Polarization Dependent Femtosecond Laser Microstructuring of Silicon

Abstract

Microstructuring of silicon is performed to alter its optical and electrical properties for use in photonic devices. Femtosecond lasers are a favourable structuring tool because they are extremely precise due to the confinement of their interaction to the focal volume. Experiments were carried out on N-type, P-type, and intrinsic silicon with a femtosecond laser operating at 800 nm, with pulse duration of 40 fs, and 1 kHz repetition rate. A single pulse produced a micro-ring structure surrounding a crater. It is caused by the motion of material according to the pressure gradient induced by the Gaussian profile of the laser. Multiple-pulse structures were similar to the single pulse except for the central protrusion of material. Two factors are responsible for multiple-pulse structures: (1) geometrical difference of the plasma compared to the single pulse (2) reflections of shockwaves produce protruding structures. Polarization dependence of all structures was observed.