smaller volumes fill up faster. For example, Charlton et al. [65] used a photonic
band-gap hollow-core fiber to detect ethyl chloride at concentration levels of
30 ppb with a sample volume of 1.5 ml, and a response time of 8 seconds,
representing an increase in sensitivity by almost three orders of magnitude over
conventional gas cells.
Hollow-core fibers have also enabled many impressive accomplishments in
nonlinear optics. For example, stimulated Raman scattering has been observed
in hollow-core PCFs filled with hydrogen gas, with up to 92% quantum effi-
ciency and threshold pulse energies six orders of magnitude lower than what was
previously reported [66, 67]. In addition, slow-light effects have been observed in
acetylene-filled hollow-core PCFs ...