Gas species monitor system

A gas species monitor system comprising:

• a sample volume for receiving a gas to be monitored;
• an external, independent laser source:
• means for directing the laser radiation to said volme;
• a multipass optical cell, responsive to said means for directing, for multiplying the laser radiation intensity in the sample volume;
• means for sensing the intensities of the laser radiation at said laser source and in said multipass optical cell after the beam of laser radiation has made predetermined number of reflections in said multipass optical cell through said sample volume;
• means for comparing said intensities of the laser radiation at said laser source and in said multipass cell to determine whether a system fault is present;
• means, responsive to said means for sensing, for controlling the power output of said laser source to maintain a predetermined value of power output;
• means for continuously flowing the gas to be monitored through the sample volume;
• a narrow bandbass filter;
• means for collecting more than a steradian of Raman scattered radiation from the sample in the volume and directing the collected radiation in parallel through said narrow bandpass filter;
• and
• means, responsive to the parallel radiation from the filter, for detecting and quantifying scattered radiation representative of the concentration of the species in the gas sample being monitored.