James R. Harries

Laser probing of the electron-impact excited c(2p) 3Πu manifold of states in H2

A stepwise laser excitation method has been used to probe individual ro-vibrational levels in the molecular hydrogen metastable c(2p) 3Πu manifold of states. Metastable states produced by electron-impact excitation are subsequently excited by the absorption of a single UV laser photon, producing a complex triplet nd Rydberg spectrum observed via field ionization and autoionization. The spectrum has been analysed to determine quantum numbers of the states associated with the transitions. Excitation functions for individual ro-vibrational states in the c(2p) 3Πu manifold are then determined as a function of electron-impact energy.

Electron-impact excitation of He and H2 in the doubly excited state energy region observed using a momentum transfer technique

We report evidence for the electron-impact excitation of doubly excited states in helium and H2 which are stable against autoionization. By detecting only long-lived (metastable) excited neutral states created by near-threshold electron scattering our technique discriminates against directly excited metastable states and is highly sensitive.

Photon-in, Photon-Out Gas-Phase Experiments at the SPring-8 Compact SASE Source SCSS

The study of the interaction of electromagnetic radiation with matter is currently undergoing a revolution with the advent of coherent, intense, ultrafast radiation sources at short wavelengths. In the extreme ultraviolet (EUV) to soft X-ray wavelength region sources based on high-harmonic generation can provide attosecond pulses, and in the soft X-ray to hard X-ray region free electron lasers provide unprecedented intensities of coherent radiation. In this article we describe some gas phase fluorescence spectroscopy experiments performed using the SPring-8 compact SASE source [1], which was originally constructed as a test facility for the SPring-8 Angstrom compact free electron laser SACLA [2].

Apparatus for measuring static electric field effects in photoexcitation experiments of gas-phase atoms and molecules using synchrotron radiation

We have developed an apparatus for performing photoexcitation experiments at a synchrotron radiation beamline in a static electric field of up to 100 kV cm−1. The design allows for the simultaneous detection of photoions, visible-ultraviolet fluorescent photons, and long-lived excited neutral particles produced during the decay of the excited states. In this article we describe the design of the electrodes which create the field (one of which incorporates a slit to allow the detection of photoions), modeling of the field-spread across the interaction regions, and methods for calibrating the observed effective field strength. We present sample spectra and calibration data obtained at the Photon Factory (Tsukuba, Japan) and the Advanced Light Source (Berkeley, CA).