The energy in a laser cavity at threshold affects the time required for the laser to go from threshold to saturation. By determining the statistical distribution of laser turn-on times, i.e., the time required for the laser to undergo its transient from threshold to saturation, the noise distribution in the cavity can be calculated. A phenomenological model is used to analyze the low-level noise in a laser cavity based on the distribution of turn-on times of a pulsed laser. The results of this analysis are used to study the effects of injecting a signal from a cw laser into the cavity of the pulsed laser. A small injected signal shortens the laser transient and changes the shape of the distribution of turn-on times. The method used allows examination of the statistical properties of photons in the cavity without the need for photon counting.