High quantum efficiency S-20 photocathodes in photon counting detectors

Abstract

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.

High-detection efficiency MCP-PMTs with single photon counting capability for LIDAR applications

“…The MCP gain is derived from the mean energy of the Pulse Height Distribution spectrum, where the measurements are done at a low level of illumination corresponding to a single photoelectron event [1]. The PHD spectra is recorded using a Charge Sensitive Preamplifier CSP10 (1.4 V/pC), a shaping amplifier CSA4, and a multi-channel analyser MCA3 [4].…”

“…Figure 1 shows the QE spectra for transmission mode S-20 based Hi-QE series photocathodes over the 200-900 nm spectral range. The new photocathodes are developed to target specific spectral ranges which are here called Hi-QE Blue, Hi-QE Aqua and Hi-QE Green [1]. These photocathodes exhibit much higher QE values than the conventional S-20, clearly exceeding 30% as seen in Figure 1.…”

“…The Hi-QE photocathodes exhibit all a very low dark rate, below typically 50 Hz/cm 2 [1]. In particular the Hi-QE Green is in that sense remarkable as it combines a good QE at 532 nm with the low dark rate property, making the Hi-QE Green a unique photocathode for photon counting in this spectral range.…”

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In this paper the focus is on the implementation of Photonis MCP-PMTs with single photon counting capability for LIDAR applications. In particular we are presenting our MCP-PMTs based on HI-QE photocathodes optimized for different spectral ranges (UV, Blue, Green with typical QE>30%) and for fixed laser wavelength of 355 nm and 532 nm [1]. In addition to the high QE, those photocathodes demonstrate low dark rates, typically below 50 Hz/cm 2 , property that is important for low-rate signal detection.

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Fast and efficient detection of 511 keV photons using Cherenkov light in PbF2 crystal, coupled to a MCP-PMT and SAMPIC digitization module

“…An increase in the number of photoelectrons generated at the photocathode will improve very significantly the time resolution. For example, Planacon XP85012 PMT features a bi-alkali photocathode with a maximum efficiency of 22% [47], but better photocathodes with efficiency up to 30% are available now [64]. An important loss in efficiency is also caused by the non-ideal optical interface as described in the section 3 and reflection of Cherenkov photons with a large incident angle from the crystal border.…”