Toward the realization of a frequency standard at 1.5 μm based on narrow-linewidth erbium lasers and saturated acetylene lines

The work is aimed at the study and development of a high-accuracy frequency standard at 1.5 μm, by combining the intrinsic frequency stability of a solid-state laser to the accuracy and reliability of Doppler-free molecular lines. A diode-pumped Er-Yb microlaser is frequency stabilized to the center of ¹³C₂H₂ saturated absorption lines by means of the frequency modulation technique. A resonant Fabry-Perot cavity containing acetylene at low pressure is used to enhance the field intensity in order to saturate the 1.5 μm overtone transitions of the molecule. Two stabilization loops are used to lock the Fabry-Perot cavity to the laser frequency and this last to the peak of the saturation dip. Preliminary experimental results on the Er-Yb laser frequency noise are reported