Two-photon transitions driven by a combination of diode and femtosecond lasers

TL;DR

This paper demonstrates a novel method for velocity-selective two-photon spectroscopy in rubidium vapor using a combined continuous-wave diode laser and femtosecond pulse train, enabling detailed state analysis.

Contribution

It introduces a new experimental scheme combining cw and femtosecond lasers for two-photon transitions, providing enhanced spectral range and selectivity.

Findings

Successful detection of fluorescence from rubidium states

Velocity selectivity achieved over a large spectral range

Results align with a simplified frequency domain model

Abstract

We report on the combined action of a cw diode laser and a train of ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from the 6P_{3/2} state is detected for a fixed repetition rate of the femtosecond laser while the cw-laser frequency is scanned over the rubidium D_{2} lines. This scheme allows for a velocity selective spectroscopy in a large spectral range including the 5D_{3/2} and 5D_{5/2} states. The results are well described in a simplified frequency domain picture, considering the interaction of each velocity group with the cw laser and a single mode of the frequency comb.