Professor Leone's research interests include ultrafast laser investigations and soft x-ray probing of valence and core levels, attosecond physics and chemistry, state-resolved collision processes and kinetics investigations, nanoparticle fluorescence intermittency, aerosol chemistry and dynamics, probing with near field optical microscopy, and neutrals imaging.
Current projects are grouped along several main themes: Ultrafast laser molecular dynamics, including x-ray probing and attosecond pulse production and investigations; chemical dynamics of molecules, nanoparticles, and clusters; nanostructured materials investigations with scanned probe microscopies. Projects include: femtosecond laser dynamics, ultrafast soft x-ray, time-resolved x-ray photoelectron dynamics, attosecond dynamics, near field and ultrafast optical microscopy of semiconductors and nanowires, infrared near field microscopy, photofragmentation and radical-radical reactions, aerosol chemistry, low temperature reactions for the chemistry of Saturn and Titan.
Several examples are considered briefly. Ultrafast lasers are used to probe the dynamics of molecular motion on the time scales of vibrational, rotational, or electronic periods. The Leone group investigates coherent properties. The study of molecular photodissociation by soft x-ray laser techniques has opened the way to analyze the simple breaking of a molecular bond in greater detail. High order harmonics are produced by high fields in a rare gas and used to probe valence shell photoelectron spectra and core level spectroscopy of time-evolving systems, ranging from atoms to small molecules to metal clusters. Phase-shaping of the high order harmonics has been investigated. Transient x-ray absorption is used to probe alignment and molecular fragmentation pathways through core level spectroscopy. By using few cycle carrier-envelope phase-stabilized laser pulses, isolated attosecond pulses are generated to study electronic timescales in molecules and clusters by ejecting inner shell electrons on attosecond timescales. An apparatus to probe photoelectron angular images with time-resolved high order harmonics is used to study outgoing electron waves and phases. Research also investigates the ultralow temperature gas phase kinetics for the atmospheres of Titan and Saturn, as well as to probe combustion dynamics through radical reactions. Heterogeneous chemistry is a significant new area of investigation, with applications to fuel droplet combustion and aerosol aging in the atmosphere.
Experiments are being explored in confocal microscopy, apertureless near field optical microscopy, and single pulse coherent anti-Stokes Raman microscopy with phase control, and studies involving quantum dot blinking and pump-probe ultrafast studies of semiconductor nanocrystals. Other projects study aerosol light scattering and spectroscopy, aerosol reactions, as well as surface probing of neutrals desorbed by scanning ion microprobes using the chemical dynamics beamline at the Advanced Light Source.
In the News
In semiconductors like silicon, electrons attached to atoms in the crystal lattice can be mobilized into the conduction band by light or voltage. Berkeley scientists have taken snapshots of this very brief band-gap jump and timed it at 450 attoseconds.
A team of German and UC Berkeley scientists, including physicist Stephen Leone, have used ultrashort flashes of laser light to directly observe for the first time the movement of an atom’s outer electrons. The technique could be valuable in the study of photosynthesis.