Real-Time Dynamic Atomic Spectroscopy Using Electro-Optic Frequency Combs

Spectroscopy is a key technology for both fundamental and applied science. A long-held desire has been the development of a means to continuously acquire broadband spectral data with simultaneous high time and frequency resolution. Frequency-comb technology can open this door: here, we use a spectroscopic technique based on an electro-optic comb to make continuous observations of cesium vapor across a 3.2-GHz spectral bandwidth with a 2-mu s time resolution and with 10-MHz frequency sampling. We use a rapidly switched pump laser to burn narrow features into the spectral line and study the response to this step perturbation. This examination allows us to see a number of unexpected effects, including the temporal evolution of the bandwidth, the amplitude, and the frequency of these burnt features. We also report on the previously unobserved effect of radiation reabsorption, which slowly produces a broad pedestal of perturbation around each feature. We present models that can explain these dynamical effects.