All-optical microwave frequency standard: a proposal

A simple method to produce a clock transition with purely optical means by modulated pumping is described. The field-independent ground state resonance of /sup 87/Rb atoms using sinusoidal modulation of the injection current of an AlGaAs laser diode emitting at 780 nm (FM modulation) is observed. The 6.835 GHz resonance with a subharmonic modulation frequency of 1.139 GHz is detected. A high-contrast resonance peak is observed and a condition for zero light shift is found. The linewidth is 3 kHz (at 6.835 GHz) in this preliminary experiment, due to the small size of the light beam ( approximately 2 mm diameter) and the low buffer gas pressure (680 Pa) that was used. A theoretical model that explains the main features of the experiment is described.<
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