Narrow-Linewidth Operation of Diode-Laser-Pumped Nonplanar Ring Oscillators

Abstract

The search for gravity waves, improved tests of relativity theory, advances in high resolution spectroscopy, and optical frequency standard development impose stringent requirements on the linewidth and frequency stability of lasers. Most efforts to produce narrow linewidth lasers have focused on He-Ne, dye, argon ion, or semiconductor lasers. These lasers exhibit free-running linewidths ranging from tens of kilohertz to several gigahertz and thus require wideband servo techniques for narrow linewidth operation [1]. Diode-laser-pumped monolithic solid-state lasers, on the other hand, can have free-running linewidths of a few kilohertz [2, 3], which makes them attractive candidates for narrow linewidth operation using low bandwith servo techniques. The short-term free-running stability is attributed to the small size and rigidity of the monolithic laser, which makes the optical cavity resistant to acoustical excitation, and to the low noise and efficiency of the diode laser pumping. Of particular interest are the diode-laser-pumped monolithic NonPlanar Ring Oscillators (NPROs) that overcome the problems of spatial hole burning and sensitivity to optical feedback inherent in linear cavity lasers [3, 4, 5]. Here we present our current NPRO design and explain its properties, discuss our recent narrow linewidth results obtained by locking a pair of diode-laser-pumped Nd:GGG NPROs to an optical cavity, and speculate about future developments.