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Investigation of phase transitions triggered by laser-induced focusing shock waves

Abstract : The ability of certain materials to change its ground state due to laser excitation has arisen a lot of opportunities for light-control of material properties. The field of photo-induced phase transitions counts a rich variety of chemical and physical processes triggered by light-matter interactions involved during the phase transition process. Recently it was reported that elastically driven cooperativity leads to the amplification of spin state in molecular crystals and prolonged the lifetime of the transient state with an ultra-short laser pulse. The cooperative response appears during the propagation of non-linear coherent strain waves, in other words shock waves, coupled with the order parameter field. Shock waves can be seen as a new challenging pathway to achieve a permanently switched state with appropriate excitations.First, we introduce time-resolved single-shot imaging combined with the laser shock focusing technique that makes it possible to generate, acoustically focus, and directly visualize under a microscope shock waves propagating and focusing along the sample surface. The spatial separation of the laser-influenced and strain-influenced regions makes it possible to disentangle the material changes produced solely by the shock waves. Second, we present experimental results involving the shock-focusing technique to materials undergoing phase transitions linked with a macroscopic change of their volume (spin-crossover systems, Mott insulators). Post-mortem analyses of the samples confirm permanent phase transition under specific experimental conditions. These innovative results open doors for a generic elastically driven cooperativity.
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  • HAL Id : tel-02886759, version 1

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Yevheniia Chernukha. Investigation of phase transitions triggered by laser-induced focusing shock waves. Materials. Université du Maine, 2019. English. ⟨NNT : 2019LEMA1038⟩. ⟨tel-02886759⟩

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