Dynamics of coupled plasmon polariton wave packets excited at a subwavelength slit in optically thin metal films

Abstract

We study by numerical simulations the excitation and propagation dynamics of coupled surface plasmon polariton (SPP) wave packets (WPs) in optically thin Ag films and a bulk Ag/vacuum interface under the illumination of a subwavelength slit by 400 nm continuous wave (cw) and femtosecond pulsed light. The generated surface fields include contributions from both SPPs and quasi-cylindrical waves, which dominate in different regimes. We explore aspects of the coupled SPP modes in Ag thin films, including symmetry, propagation and attenuation, and the variation of coupling with incident angle and film thickness. Simulations of the electromagnetic transients initiated with femtosecond pulses reveal new features of coupled SPP WP generation and propagation in thin Ag films. Our results show that, under pulsed excitation, the SPP modes in an Ag thin film break up into two distinct bound surface wave packets characterized by marked differences in symmetries, group velocities, attenuation lengths and dispersion properties. The nanometer spatial and femtosecond temporal scale excitation and propagation dynamics of the coupled SPP WPs are revealed in detail by movies recording the evolution of their transient field distributions.2

Optical nano-antennas

“…al. [267], positioning any probe, such as an AFM tip, in the vicinity of the slit stablishes standing wave oscillations between the tip and the slit, leading to a series of minima/maxima that convolve with those of the interference envelope. Having said that, measurements carried out by Verhagen et.…”

“…al. [267] modelled a free standing optically thin silver film in vacuum, where authors try to explain their findings in terms of long range SPPs, SPP Wave Packets and Quasi Cylindrical Waves (QCW) … etc. Prior to that, Verhagen et.…”

The influence of electron confinement, quantum size effects, and film morphology on the dispersion and the damping of plasmonic modes in Ag and Au thin films

“…New adsorbate-induced electronic states arise at the interface [301,302]. Hence, the remarkable plasmon broadening is due to new channels for decay into e-h pairs at the K/Ag interface.…”

Focusing surface plasmon polariton wave packets in space and time

“…Moreover, most of previous studies have employed the surface normal illumination of the planar plasmonic lens, but only a few have considered the more general case of the focusing properties for off‐normal incidence . The off‐normal incidence may be required by the experimental geometry, such as by the restricted sample access as in a PEEM, or to improve the coupling efficiency . Indeed, recently Lemke et al reported an ITR‐PEEM study for offnormal incident excitation field onto elliptical and Fresnel lens structures, which were used to focus SPP‐WPs at Au/air interface, though no design principles for the optimal focusing were given .…”