A simple rubidium-stabilised laser diode for interferometric applications

The output frequencies of some commercially available index-guided laser diodes have been stabilised to the linear absorption maxima of the rubidium D lines (780 nm and 795 nm). The linewidth of these lasers was determined to be approximately=30 MHz (FWHM) from interferometric fringe visibility measurements, equivalent to a coherence length of a few metres. Allan variance measurements were made on the beat between two Rb-stabilised lasers, and the stability found to be 4*10 -10 of the optical frequency at tau =1 s. The reproducibility is approximately 3 parts in 10 8 of the optical frequency, using a peak-to-peak modulation depth of 100 MHz. The frequencies of these stabilised lasers have been measured by interferometry to +or-1*10 -7 (3 sigma uncertainty) of the optical frequency. Doppler-free saturated rubidium spectra have been observed in a third derivative form.