Experiments on two-photon absorption in cold 87Rb atoms using an optical nanofiber
Optical nanofibers (ONFs), with subwavelength diameters, have a strong evanescent field around them. When an ONF is combined with a cold atom setup, the surrounding cold atoms can couple to guided modes of the fiber via evanescent field coupling. Here, I will talk about experiments on cold atoms and an optical nanofiber (ONF) to probe 2-photon absorption at a few nanowatts of power. Apart from its spectroscopic importance, this study will be useful for all optical switching and quantum logic gates at low powers.
In our experiment, the ONF is fabricated by the heat-and-pull technique using a hydrogen:oxygen flame. Laser-cooled 87Rb atoms are excited from 5S1/2 →5D5/2 via a 2-photon excitation process using 5P3/2 as an intermediate level. Using a few nanowatts of 780 nm (5S1/2 →5P3/2) and 776 nm light (5S1/2 →5D5/2) through the ONF, the atoms are excited to the 5P3/2 state and thereby spontaneously emit 5.2 µm (5D5/2 →6P3/2) and 420 nm (6P3/2→5S1/2) photons which are coupled to the ONF. We detect the 420 nm fluorescence photons via the ONF and study effects such as Autler-Townes splitting and power broadening in this process for such a system. Two-photon experiments on a Rb vapor will also be discussed.
Host: Luis A. Orozco