Leszek Józefowski

A 3D view on free-floating, space-fixed and surface-bound para-phenylene nanofibres

Nanofibres from para-hexaphenylene and functionalized quaterphenylene molecules are grown on mica surfaces and are thereafter transferred into solution, where they either freely rotate in water or are space-fixed in sucrose. From freely rotating aggregates highly anisotropic angular intensity distributions of emitted light for individual aggregates are determined. Luminescence is enhanced at the nanofibre tip as compared to the broad side by about an order of magnitude probably due to waveguiding along the long axis of the aggregates. For dense arrays of nanofibres on mica the increase of emitted intensity towards the substrate plane in the direction of the long axes of the nanofibres is smaller and it depends on the effective thickness of the nanofibre films. The difference between individual aggregates and aggregate arrays is interpreted in terms of light scattering at surface roughness inside the nanofibre film and on the border of the underlying mica substrate. Aggregates fixed in solution, with the help of femtosecond laser scanning microscopy, allow us to obtain two-photon absorption spectra of functionalized nanofibres between 720 and 900 nm as well as morphological features from three-dimensional optical images. The lateral resolution is about 400 nm.

Direct measurement of the evanescent-wave polarization state

We present results from a direct measurement of the elliptical character of the evanescent part of linearly in-plane polarized light, totally internally reflected from a quartz half-sphere. These results have been obtained by invoking polarization-sensitive and light-emitting organic nanofibers. The angular dependencies of the mean-square electric field vector components parallel and perpendicular to the surface plane agree with predictions from the Fresnel equations.

Light scattering from an ordered array of needle-shaped organic nanoaggregates: Evidence for optical mode launching

Pronounced peaks in both photoluminescence and light scattering from an array of almost parallel oriented, needle-shaped organic nanoaggregates on mica are observed as a function of angle of incidence. Within the framework of a simple theoretical model, we identify those peaks as originating from the launching of normal modes in the nanofibers, both radiative and waveguiding. Quantitative information is obtained about the mode spectrum and morphology of nanoscaled objects from a simple far field scattering measurement.

Evanescent light–atom interaction detected by optogalvanic effect

Abstract An evanescent light penetrating an atomic vapour near a dielectric surface could be a probe for many atom-boundary phenomena. We show the possibility of very sensitive detection of the resonant atom–light interaction near the surface by using the optogalvanic effect for an evanescent wave. We observe a narrowing of the profile of the detected atomic line, and we point out some properties of the optogalvanic effect in the evanescent wave.

Surface Plasmon Polaritons Probed with Cold Atoms

We report on an optical mirror for cold rubidium atoms based on a repulsive dipole potential created by means of a modified recordable digital versatile disc. Using the mirror, we have determined the absolute value of the surface plasmon polariton (SPP) intensity, reaching 90 times the intensity of the excitation laser beam. Furthermore, we have also directly measured thermo-plasmonic effects accompanying SPPs excitation on gold submicron structures.

Surface plasmons excited by the photoluminescence of organic nanofibers in hybrid plasmonic systems

Recent research on hybrid plasmonic systems has shown the existence of a loss channel for energy transfer between organic materials and plasmonic/metallic structured substrates. This work focuses on the exciton-plasmon coupling between para-Hexaphenylene (p-6P) organic nanofibers (ONFs) and surface plasmon polaritons (SPPs) in organic/dielectric/metal systems. We have transferred the organic p-6P nanofibers onto a thin silver film covered with a dielectric (silicon dioxide) spacer layer with varying thicknesses. Coupling is investigated by two-photon fluorescence-lifetime imaging microscopy (FLIM) and leakage radiation spectroscopy (LRS). Two-photon excitation allows us to excite the ONFs with near-infrared light and simultaneously avoids direct SPP excitation on the metal layer. We observe a strong dependence of fluorescence lifetime on the type of underlying substrate and on the morphology of the fibers. The experimental findings are complemented via finite-difference time-domain (FDTD) modeling. The presented results lead to a better understanding and control of hybrid-mode systems, which are crucial elements in future low-loss energy transfer devices.

Leakage radiation spectroscopy of organic/dielectric/metal systems: influence of SiO2 on exciton-surface plasmon polariton interaction

Leakage radiation spectroscopy of organic para-Hexaphenylene (p-6P) molecules has been performed in the spectral range 420-675 nm which overlaps with the p-6P photoluminescence band. The p-6P was deposited on 40 nm silver (Ag) films on BK7 glass, covered with SiO2 layers. The SiO2 layer thickness was varied in the range 5-30 nm. Domains of mutually parallelly oriented organic nanofibers were initially grown under high-vacuum conditions by molecular beam epitaxy onto a cleaved muscovite mica substrate and afterwards transferred onto the sample by a soft transfer technique. The sample placed on a flat side of a hemisphere fused silica prism with an index matching liquid was illuminated under normal incidence by a He-Cd 325 nm laser. Two orthogonal linear polarizations were used both parallel and perpendicular to the detection plane. Spectrally resolved leakage radiation was observed on the opposite side of the Ag film (i.e. at the hemisphere prism) as a function of the scattering angle. Each spectrum contains a distinct peak at a wavelength dependent angle above the critical angle. This way the dispersion curve was measured, originating from a hybrid mode, i.e. the interaction between the p-6P excitons and surface plasmon polaritons (SPPs) of the metal/dielectric boundary. The presence of the SiO2 layer considerably changes the dispersion curve in comparison to the one of the Ag/p-6P/air system. However, the Ag/SiO2/p-6P/air stack forms a stable structure allowing construction of organic plasmonic devices such as nano-lasers.

Leakage radiation spectroscopy of organic nanofibers on metal films: evidence for exciton-surface plasmon polariton interaction

Leakage radiation spectroscopy of organic nanofibers composed of self-assembled organic molecules (para-Hexaphenylene, p-6P) deposited on a thin (40-60 nm) Ag film has been performed in the spectral range 420-675 nm which overlaps with the nanofiber photoluminescence band. Using a soft transfer technqiue, domains of mutually parallel oriented organic nanofibers were initially grown under high-vacuum conditions by molecularbeam epitaxy onto a cleaved muscovite mica substrate and afterwards transferred onto a silver film prepared on the glass carrier. The sample placed on a flat side of a hemisphere prism with an index matching liquid was illuminated by either a He-Cd 325 nm laser or by white light from a bulb. In the case of laser excitation two orthogonal linear polarizations and two different configurations of p-6P nanofibers were applied, both parallel and perpendicular to the plane of detection. The leakage radiation was observed on the opposite side of the Ag film at the phase matching angle. The spectrally resolved intensity of the scattered radiation has been measured as a function of scattering angle at normally incident light. The spectrum contains a distinct peak at an wavelength dependent angle above the critical angle. By analyzing this dispersion curve one can argue that it originates from the interaction between the nanofiber excitons and surface plasmon polaritons of the metal film.