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The utilization of shock waves plays a pivotal role in the advancement of multiple scientific domains like aerospace, defense, geology, environment, medicine and many more. They serve as essential tools in scientific investigations, enabling the exploration of material behavior under extreme conditions, viz. elevated pressure and temperature. The present study is specifically dedicated to scrutinizing the repercussions of shock waves on an l‐ascorbic acid single crystal, to which they were intentionally applied to assess their influence on structural, optical and third‐order nonlinearity properties. Powder X‐ray diffraction analysis unveiled a discernible overall enhancement in the crystalline quality of the grown crystal following exposure to shock waves. This observation was consistently corroborated by high‐resolution X‐ray diffraction data, particularly on the (200) crystallographic planes. Furthermore, the optical transmittance of the crystal exhibited a notable increase upon the application of shock waves, while the material's band gap remained unaffected. In parallel, the third‐order nonlinearity of the crystal was found to undergo a significant augmentation as a consequence of the shock treatment, as confirmed through Z‐scan measurements. These empirical findings unequivocally demonstrate the substantial enhancement in the structural, optical and nonlinear properties of the grown crystal when subjected to shock waves, rendering it well suited for nonlinear optical applications. [ABSTRACT FROM AUTHOR]

The bulk carrier excitation influences the phonon dynamics, which can alter and modulate the surface charge density of topological insulators such as bismuth selenide (Bi2Se3). This work investigates the charge carrier and phonon dynamics in Bi2Se3 grown on various substrates. The orientation of the substrate, the size of the crystallites, and the misfit of the lattice affect the carrier and phonon dynamics. Bi2Se3 thin films are grown under the same growth conditions on SiO2, Si(111), and SiN. Bi2Se3 overlayers exhibit substrate- dependent charge carrier relaxation channels and phonon dynamics. It is evident from Raman spectroscopy and ultrafast transient absorption spectroscopy that the heterointerface interactions of all three samples affect the vibration modes of Bi2Se3 and coherent acoustic phonon oscillations in the NIR range. At 13.6, 41.2, and 34.4 GHz, the vibration modes of SiO2, Si(111), and SiN are equivalent. The propagation depth of phonon waves is shown by measuring the speed of sound in Bi2Se3 overlayers on SiO2, Si(111), and SiN. This study demonstrates that the surface and bulk-bound charge carriers of a topological insulator determine the frequency and velocity of the generated sound. [ABSTRACT FROM AUTHOR]