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.