Space-selective crystallization of glass by an optical vortex beam

We demonstrate the advantages of application of an optical vortex for direct femtosecond laser writing of crystalline tracks with substantially improved morphology in lanthanum borogermanate glass, i.e. crystalline tracks possessing a solid cross-section with an aspect ratio of close to 1 and a highly oriented crystal structure can be obtained. We report on the improvement of ultrafast laser-written track quality by using an optical vortex.