Supersaturation and Polarization Dependence of Polymorph Control in the Nonphotochemical Laser-Induced Nucleation (NPLIN) of Aqueous Glycine Solutions

The temperature and concentration dependence of nonphotochemical laser-induced nucleation (NPLIN) was studied in aqueous glycine solutions at wavelengths of 532 and 1064 nm, using linearly, circularly, and elliptically polarized light. We observed a narrow supersaturation window ( c / c 0 = 1.45−1.55, where c is the solution molality, and c 0 is the molality of a saturated solution) for “polarization switching”, i.e., different polarizations producing different polymorphs. We also observed that, within this window, a small range of ellipticities near unity could induce the nucleation of the α-polymorph and that this range depended on supersaturation. Similar “polarization switching” behavior was observed at wavelengths of 1064 and 532 nm, although the supersaturation window became narrower at lower laser intensities at both wavelengths. Order-parameter ellipsoids and triangles based on optical Kerr alignment are presented to aid in the interpretation of the experimental results.