Patent ID: 6274879
Filing Date: 2001-08-14
Classification: B01D,G01J,G01N

Abstract:
A process for the quantitative detection of a given gas, the process comprising:irradiating a gas sample, which may contain the given gas as a component, with a single mode diode laser operating free of mode jumps, whose wavelength can be tuned continuously by varying the laser control current;varying the laser control current by a sinus modulation current of a predetermined frequency superimposed to a d.c. component which is slowly varied periodically, so that a laser wavelength range in the area of an absorption line of the given gas is scanned;measuring the intensity of the laser radiation after passing through the gas sample by means of a detector and determining the d.c. component of the detector signal and the second harmonic of the detector signal corresponding to the doubled frequency of the sinus modulation current; andcalculating the concentration of the given gas on the basis of the detector signals, wherein the line width of the absorption line involved in the calculation, which depends on the unknown composition of the gas sample, is determined on the basis of the minimum and maximum of the second harmonic, which are measured during the tuning of the d.c. component of the laser control current.