The Laser Illuminated Absorptivity Spectrophone: A Method for Measurement of Weak Absorptivity in Gases at Laser Wavelengths

Abstract

A spectrophone measures absorptivity by sensing thermal expansion in a confined sample gas. Laser source excitation provides sufficient radiation to measure precisely very weak absorptivities at laser wavelengths. This paper describes the theoretical capability, design considerations, and experimental testing of a pulsed ruby laser absorptivity spectrophone and a cw CO(2) laser absorptivity spectrophone. A spectrum of the water vapor line at 6943.8 A was obtained. The peak absorptivity was 3 x 10(-6)cm(-1). In the vicinity of 9.6 micro, absorptivities of CO(2)-N(2) mixtures were measured down to 1.2 x 10(-7)cm(-1).

CO Laser Absorption Coefficients for Gases of Biological Relevance: H2O, CO2, Ethanol, Acetaldehyde, and Ethylene

“…Measured absorption coef-® cients for CO 2 and H 2 O agree reasonably well with data in the Hitran database. For laser lines showing multiple emission or having an intracavity power below about 0.3 W, agreement is less favorable.…”

Detection of Greenhouse Gases Using the Photoacoustic Spectroscopy

“…Since the 1960s, the development of Lasers, sensitive microphones and lock-in amplifiers permitted this technique to have a great technical development. In 1968, L. B. Kerr and J. G. Atwood conducted the first photoacoustic experiments using Laser as the radiation source (Kerr & Atwood, 1968). Using a continuous wave CO 2 laser as excitation source, they achieved a minimum absorption coefficient of 1.2 x 10 -7 cm -1 of CO 2 diluted in nitrogen.…”

CO2 Laser Photoacoustic Spectroscopy: I. Principles

“…This laser linewidth is usually much smaller than the molecular absorption linewidth (GHz region at atmospheric pressure), and therefore it is not an important issue in most measurements. A true revival of PA spectroscopy was due to Kerr and Atwood (Kerr & Atwood, 1968), who made the earliest experiments with a laser illuminated PA detector in 1968, and Kreuzer (Kreuzer, 1971), who first measured gas concentrations using a PA detector and a laser in 1971. Later experiments by Kreuzer and collaborators (Kreuzer & Patel, 1971;Kreuzer et.…”