Abstract

It was shown that the fluctuations of the output power of a dye laser are principally due to the noise of the argon pump laser.¹ A noise reduction of the pump laser will therefore improve the stability of the dye laser. We have been able to experimentally improve the signal-to-noise ratio of a cw multilongitudinal-mode argon laser without power loss. This reduction is achieved by reinjecting a small fraction of the output pump laser beam back into the laser cavity as in the experiment of Beaud.² A photorefractive BaTiO₃ crystal is used as a phase-conjugating mirror to form the external cavity. The advantages of this mirror over a conventional mirror is its self-alignment and the ease with which the feedback it produces can be measured. Even a very small feedback leads to an appreciable noise reduction. 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. The reduction is obtained with an external cavity shorter or longer than the laser cavity between 5 and 10 cm. The optimum stabilization occurs when the difference between the cavity lengths is ~8 cm.

© 1991 Optical Society of America