Ablation and optical third-order nonlinearities in Ag nanoparticles

Abstract

The optical damage associated with high intensity laser excitation of silver nanoparticles (NPs) was studied. In order to investigate the mechanisms of optical nonlinearity of a nanocomposite and their relation with its ablation threshold, a high-purity silica sample implanted with Ag ions was exposed to different nanosecond and picosecond laser irradiations. The magnitude and sign of picosecond refractive and absorptive nonlinearities were measured near and far from the surface plasmon resonance (SPR) of the Ag NPs with a self-diffraction technique. Saturable optical absorption and electronic polarization related to self-focusing were identified. Linear absorption is the main process involved in nanosecond laser ablation, but non-linearities are important for ultrashort picosecond pulses when the absorptive process become significantly dependent on the irradiance. We estimated that near the resonance, picosecond intraband transitions allow an expanded distribution of energy among the NPs, in comparison to the energy distribution resulting in a case of far from resonance, when the most important absorption takes place in silica. We measured important differences in the ablation threshold and we estimated that the high selectiveness of the SPR of Ag NPs as well as their corresponding optical nonlinearities can be strongly significant for laser-induced controlled explosions, with potential applications for biomedical photothermal processes.

Keywords:

• nonlinear optics
• laser irradiation
• metallic nanoparticles
• Kerr effect
• nonlinear optical absorption

Acknowledgments

We acknowledge the financial support from COFAA-IPN, from IPN through grant SIP20100800; from UNAM, through grants IN108510, IN103609-3, IN101210; from ICyT-DF through grant PICCT08-80 and from CONACyT, through grants 82708, 80024, 80019, 102937. The authors kindly acknowledge CICESE and the CNyN-UNAM for making available the nanosecond lasers. The authors acknowledge K López and FJ Jaimes for accelerator operation and JG Morales for sample preparation.

Disclosure

The authors report no conflicts of interest in this work.