Volume photoinscription of glasses: three-dimensional micro- and nanostructuring with ultrashort laser pulses
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Volume photoinscription of glasses: three‑dimensional micro‑ and nanostructuring with ultrashort laser pulses Razvan Stoian1 Received: 24 November 2019 / Accepted: 30 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Ultrafast laser photoinscription of optical materials has seen a strong development in the recent years for a range of applications in integrated photonics. Fueled by its capability to confine energy in micro-domains of arbitrary geometries, it forecasts extensive potential in optical design. The process can locally modify the material structure and the electronic properties, changing in turn the refractive index. It thus lays down a powerful concept for three-dimensional modifications of materials, with the potential to design integrated optical functions. Using fused silica as model glass, this report discusses the physical mechanisms of photoinscription, outlining the possibility of refractive index engineering. We will review basic mechanisms of light propagation, excitation of matter, and energy relaxation concurring to material structural and photophysical modification. A dynamic perspective will be given, indicating relevant times for relaxing different forms of energy (electronic, thermal, etc.). The possibility to structure beyond diffraction limit will be explored, as well as the subsequent optical response of hybrid micro–nanostructures. Different irradiation geometries for photoinscription will be presented, pinpointing their potential to generate optical and photonic systems in three dimensions. Spatiotemporal pulse engineering can optimize the material response toward the achievement of accurate positive and negative index changes. An optimality concept can thus be defined for index design and present optimization concepts will be discussed. A particular potential derives from the utilization of non-diffractive beams with engineered dispersion. Finally, we indicate a range of application domains, from telecom to optofluidics and astrophotonics, outlining the potential of volume micro- and nanoprocessing. Keywords Ultrashort laser pulses · Material processing · glass · Laser photoinscription · Refractive index engineering · 3D photonics
1 Introduction Nowadays, advances in micro- and nanotechnologies depend on the development of processing tools able to structure materials in two and three dimensions with utmost precision and reduced collateral damage. Remote control with the capability to interface and drive process parameters becomes an essential advantage. An intensively studied and utilized processing method, with an employment field ranging from macroscale applications in cutting, drilling, or welding to precise patterning in UV microelectronic lithography, relies on laser radiation. A more recent extension toward higher precision derives from the utilization of ultrashort * Razvan Stoian razvan.stoian@univ‑st‑etienne.fr 1
Laboratoire Hubert Curien, UMR 5516 CNRS, Université de Lyon, Université Je
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