Quantum-cascade laser measurements of stratospheric methane and nitrous oxide

A tunable quantum-cascade (QC) laser has been flown on NASA's ER-2 high-alt itude aircraft to produce the first atmospheric gas measurements with this newly invented device, an important milestone in the QC laser's future plan etary, industrial, and commercial applications. Using a cryogenically coole d QC laser during a series of 20 aircraft flights beginning in September 19 99 and extending through March 2000, we took measurements of methane (CH4) and nitrous oxide (N2O) gas up to similar to 20 km in the stratosphere over North America, Scandinavia, and Russia. The QC laser operating near an 8-m um wavelength was produced by the groups of Capasso and Cho of Bell Laborat ories, Lucent Technologies, where QC lasers were invented in 1994. Compared with its companion lead salt diode lasers that were also flown on these fl ights, the single-made QC laser cooled to 82 K and produced higher output p ower (10 mW), narrower laser linewidth (17 MHz), increased measurement prec ision (a factor of 3), and better spectral stability (similar to0.1 cm(-1) K). The sensitivity of the QC laser channel was estimated to correspond to a minimum-detectable mixing ratio for methane of approximately 2 parts per billion by volume. (C) 2001 Optical Society of America OCIS codes: 010.0010 , 120.0120, 140.0140, 300.0300.