The program aims at a comprehensive study of the single atom response to an intense, ultra-fast burst of electromagnetic radiation that will not only provide basic tests of basic laws of physics but also initiate some novel experimental investigations in strong field physics. One objective is to broaden the scope of experimental investigations by utilizing the wavelength scaling of the strong field interaction at frequencies lower than the intrinsic electron motion. Various aspects of the strong field interaction have an implicit wavelength-dependence that is a crucial scaling parameter and has not been explored or exploited in a systematic fashion. Addressing these scaling laws with ionization experiments using ultra-short pulses in the mid-infrared regime of the electromagnetic spectrum is crucial since it tests the very foundations of all our understanding of the intense laser-atom interaction. A second objective is to understand and connect the behavior of atoms in intense x-ray fields with the more studied optical regime. These investigations are enabled by the new generation of hard x-ray freeelectron lasers being constructed worldwide. The first of these devices, which became operational in 2009, is the Linac Coherent Light Source (LCLS) at SLAC National Laboratory. Using the unprecedented x-ray intensities available at the LCLS, this program will explore the strong-field high frequency regime. Scaling laws suggest that the behavior at x-ray frequencies will have significant fundamental differences with the optical regime.
The 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. At the core of the problem is the extreme nonlinear response of the atom to a laser pulse that imposes an external electric field comparable to the forces binding the electrons to the nucleus. The continuing interest in this fundamental atomic physics problem is derived from its broad implications in other areas of physics and technology. The single atom response is the initial condition of more complex phenomena found in plasmas, inertial confined fusion concepts, advance particle acceleration and astrophysics. The intense laser-atom interaction itself is opening new opportunities in short wavelength science, quantum control and advancing an emerging discipline in hyperfast electron physics, attophysics and molecular imaging. The novel long wavelength laser sources developed by this project have broad applications in science, national defense and technology. Furthermore, the interdisciplinary nature of this research coupled with state-of-the-art ultra-fast optical engineering provides a fertile training ground for both undergraduate and graduate students. In addition, the LCLS XFEL has provided an exceptional educational opportunity for NSF supported students and a valuable resource for preparing the next generation of physicist trained in a frontier of ultra-fast x-ray science. Former group members are contributing to various areas of science and technology in academia, national laboratories and the private sector.
