Question

What does a 0.1 photons per pulse mean?

Answer 1

a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron.

Answer 2

"The most common and straightforward way to generate single photons is to use a heavily attenuated pulsed laser. The laser produces some average power with a mean photon number per pulse of N. It is straightforward to use neutral density filters to attenuate the power until N ≤ 1. The drawback to this method is that the photon number distribution obeys Poisson statistics, which means that the probability of getting zero or two photons is also quite high. N is set at 0.1, which means that most of the pulses contain no photons at all."