Breakthrough in quantum efficiency of bi-alkali photocathodes PMTs

Bi-alkali type photocathodes are commonly used in classical photomultipliers. They provide low noise and high blue and near UV sensitivity well matched to scintillation light. The first breakthrough enhancement of standard bi-alkali photocathodes brought to the market PMTs characterized by quantum efficiencies of 30 % at 400 nm. Through a detailed understanding of the creation process of the photocathode and its optimization PHOTONIS has successfully obtained a production process achieving an average quantum efficiency of 38 % for a PMT bi-alkali photocathode. Further enhancement of the PMTs quantum efficiency was obtained by utilizing a special tulip shaped PMT glass envelope to reflect back to the photocathode the light which initially passed through without interaction. This work reports on the spectral measurements of the new CLARITY XP family of PMTs and their performance in spectrometry with different scintillators.