Fused Silica with Embedded 2D-Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation

Saturable absorbers are key elements for generation of ultrafast laser pulses. The commercially available semiconductor saturable absorber mirrors are wavelength sensitive and with complex fabrication process and high cost. Fused silica is one of the basic materials for various optical applications. Plasmonic nanoparticles can be used to efficiently modulate the optical properties of dielectric materials owing to the enhanced field effects based on localized surface plasmonic resonance. Ion implantation is a direct technique to synthesize plasmonic nanoparticles inside dielectric materials, which can simultaneously tailor the optical nonlinearity of substrates significantly. In this work, Ag ion implantation into fused silica with tunable interparticle spacing is used to generate broadband optical nonlinearities and to endow silica with ultrafast saturable absorption property. This ion implantation forms a 2D-like Ag nanoparticle monolayer buried inside fused silica wafer. The fused silica with embedded 2D-like Ag nanoparticle monolayer is further applied as a new saturable absorber to generate ultrafast laser pulses with pulse duration of 27 ps and repetition rate of 6.5 GHz through the passive mode-locking process. This work opens up a new route to develop low-cost, highly stable saturable absorbers, and offers the possibility to build novel silica-based photonic systems through nanoparticle spacing manipulation.