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Optical coupling devices to increase the effective sensitivity of PMT for biological applications.

The design and realisation of optical devices to efficiently couple light into photomultiplier tubes has been completed. Polymer optical components have been fabricated that significantly increase the effective sensitivity of photomultiplier tubes over a broad range of wavelengths (400-850nm). This was achieved by causing incoming light to undergo multiple interactions with the photocathode by being reflected within the photomultiplier tube window. A variety of PMMA (Perspex) demonstrators were trialled incorporating polymer optical fibres (POF), simple prisms and cylindrically symmetric designs. It was found that the use of POF was impractical and the modest gains achieved were easily bettered by the simpler, easier to manufacture reflecting prisms. The designs were finally refined to a cylindrical symmetry, to make optimum use of the photocathode area and facilitate the easy mounting of the devices photomultiplier tubes. The prototype devices increase the quantum efficiency of a standard blue-green sensitive bialkali photocathode photomultiplier tube over its entire working range, with an improvement in sensitivity at 550nm of up to a factor of two (i.e. 100% better than tube without device). For an S20 photocathode improvement factors of up to seven have been observed at 800nm.

Relevance of this result:
Any general increase in the quantum efficiency of our products will make them more attractive in a highly competitive world market. These devices are initially aimed at the rapidly growing market for biological luminescence where a key wavelength monitored is 550nm. At this wavelength green-enhanced bialkali photocathodes are currently used, but they give rise to a much higher dark count than a standard blue-green sensitive bialkali photocathode. It is expected that use of the new optical coupling devices will extend the viable working range for the blue-green sensitive bialkali photocathode to provide good sensitivity, low-background photomultiplier tubes for use at 550nm.

Current Status:
Prototypes have been made and tested and will shortly be distributed to selected customers for appraisal. A thorough market research report has been also been completed to assess the impact of the improved performances that are now achievable.

Informations connexes

Reported by

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