Trace analysis in gases by laser-induced Schlieren technique

Spectral quasi-coincidences between absorption lines of molecules and laser-emission lines have been widely used for the detection of pollutants. We describe a new detection scheme which exploits the fact that an absorbed laser beam creates a change of refractive index in the gas because of heating. This change is monitored by a second laser beam with different wavelength intersecting the first one. The capabilities of this method include high sensitivity, high spatial resolution and contact-free operation. © 1979.