Adiabatic Nanofocusing on Ultrasmooth Single-Crystalline Gold Tapers Creates a 10-nm-Sized Light Source with Few-Cycle Time Resolution

Slawa Schmidt†, Björn Piglosiewicz†, Diyar Sadiq†,Javid Shirdel†, Jae Sung Lee‡, Parinda Vasa†,Namkyoo Park‡, Dai-Sik Kim§, and Christoph Lienau†*

^† Institut für Physik, Carl von Ossietzky Universität, 26111 Oldenburg, Germany

^‡ Photonic Systems Laboratory, School of EECS, Seoul National University, Seoul 151-744, Korea

^§ Center for Subwavelength Optics and Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea

ACS Nano, Article ASAP

DOI: 10.1021/nn301121h

Publication Date (Web): June 8, 2012

Copyright © 2012 American Chemical Society

We demonstrate adiabatic nanofocusing of few-cycle light pulses using ultrasharp and ultrasmooth single-crystalline gold tapers. We show that the grating-induced launching of spectrally broad-band surface plasmon polariton wavepackets onto the shaft of such a taper generates isolated, point-like light spots with 10 fs duration and 10 nm diameter spatial extent at its very apex. This nanofocusing is so efficient that nanolocalized electric fields inducing strong optical nonlinearities at the tip end are reached with conventional high repetition rate laser oscillators. We use here the resulting second harmonic to fully characterize the time structure of the localized electric field in frequency-resolved interferometric autocorrelation measurements. Our results strongly suggest that these nanometer-sized ultrafast light spots will enable new experiments probing the dynamics of optical excitations of individual metallic, semiconducting, and magnetic nanostructures.