[PhD Thesis Presentation] ‐ Thomas Nieddu - Optical Nanofibers for Multiphoton Processes and Selective Mode Interactions with Rubidium

ABSTRACT:

Optical nanofibers (ONF) have been proved useful tools to probe cold atomic systems. Due to the intense evanescent field at their waist, ONFs have been used to probe or even trap atoms. However, very little experimental work has been done on exploiting the higher order modes (HOM) of such devices. The HOMs feature inhomogeneous polarization distributions around the ONF’s waist and can lead to the guiding of light carrying orbital angular momentum (OAM), via selective excitation of modes. Using modal decomposition at the output of the ONF, a transfer matrix of the atom-nanofiber system can be calculated. This information, when combined with the amplitude extinction resulting from the scattering of the guided light by the cold atomic ensemble surrounding the waist, allows to non-destructively infer the modal excitation at the waist of the ONF. In addition, ONFs feature high field intensities capable of triggering nonlinear optical effects in the surrounding atomic medium, even for input powers lower than the micro-watt. This latter property has allowed us to study fiber-induced Autler-Townes splitting and stimulated emission using a single-color two-photon excitation.