Characteristics of the light emission from CVD diamond windows

Video and infrared signals were registered from brazed and bare CVD diamond disks forming the windows of an evacuated transmission cell placed into the beam line of a high power gyrotron facility at 140 GHz (Maquette tube). Intense light emission forming spot-like patterns, that was observed under vacuum conditions, has a broad maximum around 770 nm, which is attributed to light emitting processes of non-purely thermal nature. Carbon residues, likely of amorphous structure, which can be formed by decomposition of organic fibres, such as cellulose, are shown to be one source of this spectacular phenomenon. Here, no critical limitation is seen for the performance of high power diamond windows.