Saturation Spectroscopy of Iodine in Hollow-core Optical Fibre
  We present high-resolution spectroscopy of Iodine vapour that is loaded and trapped within the core of a hollow-core photonic crystal fibre (HC-PCF). We compare the observed spectroscopic features to those seen in a conventional iodine cell and show that the saturation characteristics differ significantly. Despite the confined geometry it was still possible to obtain sub-Doppler features with a spectral width of ~6 MHz with very high contrast. We provide a simple theory which closely reproduces all the key observations of the experiment. 
Anna Lurie, Philip S. Light, James Anstie, Thomas M. Stace, Paul C.   Abbott, Fetah Benabid, Andre N. Luiten
physics.optics