Education

• Ph.D., Nuclear Physics, Rutgers University, 1977
• B.S., Physics, Massachusetts Institute of Technology, 1971

Selected Publications

• Pink-beam focusing with a one-dimensional compound refractive lens
  The performance of a cooled Be compound refractive lens (CRL) has been tested at the Advanced Photon Source (APS) to enable vertical focusing of the pink beam and permit the X-ray beam to spatially overlap with an 80 µm-high low-density plasma that simulates astrophysical environments.

• Ultrafast x-ray-induced nuclear dynamics in diatomic molecules using femtosecond x-ray-pump–x-ray-probe spectroscopy
  The capability of generating two intense, femtosecond x-ray pulses with a controlled time delay opens the possibility of performing time-resolved experiments for x-ray-induced phenomena. We have applied this capability to study the photoinduced dynamics in diatomic molecules. 

• Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics
  New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. 

• Resonance-mediated atomic ionization dynamics induced by ultraintense x-ray pulses
  We describe the methodology of our recently developed Monte Carlo rate equation (MCRE) approach, which systematically incorporates bound-bound resonances to model multiphoton ionization dynamics induced by high-fluence, high-intensity x-ray free-electron laser (XFEL) pulses. 

• Dipole and nondipole photoionization of molecular hydrogen
  We describe a theoretical approach to molecular photoionization that includes first-order corrections to the dipole approximation. The theoretical formalism is presented and applied to photoionization of H2 over the 20- to 180-eV photon energy range. 

• Feasibility of Valence-to-Core X-ray Emission Spectroscopy for Tracking Transient Species
  X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. 

• Ultra-fast and ultra-intense x-ray sciences: First results from the Linac Coherent Light Source free-electron laser
  X-ray free-electron lasers (FELs) produce femtosecond x-ray pulses with unprecedented intensities that are uniquely suited for studying many phenomena in atomic, molecular, and optical (AMO) physics. 

• Sequential multiple ionization and fragmentation of SF6 induced by an intense free electron laser pulse
  We investigate the multiphoton ionization and the subsequent fragmentation of SF6 molecules with intense x-ray-free electron laser pulses at different photon energies. We observe highly charged molecular and atomic ions which were absent in previous experiments with conventional x-ray sources.

• Spin-state studies with XES and RIXS: From static to ultrafast
  We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. 

• Multiphoton L-shell ionization of H2S using intense x-ray pulses from a free-electron laser
  Sequential multiphoton L-shell ionization of hydrogen sulfide exposed to intense femtosecond pulses of 1.25-keV x rays has been observed via photoelectron, Auger electron, and ion time-of-flight spectroscopies.