Determination of the photoelastic coefficients in lithium heptagermanate crystals

The photoelastic (piezo-optic) property of the ferroelectric crystals lithium heptagermanate Li2Ge7O15 (LGO) were studied in para-and ferro-electric phases for different orientations. The value of stress optical coefficient C-ijk (in Brewsters) along a, b, c-axes were determined at RT (291 K) and 278 K and were compared with some other ferroelectric systems like Rochelle-salt (RS), potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP). Large photoelastic coefficients and other properties like good mechanical strength, or transition temperature close to RT and stability in ambient environment favour LGO as a potential candidate for photoelastic applications.