This work aims to answer the question: what happens when an electron (one of the fundamental building blocks of all atoms) scatters from an atom or molecule in the presence of light from a laser? One of the simplest classes of things that can happen is "elastic scattering" in which the electron and the atom do not exchange energy and continue on their way after the collision with the same energies that they had before the collision (but perhaps changing their direction). These are called laser-assisted free-free (LAFF) processes because the electron is free (i.e., not bound to an atom or molecule) both before, and after, the collision. This work will involve experimental LAFF studies, with the broad aim of increasing our basic understanding of these processes. Particular attention will be paid to resolving long-standing discrepancies between theory and experiment (there are several sets of experimental data that have defied theoretical explanation for over twenty years) and examining how two-color laser fields affect, and can be used to control, scattering processes. In addition to the advancement of our basic understanding of scattering processes, this work has applications to a variety of fields, both basic and applied. For example, similar processes are important for understanding the interiors and atmospheres of stars. Free-free transitions also play a major role in the gas breakdown that occurs in electrical discharges, and provide a method for laser heating of a plasma (a gas of ionized atoms). Understanding these processes helps form a more solid scientific foundation for the field of plasma physics which underlies the manufacturing of the microelectronics at the heart of our computers and cell phones. This work will primarily take place at an undergraduate institution, and will directly involve several undergraduate students in research.
To accomplish the above stated aims, two different sets of experimental LAFF studies will be performed. The first set of experiments will continue this group's previous work which is well described by theory in spite of the fact that some similar experiments done by another group contradict current theoretical understanding. There are three significant differences between the experiments performed by the two groups: the electron energy, the photon energy, and the photon polarization. The new experiments will investigate a range of incident energies, as well as geometries that have not previously been investigated; e.g., laser propagation direction perpendicular to the scattering plane, and laser polarization direction perpendicular to the scattering plane. Essentially, the experiments will go from perturbative, to non-perturbative regimes. This data will test current theory, as well as provide insight to the development of more complex theoretical descriptions of the LAFF processes. In addition, the new experiments will look for interference effects in LAFF experiments that use a two-color (photon energy = 1.17 eV, and 2.34 eV) laser field. Electrons scattered in such a two-color field that have an energy 2.34 eV below the elastic peak may have emitted either a single 2.34 eV photon or two 1.17 eV photons. The research group will perform experiments that vary the relative phase of these two colors to observe predicted interference effects.
