May 14 2014 Wednesday 15:30
Onur Tokel, Bilkent University
Light-Matter Interactions: From Fundamental Interactions to Nonlinear Sculpturing

Abstract: This talk will chart a course spanning interactions of laser radiation with matter, from individual atoms in gas form to bulk semiconductors and to liquid phase for biosensing. This course also charts the interdisciplinary background of the speaker, spanning engineering, physics and chemistry.

Since its first introduction by Chandler and Houston, 2D ion/photoelectron imaging has set the experimental paradigm for measuring angle-, energy- and state-resolved ion or electron velocity distributions that result from photoionization or molecular photodissociation events. We have further developed and applied this technique to answer fundamental questions, such as what happens when laser light interacts with a molecule or atom. If the target is a molecule, does it fall apart; if so, what products does it create? What are the dynamical details of the interaction event, and can we image the events with quantum state selectivity? We answer these questions by looking at the interaction of single photons with an atom or molecule.

A different picture emerges if we get multiple photons to interact simultaneously with an atom or molecule. Using state-of-the-art femtosecond lasers, we access new experimental modalities, such as multi-photon structuring of transparent materials, and non-thermal processing, where photons transfer all their energy to electrons without increasing the lattice temperature. Combining these leverages, we are investigating nonlinear laser lithography and associated emergence of spatial order from feedback and noise. In parallel, I am exploring 3D laser processing of silicon deep below the surface, for the first time, without affecting the surface. This new capability can open new vistas in photovoltaics and silicon photonics.

I will proceed with applications to biology. These include a novel nanoplasmonic HIV (Human Immunodeficiency Virus) capture, detection and quantification platform from unprocessed whole blood. This work is the first nanoplasmonic detection and quantification of any pathogen from whole blood in the literature. Real-life implementation of our multiple-award-winning technology will potentially have far-reaching societal and economic impact.

This talk summarizes my work in laser-matter interactions in the solid, liquid and gas phases. Finally, I will discuss exciting possibilities of using the fourth state of matter to provide reactive chemical species, which will undergo nonlinear interactions with surfaces activated by ultrafast laser pulses. This completely unexplored capability creates the possibility to synthesize an unlimited range of nanopatterns, composed of a wide variety of materials.