Enhanced Optical Limiting in Plasmonic Cu-Integrated Silica Nanocomposites

Abstract

Plasmon-engineered dielectric nanocomposites are promising materials for enhancing nonlinear optical (NLO) responses. With the rapid advancement of high-intensity laser technologies, there is a growing demand for efficient optical limiting systems to safeguard sensitive photonic components and human vision from high-intensity laser radiation. In this context, this study reports the development of metal-based optical limiters by integrating copper nanoparticles into a silica matrix, offering an efficient platform for an enhanced nonlinear optical response. The nanocomposites were synthesized via the sol–gel route, and their structure and morphology were examined using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM), respectively. The elemental composition and chemical state were analyzed by X-ray photoelectron spectroscopy, and the third-order nonlinear optical properties and optical-limiting performance were evaluated using the Z-scan technique. Copper nanoparticles introduce pronounced plasmon–matrix coupling within the silica host, enabling bandgap modulation and strong local electromagnetic field enhancement, which collectively promote efficient two-photon absorption and nonlinear optical responses. Plasmonic states at the metal–dielectric interface modulate charge transport and amplify excited-state absorption, yielding dominant reverse-saturable absorption and robust optical limiting properties. The nanocomposites exhibited an optical limiting threshold of 1.66 Jcm⁻² at an input energy of 0.5 mJ under 532 nm excitation (5 ns, 10 Hz). The results reveal a clear correlation between nonlinear absorption dynamics and plasmon-mediated charge transport, establishing copper-silica (Cu–SiO₂) nanocomposites as efficient platforms for photonic protection and laser-sensitive-sensor applications.