Spontaneous Emission Enhanced Spectroscopy of Broadened Transitions

Efficient control and manipulation of quantum states as well as molecular spectroscopy for fundamental physics research requires a precise matching of laser frequency to the state transition frequency. Quantifying the laser detuning from resonance is not always a trivial measurement to perform. It is often difficult to measure in experiments performed on atomic ensembles with large Doppler detuning spreads due to temperature, or on atoms and molecules embedded in solids. The measurement can further be complicated in experiments where Doppler-free measurement schemes are not available or where other frequency broadening mechanisms are unavoidable. Under these restrictions, we propose an alternative method to the traditionally used Ramsey spectroscopy method. The new method involves a sequence of laser pulses to build up a cumulative atomic phase in the steady-state limit, consisting of atoms that have undergone spontaneous emission. The cumulative phase is highly sensitive to the detuning of the laser and can be utilized to find a precise zero-detuning laser frequency for an atomic ensemble or similarly broadened state transition.