Johnson, T.J.Wienhold, F.G.Burrows, J.P.Harris, G.W.2010-06-112010-06-111991Applied Optics, 30, 407-413.http://hdl.handle.net/10315/4199Two-tone frequency modulation spectroscopy has been used in conjunction with InGaAsP lasers in the 1.3¬,um region to monitor weak water vapor absorptions in a long path White cell. Detection electronics that reduce the effect of Johnson noise are described. The system was capable of detecting optical densities corresponding to <1.7 X 10-6 in a 1-Hz bandwidth. Factors limiting the difference between observed and shot noise limited performance for these types of laser and condition are discussed.enFrequency modulation spectroscopytunable diode lasersArticlehttp://www.opticsinfobase.org/ao/Issue.cfm