Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Quantum efficiency enhancement utilising a waveguide to achieve many interactions with a photomultiplier tube photocathode

ETL has designed and built photomultiplier tubes to demonstrate the potential of using a waveguide structure to improve the quantum efficiency over a broad spectral range. These photomultipliers used a photocathode deposited onto a thin sheet of glass that acted as a waveguide for the incoming light. These photomultiplier tubes were of novel design, as the necessarily thin waveguides could not be used to support a vacuum within the device against atmospheric pressure on the outside.

The use of a waveguide to achieve many interactions with a photomultiplier tube photocathode has led to significant improvements in quantum efficiency, especially towards the red end of the spectrum where current photocathodes typically have low sensitivity. The increase in QE of waveguide photocathodes compared to standard mode illumination is x2 at 400nm, x3 at 550 nm, x4 at 650nm and x9 at 800nm

Relevance of this result:
As time progresses there is an increasing demand for low background photomultipliers with greater sensitivity towards the green and red regions of the spectrum (especially for biological applications). The use of multiple interactions of light with the photocathode means that as much of the available radiations as possible will be absorbed and may be converted into photoelectrons. It is also becoming more common for the light to be detected to be transported to the photomultiplier tube by a small fiber-optic. These sources are very suitable to be optically coupled into a narrow waveguide.

Current Status:
The large gains that have been demonstrated within this project make this an attractive possibility to incorporate into the design of the next generation of photomultiplier tubes. Further exploitation of this technology will depend on the future development of the photomultiplier tube market.

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Electron Tubes Ltd
Bury Street
HA4 7TA Ruislip - Middx
United Kingdom
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