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

Femtosecond interferometry combined with acousto-optical phase modulation is an effective approach to implement various types of coherent nonlinear and multidimensional spectroscopy schemes. The high sensitivity of this method has recently enabled the study of highly dilute gaseous and ultracold quantum systems for which the attainable spectral resolution is of particular interest. Here, we directly compare the performance and spectral resolution between two experimental implementations, that are step-wise and continuous rapid scanning of the underlying Fourier transform 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.