The Interactions Between the Excited States in Stabilized Lasers

Abstract

Stable lasers are necessary as local oscillators in many applications including coherent communications, high resolution spectroscopy and
gravity wave detection. Recent developments in the active stabilization of lasers have led to light sources of extremely narrow linewidth and
correspondingly long coherence times. Such stability enables several new laser measurement techniques. Stabilized lasers can provide a probe of
the interactions between the excited states of laser transitions and the laser cavity itself. Two derivations of the fundamental laser linewidth are
presented that have been used successfully in introductory courses. The cause of the finite linewidth is identified with phase fluctuations in the
electric field due to spontaneous emission. This paper will review frequency modulation techniques for stabilizing lasers, with emphasis on the
relations between the laser linewidth and random processes within the lasing medium. An experiment to test stabilized lasers in the vibration free
and microgravity environment of space and applications of ultra-stable lasers in space will be described.