Derrek Wilson, Department of Physics, Kansas State University

The scaling of strong field interactions with wavelength

An important aspect of light-matter interactions is their dependence on the frequency of the light. In the ultrafast, strong-field regime, the wavelength can be responsible for how matter responds to an intense field, governing phenomena related to the dynamics of accelerating free (or quasi-free) electrons. In this presentation, I will discuss two studies whose aims are to answer questions on the role wavelength in strong field interactions.

In the first study, we will look into strong field absorption in solid state materials, which have been shown to depend on the density of states. We consider the role of wavelength on this process by scanning across an octave of central wavelengths, covering two photon and three photon absorption for Gallium Arsenide. When varying the density of states, we see that the response changes with wavelength. Our current explanation is based on the dynamics of the electron in the conduction band, with longer wavelengths capable of inducing Bragg reflections more readily.

The second project shows progress on a light source suitable of studying strong field science in the long wave infrared (LWIR). The source, which is based on difference frequency generation of an optical parametric amplifier, is capable of generating few-cycle pulses with central wavelengths spanning 5-9 microns, and peak intensities in the 100 TW/cm^2 region. As a proof of principle for this sources ability to extend strong field science into the LWIR, we perform strong field ionization of Xenon gas across this wavelength range.