Threshold characteristics and intensity fluctuations of lasers with excess quantum noise

We discuss the threshold characteristics and intensity noise of a laser with excess quantum noise as occurs, e.g., in an unstable-cavity laser. We give a theoretical description of the intensity aspects of excess noise based on laser rate equations, including bad-cavity effects. Experimentally, we have measured spectra of intensity noise and phase noise of small HeXe gas lasers. We operate the laser on either a stable or an unstable cavity, in order to change from a situation of no excess noise to large excess noise. By comparing the measured spectra with the theory, we deduce the excess-noise factor $K$ and the spontaneous-emission factor β.