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Research

Attosecond Physics

time_scaleThe new millennium witnessed the addition of the word "attosecond" (1 as = 10-18 s) to the vocabulary of physics.  Light pulses with attosecond duration are generated either by nonlinear frequency conversion of an ultra-short infrared pump pulse or Fourier synthesis of broad bandwidth radiation, whereas the shortest laser pulses are ~1fs as seen in the time scale to the left.  Attosecond light pulses are an important scientific advance because the duration corresponds to the electron motion time-scale in the atomic ground state (atomic unit of time = 24 as).  The goal of attosecond science is to observe and control ultra-fast electron motion on the natural atomic timescale.
Subtopics:
High Harmonic Generation, Laser-Cluster Interactions and HHG from Clusters

Spatio-Temporal Molecular Imaging

film_reelDuring the past century, our ability to follow initial steps in chemical reactions has progressed from the millisecond timescale of human reaction to the femtosecond regime.  Chemical reactions, of course, begin with the electron motion on the attosecond timescale (1 attosecond = 10-18 s) followed by a restructuring of the potential energy surface causing nuclear dynamics on the femtosecond timescale (1 femtosecond = 10-15s).  Therefore, in order to fully understand and control chemical reactions, it is necessary to understand both electron orbital and nuclear dynamics.  Our research is built around two facets of the molecular self-probing paradigm derived from the strong-field rescattering model and scaled to long wavelengths:  Electron Orbital Tomography and Molecular Geometry Reconstruction.  We want to use these two methods to effectively make "movies" of the molecules as depicted in the illustration to the left.
Subtopics:
Electron Orbital Tomography, Molecular Structure and Dynamics

Strong Field Physics

Strongfield physics imageThe interaction of an isolated atom with an intense electromagnetic field is the basis for one of the forefront problems in atomic, molecular and optical physics.  The ability to couple large amounts of energy into an atom by the absorption of many photons posed many intriguing questions and has led to many new discoveries such as above-threshold ionization, high-harmonic generation, multiple ionization and adiabatic stabilization.  With the intention of extending our basic knowledge of Strong-Field physics, our group is pursuing research into single atom response to an ultra-fast burst of electromagnetic radiation that will not only provide basic tests of scaling laws and theory but also initiate some novel experimental investigations in strong field physics.
Subtopics:
Keldysh Scaled Systems, X-Ray Free Electron Laser

Ultra-Fast Optical Technology

Fiber Compressor

Advances in the generation, amplification, control, and measurement of femtosecond laser pulses has had tremendous impact on many facets of science, technology, medicine and national security. Our group is active in the state-of-the-art development of the optical “tools” needed for studying strong-field atomic physics and laser sources that will enable various applications. Seen above is an Argon-filled hollow core glass capillary. Spectral broadening due to self-phase modulation followed by dispersion compensation using a piece of glass with negative group delay dispersion [1] result in the compression of mid-IR pulses down to the few-cycle regime.

[1] Bruno. E. Schmidt et al, 'Compression of  laser pulses to sub two optical cycles with bulk material' Appl. Phys. Lett. 96, 121109 (2010)