Razvan Stoian graduated in 1995 from the Bucharest University with a degree in Physics and received his doctoral degree in Natural Sciences in 2000 from the Free University, Berlin. He was with the Ultrafast Laser Material Processing Group at the Max-Born Institute, Berlin between 1997 and 2004. In 2004 he joined the Centre Nationale de la Recherche Scientifique (CNRS) France where he is currently research director. He is leading the Laser-Matter Interaction group at Laboratoire Hubert Curien, St. Etienne, France, a joint research unit of the CNRS and Jean Monnet University. His research interests include laser matter interactions and material processing. His work focuses on ultrafast laser micro-nano fabrication, process monitoring, and the development of smart, adaptive techniques based on pulse spatio-temporal engineering for processing functional surfaces and photonic systems.
Ultrafast lasers contribute essentially to the development of micro/nanotechnologies, being able to structure materials with utmost precision. This originates specifically in their strong ability to confine light energy in nonlinear interactions and to suppress thermal effects, reducing thus collateral damage. I will discuss in my talk ultrafast laser irradiation concepts capable of achieving structuring features with sub-wavelength characteristic sizes. After briefly introducing achievements in surface texturing based on self-induced periodic patterns. I will focus on laser fabrication of embedded optical systems.
Present advances in photonics include the development of optical devices based on laser-induced refractive index engineering. Relying on nonlinear energy deposition, ultrafast laser photoinscription can locally modify the material molecular structure and thus the material refractive index. This operation can be performed in arbitrary geometries in bulk optical materials, laying down the concept of 3D design for efficient optical functions. Here nanoscale precision can deliver high levels of performance. Therefore bypassing the diffraction limit is key for a new range of applications in optics requiring optical access at the nanoscale. I will discuss the capability of Gauss and Bessel-Gauss pulses with engineered dispersion to localize light on subwavelength scales. I’ll show how sculpting beams in space and time can bring advantages for controlling the interaction between light and matter and for achieving extreme confinement of energy. Then I will discuss physical mechanisms of photoinscription by following the time dynamics of excitation over the entire evolution cycle, serving as guidelines for control. The talk will explore the influence of pulse temporal and spatial design in achieving index structures on 100 nm scales, either in direct focusing or in self-organization schemes in fused silica. Non-diffractive beam excitation takes advantage of this localization and achieve unprecedented high-aspect-ratio structuring. Subsequently I will present photonic systems where hybrid micro/nanoscale features can develop advanced optical functionalities. The results show a high capability to transport, manipulate and access electrical fields in integrated optical systems, either for Bragg sensing or for reconstruction spectral information. Finally I will indicate a range of applications, from telecom to astrophotonics.