High-resolution rapid-scanning Fourier transform spectroscopy of ultracold atoms

Femtosecond (fs) interferometry combined with acousto-optical phase modulation is an effective approach to implement various types of coherent nonlinear and multidimensional spectroscopy schemes. Here, we focus on gaseous and ultracold samples and compare directly the performance and spectral resolution between two experimental implementations of the phase modulation technique, which are stepwise and continuous rapid scanning of the underlying Fourier transform (FT) interferometers. We show the performance advantage of the rapid-scanning approach and demonstrate a spectral resolution of 250 MHz in the spectroscopy of laser-cooled Li atoms. This is a 10-fold resolution improvement compared to previous experiments.