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

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.