5.4 Suppose we are measuring second harmonic generation when pulsing a laser on a solid. However, the detector we have available is only a threshold detector and the time resolution is such that it can only tell us whether or not there were any second harmonic photons on that pulse. Assume the generated second harmonic photons have a Poisson distribution. Show that by using a number of pulses and measuring the probability of count(s) versus no count, we can measure the average number of second harmonic photons per pulse. (In practice, this method was used successfully over a range of six orders of magnitude of intensity of the final photons.)