Toward precision measurements of methane with interband cascade lasers

Abstract

Measurement of the isotopic composition of atmospheric methane is a valuable tool for understanding the sources and sinks of the global carbon budget. One promising carbon isotope ratio measurement technology is optical spectroscopy using inter-band cascade (IC) lasers. Ongoing development of these light sources has the goal of providing, from a package operating near room temperature, a single mode laser source in the wavelength range of 3 &mgr;m. The spectral features of methane are sufficiently strong at this wavelength that a path length of about 100 m should suffice for measuring 12- and 13-C isotopes in air without pre-concentrating the sample. Experimental IC lasers are described and their use for isotope sensing by wavelength modulation spectroscopy is evaluated.