ABSTRACT: Spatially selective heating with a laser offers a unique capability of fabricating complex single crystal architecture in an otherwise inexpensive glass matrix. The use of continuous wave (CW) laser is useful for fabricating 1D or 2D single crystal architecture at or near the surface, whereas pulsed femtosecond (fs) laser can be exploited to form 3D single crystal deep inside the glass. Thus, we fabricted the very first functioning single crystal waveguide deep inside a glass (see figure). With these results, a new frontier of crystal growth applications has been opened, ready for exploitation in new micro/integrated optical devices, or as substrate for low cost epitaxial growth, active planar devices, etc.
In laser crystallization, the local heating facilitates nucleation of crystalline phase. Then the challenge remains how to grow the initial nucleus into a single crystal without forming additional nuclei that would lead to the usual glass-ceramics. For this reason, most single crystals are produced today by liquid-solid transformation where formation of extraneous nuclei during the growth of the initially formed nucleus is unstable in the surrounding liquid phase. Unfortunately, single crystal growth from melts is not useful for fabricating crystals of compositions that decompose, transform to some undesirable phase, or melt incongruently on heating. Consequently, single crystals of many such complex, but highly useful, compositions have not been made. For these materials, elevated temperatures and melting need to be avoided. We will describe our strategy to overcome these challenges, employing solid®solid transformation, and thus fabricate single crystals that were impossible to make previously (see Figure). We will also discuss complexities of crystal growth that result from its confinement within the solid glass matrix. In particular, a new form of solid, ‘rotating lattice single (RLS)’ crystal is produced, whose characteristics will be presented.Bio: Himanshu Jain is the T.L. Diamond Distinguished Chair in Engineering and Applied Science, and Professor of Materials Science and Engineering at Lehigh University. An author of six patents and over 360 research publications, he is the editor or author of nine books on glass science and technology. Over the past three decades he has focused on introducing new functionality and novel processing of glass through fundamentals, and making glass education available worldwide freely. Jain is a recipient of Otto Schott Research international prize for his ‘jellyfish’ model of atomic fluctuations in glass, Zachariasen international award for outstanding contribution to glass research through the discovery of isotope mass effect in lithium transport in glass, Alfred University’s Scholes Lecture award for the development of active glasses, Lehigh University’s Libsch award for research and Hillman award for long-term excellence, Fulbright Fellowship for lecturing and research at Cambridge and Aberdeen universities in UK, and a Humboldt Fellowship for research in Germany. He is a Fellow of the American Ceramic Society.