Investigating the effects of Ag/Au nanoparticle mixing ratios on nonlinear optical properties using femtosecond laser light

This study investigates the nonlinear optics (NLO) characteristics of colloidal silver–gold (Ag/Au) nanoparticles (NPs), synthesized in varying mixing ratios under femtosecond laser excitation. We show how to create Ag/Au NPs using a two-step procedure that involves laser irradiation and laser ablation. Using a Nd: YAG pulsed laser’s second-harmonic (532 nm) and the same average power and ablation time, Ag and Au NPs were first produced independently in distilled water. These individual Ag and Au colloids were then combined and re-irradiated with the pulsed laser to induce mixing. Multiple Ag/Au mixing ratios were similarly treated to explore the impact of composition. Transmission electron microscopy (TEM) was used to analyze the morphological characteristics of the resultant colloids, and UV–visible absorption spectroscopy was used to characterize their optical characteristics. By systematically varying the Ag/Au composition, we evaluated how changes in the mixture content influence NLO phenomena, particularly nonlinear absorption and scattering, which are critical for optical limiting applications. The Z-scan technique was used to determine NLO parameters using femtosecond laser pulses (a wavelength of 800 nm, a repetition rate of 80 MHz, a pulse width of 100 fs, and an average power of approximately 1 W). The findings show that changes in plasmon resonance and localized field enhancement effects are the main causes of the NLO response’s high sensitivity to the Ag/Au ratio. These findings underscore the significance of compositional tuning in optimizing the optical performance of bimetallic NPs for photonic applications.