Ultrafast nano-focusing with full optical waveform control
Journal Article
Overview
abstract
The spatial confinement and temporal control of an optical excitation on; nanometer length scales and femtosecond time scales has been a long-standing; challenge in optics. It would provide spectroscopic access to the elementary; optical excitations in matter on their natural length and time scales and; enable applications from ultrafast nano-opto-electronics to single molecule; quantum coherent control. Previous approaches have largely focused on using; surface plasmon polariton (SPP) resonant nanostructures or SPP waveguides to; generate nanometer localized excitations. However, these implementations; generally suffer from mode mismatch between the far-field propagating light and; the near-field confinement. In addition, the spatial localization in itself may; depend on the spectral phase and amplitude of the driving laser pulse thus; limiting the degrees of freedom available to independently control the; nano-optical waveform. Here we utilize femtosecond broadband SPP coupling, by; laterally chirped fan gratings, onto the shaft of a monolithic noble metal tip,; leading to adiabatic SPP compression and localization at the tip apex. In; combination with spectral pulse shaping with feedback on the intrinsic; nonlinear response of the tip apex, we demonstrate the continuous micro- to; nano-scale self-similar mode matched transformation of the propagating; femtosecond SPP field into a 20 nm spatially and 16 fs temporally confined; light pulse at the tip apex. Furthermore, with the essentially wavelength and; phase independent 3D focusing mechanism we show the generation of arbitrary; optical waveforms nanofocused at the tip. This unique femtosecond nano-torch; with high nano-scale power delivery in free space and full spectral and; temporal control opens the door for the extension of the powerful nonlinear and; ultrafast vibrational and electronic spectroscopies to the nanoscale.
