Pulse Duration and Temporal Contrast as Critical Parameters for Internal Structuring of Silicon

The advent of infrared laser technologies creates a new avenue for directly creating 3D microdevices inside silicon chips by laser writing. However, challenges persist due to material nonlinearities that prevent to reach writing conditions with the shortest femtosecond pulses [1]. When turning to longer pulses up to nanosecond duration, the situation progressively improves. Decreased power and nonlinear effects make bulk modification become usually achievable [2]. However, the literature remains very contradictory on the conditions for bulk Si modifications. Some report waveguide writing with ultrashort pulses [3] while others show very hardly achievable modifications with relatively long pulses [4]. This is the opposite of current understanding and provides a motivation to study laser-technology-dependent parameters. After studying the pulse duration dependence [2], we have found that by combining different pulse durations, the temporal contrast corresponding to the intensity ratio of the background or pre/post - pulses to the main peak pulse is another key parameter in these situations.