Ultrafast laser-material interactions have diverse scientific, industrial and medical applications. Prior to our work, this process has largely been idealized as a one-way interaction — the laser beam modifies the material — end of the story. The idea of the material modifying the laser beam, in return, and that this could open new doors was apparently overlooked. Such two-way interactions either did not occur, or were unrecognized, if present, and actively prevented, when recognized. Our approach is to explicitly design for and exploit such interactions, and has already led to several striking advances. We developed our approach motivated by our prior experience in mode-locking of lasers: Mode-locking works by creating higher "gain" for modes that lock up in phase over having random phases, which leads to a coherent structure in time. Could we do something similar in laser-material interactions? Here, higher "gain" is achieved by invoking nonlinearities in the form of positive feedback between laser beam-induced changes in the material and material change-induced effects back on the laser beam. With this approach, we first showed that we could create laser-induced spatial nanostructures on various material surfaces with unprecedented uniformity (Ilday et al., Nature Photon., 2013) by locking the modes in space. Afterwards, we have applied the same concept to invent a new regime of laser-material ablation (Ilday et al., Nature, 2016), to create self-organized 3D structures inside silicon (Ilday et al., Nature Photon., 2017), to drive self-assembly of colloidal nanoparticles (Ilday et al., Nature Commun., 2017), which will be discussed briefly.
Dr. F. Ömer Ilday received the BS degree in theoretical physics from Boğaziçi University, Istanbul, Turkey, in 1998. He took his PhD in applied physics from Cornell University, Ithaca, NY, USA, in 2003. He worked in the Department of Electrical Engineering at Massachusetts Institute of Technology (MIT) from 2003 to 2006. In 2006, he joined Bilkent University as faculty member. Dr. Ilday was the first to propose to manage nonlinear dynamics of mode-locked lasers in order to improve their performance (J. Opt. Soc. Am. B, 2002). This vision led to his invention of the similariton laser, the first laser to operate better with stronger nonlinear effects (Phys. Rev. Lett., 2004). In 2010, he invented the soliton-similariton laser (Nature Photon., 2010). Applying a similar approach to laser-material interactions, he developed Nonlinear Laser Lithography (Nature Photon., 2013), which was extended to 3D volume structures (Nature Photon., 2017) and invented ablation-cooled laser-material removal (Nature, 2016). Based on the original concept, he was awarded the European Research Council's prestigious Consolidator Grant in 2013, the first of its kind in Turkey. Dr. Ilday received numerous awards from MIT, Cornell University, Turkish Academy of Sciences (TÜBA-GEBIP), Scientific and Technological Research Council of Turkey (TÜBİTAK). He is a full member of the Science Academy of Turkey and a senior member of the Optical Society of America. He has served as editor and guest editor for Optics Letters, Optics Express and Optical Fiber Technology, in addition to serving on the technical committee of numerous international conferences.
This seminar is sponsored by Stanford OSA