High refractive index modification of SiO₂created by femtosecond laser nanostructuring

Abstract

By comparing simulations with experiment, we show that the effective refractive index of fused SiO 2 can be locally reduced by (1.8 ± 0.2)% by femtosecond laser nanostructuring. We create a microlens of material containing a planar array of nanocracks embedded inside fused silica and probe how it refracts or absorbs light as a function of pulse energy. The self-generated microlens lowers the peak light intensity by deflecting the light around the focus. We obtain the refractive index by simulating the beam transport using the 3D wave equation in conjunction with the measured dimensions of the modified material.

Non-linear absorption of focused femtosecond laser pulses at 1.3μm inside silicon: Independence on doping concentration

“…One of the advantages of using infrared wavelength above 1 m is to make accessible the interior of silicon for laser-matter interactions. Then, direct femtosecond laser 3D-writing technologies similar to those developed for microfabrication inside optically transparent dielectrics [4][5][6][7] can be envisioned for semiconductors. As we show in this paper, by tightly focusing a very modest energy infrared femtosecond laser pulse inside silicon, it is possible to reach sufficient intensities in the focal volume to initiate local non-linear absorption.…”

Internal Structuring of Semiconductors with Ultrafast Lasers: Opening a Route to Three-Dimensional Silicon Photonics

“…Second, with repeated irradiations at higher fluences, the modification generally becomes heterogeneous with the formation of defects (from excitons [13] to lattice distortions, and reorganization on a subwavelength scale [14]). In fused silica, this culminates with the formation of well-ordered planar nanogratings perpendicular to the laser polarization [15,16] attracting considerable interest for advanced technologies including photonics [17,18,19,20,21,22]. Third, when extremely tight focusing conditions are employed, the extraordinary space-time confinement of the interactions leads to pressure and temperature conditions that are not accessible with other techniques [23,24].…”