Imaging/Detectors: Photomultipliers

Kenneth J. Kaufmann, Hamamatsu Corp.

Application demands for increased performance are stimulating photomultiplier manufacturers to continuously improve detectors and develop innovative devices. The demands are coming both from traditional applications such as gamma cameras and underwater lidar and from newer ones such as gene chip technology. These customers are requesting improvements in device size, wavelength sensitivity and user-friendliness. In response, manufacturers are developing new photomultiplier technologies, including photocathode designs, packaging and noise-reduction schemes.

Negative-affinity photocathodes made from III-IV materials will be crucial to improving photocathode performance. They will accomplish this by improving sensitivity and extending the spectral range of operation. GaAsP, GaAs and blue-enhanced GaAs will increase the quantum efficiency of photocathodes by at least a factor of two in the near term. Continuous improvements in these materials could result in even higher values. Reaching quantum efficiencies of more than 50 percent in GaAsP in the visible would result in higher throughput for gene chips and other medical diagnostic instruments. Quantum efficiencies of 20 to 30 percent in GaAs photocathodes will make it easier to develop optical computed tomography technologies for mammography.