NOISE-REDUCTION IN AN ARGON-LASER WITH A PHASE-CONJUGATING EXTERNAL CAVITY

The reinjection of a small fraction of the output beam back into the laser cavity is shown to improve the signal-to-noise ratio of a cw multilongitudinal mode Ar+ laser efficiently. The argon laser is coupled to an external cavity terminated by a phase-conjugate mirror in order to obtain a self-aligned coupled cavity. With the external cavity, the signal-to-noise ratio has been significantly improved. The low-frequency noise components are reduced by up to 15 dB, and the frequency components of the spectrum of the longitudinal-mode beating are attenuated by factors reaching 46 dB.