title: Dual quantum cascade laser trace gas instrument with astigmatic Herriott cell at high pass number.
abstract: We have developed and demonstrated a high-sensitivity trace gas instrument employing two mid-infrared quantum cascade lasers and an astigmatic Herriott sample cell with up to a 240 m path length. Several aspects of astigmatic Herriott cell optics have been addressed to enable operation at a high pass number (up to 554), including aberrations and pattern selection to minimize interference fringes. The new instrument design, based on the 200 m cell, can measure various atmospheric trace gases, depending on the installed lasers, with multiple trace gases measured simultaneously. Demonstrated concentration noise levels (1 s average) are 40 parts per trillion [(ppt) 10(-12)] for formaldehyde, 10 ppt for carbonyl sulfide, 110 ppt for hydrogen peroxide (H2O2), and 180 ppt for nitrous acid (HONO). High-precision measurements of nitrous oxide and methane have been recorded at the same time as high-sensitivity measurements of HONO and H2O2.
authors.affiliation: Aerodyne Research, Inc., Billerica, Massachusetts 01821-3976, USA. mcmanus@aerodyne.com
authors.forename: J Barry
authors.initials: JB
authors.lastname: McManus
authors.forename: Mark S
authors.initials: MS
authors.lastname: Zahniser
authors.forename: David D
authors.initials: DD
authors.lastname: Nelson