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.