Collisional broadening coefficients of singlet ($a^{1}\Delta _{g})$ oxygen with helium

A novel laser-based technique applicable to metastable species detection is discussed. Off-axis integrated-cavity-output spectroscopy (ICOS) has been applied to the study of singlet ($a^{1}\Delta _{g})$ oxygen. Singlet oxygen was generated in a microwave plasma, and the afterglow passed through an off-axis ICOS measurement system consisting of an 82-cm long, high-finesse optical cavity bounded by two highly reflective mirrors. The mirror reflectivity was determined by performing cavity-ringdown measurements and observing ringdown times of 220-250 $\mu $s in a range from 1494 nm to 1512 nm. A diode laser was current tuned, and light exiting the cavity was focused onto an InGaAs detector. The cavity transmission was recorded as a function of laser frequency. Details of the method will be presented as well as the spectroscopic characterization of selected transitions of the (1,0) band of the $b^{1}\Sigma _{g}^{+ }$- $a^{1}\Delta _{g}$ Noxon system of oxygen (radiative lifetime 160 minutes). Pressure broadening coefficients with helium as the collision partner for selected transitions will also be presented.