Enhanced Fundamental Linewidth of a Laser Due to Outcoupling
A laser can be thought of as an amplitude-stabilized oscillator. Such an oscillator has a finite linewidth, due to phase-changing events. In most cases these events have a “technical” origin, such as fluctuations in the cavity length due to acoustic perturbations. However, even in a perfectly stable environment there is still phase diffusion due to spontaneous emission; this leads to the quantum-limited or fundamental linewidth as first discussed by Schawlow and Townes . In recent years it has been shown by others [2,3,4,5] and by us [6,7,8,9] that the standard (Schawlow-Townes) formula for the fundamental linewidth must be modified if the outcoupling through the mirrors is large. In this paper we review our work [6,7,8,9] in this field, starting in section 2 with theory. In section 3 we report on the diagnostics of the semiconductor lasers used in the experiments. The technique of linewidth measurement is discussed in section 4 and actual results are given in section 5, together with a comparison with theory.
KeywordsSpontaneous Emission Semiconductor Laser Phase Diffusion Laser Linewidth Spontaneous Emission Rate
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© Plenum Press, New York 1993