Extremely early stage of ferroelastic domain formation observed by laser refraction

The initial domain formation process in a ferroelastic crystal ${\mathrm{KD}}_3$(${\mathrm{SeO}}_3$ ${)}_2$ is observed by a method that utilizes laser light refraction at the ferroelastic domain structures. The high sensitivity of this method enables us to detect the refracted light even above the transition point (${\mathit{T}}_{\mathit{c}}$). The intensity level extends down three orders of magnitude smaller than that caused by the domains below ${\mathit{T}}_{\mathit{c}}$. This implies the embryos of the ferroelastic domains already exist in the high-temperature phase as the inhomogeneous strain field.