Berlin 2001 – scientific programme
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Q: Quantenoptik
Q 25: Quantum Effects II
Q 25.6: Talk
Thursday, April 5, 2001, 17:00–17:15, H 3010
Quantum-limited linewidth of a good-cavity laser: An analytical theory from near to far above threshold — •Ulrike Herzog1 and János A. Bergou2 — 1Institut für Physik, Humboldt-Universität zu Berlin, Invalidenstr. 110, D-10115 Berlin — 2Department of Physics, Hunter College, City University of New York, 695 Park Avenue, New York, NY 10021
The problem of the quantum-limited or intrinsic linewidth of a good-cavity laser is revisited. Starting from the Scully-Lamb master equation, we develop an analytical approximation method which implicitly incorporates the microscopic fluctuations of both the phase and intensity of the field, and, in addition, takes full account of the saturation of the nonlinear gain. Our main result is a simple formula for the quantum-limited linewidth which is valid from near to far above threshold [1]. Close to the threshold, the linewidth is twice as large as predicted by the standard phase-diffusion treatment neglecting intensity fluctuations. Quantum fluctuations of the intensity are present and continue to influence the linewidth as long as the photon-number distribution is not strictly Poissonian. This inherent relationship is displayed by a formula relating the linewidth and the Mandel Q-parameter. More than 100% above threshold the linewidth is found to be smaller than predicted by the standard treatment, since the simple phase-diffusion model increasingly overestimates the rate of phase fluctuations by neglecting gain saturation. In the limit of a very large mean photon number the expected perfectly coherent classical field is obtained.
[1] U.Herzog and J. A. Bergou, Phys. Rev. A 62, 063814 (2000)