Vacuum UV broad-band absorption spectroscopy: a powerful diagnostic tool for reactive plasma monitoring

Broad band UV-visible absorption spectroscopy is widely used to measure the concentration of radicals in reactive plasmas. We extended the applicability of this technique to the VUV (115 nm to 200 nm), the spectral range in which the electronic transitions from the ground state to the Rydberg or pre-dissociated states of many closed-shell molecules are located. This gives access to the absolute densities of species which do not, or weakly absorb in the UV-visible range. The technique is demonstrated by measuring the densities of HBr and Br2 molecules in HBr high-density ICP plasmas. (fast track communication)