METHOD AND APPARATUS FOR ANALYSIS OF GAS BY SEMICONDUCTOR-LASER MULTIPLE-REFLECTION ABSORPTION SPECTROSCOPY

摘要

PROBLEM TO BE SOLVED: To provide a method and an apparatus, for the analysis of a gas by semiconductor- laser multiple-reflection absorption spectroscopy, in which an optical interference noise is reduced and in which a high-sensitivity performance is provided. ;SOLUTION: In a spectroscopic analytical method, in the multiple-reflection absorption spectroscopic analysis of a gas by a semiconductor laser beam, a reflecting mirror M1, a reflecting mirror M2 and a reflecting mirror M3 in a multiple-reflection sample cell 7 on which a first laser beam B1 is projected are arranged according to an expression of L.W02.5 in a relationship that the arrangement distance between the reflecting mirror M1 and the reflecting mirrors M2, M3 is designated as L (cm) and that the line width of a quadratic differential absorption spectrum under an optimum condition under which the S/N ratio of the absorption spectrum of an absorption beam B1A passing the multiple-reflection sample cell 7 becomes maximum is designated as W0, a part of a projection laser beam is divided so as to form a second semiconductor laser beam B2, its quadratic differential spectrum is collected, the spectrum is subtracted from the quadratic differential absorption spectrum of the absorption beam B1A passing the multiple-reflection sample cell 7, and a light source noise to the multiple-reflection sample cell 7 is reduced. A spectroscopic analyser is provided with a mechanism which executes the method.;COPYRIGHT: (C)2001,JPO