Time-Resolved Studies of Atoms and Ions in the Short-Wavelength Region

Abstract: Radiative lifetimes have been studied in neutral copper, gold, magnesium, zinc, tellurium, sulphur, selenium, bismuth and helium and in singly ionised platinum and palladium. The radiative lifetimes were determined by time-resolved spectroscopy following single, two-photon or stepwise laser excitation. The excitations required short wavelengths, obtained by frequency mixing of radiation from pulsed lasers in crystals and gases. Efficient mixing schemes in gases, such as resonant sum-difference mixing in krypton, stimulated Raman scattering in hydrogen and high-order harmonic generation in rare gases have been employed. Several techniques have been utilised for the production of free atoms and ions such as evaporation into an atomic beam, thermal dissociation in cells and laser-produced plasmas. The Landé factors of one state in selenium and several in ytterbium have been measured by utilising optical double-resonance and quantum-beat spectroscopy. The ionisation potential in CO has been determined by multiphoton ionisation mass spectroscopy. Molecular ionisation structure in NO has been studied by tuning the wavelength of the seventh harmonic. Control of the angular emission of high-order harmonics by manipulating the laser beam ellipticity was demonstrated.