Abstract

In the interest of developing a sensitive detection technique for molecular fluorine, we attempted two-photon-excited ionization detection of the F¹∏_g state. The frequency-doubled output of a Nd:YAG-pumped dye laser was Raman shifted and the third anti-Stokes line selected with a Pellin-Broca prism. This light at around 207 nm was focused into a cell containing ~120 Torr of 10% F₂ in He gas mixture. The ions produced were detected with a pair of electrodes biased to 500 V and amplified with a charge amplifier. High-resolution spectra of both the F¹∏_g state and the near-lying f³∏_g state were obtained. The f³∏_g state, a spin-forbidden transition from the ground state, is of interest because it is thought to be the upper level of the F₂ laser transition at 157 nm, possibly the spectrally brightest source in the VUV today. In a recent theoretical investigation¹ of the f³∏_g state in fluorine it was found that the 157-nm laser transition could not be conclusively assigned. We are currently attempting to observe VUV fluorescence from the two-photon excited f³∏_g state. If this experiment is successful, it would definitively assign the upper level of the F₂ laser, allow further spectroscopy measurements of this important level, and demonstrate a fluorescence-based detection technique for molecular fluorine.

© 1988 Optical Society of America