Optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) in a ring cavity

Optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) has been demonstrated by coupling a distributed feedback diode laser to a ring cavity. Frequency-selected light decaying from the ring cavity is retro-reflected, inducing a counter-propagating intra-cavity beam, and providing optical feedback to the laser. At specific laser-to-cavity distances, all cavity mode frequencies return to the diode laser with the same phase, allowing spectra to be accumulated across the range of frequencies of the current-tuned laser. OF-CEAS has been used to measure very weak oxygen isotopologue ( 16O 18O and 16O 17O) absorptions in ambient air at wavelengths near 762 nm using the electric-dipole forbidden O 2 A-band. A bandwidth reduced minimum detectable absorption coefficient of 2.2 × 10 -9 cm -1 Hz -1/2 is demonstrated. © Springer-Verlag 2009

Photofragment slice imaging studies of pyrrole and the Xe..pyrrole cluster

The photolysis of pyrrole has been studied in a molecular beam at wavelengths of 250, 240, and 193.3 nm, using two different carrier gases, He and Xe. A broad bimodal distribution of H-atom fragment velocities has been observed at all wavelengths. Near threshold at both 240 and 250 nm, sharp features have been observed in the fast part of the H-atom distribution. Under appropriate molecular beam conditions, the entire H-atom loss signal from the photolysis of pyrrole at both 240 and 250 nm including the sharp features disappear when using Xe as opposed to He as the carrier gas. We attribute this phenomenon to cluster formation between Xe and pyrrole, and this assumption is supported by the observation of resonance enhanced multiphoton ionization spectra for the Xe¯pyrrole cluster followed by photofragmentation of the nascent cation cluster. Ab initio calculations are presented for the ground states of the neutral and cationic Xe¯pyrrole clusters as a means of understanding their structural and energetic properties