Optical frequency standard by HI Doppler-broadened absorption and external-cavity laser diode at 1.541 mu m

An external-cavity laser diode was frequency locked on the molecular absorption line R(3) of hydrogen iodide at 1.541 mu m using the wavelength-modulation technique. Stabilization is realized by means of two feedback loops acting on two different frequency ranges. Measurements of the closed-loop error signal provided a relative frequency stability of a few parts in 10(-10) in a 50-kHz acquisition bandwidth.