A plasma ashing apparatus for removing organic matter from a substrate including a low k dielectric, comprising a first gas source; a plasma generating component in fluid communication with the first gas source; a process chamber in fluid communication with the plasma generating component; an exhaust conduit in fluid communication with the process chamber; wherein the exhaust conduit comprises an inlet for a second gas source and an afterburner assembly coupled to the exhaust conduit, wherein the inlet is disposed intermediate to the process chamber and an afterburner assembly, and wherein the afterburner assembly comprises means for generating a plasma within the exhaust conduit with or without introduction of a gas from the second gas source; and an optical emission spectroscopy device coupled to the exhaust conduit comprising collection optics focused within a plasma discharge region of the afterburner assembly. An endpoint detection process for an oxygen free and nitrogen free plasma process comprises monitoring an optical emission signal of an afterburner excited species in an exhaust conduit of the plasma asher apparatus. The process and apparatus can be used with carbon and/or hydrogen containing low k dielectric materials.