Midinfrared sensors meet nanotechnology: Trace gas sensing with quantum cascade lasers inside photonic band-gap hollow waveguides

An integrated midinfrared sensing system for trace level (ppb) gas analysis combining a quantum cascade laser with an emission frequency of 10.3 mu m with a frequency matched photonic band-gap hollow core waveguide has been developed, demonstrating the sensing application of photonic band-gap fibers. The photonic band-gap fiber simultaneously acts as a wavelength selective waveguide and miniaturized gas cell. The laser emission wavelength corresponds to the vibrational C-H stretch band of ethyl chloride gas. This sensing system enabled the detection of ethyl chloride at concentration levels of 30 ppb (v/v) with a response time of 8 s probing a sample volume of only 1.5 mL in a transmission absorption measurement within the photonic band-gap hollow core waveguide, which corresponds to a sensitivity improvement by three orders of magnitude compared to previously reported results obtained with conventional hollow waveguides. (c) 2005 American Institute of Physics.