, in particular to a cascade enhanced optical input window for photocathode. BACKGROUND

[0002] Photocathode is widely used in various types of vacuum photodetector and imaging devices such as photomultiplier, image intensifier, and plays an important role in the field of low-light-level detection and imaging technology. In addition, as a vacuum electron source capable of generating high-quality electron beams, photocathode is used in scientific devices such as accelerator light injectors and electron microscopes.

[0003] The quantum efficiency (QE) of photocathode is an important indicator to measure the photoelectric response performance of photoelectric devices, which refers to the ratio of photons converted into electron escape by photocathode. The traditional photocathode is usually composed of transparent glass substrate and photoemissive material, which has the problems of low quantum efficiency and narrow response spectrum. SUMMARY

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

[0005] To achieve the above purpose, the present application provides a cascade enhanced optical input window for photocathode, comprising: a substrate layer and a cascade structure; the cascade structure is located between the substrate layer and the photoemissive layer; the cascade structure is used for modulating incident light;

[0006] The cascade structure is in turn a nano-pattern layer, a waveguide layer and a plasmonic layer along the direction of incident light; the incident light enters from one side of the substrate layer, is deflected after modulation by the nano-pattern layer, forms a waveguide in the waveguide layer, and makes the plasmonic layer produce localized plasmon resonance effect to promote the photoemissive 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 indexes alternately arranged according to a certain rule.

[0009] Optionally, the material of the nano-pattern layer is an 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 plasmonic 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 the target waveband.

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

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

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

[0015] According to the specific embodiments of the present application, the following technical effects are disclosed: the present application uses a cascade structure composed of a nano-pattern layer, a waveguide layer and a plasmonic layer to manufacture a double-layer waveguide at a target wavelength, thereby enhancing the light absorption performance of the photoelectric cathode; compared with a single-layer structure, the present application can more significantly improve the quantum efficiency and the response wavelength range of the photoelectric emission layer, and still maintain a high enhancement effect at a position far from the plasmonic resonance waveband. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described in the following are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1 The structure schematic diagram of the cascade enhanced optical input window for the photoelectric cathode provided by the present application is shown in the figure.

[0018] Figure 2 The structure schematic diagram of the waveguide layer, the plasmonic layer and the photoelectric emission layer in embodiment 1 is shown in the figure.

[0019] Figure 3 The structure schematic diagram of the cascade enhanced optical input window for the photoelectric cathode in embodiment 1 is shown in the figure.

[0020] Figure 4 The structure schematic diagram of the waveguide layer, the plasmonic layer and the photoelectric emission layer in embodiment 2 is shown in the figure.

[0021] Figure 5 The structure schematic diagram of the cascade enhanced optical input window for the photoelectric cathode in embodiment 2 is shown in the figure.

[0022] Figure 6 The structure schematic diagram of the photoelectric cathode control group without adding a cascade structure is shown in the figure. Figure 1 ​

[0023] Figure 7 Structure diagram of the control group of the photocathode without the added cascade structure Figure 2 ;

[0024] Figure 8 Comparison chart of the absorption rate of the photocathode of Example 1 and the photocathode without the added cascade structure;

[0025] Figure 9 Comparison chart of the absorption rate of the photocathode of Example 2 and the photocathode without the added cascade structure.

[0026] Symbol explanation: 1-substrate layer, 2-nanopattern layer, 3-waveguide layer, 4-plasmonic layer, 5-photoemission layer. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to 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 skilled in the art without creative labor fall within the scope of protection of the present application.

[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 capability of the photoelectric device. For example, a photocathode coated with a multilayer dielectric antireflection film preparation method (patent publication number CN111261489A) and a micro-nano grating structure prepared on an anti-halo glass (patent number 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.

[0029] 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 nanometer pattern composed of a dielectric material and a local surface plasmon cascade structure composed of a metal material. The cascade effect between the structures is utilized to further enhance the photoelectric response capability of the photocathode. This combination of structures can achieve the effect of 1+1>2 and has great development potential.

[0030] 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 with reference to the drawings and specific embodiments.

[0031] As Figure 1As shown, the application provides a cascade enhanced optical input window for a photocathode, which comprises a substrate layer 1 and a cascade structure. 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 set of optical resonators at the target wavelength.

[0032] The cascade structure sequentially comprises a nano-pattern layer 2, a waveguide layer 3 and a plasmonic layer 4 along the direction of incident light. That is, the nano-pattern layer 2, the waveguide layer 3 and the plasmonic layer 4 are sequentially arranged on the substrate layer 1 and located on the back of the photoemission layer 5. Through the combined action of the nano-pattern layer 2, the waveguide layer 3 and the plasmonic 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.

[0033] The incident light at 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 plasmonic layer 4 produce localized plasmonic resonance effect 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 plasmonic layer 4 jointly act on the modulation of incident light, and realize the absorption enhancement of the photoemission layer 5 of the photocathode.

[0034] Specifically, the material of the substrate layer 1 is a transparent material. The transparent material refers to a transmittance close to 100% and extremely 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.

[0035] The nano-pattern layer 2 is composed of two or more than two materials with different refractive indexes alternately arranged in 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 selected from silicon oxide, hafnium oxide, zirconium oxide, titanium oxide, aluminum oxide, aluminum nitride or other one or more oxide, fluoride or nitride materials.

[0036] In the application, the nano-pattern layer 2 is located on the upper surface of the substrate layer 1 and is a nano-topological structure arranged in a certain rule. The arrangement in a certain rule refers to protrusions or recesses arranged at a certain interval, or refers to a pattern with a certain periodicity, including but not limited to circular, triangular, polygonal, conical, spherical, hemispherical, annular and the like, and the periodicity includes but is not limited to orthogonal periodicity, triangular periodicity and other regular periodic arrangements; the pattern can be manufactured by ion beam etching, laser etching, chemical etching and the like.

[0037] The size and pitch of the nano-patterns are adjusted according to the size of the target wavelength, and the nano-patterns should be between one-tenth and ten times of the target wavelength. The size of the nano-patterns is not more than the pitch of the nano-patterns in principle. The substrate layer 1 and the nano-pattern layer 2 are composed of at least two or more different refractive index materials.

[0038] The waveguide layer 3 is one or more layers of oxide film, fluoride film or nitride film. The materials of the waveguide layer 3 include but are 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 plasmonic layer 4. Thin film deposition can be realized by atomic layer deposition, sputtering, evaporation, vapor deposition, etc. 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 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 plasmon surface.

[0039] The plasmonic 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 excited by the light intensity near the interface between the waveguide layer 3 and the photoelectric emission layer 5 to produce localized plasmon resonance effect in the target waveband. The material of the plasmonic layer 4 is metal or metal composite.

[0040] Specifically, 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, hemispherical, 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 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 realized by evaporation, sputtering, chemical method, etc.

[0041] 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.

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

[0043] The application manufactures a double-layer waveguide at a target wavelength through a 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 photocathode, and enhances the light field distribution between the two layers of waveguide, so that the cascade structure obtains more obvious purcell enhancement in a larger range. Compared with a single-layer structure, the cascade effect of the medium-metal double-layer structure provided by the application can more significantly improve the quantum efficiency of the photoemission layer 5, and still maintain a high enhancement effect at a position far from the plasmonic resonance band. Meanwhile, 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.

[0044] In order to better understand the scheme of the application, the following further describes the application in combination with specific embodiments.

[0045] Embodiment 1

[0046] As shown in Figure 2 and Figure 3 , the structure of the cascade enhanced optical input window for the photocathode provided by the embodiment has obvious absorption enhancement at a wavelength of 400nm-600nm. SiO2 is selected as the substrate material. SiO2 and ZrO2 arranged alternately are used as the nano-pattern layer 2, the nano-patterns are arranged in a square array, and are 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.

[0047] In order to highlight the gain of the photocathode device based on the cascade structure of the application, the embodiment also designs an experimental control group, as shown in Figure 6 and Figure 7 , wherein the photoelectric conversion device based on a common substrate is used as the control group 1, and the structure is as shown in Figure 6 . The photoemission layer 5 of the device is directly placed on the plane substrate, and there is no 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-layer waveguide is used as the control group 2, and the structure is as shown in Figure 7 . The plane substrate materials of the two are both quartz.

[0048] Figure 8 The absorption spectra of the light input devices of the embodiment and the control group are combined with the photocathodes with the same thickness, respectively. The material of the photoemission layer 5 of the selected photocathode is S25 multialkali cathode, and the thickness is 40nm-120nm. Preferably, the diameter of the silver hemisphere of the plasmonic layer 4 is 80nm, the height is 40nm, and the center distance is 300nm. The thickness of the photoemission layer 5 is preferably 80nm.

[0049] Observation Figure 8 It can be seen that the photoelectric cathode provided in the embodiment has obvious absorption enhancement at 400nm-600nm. In particular, the cascade structure provides further improvement of the absorption capacity around 550nm. The adoption of the positive hemisphere structure increases the contact area between the plasmonic particles and the photoelectric absorption layer, which can effectively improve the absorption efficiency of photons and enhance the photoelectric response performance of the photoelectric cathode.

[0050] Embodiment 2

[0051] As shown in Figure 4 and Figure 5 , the structure of the cascade-enhanced photoelectric cathode provided in the embodiment has obvious absorption enhancement at 400nm-750nm. 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 hexagonal array and prepared by etching technology. The radius of the nano-patterns is 155nm, the duty cycle is 0.35, and the thickness is 240nm. TiO2 is deposited on the nano-pattern layer 2 as the waveguide layer 3, and the thickness is 150nm.

[0052] 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 hemisphere flush with the upper edge of the waveguide layer 3. The metal material is selected as aluminum. First, metal spheres are prepared by using a solution method, then the waveguide layer 3 is deposited, and then chemical mechanical polishing technology is used for surface polishing to obtain metal hemispheres inlaid in the waveguide layer 3. The diameter of the hemisphere particles is 60nm-150nm, the center distance is 100nm-600nm, and the height is 30nm-100nm.

[0053] In order to highlight the gain of the photoelectric cathode device based on the cascade structure of the present application, the embodiment also designs an experimental control group, as shown in Figure 6 and Figure 7 , wherein the photoelectric conversion device based on a common substrate is used as control group 1, and the structure is as shown in Figure 6 . The photoemission 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 containing only a single waveguide is used as control group 2, and the structure is as shown in Figure 7 . The plane substrate materials of the two are both SiO2.

[0054] Figure 9The light absorption spectrum of the light input device of the embodiment and the control group is combined with the photoelectric cathode with the same thickness, and the photoemission layer 5 of the photoelectric cathode is S25 multialkali cathode with a thickness of 40nm-120nm. Preferably, the diameter of the metal hemisphere of the plasmonic layer 4 is 60nm, the height is 40nm, and the distance between the centers of the hemispheres is 480nm. The thickness of the photoemission layer 5 is preferably 80nm.

[0055] Observation Figure 9 It can be seen that the photoelectric cathode provided by the embodiment has obvious absorption enhancement at 400nm-750nm, and in particular, the cascade structure provides significant further enhancement of the photoelectric cathode absorption at 650nm-750nm. Compared with the positive hemisphere structure, the plasmonic layer 4 with the inlaid hemisphere structure of the waveguide layer 3 reduces the contact area with the photoelectric absorption layer, but through the mechanical polishing technology, the surface of the plasmonic layer 4 can be smooth and have low roughness, which is beneficial to improve the resolution of the photoelectric cathode and meet the application of micro-light imaging and the like.

[0056] In summary, by designing a reasonable medium-metal combined structure, the present application can regulate the light field near the incident surface of the photoelectric cathode, significantly increase the light absorption performance of the photoelectric cathode in a wide spectral range, thereby greatly improving the photoelectric response performance of the photoelectric cathode and widening the application scenarios of the photoelectric cathode.

[0057] Through the cascade effect, the multilayer waveguide increases the probability of photon absorption by the photoelectric cathode, and compared with the single-layer structure, more significant improvement of the photoelectric performance can be obtained in a larger range; by adjusting and optimizing the material and geometric parameters of the structure, further enhancement of the photoelectric cathode absorption rate in one or more target wavebands can be realized.

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

[0059] The principles and implementation modes of the present application are described by using specific examples in this paper, and the above description of the embodiments is only used to help understand the method and core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. 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, 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; The cascade structure is in sequence of a nano-pattern layer, a waveguide layer and a plasmonic layer along the direction of incident light; incident light enters from one side of the substrate layer, is deflected after modulation by the nano-pattern layer, forms a waveguide in the waveguide layer, and causes the plasmonic layer to generate a localized plasmonic resonance effect to promote the photoemission layer to absorb light; the nano-pattern layer is composed of two or more than two materials with different refractive indexes alternately arranged according to a certain rule.

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 of claim 1, wherein, The material of the nano-pattern layer is an oxide, fluoride or nitride material.

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

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

6. The cascade enhanced optical input window for a photocathode according to claim 1 or 5, characterized in that, The plasmonic layer is embedded in the waveguide layer, and the upper edge of the plasmonic layer is flush with the upper edge of the waveguide layer.

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

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

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