Methods of preparation and performance of sealed gas photomultipliers for visible light

We describe the preparation of a sealed gas-filled photomultiplier (GPMT) for the visible spectral range and present the properties of the first prototypes. They consist of a 50 mm diameter semitransparent bialkali (K-Cs-Sb) photocathode coupled to a 30 mm×30 mm Kapton multi-gas electron multiplier (GEM). High gain of 2×10⁴ in two-GEM mode and a quantum efficiency of 13% at 405 nm have been reached at 700 Torr of Ar/CH₄ (95:5). The detector structure and experimental setup are described; results are presented on the GPMT gain, ion-feedback and its suppression, stability, and other critical parameters in various gas mixtures. Hot sealing techniques with In/Sn and In/Bi solders are discussed.