Abstract : Among nonlinear optical effects, Second Harmonic Generation (SHG) is an extremely sensitive and rapid technique to detect absence of inversion centers in crystalline structures. [1] In addition, while combined with microscopy (SHG- M), it permits (i) to monitor temperature-induced phase transitions; (ii) to detect non-centrosymmetric zones inside heterogeneous materials. Therefore, as an analytical tool, SHG-M covers a large domain of applications, in complement with other classical techniques (e.g. XRPD, DSC, optical microscopy). While non-centrosymmetric structures are not the most popular among crystalline materials (i.e. 24.1% of the structures reported in the Cambridge Structural Database) [2], they are preponderant in many industrial applications (e.g. production of pharmaceuticals and optoelectronic devices); thus, their studies correspond to important issues. The present work illustrates the use of SHG-M in selected monophasic and multiphasic sample studies. Particularly, reinvestigation of Phenanthrene and Adamantane (Figure 1) phase transitions by means of SHG and/or Third Harmonic Generation (THG).
