Spectral broadening of a single-photon transition in the evanescent field of an exposed-core fiber

Abstract

We theoretically and experimentally examine the spectroscopy of warm atoms traversing the evanescent field of a guided mode in silica glass. The subwavelength scale of the evanescent field leads to a large spectral broadening dominated by transit-time dephasing, creating a lineshape quite different from that of atoms in free space, and also distinct from that arising from transit-time-limited interactions in a field with a Gaussian intensity profile. We show reasonable agreement between our modeling of this scenario and experimental D2-line spectra obtained from an exposed-core fiber immersed in rubidium vapor.