Abstract

A long-path absorption cell was developed for the measurement of gaseous contaminants in the atmosphere and for the studies of reactions of contaminants in the laboratory. The instrument is based on the White multiple-reflection system, having two large spherical mirrors at one end of the 3-meter cell and one smaller one at the other end of equal radius. To avoid excessive loss of radiant energy, the infrared source image is magnified and demagnified to match the cell to the spectrometer. Optimum path-length for maximum signal is reached when reflection losses reduce the energy to 1/e of its initial value. CO₂ and water vapor interfere with, but do not prohibit, useful analyses of the atmosphere. Two of these cells are in use, one in the Philadelphia laboratory and one in a field-study trailer in the Los Angeles area.

Very long optical paths in air

John U. White
J. Opt. Soc. Am. 66(5) 411-416 (1976)

Air pollution measurement by Fourier transform spectroscopy

Philip L. Hanst
Appl. Opt. 17(9) 1360-1366 (1978)

Mid-infrared dual-comb spectroscopy of volatile organic compounds across long open-air paths

Gabriel Ycas, Fabrizio R. Giorgetta, Kevin C. Cossel, Eleanor M. Waxman, Esther Baumann, Nathan R. Newbury, and Ian Coddington
Optica 6(2) 165-168 (2019)

Long-Path Study of Infrared Absorption and Emission

D. J. Lovell and John Strong
Appl. Opt. 8(8) 1673-1676 (1969)

Mobile Fourier-transform infrared spectroscopy monitoring of air pollution

R. Haus, K. Schäfer, W. Bautzer, J. Heland, H. Mosebach, H. Bittner, and T. Eisenmann
Appl. Opt. 33(24) 5682-5689 (1994)