Analysis of gas dispersed in scattering media

Monitoring of free gas embedded in scattering media, such as wood, fruits, and synthetic materials, is demonstrated by use of diode laser spectroscopy combined with sensitive modulation techniques. Gas detection is made possi ble by the contrast of the narrow absorptive feature of the free-gas molecu les with the slow wavelength dependence of the absorption and scattering cr oss sections in solids and liquids. An absorption sensitivity of 2.5 x 10(- 4), corresponding to a 1.25-mm air column, is demonstrated by measurements of dispersed molecular oxygen. These techniques open up new possibilities f or characterization and diagnostics, including internal gas pressure and ga s-exchange assessment, in organic and synthetic materials. (C) 2001 Optical Society of America. OCIS codes: 300.6360, 290.7050, 290.5820, 170.3660, 02 0.3690, 160.4890.