A proposal for optical high-accuracy atomic references using thin cell spectroscopy

We analyze here a scheme for sub-Doppler spectroscopy of an atomic transition connecting a ground state level with a metastable one, which exploits the asymmetric absorption properties of a single pump beam, propagating along the axis of a shallow cell. If the metastable lifetime is large enough, the interaction between the atom and the resonant radiation is interrupted mainly by the collisions against the walls, and only atoms with a small longitudinal velocity component interact with radiation long enough to undergo a transition, producing sub-Doppler selective excitation. Possible application to optical atomic reference standard is discussed, based on alkali-earth atom forbidden transitions.