Picosecond expansion in LaAlO3 resonantly driven by infrared-active phonons

2024/12/22 by Jakob Gollwitzer, Gollwitzer, Jakob, Jeffrey Z. Kaaret +40
Engineering · Physics and Astronomy · Materials Science · #Solid State Laser Technologies #Photorefractive and Nonlinear Optics #Luminescence Properties of Advanced Materials

paper · pdf · doi:10.48550/arxiv.2412.17192

Abstract

We investigate the ultrafast structural dynamics of LaAlO3 thin films driven by short mid-infrared laser pulses at 20 THz. Time-resolved X-ray diffraction reveals an immediate lattice expansion and an acoustic breathing mode of the film. First-principles theory and a spring-mass model identify the direct coupling between coherently driven infrared-active phonons and strain as the underlying mechanism. Time-resolved optical birefringence measurements confirm that the amplitude of this acoustic mode scales linearly with the pump fluence, which agrees with the theory. Furthermore, time-resolved X-ray diffuse scattering indicates that THz excitation enhances crystallinity by inducing a non-thermal increase in structural symmetry originating from preexisting defects. These findings highlight the potential of a multimodal approach-combining time-resolved X-ray and optical measurements and first-principles theory-to elucidate and control structural dynamics in nanoscale materials.

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