This document discusses three types of photon detectors: photovoltaic cells, phototubes, and photomultipliers. Phototubes use a photocathode and anode to measure photon flux by current flow. Photomultipliers consist of a photocathode, dynode stages, and gain up to 109 electrons per photon through secondary electron emission across multiple dynode stages. Photovoltaic cells convert photons to electricity using a barrier layer.

2. Detector
Barrier Layer/Photovoltaic

3. Photovoltaic cell/photronic cell

4. Principle of Barrier Layer/Photovoltaic
Detector

5. Detector
Phototube

6. Photo tubes

7. Principle of Phototube Detector
• This detector is a vacuum tube with a cesium-
coated photocathode.
• Photons of sufficiently high energy hitting the
cathode can dislodge electrons, which are
collected at the anode.
• Photon flux is measured by the current flow in
the system.

8. Detector
Photomultiplier

9. Photo emissive cell

10. Principle of Photomultiplier
Detector
• The type is commonly used.
• The detector consists of a photoemissive
cathode coupled with a series of electron-
multiplying dynode stages, and usually called
a photomultiplier.
• The primary electrons ejected from the photo-
cathode are accelerated by an electric field so
as to strike a small area on the first dynode.

11. of Photomultiplier Detector
• The impinging electrons strike with enough
energy to eject two to five secondary electrons,
which are accelerated to the second dynode to
eject still more electrons.
• A photomultiplier may have 9 to 16 stages, and
overall gain of 106~109 electrons per incident
photon.