Intellectual merit: The goal of the proposed research is to develop a nonlinear nanoprobe for nano-femto scale spatiotemporal characterization of ultrafast optical near fields. The proposed nanoprobe consists of a nonlinear nanoparticle attached to a nanowire, which is in turn attached to a silica fiber taper. The nonlinearity of the nanoparticle enables temporal characterization through autocorrelation or frequency resolved optical gating measurements while the nanoscale spatial resolution is achieved through near field scanning of the nonlinear nanoparticle. We will develop two-photon fluorescent and second harmonic nanoprobes, develop and optimize nanoprobe based spatiotemporal characterization technique, and investigate the precision of the proposed nanoprobe based method. With the unique capabilities of the proposed nonlinear nanoprobes, we also plan to investigate their applications to probing several interesting ultrafast optical near fields.
Broad impact: The proposed nanoprobe can significantly advance the state of the art of nano & ultrafast technology, which can in turn create far-reaching impacts in many scientific disciplines in which they play a central role. With its unique capability in providing nano-femto scale spatiotemporal mappings, the proposed nonlinear nanoprobe can find many important applications. Fundamental questions with regard to light-matter interaction in the ultrafast regime, ultrafast dynamics of complex nanostructures, and nonlinear optics in nanoscale plasmonic structures, can all benefit from the development of the proposed nanoprobe. As a result, the proposed research can have considerable impact on areas such as nonlinear optical microscopy and nanophotonics. The proposed research is highly interdisciplinary and can also provide excellent education opportunities for students.
We have developed a nonlinear nanoprobe for characterizing ultrafast optical field at nano-femto spatiotemporal scale. The nanoprobe consists of a silica fiber taper to provide an interface for macroscopic handling and positional control, a single nanowire (or nanotube) attached to the taper, and a single or multiple nonlinear nanoparticles attached to the nanowire (or nanotube). The nonlinearity of the nanoparticles enables temporal characterization at femtosecond scale while nanoscale spatial resolution can be achieved due to the nanoscale dimensions of the nanoprobe. We have developed method to fabricate the nanoprobe. A scanning electron microscopy image of a nanoprobe is provided in the supplementary figure. We demonstrated in situ characterization of both the amplitude and the phase of pulses directly at the focal point of an objective lens and in the air core of a photonic crystal fiber. These results indicate that the nanoprobe can be utilized to probe the evolution of ultrafast optical fields in complex 3D micro- or nanostructures. We have also characterized the nonlinear response of several nonlinear probes fabricated using different combinations of nano-crystals and nanowires, and observed anomalous behavior in one type of probe. We attributed this anomaly to the phase transition of the constituent nanocrystals due to heating by the ultrashort optical pulses. We have also conducted preliminary study of a new method to map the spatiotemporal pulse evolution. Our research has led to three journal publications. The research addresses an important need in nano femto optics, an emerging area where two remarkable technology - ultrafast optics and nanotechnology meet. With the unique capability to characterize an ultrafast optical near field in situ, the nonlinear nanoprobe can find many important applications, both on fundamental study such as nonlinear optics and ultrafast dynamics at nanoscale, and more practical ones such as optimization of nonlinear optical imaging systems. The nanoprobe can help elucidate the interesting physics of ultrafast nonlinear light-matter interaction at nanoscale. On education, graduate students have actively participated in the research work. The research results become part of their theses. One M.S. student and two Ph.D. students graduated.
