While large-area crystal growth techniques, such as CVD, are successfully used for the production of GRMs, the presence of grain boundaries, vacancies and differently oriented grains, arising in such growths, substantially affect the crystal quality. This is unavoidably reflected in the physical properties of the GRMs which by definition depend stronger on the interatomic position of the few neighboring atoms as compared to bulk materials. There is currently no easily applicable, non-invasive, fast characterization method for determining with high-resolution these grain boundaries and orientations, over a large sample area. Our goal is to assess whether or not an optical technique could serve as a robust tool for early identification of common imperfections in the crystal structure of GRMs, during production. Furthermore, to get the produced GRMs back to the tray and provide quantitative feedback in real time, so that one can optimize crystal quality while still performing the growth. For this purpose, we will use polarization resolved second-harmonic generation (PSHG) optical microscopy for the eventual mapping of grain boundaries and crystal orientations, thus determining optically the crystalline quality of the produced GRMs.