This paper considers a range of plasmonic-black-metal polarizers suitable for ultra-short pulses. The polarizers consist of
a metal surface being nanostructured with a periodic array of ultra-sharp grooves with periods of 250-350 nanometers,
and groove depths around 500 nanometers. The surfaces can be designed such that practically all incident light with
electric field perpendicular to the groove direction is absorbed. The efficient absorption is due to incident light being
coupled into gap-plasmon polaritons that propagate downwards in the gaps between groove walls towards the groove
bottom, where it is then subsequently absorbed during propagation. Reflection is largely avoided due to an adiabatic
groove taper design. The other polarization, however, is very efficiently reflected, and the main point of this paper is that
the reflection is with negligible dispersive stretching even for ultra-short pulses of 5-10 femtoseconds temporal width in
the visible and near-infrared. Temporal pulse shapes after reflection are calculated by decomposing the incident laser
pulse into its Fourier components, multiplying with the reflection coefficient in the frequency domain, and then Fouriertransforming
the product back to the time-domain. Reflection of pulses is compared for polarizers based on different
metals (gold, nickel, chromium). Polarizers are studied for two groove-array designs and two directions of light
incidence, center wavelengths 650 nm and 800 nm, and pulse widths 5 fs and 10 fs for the incident pulse.
Surface plasmon polariton (SPP) excitation at a gold-vacuum interface via 800 nm light pulses mediated by a periodic
array of gold ridges is probed at high lateral resolution by means of photoemission electron microscopy (PEEM). We
directly monitor and quantify the coupling properties as a function of the number of grating ridges and compare the
PEEM results with analytic calculations. An increase in the coupling efficiency of ≈ 3 is observed when increasing the
number of ridges from 1 to 6. We observe, however, that a further addition of ridges is rather ineffective. This saturation
behavior is assigned to the grazing incidence excitation geometry intrinsic to a conventional PEEM scheme and the
limited propagation distance of the SPP modes at the gold-vacuum interface at the used wavelength.
Photoemission spectroscopy using femtosecond XUV light pulses is applied to probe the isomerization state of the
molecular switch 3-(4-(4-hexyl-phenylazo)-phenoxy)-propane-1-thiol deposited by liquid phase self-assembly on
Au(111). Spectral shifts of valence-electronic signatures that we associate with the carbon C2s orbital enable us to
distinguish the trans and the cis isomerization state of the adsorbed molecules. These preliminary results envision the
potential to probe reversible switching processes of surface-mounted molecules in real time by tracking the temporal
evolution of the electronic and nuclear degrees of freedom in a femtosecond XUV photoemission experiment.
In combining time-resolved two-photon photoemission (TR-2PPE) and photoemission electron microscopy (PEEM) the ultrafast dynamics of collective electron excitations in silver nanoparticles (localized surface plasmons - LSP) is probed at femtosecond and nanometer resolution. In two examples we illustrate that a phase-resolved (interferometric) sampling of the LSP-dynamics enables detailed insight into dephasing and propagation processes associated with these excitations. For two close-lying silver nano-dots (diameter 200 nm) we are able to distinguish small particle to particle variations in the plasmon eigenfrequency, which typically give rise to inhomogeneous line-broadening of the plasmon resonance in lateral integrating frequency domain measurements. The observed spatio-temporal modulations in the photoemission yield from a single nanoparticle can be interpreted as local variation in the electric near-field and result from the phase propagation of the plasmon through the particle. Furthermore, we show that the control of the phase between the used femtosecond pump and probe laser pulses used for these experiments can be utilized for an external manipulation of the nanoscale electric near-field distribution at these particles.
Modification of metal nanoparticles with laser light has been a well-known technique for several years. Still, selective tailoring of certain sizes or shapes of nanoparticles has remained a challenge. In this paper, we present recent studies on tailoring the size and shape of supported nanoparticles with continuous-wave and femtosecond
pulsed laser light and compare them to our results obtained with ns pulsed laser light. The underlying method is based on the size and shape dependent plasmon resonance frequencies of the nanoparticles. In principle, irradiation with a given laser photon energy excites and heats nanoparticles of certain sizes or/and shapes and leads to diffusion and evaporation of surface atoms. Thus, tailoring the dimensions of the nanoparticles can be accomplished. In our experiments, gold and silver nanoparticles were prepared under ultrahigh vacuum conditions by deposition of atoms and subsequent diffusion and nucleation, i.e. Volmer-Weber growth. This gives particle ensembles with size and shape distributions of approximately 30% - 40%. The nanoparticle ensembles were irradiated with laser light either during or after growth. It turns out, that irradiation with cw or ns laser light makes possible selective modification of the nanoparticles. In contrast, application of fs laser pulses results in non-selective modification. For example, post-grown irradiation of supported gold nanoparticles with ns laser pulses (photon energy = 1.9 eV) causes a clear reduction of the width of the surface plasmon resonance from 0.52 eV to 0.20 eV (HWHM). Similar experiments were carried out with fs pulsed laser light (photon energy = 1.55 eV), which result in a slightly reduced line width but also, to an overall decrease of the extinction. A
comparison of all experiments revealed, that for size or shape tailoring of supported metal nanoparticles best results have been achieved with ns pulsed laser light.
A new generation of compact Fluorine lasers has been developed for repetition rates up to 2 kHz. The output powers are in the range of 3 W at 157 nm. Due to the introduction of new concepts for the laser tube and the pulsed power module it was possible to increase the maximum repetition rate from 1 kHz to 2 kHz without any loss in the performance of the laser output parameters. The pulse-to-pulse stability of the laser energy is improved in comparison to previous laser generations. The results of long term tests and measurements of the laser output characteristic will be reported in detail. The state-of-the-art of compact excimer lasers will be presented and an outlook for future trends will be given.
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