Energy windowing with Hamamatsu microchannel plate photomultipliers

Abstract

To obtain high quality decay data using time-correlated single photon counting, it is essential to eliminate multiplephoton events. Events should be counted only when one photon is detected for a given excitation flash. An easy way to eliminate multiple photon events is to gate data collection, permitting an event to be registered only if the energy of the pulse is within limits appropriate for the detection of a single photon. This method, called energy windowing, was first described by Schuyler and Isenberg [R. Schuyler and I. Isenberg, Rev. Sci. Instrum. 42, 813-817 (1971)]. In this paper we present a formalism for describing the statistics of multiple photon events. This formalism gives us a means of characterizing the pulse height distribution and estimating the fraction of multiple events which leak through our energy window. It also describes how multiple photon events distort a decay function and behave as contaminant decays. We then present a method for using energy windowing with Hamamatsu microchannel photomultipliers, and examine the ability two tubes of different design to differentiate between single and multiple events.