Modal content and noise characteristics of a cw argon ion laser with an optical feedback: Numerical simulations of experimental results

We have shown that significant reduction of the optical noise can occur in a cw argon ion laser when the laser cavity is coupled to an empty external cavity. When the external cavity was terminated by a phase conjugate mirror, noise reduction reaching 15 dB for the frequency components below 1 MHz and reaching 58 dB at the frequencies of the beating of the longitudinal modes has been observed experimentally. It was also possible to reduce the number of oscillating longitudinal modes from ∼40 to 2 without loss of optical power. A numerical model taking into account the description of the lineshape by a Voigt profile and the presence of an optical feedback has been developed. The numerical results were found to be in good agreement with experimental results.