Section of Graduate Studies and Research, School of Mechanical and Electrical Engineering, National Polytechnic Institute, Zacatenco, Distrito Federal, Mexico.
Int J Nanomedicine. 2010 Nov 18;5:925-32. doi: 10.2147/IJN.S12463.
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.
研究了高强度激光激发银纳米粒子（NPs）所产生的光损伤。为了研究纳米复合材料的光学非线性机制及其与烧蚀阈值的关系，用高纯二氧化硅样品进行了离子注入，然后用纳秒和皮秒激光进行了不同的辐照。采用自衍射技术，在银纳米粒子表面等离子体共振（SPR）附近和远离 SPR 的位置测量了皮秒折射和吸收非线性的大小和符号。确定了与自聚焦相关的可饱和光吸收和电子极化。线性吸收是纳秒激光烧蚀涉及的主要过程，但当吸收过程显著依赖于辐照度时，皮秒超短脉冲的非线性很重要。我们估计，在近共振时，皮秒带内跃迁允许能量在 NPs 之间扩展分布，与远共振时的能量分布相比，在远共振时，大部分吸收发生在二氧化硅中。我们测量了烧蚀阈值的重要差异，并估计 Ag NPs 的 SPR 及其相应的光学非线性的高选择性可能对激光诱导的受控爆炸具有重要意义，在生物医学光热过程中有潜在的应用。
