Abstract: A detection system for detecting the emission (i.e., the fluorescence or phosphorescence) from a contaminant contained in a sample gas. In order to keep the optics of the system clean and maintain a high signal-to-noise ratio in the detected signal, the detection system contains a housing separated into illumination and sample chambers by an aperture-containing partition. A sample inlet port is connected to the sample chamber, and a purge inlet port is connected to the illumination chamber to direct the purge and sample gasses into their respective chambers. A vacuum system is connected to a vacuum port on the sample chamber to simultaneously draw the sample and purge gasses into their chambers through the inlet ports; the purge gas is then drawn through the aperture and into the sample chamber. Finally, both gasses are drawn out of the sample chamber through the vacuum port.