Watching plasmons spin on atomically flat single crystalline gold

Datum

06.12.2018

Zeit

11:00 - 12:00

Sprecher

Prof. Dr. Harald Giessen

Zugehörigkeit

4th Physics Institute, University of Stuttgart, Stuttgart, Germany

Serie

IFW Kolloquium

Sprache

en

Hauptthema

Materialien

Andere Themen

Materialien, Physik

Host

Beschreibung

We use single crystalline gold flakes on atomically flat silicon substrates to generate ideally suitable interfaces for plasmon propagation. By electrochemical means, the thickness is tunable from a few tens to over 100 nm. Using sub-20 fs laser pulses around 800 nm, we excite surface plasmons, whose dynamics can be observed using time-resolved two-photon excitation electron emission (PEEM). Plotting the dispersion of surface plasmons in a thin gold slab on silicon, one finds that excitation at 800 nm can lead to extreme wavelength reduction due to the dispersion slop of over five. Using focused ion beam for cutting rings with appropriate periodicity into the samples (see left image), we can excite concentric surface plasmons that create a nanofocus of only 60 nm width for 800 nm excitation (see center image) [1]. Figure 1. Atomically flat single crystalline gold with PEEM images of short-range surface plasmons. Nanofocusing down to 60 nm at 800 nm wavelength is observed, as well as orbital angular momentum plasmons up to l=4. Archimedean spirals with broken n-fold radial symmetry excite surface plasmons with angular orbital momentum on the gold flakes (see right image). This leads in case of 4-fold symmetry to cloverleaf-type nanofoci on the order of 100 nm, which rotate during four optical cycles by 360 degrees [2]. Two-pulse experiments with a subwavelength-stabilized Michelson interferometer, allow investigation of the surface pattern dynamics with (sub-) femtosecond resolution, thus giving insight into the dynamics of the nanofocus formation as well as on the plasmonic spin-orbit coupling [3].

Links

• Seminars at the IFW

Letztmalig verändert: 06.12.2018, 01:05:23