Deflection of Light and Domain Structure in KH₃(SeO₃)₂ and NaH₃(SeO₃)₂

Abstract

Properties of the light deflected by ferroelastic domains in KH 3 (SeO 3 ) 2 and NaH 3 (SeO 3 ) 2 were examined. Above a critical angle of incidence, five deflected beams were observed with a He–Ne laser incidence for a y -cut plate of KH 3 (SeO 3 ) 2 and z - and y -cut plates of NaH 3 (SeO 3 ) 2 . Only two deflected beams appear at the incident angle of 0°; the deflection angles are ±21.0°, ±31.4° and ±26.0° for the y -cut plate of KH 3 (SeO 3 ) 2 and the z - and y -cut plates of NaH 3 (SeO 3 ) 2 , respectively. The intensity of the deflected beams in both crystals increases abruptly just below the transition points on warming process. It was found that the increase of the intensity is due to the formation of a number of fine domains in the vicinity of the transition points.