Quantitative estimate of fs-laser induced refractive index changes in the bulk of various transparent materials

Abstract

Over the past years, many applications based on laser-induced refractive index changes in the volume of transparent materials have been demonstrated. Ultrashort pulse lasers offer the possibility to process bulky transparent materials in three dimensions, suggesting that direct laser writing will play a decisive role in the development of integrated micro-optics. At the present time, applications such as 3D long term data storage or embedded laser marking are already into the phase of industrial development. However, a quantitative estimate of the laser-induced refractive index change is still very challenging to obtain. On another hand, several microscopy techniques have been recently developed to characterize bulk refractive index changes in-situ. They have been mostly applied to biological purposes. Among those, spatial light interference microscopy (SLIM), offers a very good robustness with minimal post acquisition data processing. In this paper, we report on using SLIM to measure fs-laser induced refractive index changes in different common glassy materials, such as fused silica and borofloat glass (B33). The advantages of SLIM over classical phase-contrast microscopy are discussed

Structural relaxation phenomena in silicate glasses modified by irradiation with femtosecond laser pulses

“…The sample was scanned longitudinally with respect to the direction of the laser propagation with a constant velocity of 15 μm/s, resulting in line-shaped optical structures. The refractive index of those fs-laser induced structures was measured using a spatial light interference microscopy (SLIM) 35 setup which has been used before by the authors to characterize fs-laser induced refractive index changes in fused silica 36 .…”