Klas Lindfors

Spectral analysis of resonant transmission of light through a single sub-wavelength slit

We analyze the spectral properties of resonant transmission of light through a sub-wavelength slit in a metal film. We show that the enhanced transmission can be understood in terms of interfering surface-wave-like modes propagating in the slit. We characterize the effect of geometrical and material properties of the slit on the transmission spectrum. Furthermore, we show that the wavelength of the transmission resonance strongly depends on the surrounding medium. This effect may be utilized in sensors, imaging, and the detection of, e.g. biomolecules.

Degree of polarization in 3D optical fields generated from a partially polarized plane wave.

We show that, for 3D random electromagnetic fields that are created by optical systems from a partially polarized plane wave, two different definitions of the 3D degree of polarization proposed in literature have a monotonic one-to-one correspondence, thus providing the same information about the fields polarization state. Examples of 3D fields obeying this result are the evanescent wave generated in total internal reflection, the tightly focused beam, and the far field scattered from an electric point dipole.

Intensity fluctuations and degree of polarization in three-dimensional thermal light fields

The normalized intensity fluctuations of arbitrary electromagnetic wave fields obeying Gaussian statistics are expressed in terms of the three-dimensional degree of polarization. This general formulation implies an important physical result concerning the polarization of planar fields and the dimensionality of the formalism. The results are expected to be particularly useful in intensity interferometry.

Dependence of resonant light transmission properties of a subwavelength slit on structural parameters.

We perform a systematic study of the resonant transmission of visible and near-infrared (NIR) light through a single subwavelength slit in a gold film when the parameters defining the structure are varied. We further examine the optical properties of a related nanostructure, a cross with subwavelength sized features. Focused ion beam (FIB) milling was used to fabricate nanoslits and crosses with linewidths ranging from 26 nm to 85 nm. The dimensions of the structure are found to affect strongly the transmittance spectrum. For example, as the slit becomes narrower the resonance is observed to both sharpen and shift significantly. Our observations are in good agreement with our earlier numerical calculations on the optical properties of nanoslits.

Dipole-dipole interaction between molecules mediated by a chain of silver nanoparticles

We study the dipole-dipole coupling between two fluorescent molecules in the presence of a chain of metallic nanoparticles. We analyze the spectral behavior of the coupling strength and its dependence on the molecular orientation. Our results show that for certain resonant wavelengths the coupling strength between the molecules is greatly enhanced and is strongly polarization sensitive. We also demonstrate how metallic nanoparticles can be utilized in implementing a polarization-sensitive coupler.

Intensity fluctuations and the degree of polarization in Gaussian random electromagnetic fields

For an electromagnetic beam described by Gaussian statistics the normalized intensity fluctuations are known to depend on the beams degree of polarization. With general non-paraxial random electromagnetic waves, such as optical near fields, a complete characterization of the polarization state requires a 3 x 3 coherence matrix and a three-dimensional degree of polarization. We demonstrate that, under the assumption of Gaussian statistics, the normalized intensity fluctuations in the three-dimensional case are expressible in terms of the three-dimensional degree of polarization. Since such a general description can be employed even for beams with only a transverse electric field, several important physical results follow from comparison of the three-dimensional and usual two-dimensional formulations. The results are expected to be particularly important in intensity interferometry.

Self-Organization of Nitrogen-Containing Polymeric Supramolecules in Thin Films

Rigid rod-like poly(2,5-pyridinediyl), semi-rigid polyaniline and flexible poly(4vinylpyridine) are nitrogen-containing polymers that with selected amphiphilic oligomers form self-organized comb-shaped supramolecules due to protonation, hydrogen bonding and polarnonpolar effects combined. Luminescent or conductive ordered structures are demonstrated in thin films. The structures are characterized using small-angle x-ray scattering (SAXS) and grazing-incidence small-angle x-ray scattering (GISAXS). The uniformity is studied using atomic force microscopy and scanning near-field optical microscopy (SNOM).

Efficient surface-relief gratings in hydrogen-bonded polymer-azobenzene complexes

Azobenzene-containing polymers have been extensively investigated due to the unique response of the azobenzene moiety to light fields. The trans-cis-trans photoisomerization of azobenzene can be utilized to induce molecular angular reorientation as well as macroscopic mass migration in the material. These motions can result in large and stable in-plane anisotropy, nonlinear optical activity, strong refractive-index modulation, and surface-relief gratings, showing great potential for rewritable optical recording and various photonic applications [1]. Stable control over the molecular alignment as well as the efficient inscription of surface-relief gratings typically requires chemical linkage between the photoactive chromophores and the host polymer. We demonstrate that surface-relief gratings (SRGs) with modulation depth of up to 440 nm (Fig. 1a) can be inscribed through the use of hydrogen bonding between the polymer and the chromophores [2]. Such spontaneous linkage simplifies the preparation process compared to covalent functionalization while still being strong enough to induce macroscopic motions of the polymer chains.

An evanescent-wave pumped microcavity laser with intense output radiation

The laser reported in this work has a gain medium pumped directly with an evanescent optical wave. Bright disk laser radiation is observed to propagate isotropically in a plane perpendicular to the capillary axis.