Coherent diffraction rings induced by thermal–mechanical effect of a flexible Dirac semimetallic composite structure

Abstract

Concentrically elliptical coherent diffraction rings are observed when a collimated laser beam is reflected from a mica substrate with Cd3As2 nano-films grown on it. The diffraction pattern is found to be an interference effect of light reflected from the elastic deformation of the mica substrate. The deformation of the substrate is induced by the in-plane thermal expansion caused by the heat transfer from the Cd3As2 thin film, which acts as an efficient light absorber. This thermal–mechanical effect is different from various other mechanisms that can produce similar coherent diffraction patterns from a large variety of materials. Furthermore, we show that a quantitative analysis based on a simple optical interference of light beam reflected from the mechanically deformed substrate can interpret all main features of the observed diffraction pattern. The light induced thermal–mechanical effect provides an interesting novel approach to characterize the thermal and mechanical properties of elastic materials through their coherent interaction with light. Our findings may provide interesting opportunities for optical control of the mechanical properties of flexible materials and for in situ characterization of the deformation process.

Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission

“…Because the Cd 3 As 2 has strong light absorption at the 800-nm excitation wavelength (~50% for 50-nm thick film 31 ), the light intensity decays quickly when penetrating into Cd 3 As 2 , which builds up transient temperature gradient of absorbed light energy and thus the electron temperature gradient along the direction perpendicular to the surface. On the other hand, as a result of the radial thickness gradient of Cd 3 As 2 film, the ultrafast pulse excitation can also produce a temperature gradient along the in-plane direction.…”