Ultrahigh-speed microchannel photomultiplier

Use of a microchannel-water electron multiplier makes possible a new, compact photomultiplier with time-resolution capabilities better than can be obtained from classical photomultipliers using cascaded dynode structures. The small thickness of the wafer, together with proximity focusing in the electron optics of the input and output of the wafer, results in reduction of the electron transit-time to about 1 ns. The electron transit-time spread is about 10^-10seconds. Short pulses from a mode-locked laser were used to measure the impulse response of the photomultiplier. The experimental value of <500 ps (full width at half maximum) is in good agreement with the predictions of a computer analysis. Other salient characteristics of the new tube are: S 20 photocathode diameter of 11 mm; electron gain of about 10⁵; dark current <10^-16amperes (referred to the cathode); and 50-ohm output impedance.