Measurement of density in a discharge by intracavity laser absorption spectroscopy and CW cavity ring-down spectroscopy

Two highly sensitive and quantitative absorption techniques have been applied to the detection of in an argon-5% silane DC discharge, the new method of CW cavity ring-down spectroscopy (CWCRDS) and intracavity laser absorption spectroscopy (ICLAS). Doppler-limited absorption lines of the transition around 580 nm could be observed. By using the rotational constants and the electronic transition moment available in the literature, we have calculated the line intensity of some specific rovibronic transitions from which we deduced the concentration of in the discharge to be about . Taking into account the signal-to-noise ratio, concentrations as small as a few times can be detected by both methods. We also observed a weak broadband absorption of several due to the dust particles formed in the plasma volume, which for particles of 1 nm diameter would correspond to a few times . The performances of ICLAS and CWCRDS are compared.