微/纳小尺度体系的近场飞秒光动力学研究

项目名称： 微/纳小尺度体系的近场飞秒光动力学研究

项目编号： No.10804004

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 建筑科学

项目作者： 李智

作者单位： 北京大学

项目金额： 24万元

中文摘要： 本项目主要利用我们搭建的目前国内唯一的一套飞秒时间分辨近场光学系统研究微/纳空间小尺度体系中的超快光动力学过程。通过双波长泵浦探测配置，特别是将探测波长选择在金的带间跃迁波长，我们成功消除了金属表面等离激元共振对信号探测的影响，实现了局域探测，首次在金属纳米结构中观察到时空同时高分辨的热电子弛豫过程，为进一步设计基于金属热电子和表面等离激元的超快响应器件打下了基础。在此基础上，通过结合飞秒脉冲光和表面等离激元透镜，我们成功在表面等离激元透镜的焦点获得了超小超快的全光调制，实验测得调制点的空间尺寸只有约600nm，而调制的响应时间只有约1.5ps。此外，基于非对称单缝结构，我们成功设计实现了超紧凑的表面等离激元全光调控、单向激发和分束等，特别是全光调控，通过利用腔效应和集成设计，实验上在横向尺寸只有2 μ#30340;器件上获得了大于20 dB的开关比和大于π30340;相位调制，是目前在这么小的尺寸下实现的最大的开关比。

中文关键词： 飞秒近场；时间空间高分辨；表面等离激元；纳米结构；超快动力学；

英文摘要： Based on a femtosecond time-resolved scanning near-field optical microscope (femtosecond-SNOM) establish by us, we mainly studied the ultrafast optical processes in nanostructures in the project. By employing two-color pump-probe configuration and probing at the interband transition wavelength of the gold, signal contributed by surface plasmon polaritons (SPPs) was avoided and spatiotemporal evolvement of excited electrons was successfully observed. Then, by exciting a plasmonic lens with femtosecond laser and utilizing the optical nonlinearity of the gold, an ultrasmall and ultrafast all-optical modulation spot was successfully achieved inside a thin gold film. Near-field pump-probe measurements indicated a modulation spot size of only 600 nm, and a response time of only 1.5 ps. Furthermore, ultracompact plasmonic devices including SPP unidirectional generator, splitter and all-optical switch were experimentally demonstrated based on asymmetric single-nanoslit structrues. For the all-optical SPP switch, the nonlinear light-matter interaction was enhanced because of the cavity effect, which increases the sensitivity of SPPs to the surrounding dielectric. Moreover, the SPP generation and modulation processes are integrated in the same asymmetric single slit, which makes the device ultracompact. Experimentally, a high on/off switching ratio of > 20 dB and phase variation of > πere observed with the device lateral dimension of only about 2 μ

英文关键词： femtosecond SNOM; spatiotemporal high resolved; surface plasmon polaritons; nanostructure; ultrafast dynamics