Measurement of SiH2 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 SiH2 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 (A) over tilde B-1(1)(020) <-- (X) over tilde (1)A(1)(000) 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 SiH2 in the discharge to be about 10(10) cm(-3). Taking into account the signal-to-noise ratio, concentrations as small as a few times 10(8) cm(-3) can be detected by both methods. We also observed a weak broadband absorption of several 10(-7) cm(-1) due to the dust particles formed in the plasma volume, which for particles of 1 nm diameter would correspond to a few times 10(9) cm(-3). The performances of ICLAS and CWCRDS are compared.