Abstract

Nonlinear propagation phenomena impose severe limitations on the energy deposition in the bulk of crystalline silicon (c-Si) with single fs laser pulses [1], and make the functionalization of this material particularly challenging [2]. These restrictions have been successfully bypassed employing ns pulses for inscribing numerous elements inside c-Si [3–5]. However, because of the thermal effects unavoidable in the ns regime, one cannot expect performances equivalent to the analogous achievements in glasses with fs pulses existing for decades. In order to solve this problem, ps or sub-ps irradiations at high repetition rate (>100 kHz) have recently offered the possibility to write waveguides inside c-Si [6,7]. While this emerging regime is promising for in-volume structuring of silicon [8], the underlying material transformations responsible for the refractive index change associated with the waveguiding as well as the guiding losses need to be characterized.

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