Frequency fluctuations of a diode-pumped Nd:YAG ring laser

We have measured the spectral density of the frequency fluctuations of a diode-pumped single-mode monolithic Nd:YAG ring aser by locking a Fabry-Perot resonator to the laser frequency. The fluctuations approach the limit due to spontaneous emission (the Schawlow-Townes limit) at frequencies above 80 kHz. The inherent frequency stability of these lasers makes them attractive as a potential light source for gravitational-wave interferometers.