Selective manipulation of L-cysteine crystal polymorphs using focused laser beams.

The selective manipulation of crystal polymorphs holds profound implications across diverse scientific and industrial fields, as distinct polymorphs exhibit unique physical and chemical properties. This study demonstrates selective polymorphic manipulation by laser trapping - a technique enabling contactless manipulation and condensation of matter at the nanometer-scale and micrometer-scale. L-cysteine, a ubiquitous amino acid employed in pharmaceuticals and food additives, was targeted. We reveal that continuous-wave laser irradiation yields single crystals of the metastable polymorph, whereas continued irradiation with high-repetition-rate femtosecond laser pulses induces poly-crystallization of the stable form. Crucially, by strategically alternating between these two laser modalities during crystal growth, we can open up new crystallization pathways, including the single crystal growth of the stable phase. These findings underscore the significant potential of focused laser beams for precision polymorphic engineering, paving the way for the development of advanced materials with tailored properties.