Multi-channel molecular gas analysis by laser-activated raman light

Abstract

The concentration of multiple polyatomic gases are determined simultaneously by Raman light scattering. The gas sample is placed in a sampling cell and a polarized laser beam is passed through the cell, along a longitudinal axis. A portion of the light scattered by the gas sample is captured and detected by means of multiple collection optics-filter-detector channels. The scattered light exits the gas cell via windows located in the sides of the gas cell and enters the collection channels which are aligned with the cell windows. The cell windows are along the longitudinal axis of the laser beam and gas cell. Light scattered by the gas sample provides signals of both inelastic Raman scattered light and elastic laser scattered light which are directed to the collection channels. The optics of each channel transports the scattered light signals onto a laser line rejection filter where the elastic scattered laser signals are attenuated. The remaining inelastic Raman scattered signals are caused to be incident upon an interference filter which is specific to the transmission of one or more specific Raman lines. The interference filter in each collection channel is selected to a specific wavelength which is characteristic of Raman scattering from a particular polyatomic gas. The optical signals representative of these specific Raman lines passing through the interference filters are sensed by optical detectors, and amplified and converted into digital electrical pulses which are processed into simultaneous visual readouts indicative of the identity and concentration of each of the polyatomic gas molecules present in the sample of gas being analyzed.