Velocity-selective direct frequency-comb spectroscopy of atomic vapors

Abstract

We present an experimental and theoretical investigation of two-photon direct frequency-comb spectroscopy performed through velocity-selective excitation. In particular, we explore the effect of repetition rate on the $5{S}_{1/2}\ensuremath{\rightarrow}5{D}_{3/2,5/2}$ two-photon transitions excited in a rubidium atomic vapor cell. The transitions occur via stepwise excitation through the $5{P}_{1/2,3/2}$ states by use of the direct output of an optical frequency comb. Experiments were performed with two different frequency combs, one with a repetition rate of $\ensuremath{\approx}925$ MHz and one with a repetition rate of $\ensuremath{\approx}250$ MHz. The experimental spectra are compared to each other and to a theoretical model.