Sub-Doppler spectroscopy with a narrow linewidth pulsed optical parametric oscillator: hyperfine structure in the PF radical

A preliminary version of a very high-resolution pulsed optical parametric oscillator laser system is described. It is seeded by a tunable diode laser around 790 nm to give tunable, narrow-bandwidth (∼160 MHz) light around 645 nm. This is frequency doubled and used to take sub-Doppler spectra of the A 3Π–X 3Σ−(3,0) transition of the PF radical in a molecular beam. The resolution achieved (0.015 cm−1=450 MHz in the UV) is sufficient to resolve hyperfine structure clearly. An analysis of this is presented, together with a discussion of the bonding in PF as revealed by the hyperfine constants.