Large thermally induced nonlinear refraction of gold nanoparticles stabilized by cyclohexanone

Abstract

AbstractStabilized gold nanoparticle (AuNP) colloids have been fabricated by nanosecond pulsed laser ablation of a pure gold plate in cyclohexanone. The AuNPs colloid exhibits a UV–Vis absorption spectrum with a surface plasmon absorption peak at about 540 nm. Scanning electron microscopy has shown the formation of spherical AuNPs with average size about 53 nm. The shift of 24 cm−1 is observed in the carbonyl band of the colloid using FTIR spectroscopy. This shift indicates that the monomer carbonyl group of cyclohexanone interacts with the surface of the AuNPs and leads to stabilizing the colloid. A large nonlinear refractive index of −2.92 × 10−7 cm2/W is measured using the Z‐scan technique under continuous wave laser irradiation at 532 nm. Our results show that the large induced nonlinear refraction is attributed to the surface plasmon resonance (SPR) enhancement effect of AuNPs, high thermo‐optic coefficient and low thermal conductivity of cyclohexanone. Observation of far‐field diffraction ring patterns confirm a thermally induced negative lens effect and spatial self‐phase modulation in the laser beam as it traverses the colloids.