Structural Studies Of Materials Using Time-Resolved X-ray Diffraction

Sammanfattning: This work consisted of the application of X-ray diffraction methods to the study of ultrafast phenomena in various materials. Since the X-ray pulses generated from the bending magnet at the MAX II ring, where most of the experimental work was conducted, have a duration of the order of 300 ps, they can not be used directly as probe pulses in experiments where higher temporal resolution is required. A streak camera used as the detector was tested and improved to be able to resolve ultrafast processes. Another aspect of this work was the development of an experimental method for ultrafast time-resolved measurements at a high repetition rate. Various experiments were performed to further the development of this method, such as the investigation of the accumulated damage to the surface of InSb after repetitive ultrafast melting. Therefore laser-exposed InSb surfaces were studied post-mortem using different microscopy techniques. Time-resolved X-ray diffraction in a high-repetition-rate configuration was then applied in a study of liquid scattering from molten InSb. The experiment provided insight into the non-equilibrium liquid state of InSb. Studies of acoustic waves created by non-thermal melting of InSb due to rapid changes in the density were also conducted. The ferroelastic switching between different structures in the ferroelectric phase of potassium dihydrogen phosphate (KDP) was observed via time-resolved X-ray diffraction. This material undergoes a phase transition from the paraelectric phase above the Curie Temperature (Tc) to the ferroelectric phase below Tc. An alternative method of initiating ultrafast structural changes in a ferroelectric material was studied at the Stanford Linear Accelerator Centre, where THz radiation was used as a pump, and femtosecond laser pulses as the probe, in order to study the nonlinear response of ferroelectric material to THz radiation.

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