Measurements of the laser linewidth due to quantum phase and quantum amplitude noise above and below threshold. I

Abstract

The natural linewidths and line shapes due to quantum phase and quantum amplitude noise have been investigated above, within and below the threshold region of laser operation using a Fourier spectroscopic technique. Outside the threshold region the linewidths of the laser spectrum were found to be inversely proportional to the laser power, and measurements confirm the “factor of two” difference in the linewidth equation. Within the threshold region the results are in agreement with calculations of Hempstead, Lax and Risken. A Mach-Zehnder interferometer with optical path differences up to 1500 meters was used for the measurements. The method of investigation combines a high spectral resolution with a good signal-to-noise ratio. The method is suited to linewidth measurements of a laser both above and below threshold and allows the technical and natural linewidths to be clearly distinguished.