The time evolution of the microscopic lateral diffusion and dynamic reorientation of individual dye molecules dispersed in a thin polymer film is probed by means of scanning near-field optical microscopy at room temperature and ambient conditions. On a sub-micrometer scale we identify regions where the diffusion is drastically non-random, while the statistical average of the trajectories of 97 molecules in a 4 μm × 4 μm section displays random-walk behavior.

We have measured the temperature profile of aluminum coated fiber tips used for illumination-mode scanning near-field optical microscopy as a function of the optical input power with a micron sized thermocouple. The temperature coefficients vary from 20 K/mW for tips with a large cone angle to 60 K/mW for the narrow long ones. Temperatures of up to ≊470 °C have been measured close to the aperture with an optical input power of several mW before thermal damage of the coating occurred. The temperature profiles are analyzed theoretically taking into account the optical absorption, the thermal conductivity of the tip, as well as the heat loss to the environment.

Pure and mixed monolayers of 4-n-octyl-4′-cyanobiphenyl (8CB) and stearic acid (SA) at the air–water interface have been investigated by a combination of surface balance measurements and polarization sensitive, optical second harmonic spectroscopy. These measurements make it possible to carry out in situ studies of the formation of the monolayer and to identify different regimes upon compression of the film. These regimes cover the whole range from an isotropic monolayer, a highly oriented phase, up to phase separation at a critical surface pressure π*. It is shown that the polarization dependence of the second harmonic intensity is a very sensitive method to investigate the orientation of the optically nonlinear 8CB chromophores in the mixed film as a function of surface pressure as well as concentration. A comparison of monolayers of different mole fractions of 8CB and SA shows that the alignment of the 8CB molecules in the mixed film depends on the surface pressure and not on their concentration in the monolayer only. This behavior can be explained by assuming an ideal mixed monolayer, where the orientation of the 8CB chromophores is due only to the hydrophobic interaction with the alkyl chains of the SA. In addition, the critical surface pressure of the mixed film πmix* can be calculated as a function of the 8CB mole fraction x8CB.

The formation of pure and mixed monolayers of 4-n-octyl-4'-cyano-biphenyl (8CB) and stearic acid at the air-water interface is investigated by a combination of surface balance measurements and polarization sensitive, optical second harmonic spectroscopy. These measurements allow one to identify four different regimes upon compression of the monolayer. These regimes are an isotropic monolayer, a polar oriented phase, a compacting of the polar oriented phase, and the formation of a centrosymmetric structure. From a fit of the polarization dependence of the second harmonic intensity, the orientation of the optically nonlinear 8CB chromophores is deduced. A comparison of monolayers of different mixing ratios of 8CB and stearic acid shows, that the orientation of the 8CB molecules depends only on the surface pressure and not on their concentration in the film.

X-ray crystallography has allowed to identify new solid solutions with the formulae LiPb1–xMxPO4, NaBa1–yM′yPO4 and NaPb1–zSrzPO4. When M = Sr, Ba, × varies between 0.0 and 0.4 in the vicinity of LiPbPO4 and between 0.8 and 1.0 close to LiMPO4 while for M″=Sr, 0.2 ≤y≤0.8 and M″=Pb, 0.0 ≤y≤ 1.0. The third system corresponds to a continuous solid solution between z=0 and z=0.8. Phase transitions were determined along the solid solutions investigated. Second harmonic generation tests has shown that the highest yield frequency doubling was recorded for compounds of the systems LiPbPO4-LiMPO4 (M=Sr, Ba).

We present the analysis of a standing evanescent wave which is caused by total internal reflection of an Ar-ion laser beam on a glass prism, and investigate the coupling to a sub-wavelength dielectric tip of a scanning near-field optical microscope (SNOM) which is raster scanned at close distance over the prism surface. The intensity of the evanescent field is spatially modulated with a period of 239.2 nm. It decays exponentially with a constant of 103.9 nm with increasing distance from the prism surface. Precise measurements of the standing evanescent wave allow to determine the spatial resolution to better than 160 nm and the coupling efficiency of the tip to 63%.

We report on nonlinear optical properties of a new class of efficient nonlinear optical compounds built of trihalides interacting weakly with donor type molecules. Adducts of iodoform with sulphur (CHI3 · 3S8) and quinoline (CHI3 · 3C9H7N) exhibit sizeable electrooptic effects and second harmonic generation comparable to POM and better than urea. Angle-tuned phase matching of type I and II has been observed for both compounds. The comparison between the electrooptic effect and the second harmonic generation suggests that the electrooptic effect is mostly electronic in origin. The atomic force microscope was used to record the molecular structure on free-standing iodoform-sulphur crystal plates. The intermolecular spacings on the crystal surface correspond remarkably closely with those in the bulk.

The mechanism of phosphorescence hole burning of coronene embedded in a glassy matrix is investigated. We find a linear relation between the phosphorescence hole burning rate and the incident light intensity. This supports the single photon hole burning process in contrast to a photon gated process involving triplet—triplet transitions.

Nonphotochemical hole burning in glassy host/guest matrices generates a change of the site energy distribution of the guest molecules. This distribution of shifted energies has been determined by deconvoluting the difference of white-light excited fluorescence spectra before and after hole burning. For this aim, a special numeric algorithm has been developed. For the host/guest-system tetracene in ethanol, the observed shifts are within the inhomogeneously broadened line, but a shift to higher energies is predominant and amounts to about 20 wave numbers.

Phosphorescence hole burning in coronene embedded in glassy matrices at 1.9 to 3.0 K is reported. The external heavy-atom effect strongly increases the hole burning rate. The quantum yield for hole formation is evaluated to be 10-3-10-2. The influences of weak magnetic fields on hole shapes are studied, which leads to a technique to measure the hole width without using a tunable laser.

The site selection spectra of highly photostable perylene fluorescent dyes at 4.2 K in a glassy matrix of three different organic solvents (ethanol, methyl tetrahydrofuran, n-butyl acetate) are presented. The spectra ofthe two isomers are identical for a given solvent and only very minute differences are detectable between different solvents. We conclude that the influence of the matrix on the fluorescence spectra is of only minor importance. The influence of the orientation in the matrix is negligible.

We show theoretically and experimentally that the effect of hole-burning can be utilized to eliminate almost completely the usually present large inhomogeneous broadening of luminescence spectra of organic molecules in glassy matrices. This makes it possible to measure the correct shape of the phonon wings. In an application of the method, we find that the fluorescence spectra of tetracene in an ethanol glass at 4.2 K do not only show the usual inhomogeneous distribution of transition energies, but also an additional inhomogeneous distribution of either the electron-phonon coupling and/or the linewidth of the 0-0 transition.

Spectroscopic hole-burning data are reported for four dyes in two organic glasses. Hole depths, monitored via fluorescence, vary neither exponentially nor logarithmically with time, but can be interpreted in terms of two-level systems as due to Gaussian distributions of barrier widths.

Crystals of the 1:3 adduct of iodoform and sulphur (CHI3·3 S8) have been found to exhibit a strong electro-optic effect. The values of the linear Pockels effect coefficients determined by using a modulation technique are: ∣r12∣ = (4.4 ± 2.4) × 10−12 m/V and ∣r13 − 0.5 i 2r33 ∣ = (0.29 ± 0.12) × 10−12 m/V. A comparison of the electro-optic susceptibility derived from these data with that deduced from powder second-harmonic generation tests shows the electro-optic phenomenon to be mainly of electronic origin.