XPP Experimental Methods

Dynamics of Photo-induced Phase Transitions

Optical manipulation of solids can lead to photo-induced phase transitions on the ultrafast time scale. For many of these materials, a change in crystal symmetry accompanies a magnetic, ferroelectric, or metal-insulator phase transition. These materials have the potential to be utilized as ultrafast switches in magnetic and electro-optic devices and time-resolved X-ray crystallography provides an ideal tool for tracking the changes in atomic structure. For those systems that undergo a 1st-order photo-induced phase transition, time-resolved X-ray scattering has the potential to provide information about the structure and size of the new phase nucleus with previously unachievable detail.

Studies of Intense Laser-matter Interactions

The structural response of materials to femtosecond laser excitation differs fundamentally from the response to excitation with longer pulses, because the generation of carriers by linear and nonlinear absorption occurs faster than the time scale for carrier diffusion and carrier-phonon scattering. Consequently, the photon field can deposit enormous quantities of energy into electronic degrees of freedom, while the vibrational internal energy remains comparatively unperturbed. Excitation of carriers can alter the ionic potential energy landscape of a material and can lead to atomic motion [1,2] (see Figure 1). Identifying the important distinctions between materials and further correlating the material response with material electronic structure remains an important objective for understanding the light-matter interaction. Further knowledge in this field will enhance our ability to manipulate and control material structure with light.

References

1. A. M. Lindenberg et al., Science, 308, 392-395 (2005).
2. D. M. Fritz et al., Science, 315, 633-636 (2007).