Gain and noise characteristics of a continuous-wave Raman laser

Abstract

The spectrum of the stimulated electronic Raman gain at 650 nm in Ne I, pumped by a 633-nm He–Ne cw laser in the same cavity, is derived. The question of the proper Raman-gain linewidth is addressed. It is shown that the gain has a nearly Doppler-free component whose width is measured as 30 ± 10 MHz (FWHM) at 6 Torr. This value agrees reasonably well with the residual Doppler broadening but not with collisional broadening rates. A simple calculation is included that shows the quantum-limited frequency uncertainty of the 650-nm laser to be higher by a factor of 1.5 than the frequency uncertainty of the 633-nm laser at equal power.