Monitoring an effluent from a chamber

The invention relates to the monitoring of an effluent from a process chamber. An effluent monitoring apparatus comprising an energizing cell adapted to receive an effluent, a gas energizer that is capable of energizing the effluent in the cell thereby emitting a radiation, a radiation permeable window that is spaced apart from the wall of the cell by a distance d that is sufficiently high to reduce a deposition of effluent residue from the energized gas on the window , and a detector to detect the radiation.