In situ opticaJ eAnssion spectra for an electron assisted hot filament diamond growth process were successfully measured with spatial resolution of better than 1 mm.The ethession lines from atoAnc hydrogen, molecular hydrogen, CH and CH+ radicals were observed in the visible region. Effects of the substrate bias on ethession spectra and diamond nucleation were also investigated. It is found that substratboan enhance the nucleation density, which may due to the changes of atoAnc hydrogen concentration and the increase of electron mean temperatuxe.
