Photomultiplier Tubes (PMT): Advantages and Disadvantages

This page explores the pros and cons of Photomultiplier tubes (PMTs), highlighting both their strengths and weaknesses.

Introduction:

• PMTs (Photomultiplier Tubes) are devices used for detecting very weak light signals.
• They are photo-emissive devices where the absorption of a photon leads to the emission of an electron.
• PMTs belong to the class of vacuum tubes, also known as vacuum phototubes.
• They are primarily used as visible range photon sensors.
• Early PMTs were larger, featuring glass vacuum envelopes. Modern PMTs are available in smaller sizes.
• While avalanche photodiodes are increasingly replacing PMTs, they are still used in diverse applications like Raman spectrophotometry, fluorescent molecular tagging, and single bubble sonoluminescence.

Advantages of Photomultiplier Tubes (PMT)

Here are the advantages of using Photomultiplier tubes:

• Higher responsivity in A/W (Amps per Watt)
• Lower dark current
• High output Signal-to-Noise (S/N) ratio
• Low transport delay
• Wide spectral response
• High stability

Disadvantages of Photomultiplier Tubes (PMT)

Here are the disadvantages associated with Photomultiplier tubes:

• Mechanically fragile (due to their glass envelope).
• Limited shapes and sizes, and they can be physically large.
• Require stable, high-voltage power supplies.
• Expensive, often costing hundreds of dollars.
• Responsivity is affected by magnetic fields, necessitating magnetic shielding in sensitive applications.
• May require cooling to liquid nitrogen (LN2) temperatures for noise reduction in critical applications.