Molecular gas analysis by raman scattering in intracavity laser

Abstract

The concentration of multiple polyatomic gases are determined almost simultaneously by Raman scattering. The gas sample is placed in a sampling cell located in the resonance cavity of a laser and a polarized laser beam having sufficient intensity to produce detectable signals of Raman scattered light is passed through the cell. The scattered light is captured and redirected by means of a reflection mirror located parallel to the axis of the laser beam adjacent to and outside of the cell. Signals of both inelastic Raman scattered light and elastic laser scattered light are collected by a collection lens means opposite the reflection mirror and outside the gas cell. The collection lens is also parallel to the axis of the laser beam. The collected scattered signals are directed onto a laser line rejection filter where the scattered elastic laser signals are filtered out and the inelastic Raman scattered signals are transmitted to come in contact with a rotating filter wheel containing a series of interference filters with each filter being specific to the transmission of one Raman line. The Raman lines passing through the rotating filters are sensed sequentially by a single detector means and amplified and converted into digital electrical pulses which are processed and converted into visual readouts indicative of the concentration of each of the polyatomic molecules in the gas being determined.