Question

A PMT has 10 dynodes. At each dynode one incoming primary electron
creates four secondary electrons. The PMT is used to detect a faint laser
beam that is operating at 632.8 nm. The quantum efficiency of the cathode at
this wavelength is 25 %. The laser power incident on the PMT is 1nW.
(a) Show that the number of incident photons per second at the cathode is
3.19 × 109 photons/s. Recall that power is equal to photon energy times
the number of arriving photons per second.
(b) Show that 7.97 × 108 photoelectrons are generated at the cathode per
second.
(c) Show that the gain of this PMT is 1048576.
(d) The anode current is the cathode current multiplied by the gain of the
PMT. Show that the anode current is 133.6 μA. Recall that
q = 1.6 × 10−19 C.

Answer 1