Semi-Transparent Photocathode Grating Absorption
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Solution Overview
Problem
Semi-transparent photocathodes in electromagnetic radiation detectors face challenges in achieving high quantum yield due to the trade-off between absorption and transport rates of photons, particularly at longer wavelengths, where increasing the thickness of the photoemissive layer improves absorption but degrades transport, leading to suboptimal performance.
Innovation Solution
Incorporating a transmission diffraction grating in the support layer to diffract photons towards the photoemissive layer, increasing the apparent thickness and thus absorption without affecting the actual transport of electrons, which are emitted from the opposite face.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the photoemissive layer is increased to improve absorption rate, then the absorption rate increases, but the transport rate of electrons decreases
Solution Approach 1:
The patent introduces a diffraction grating that redirects photons from normal incidence to oblique angles, effectively increasing the optical path length through the photoemissive layer without increasing the physical thickness. This dimensional change in light propagation direction allows photons to traverse a longer effective path (increasing absorption) while maintaining the same electron transport distance to the emitting face (preserving transport rate).
Solution Approach 2:
The diffraction grating acts as an intermediary element between the transparent support layer and the photoemissive layer. It modifies the incident photon trajectories by diffracting them at specific angles, thereby controlling the interaction between photons and the photoemissive material without requiring changes to the layer thickness. This intermediary structure enables independent optimization of absorption and transport parameters.
2Quantity of substance
If the thickness of the photoemissive layer is increased to improve absorption at long wavelengths, then the absorption rate improves, but the quantum yield decreases due to reduced electron transport
Solution Approach 1:
The diffraction grating changes the propagation dimension of photons from normal incidence to oblique angles, effectively multiplying the absorption opportunity without proportionally increasing electron transport distance. For long wavelengths that are poorly absorbed at normal incidence, the diffracted paths provide multiple absorption chances while electrons still travel the same short distance to the emitting face, thereby improving quantum yield at long wavelengths.
Solution Approach 2:
The patent changes the optical parameters by introducing a diffraction grating with specific period and geometry, which transforms the photon incident angles. This parameter change in light propagation direction enables enhanced absorption at long wavelengths without the detrimental effect of increased electron transport distance, thus improving quantum yield in the long-wavelength region.
3Productivity
If a diffraction grating is added to increase absorption, then the quantum yield improves, but the device complexity increases
Solution Approach 1:
The diffraction grating serves multiple functions simultaneously: it acts as an optical element to redirect photons, an absorption enhancer for the photoemissive layer, and a wavelength-selective element that can be optimized for specific spectral regions. This multi-functionality justifies the added structural complexity by delivering comprehensive performance improvement across multiple operational parameters.
Solution Approach 2:
The diffraction grating can be implemented as a periodic structure with varying transparency or refractive index regions, creating an optical pathway modulation similar to porous structures. This approach enables controlled light-matter interaction that enhances absorption while maintaining a relatively simple geometric pattern that can be manufactured using standard fabrication techniques.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances the quantum yield by increasing absorption while preserving the transport rate of electrons, particularly at wavelengths close to the photoemission threshold, resulting in improved detector performance.
Implementation Method 1
a transmission diffraction grating able to diffract the incident photons, provided in the support layer and located at said back face
Implementation Method 2
They are then absorbed in the photoemissive layer 20 and generate electron-hole pairs therein
Implementation Method 3
the absorption of the incident photon and the formation of an electron-hole pair; the transport of the generated electron up to the emitting face of the photoemissive layer; and the emission of the electron in vacuum
Data Source
AI summary
The invention relates to a semi-transparent photocathode (1) for a photon detector having an increased absorption rate for a preserved transport rate. According to the invention, the photocathode (1) includes a transmission diffraction grating (30) able to diffract said photons and provided in the support layer (10) on which the photoemissive layer (20) is deposited.