OPTICAL HETERODYNE SPECTROSCOPY ENHANCED BY AN EXTERNAL OPTICAL CAVITY - TOWARD IMPROVED WORKING STANDARDS

We study the use of an external resonator to enhance sub-Doppler signals observable with the high sensitivity techniques of optical heterodyne spectroscopy. The case of modulation-transfer spectroscopy in a ring resonator is considered in detail. By exciting the I-127(2) resonance at 612 nm with a low-power He-Ne laser, we observed a S/N of 250:1 in a 10 kHz bandwidth. Used in an optimal control loop, this performance would provide a laser stability of 10 Hz at 1 s. Such a > hundredfold improvement in stability should lead to interesting increases in accuracy as well.