Seminars and Colloquia
Physics
First-Principle studies on the Structural Response of Solids to Ultrashort-laser and XUV Pulses
Fri, Jun 01, 2018,
04:00 PM to 05:00 PM
at Physics Seminar Room 31, 2nd floor, Main Building
Dr. Fairoja Cheenicode Kabeer
Department of Physics and Astronomy, Uppsala University, P. O. Box 516, S-75120 Uppsala,
Sweden
The theoretical model and underlying physics described in this work are about the interaction
of femtosecond-laser and XUV pulses with solids. The key to understand the basics of
such interaction is to study the structural response of the materials after the laser interaction.
Depending on the laser characteristics, laser-solid interaction can result in a wide range of
structural responses such as solid-solid phase transitions, vacuum phonon squeezing, ultrafast
melting, generation of coherent phonons, etc. Here modeled the systems irradiated by
low-, medium- and high-laser intensities, and studied different types of structural dynamics
of solids at various laser fluences.
In the high fluence regime, we have studied the changes in the bonding properties of
warm dense noble metals, in particular copper and silver are analyzed and found that extreme
hardening of phonon modes shown by warm dense noble metals cause their relaxation
processes to be 3 to 6 times faster than the theoretically expected. Vacuum phonon squeezed
states can be generated at intermediate laser intensities depending upon the electron-phonon
coupling and bonding properties of the systems upon laser excitation. We found phonon
hardening may result in phonon vacuum squeezed states of noble metals with an optimal
squeezing factor. In the low fluence regime, we develop a non-perturbative method to elucidate
the microscopic mechanisms underlying the decay of laser-excited coherent phonons in
antimony. We found that the decay of the A1g phonon mode at low laser fluences can be accounted
mainly to three-body down-conversion processes and for higher excitation strengths
a crossover to a four-phonon process.
