Abstract

Reduction of the effective cathode area of photomultiplier tubes is known to yield lower dark currents and an improved signal-to-noise ratio. This can be accomplished either by electrostatic or magnetic defocusing of the electron beam between the cathode and the first dynode. Three magnetic lenses with different field geometries were tried with an EMI 9558B photomultiplier tube, and a noise reduction of more than an order of magnitude was observed. Magnetic defocusing changes the pulse height characteristics of the tube as well and improves the discrimination between signal pulses and dark pulses when using simple pulse height discrimination techniques. If the tube is operated as a photon counter, the light-to-dark count ratio may be improved by nearly two orders of magnitude with the application of a suitable magnetic lens.

© 1968 Optical Society of America

The Use of Photomultiplier Tubes for Photon Counting

R. Foord, R. Jones, C. J. Oliver, and E. R. Pike
Appl. Opt. 8(10) 1975-1989 (1969)

Synchronous Detection vs Pulse Counting for Sensitive Photomultiplier Detection Systems

J. K. Nakamura and S. E. Schwarz
Appl. Opt. 7(6) 1073-1078 (1968)

Some Statistical Properties of Pulses from Photomultipliers

M. Gadsden
Appl. Opt. 4(11) 1446-1452 (1965)

A Comparison of Photon Counting and Current Measuring Techniques in Spectrophotometry of Faint Sources

Robert G. Tull
Appl. Opt. 7(10) 2023-2029 (1968)

The Efficient Use of Photomultiplier Tubes for Recording Spectra

J. Rolfe and S. E. Moore
Appl. Opt. 9(1) 63-71 (1970)