A5042841601- Atomic and Molecular Physics
- Laser-induced spectroscopy and plasma
- Advanced Chemical Physics Studies
- Mass Spectrometry Techniques and Applications
- X-ray Spectroscopy and Fluorescence Analysis
- Laser-Plasma Interactions and Diagnostics
- Laser-Matter Interactions and Applications
- Laser Design and Applications
- Electron and X-Ray Spectroscopy Techniques
- Analytical chemistry methods development
- Ion-surface interactions and analysis
- Advanced X-ray Imaging Techniques
- Cold Atom Physics and Bose-Einstein Condensates
- Plasma Diagnostics and Applications
- Spectroscopy and Laser Applications
- Particle Accelerators and Free-Electron Lasers
- Advanced Electron Microscopy Techniques and Applications
- Nuclear Physics and Applications
- History and advancements in chemistry
- Molecular Junctions and Nanostructures
- Solid State Laser Technologies
- Cultural Heritage Materials Analysis
- Quantum optics and atomic interactions
- Photorefractive and Nonlinear Optics
- Atomic and Subatomic Physics Research
Dublin City University
2013-2023
Beaumont Hospital
2023
National University of Ireland
2022
22q11 Ireland
2018
University College Dublin
1977-2001
Université Paris-Sud
1996
Centre National de la Recherche Scientifique
1996
University of Amsterdam
1989
Physical Sciences (United States)
1984
In a technique using continuum generated by focusing laser beam on target of high atomic number, the spatially resolved absorption spectrum ${\mathrm{Li}}^{+}$ formed in second laser-produced plasma was studied from 200 to 50 \AA{}. The doubly excited resonances, $1{s}^{2}_{1}S\ensuremath{-}2\mathrm{snp}^{1}P$, as well principal series and its adjoining photoionization were observed. Fano parameters, $q$ $\ensuremath{\Gamma}$, $2s2p^{1}P$ derived profile. Comparison is made with theory.
Abstract The advent of free electron laser (FEL) facilities capable delivering high intensity pulses in the extreme-UV to X-ray spectral range has opened up a wide vista opportunities study and control light matter interactions hitherto unexplored parameter regimes. In particular, current short wavelength FELs can uniquely drive non-linear processes mediated by inner shell electrons fields where photon energy be as 10 keV so corresponding optical period reaches below one attosecond. Combined...
Recent work has shown that with appropriate targets, laser-produced plasmas provide clean essentially linefree continua suitable for absorption spectroscopy from 40 to 2000 A. A systematic study of the emitted by elements samarium ytterbium is reported, and their use in demonstrated. The temporal profiles continuum pulses at different wavelengths are studied a photomultiplier system found have same halfwidths as pulse exciting Q-switched ruby laser (~25 nsec). Pulse heights be reproducible...
Using a dual laser plasma technique we have measured for the first time photoabsorption spectrum of atomic lithium at energies corresponding to simultaneous excitation both 1s electrons. We observed main triply excited 1${\mathit{s}}^{2}$2s${(}^{2}$S)\ensuremath{\rightarrow}2${\mathit{s}}^{2}$p${(}^{2}$P) transition with Fano parameters ${\mathit{E}}_{0}$=142.32\ifmmode\pm\else\textpm\fi{}0.05 eV \ensuremath{\Gamma}=0.20\ifmmode\pm\else\textpm\fi{}0.04 eV, and...
Two-photon ionization of atomic helium has been measured by combining femtosecond extreme-ultraviolet pulses from the free-electron laser in Hamburg (FLASH at DESY) with intense light a synchronized neodymium-doped yttrium lithium fluoride laser. Sidebands appear photoelectron spectra when two overlap both space and time. Their intensity exhibits characteristic dependence on relative time delay between ionizing dressing provides an inherent marker for time-resolved pump-probe experiments....
Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In photoelectron spectrum, lines associated direct and above-threshold show strong variations their amplitudes as a function both intensity dressing field relative orientation linear polarization vectors two fields. The dependence provides insight into symmetry outgoing electrons ionization....
Abstract When the output of a typical Q-switched laser is focused onto solid target, short-lived, localized plasma, characterized by very high ion and electron densities temperatures, formed. The present article begins with an outline essential features systems used to generate such plasmas followed summary some concepts in plasma physics necessary for their proper interpretation. theory evolution presented terms hydrodynamic model relationship between irradiance temperature discussed....
We present absolute L-shell photoionisation cross sections for the S+, S2+, S3+ions. The were obtained using monochromatised photon beam delivered by SOLEIL synchrotron source coupled with an ion extracted from electron cyclotron resonance (ECRIS) in merged dual-beam configuration. single, double and triple ionisation measured combined to generate total sections. For each of S3+ ions, energy regions corresponding excitation a 2p or 2s (175-230 eV) investigated. experimental results are...
Abstract We present absolute L-shell photoionisation cross sections for the S+, S2+, S3+ ions. The were obtained using monochromatised photon beam delivered by SOLEIL syn- chrotron source coupled with an ion extracted from electron cyclotron resonance (ECRIS) in merged dual-beam configuration. single, double and triple ionisation measured combined to generate total sections. For each of S2+ ions, energy regions corresponding excitation a 2p or 2s (∼ 175-230 eV) investigated. experimental...
Two-color above threshold ionization of helium and xenon has been used to analyze the synchronization between individual pulses femtosecond extreme ultraviolet (XUV) free electron laser in Hamburg an independent intense 120fs mode-locked Ti:sapphire laser. Characteristic sidebands appear photoelectron spectra when two overlap spatially temporally. The cross-correlation curve points a 250fs rms jitter sources at experiment. A more precise determination temporal fluctuation XUV infrared is...
Using a noninvasive, electro-optically based electron bunch arrival time measurement at FLASH (free laser in Hamburg) the temporal resolution of two-color pump-probe experiments has been significantly improved. The system determines relative extended ultraviolet pulse and an amplified Ti:sapphire femtosecond-laser interaction region better than 90 fs rms. In benchmarking experiment using above threshold ionization noble gases, enhancement timing by factor 4 compared to uncorrected data is obtained.
The 4d absorption spectra of I, ${\mathrm{I}}^{+}$, and ${\mathrm{I}}^{2+}$ have been observed in the 45--300-eV region using dual laser-produced plasma technique. At lower energies each spectrum is dominated by intense 4d\ensuremath{\rightarrow}5p transitions, which are identified with aid multiconfiguration Hartree-Fock calculations. excited states decay direct autoionization involving 5s or 5p electrons rates for different processes resulting linewidths were calculated compared, where...
Using monochromatized extreme-UV radiation from the undulator beamline BW3 at HASYLAB we have measured high resolution (E/ Delta E approximately 7000) Li+ photoion yield spectrum excitation energies corresponding to transitions double K-shell vacancy states. A number of such resonances including single-photon-three-electron excitations, e.g. 1s22s(2S) 2p3(2p), been observed for first time. The is tentatively classified with aid Hartree-Fock calculations.
A dual-laser-plasma technique has been used to measure photoabsorption by atomic Cr and Mn their ions at photon energies between 40 70 eV, where the dominant absorption mechanism is excitation of 3p subshell. No dramatic differences are observed spectra ${\mathrm{Mn}}^{+}$, these similar those metal ${\mathrm{MnCl}}_{2}$. The ${\mathrm{Cr}}^{+}$ strikingly dissimilar, mean energy being about 5 eV greater in ion. We attribute this strong mixing localized 3${\mathit{d}}^{6}$ configuration with...
Photoelectron data are reported for the first measurement of even-parity hollow lithium states produced by triple photoexcitation laser-excited atoms. Calculations using R-matrix approximation energy these and partial photoionization cross sections also reported. Experiment theory in excellent agreement on a relative scale.
Spectral probes for the ${\mathrm{CH}}^{+}, {\mathrm{OH}}^{+}$, and ${\mathrm{SiH}}^{+}$ hydride molecular ions that play key roles in astrophysics plasma processes are presented. The merged-beam technique at SOLEIL synchrotron was used to record photoionization (ion yield) spectra of their parent atomic ions, $K$-shell $L$-shell regions, respectively. Energies oscillator strengths $K\ensuremath{\alpha}$ (${\mathrm{CH}}^{+}$ ${\mathrm{OH}}^{+}$) $L\ensuremath{\alpha}$ (${\mathrm{SiH}}^{+}$)...
Photoelectron data for hollow lithium states obtained with unprecedented high spectral resolution and sensitivity are presented. A critical comparison is made the most recent theoretical results. Partial cross sections measured providing first definitive test of advanced ab initio calculations this highly excited four-body atomic system.
A detailed optimization study for laser-produced steel plasmas using time-integrated, spatially resolved emission spectroscopy in the vacuum ultraviolet (VUV) (40–160 nm) is presented. The influences of laser focusing lens type, power density, wavelength, pulse energy, ambient atmospheres, and pressure, as well spatial distribution emitting species, on characteristics are investigated. aim work to improve detection technique quantitative determination carbon solid alloys. In most work,...
A new multilaser multichannel spectrometer system has been developed that allows a wide range of investigations the interaction extreme-ultraviolet (EUV) photons with matter in form free atoms or ions, e.g., gases plasmas bound as solids. The EUV are generated by laser-produced plasma. Applications to study photoabsorption thin foils, gases, and ground- excited-state ions described. design performance collimated, quasi-monochromatic, intense source radiation based on combination plasma...
The spectra of plasmas produced by focusing the output a Q-switched ruby laser (output 1 J) on rare-earth metals have been studied. From samarium (Z = 62) to ytterbium 70), strong quasi-uniform continua are emitted in wavelength range 40–2000 Å. Line emission from target elements is absent over most this region, particularly below about 600 use these as simple, reliable background sources for absorption spectroscopy vacuum-ultraviolet and soft x-ray region down 40 Å demonstrated.
Laser plasma plumes were generated in aluminum rectangular cavities of fixed depth (6 mm) and varying height (2.0, 1.5, 1.0 mm). Space time resolved visible emission spectroscopy, gated intensified imaging, Langmuir probe diagnostics utilized to diagnose the evolution confined comparison freely expanding plume from ablation a planar target. The constrained behavior displayed multiphase history. Early stage interactions (t<100 ns) resulted enhanced continuum line emission, shockwave...