Determination of the refractive indices by variable azimuth reflectometry from a single sample face

We have investigated a method for the evaluation of the indices of refracti on of crystalline materials of any symmetry based on the measurement of the reflectance from one single face of the sample for several azimuthal orien tations. After a consistency test performed on fused silica and crystalline quartz we have applied the method to as-grown crystals of monomethylurea, a biaxial nonlinear optical material recently synthesized. The phase matchi ng loci calculated from the refractive indices determined in this way are i n good agreement with the experimental ones, thus demonstrating the viabili ty of the procedure also for biaxial systems. The limits and the advantages of the method are briefly discussed.