A photon counting, microchannel plate (MCP) optical
imaging tube has been fabricated using a 2 × 2 array of Timepix application
specific integrated circuits (ASICs) as the readout anode. A Timepix ASIC is
a 256 × 256 pixellated CMOS readout chip with each pixel containing an
amplifier, discriminator and counter. The counter values, representing
either time of arrival, total count or time over threshold, can record the
position and time of arrival of the electron pulses from the MCP if the
charge collected on its input pads exceed the adjustable lower threshold
value. Below we present initial results of the tube's performance, the
quantum efficiency of the bi-alkali photocathode, uniformity of response,
spatial and temporal resolution, and dynamic range. Planned improvement to
the design based on the new Timepix3 chip will be discussed.
Based on conventional S-20 processes, a new series of high quantum efficiency (QE) photocathodes has been developed that can be specifically tuned for use in the ultraviolet, blue or green regions of the spectrum. The QE values exceed 30% at maximum response, and the dark count rate is found to be as low as 30 Hz/cm 2 at room temperature. This combination of properties along with a fast temporal response makes these photocathodes ideal for application in photon counting detectors, which is demonstrated with an MCP photomultiplier tube for single and multi-photoelectron detection.
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