NON-LINEAR REFRACTIVE INDEX MEASUREMENT OF (2E)-3-[4-(DIMETHYLAMINO)PHENYL]-1-(2,5-DIMETHYLTHIOPHEN-3-YL)PROP-2-EN-1-ONE AND (2E)-3-(3,4-DIMETHOXYPHENYL)-1-(2,5-DIMETHYLTHIOPHEN-3-YL)PROP-2-EN-1-ONE