Factors Controlling Polymorph Formation in Nonphotochemical Laser-Induced Nucleation (NPLIN) of Aqueous Glycine Solutions

The supersaturation and polarization 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 (SS=1.45-1.54) 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 alpha 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 the interpretation of the experimental results.