X-Ray Flash Crystallography to Study Directed Energy Transfer in Materials

摘要

This report describes both theoretical, computational and experimental efforts to develop a technique which we call x-ray flash crystallography (XRFC). In XRFC, time dependent x ray diffraction from a crystal is monitored before, during and after the arrival of an intense, short pulse length infrared (IR) laser beam. The IR beam rapidly heats the crystal to high temperature. This induces temperature dependent changes in the crystals form factor which change the x ray reflectivity of the crystal; this is just the well known Debye Waller effect. The temperature sensitive effects are incorporated into a model which is used to predict the change in x ray reflectivity as a function of temperature; the temperature rise itself is determined by a knowledge of the energy deposition profile, and perhaps the dynamics of the lattice heating. This model then allows the extraction of the time dependent temperature from the time dependent x ray reflectivity which is measured. Using x rays as the probe, rather than an optical probe, ensures that the temperature measured is truly that of lattice. It also avoids contamination of the data due to electron-hole plasma related changes in the optical reflectivity.