A processing system having a chamber for in-situ optical interrogation of plasma emission to quantitatively measure normalized optical emission spectra is provided. The processing chamber includes a confinement ring assembly, a flash lamp, and a set of quartz windows. The processing chamber also includes a plurality of collimated optical assemblies, the plurality of collimated optical assemblies are optically coupled to the set of quartz windows. The processing chamber also includes a plurality of fiber optic bundles. The processing chamber also includes a multi-channel spectrometer, the multi-channel spectrometer is configured with at least a signal channel and a reference channel, the signal channel is optically coupled to at least the flash lamp, the set of quartz windows, the set of collimated optical assemblies, the illuminated fiber optic bundle, and the collection fiber optic bundle to measure a first signal.