17 research outputs found
Ultrafast nano-focusing with full optical waveform control
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.Comment: Contains manuscript with 4 figures as well as supplementary material
with 2 figure
Superfocussing in a metal-coated tetrahedral tip by dimensional reduction of surface-to edge-plasmon modes
Adiabatic Nanofocusing on Ultrasmooth Single-Crystalline Gold Tapers Creates a 10-nm-Sized Light Source with Few-Cycle Time Resolution
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