High refractive index change in Type A laser modification using a multi-scan approach

The focusing of femtosecond laser pulses is an efficient and robust way to fabricate integrated optical components in glasses. However, the induced refractive index changes are weak if compared with those obtained in lithography. Several solutions have been found to overcome such problem, the multi-scan technique being one of these. The present work implements the multi-scan approach on the femtosecond inscription of Type A laser modifications in high repetition rate regime. Therefore, a study on the effects of the absorption of subsequent laser pulses on the increase of the induced refractive index is conducted. As a result, the achievement of high and smooth refractive index change, up to 2 × 10⁻², in a commercial silver-glass is reported. Moreover, such high and controlled index contrast is exploited for the fabrication of low-propagation-losses and engineered waveguides exhibiting single-mode operation in the VIS-NIR range.