Long-term stability of two diode-laser-pumped nonplanar ring lasers independently stabilized to two Fabry-Perot interferometers.

We have locked two 1064-nm diode-laser-pumped Nd:YAG lasers to two ultralow-expansion glass-ceramic Fabry-Perot interferometers by using the Pound-Drever discriminator technique. The interferometers have finesses of approximately 200,000 and 5-kHz linewidths and are housed in separate temperature-stabilized vacuum vessels. Allan variance measurements of the beat note between the two lasers are as low as 10(-14) for delay times between 0.5 and 2 s and increase with the time interval for times longer than 2 s, an improvement of 4 orders of magnitude over the free-running performance. Daily variations of the beat-note frequency are less than 1 MHz, which corresponds to a relative temperature change of approximately 100 mK between the interferometers.

Stabilization of laser beam alignment to an optical resonator by heterodyne detection of off-axis modes.

We demonstrate a method for real time alignment of a Gaussian beam to an optical resonator. While thefrequency of a source laser is stabilized to a fundamental cavity mode resonance, phase modulation sidebands are applied at the off-axis mode frequencies. Asymmetrical transmission of the sideband at the frequency of each off-axis mode produces amplitude modulated optical signals and indicates the extent of the misalignments. Phase sensitive detection of these optical signals provides the error signals which are minimized by a control system that steers the input beam. In this way, optimum coupling of an injected source beam can be maintained to the fundamental mode of the resonator. This active alignment technique has demonstrated a sensitivity to tilts of 0.1 nrad/ radicalHz and to lateral beam displacements of 0.08 nm/ radicalHz in the ~1-Hz-1-kHz frequency range. These values correspond to 2 parts in 10(7) radicalHz for both the far-field divergence angle and the beam waist size. Such performance is within a factor of 2 of the shot noise limitation of the error signal measurement for a detected power of 160 microW.