Photomultiplier single photon counting efficiency

Area of Science:

• Photon detection
• Optical physics
• Quantum optics

Background:

• Photomultiplier tubes (PMTs) are crucial for detecting low light levels.
• Cathode quantum efficiency (QE) is a key performance metric for PMTs.
• Single photon counting efficiency (SPCE) is critical for applications requiring high sensitivity.

Purpose of the Study:

• Investigate the discrepancy between cathode quantum efficiency and single photon counting efficiency in an RCA C31000F photomultiplier.
• Identify the source of signal loss in photon counting measurements.
• Understand the origin of sub-threshold pulses in the output spectrum.

Main Methods:

• Characterization of an RCA C31000F photomultiplier tube.
• Measurement of cathode quantum efficiency at 633 nm.
• Analysis of the output pulse height spectrum for single photon events.
• Comparison of measured QE with observed SPCE.

Main Results:

• The RCA C31000F photomultiplier exhibited a cathode quantum efficiency of 5.5% for 633-nm light.
• The measured single photon counting efficiency was significantly lower at 3.3%.
• A population of small output pulses, below the typical single electron peak, was observed in the pulse height spectrum.
• These sub-threshold pulses are not registered by standard counting discriminators.

Conclusions:

• The reduced SPCE is attributed to uncounted sub-threshold pulses.
• The underlying cause for these small pulses in the RCA C31000F PMT remains unidentified.
• Further investigation is needed to understand and potentially mitigate the generation of these pulses for improved photon detection.