Extremely early stage of ferroelastic domain formation observed by laser refraction

The initial domain formation process in a ferroelastic crystal KD₃(SeO₃{)}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 (Tc). The intensity level extends down three orders of magnitude smaller than that caused by the domains below Tc. This implies the embryos of the ferroelastic domains already exist in the high-temperature phase as the inhomogeneous strain field.