Over the last decade, the tailoring of a light field for manipulating the
dynamics of a system at the quantum level has taken a prevalent role in
modern atomic, molecular and optical physics. As first described by
Keldysh1, the ionization of an atom by an intense laser field will evolve
depending upon the light characteristics and atomic binding
energy. Numerous experiments have thoroughly investigated the dependence of
the intensity and pulse duration on the ionization dynamics of inert
gases. However, exploration of the wavelength dependence has been mainly
limited to wavelengths ? 1 ?m or in the language of Keldysh to the
multiphoton or mixed ionization regime. It is now technically possible to
more thoroughly test scaling laws at longer mid-infrared wavelengths with
the same sensitivity available at near-visible wavelengths. In
addition, excitation with mid-infrared light augments the number of atomic
systems which can be studied in the tunneling regime, as well as posing
different model atomic structure, e.g. one- and two-electron like
In this talk, we will discuss two topics. The first topic examines the long wavelength scaling of the strong field physics and its utility for experiments investigations. In the experiment alkali metal atom interact with an intense mid-infrared (3-4 ?m) laser field. In a Keldysh picture this scaled interaction should show similar ionization dynamics to the more familiar situation of a near visible light interacting with inert gas atoms. However, the interpretation of the spectra is greatly simplified since the alkali metal atoms are "good" one-electron like systems. Both ionization and harmonic processes are currently under investigation. The results show many similarities with the more extensively studied inert gas atom spectrum but significant differences do exist.
The second topic deals with inert gas atoms in large ponderomotive potentials. Both theoretical and experimental results will be presented that show neutral atoms experiencing nearly 400 eV of ponderomotive potential and ionization deep into the tunnel regime. These studies are fundamentally interesting but also provide a roadmap to light pulses that have both the atomic unit of time and length.
1. L.V. Keldysh, Sov. Phys. JETP 20, 1307 (1965).
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