Rudolf Sprik

Phase‐sensitive interferometry with ultrashort optical pulses

Reliable phase‐sensitive time‐resolved interferometry with ultrashort pulsed lasers is performed with the use of a closed scanning Michelson interferometer in combination with a fixed Mach–Zehnder interferometer at the front end. The technique is based on measuring the full phase and frequency properties of the pulse distortion of an ultrashort optical pulse introduced by linear or nonlinear interaction with a sample. The necessary stability and reproducibility to perform an interferometric measurement is provided by a commercially available Fourier transform spectrometer enabling time‐resolved measurements from the IR well into the visible part of the optical spectrum. The feasibility of the technique is demonstrated by measuring the distortion introduced by an etalon and a surface‐plasmon polariton.

Femtosecond time-resolved measurements of weak localization of light

Abstract Time-resolved backscattering of coherent light from a disordered medium under weak localization conditions has been observed for the first time with femtosecond resolution using a light-gating technique based on second-harmonic generation. The time dependence of the observed enhanced backscattering is consistent with simple diffusion theory.

Acoustic band gaps in composites of solids and viscous liquids

Abstract The propagation of sound in three dimensional periodic lattices of solid-solid and solid-liquid composites is determined by calculating the acoustic band structure. Inclusion of viscous damping in the liquid is essential in understanding the acoustical properties of the solid-liquid composite when the characteristic length scale of the system matches the viscous penetration depth in the liquid. By using complex sound velocities to model the visco-elastic properties of the liquid we show that the solid-viscous liquid composite displays acoustic band gaps. These results are consistent with the hydrodynamic analysis of viscoelastic modes in porous media, binary mixtures and with a stratified layer model. As a characteristic example the ultrasonic band structure of silica spheres in ice and of colloidal crystals of silica in glycerol/water mixture are presented. Both systems display gaps under experimentally obtainable conditions.

Streaming Potential and Electroosmosis Measurements to Characterize Porous Materials

Characterizing the streaming potential and electroosmosis properties of porous media is essential in applying seismoelectric and electroseismic phenomena for oil exploration. Some parameters such as porosity, permeability, formation factor, pore size, the number of pores, and the zeta potential of the samples can be obtained from elementary measurements. We performed streaming potential and electro-osmosis measurements for 6 unconsolidated samples made of spherical polymer particles. To check the validity of the measurements, we also used alternative analysis to determine the average pore size of the samples and, moreover, used a sample made of sand particles to determine the zeta potential.

Experimental determination of the effective refractive index in strongly scattering media

Measurements of the angular-resolved-optical transmission through strongly scattering samples of porous gallium phosphide are described. Currently porous GaP is the strongest-scattering material for visible light. From these measurements the effective refractive index and the average reflectivity at the sample interface can be obtained. These parameters are of great importance for an accurate interpretation of optical experiments, and are for the first time determined in strongly scattering samples.

Vibrational dephasing in highly compressed liquid nitrogen studied by time-resolved stimulated Raman gain spectroscopy

Abstract In liquid nitrogen at 295 K the minimum in the variation of the vibrational dephasing rate T 2 −1 with density is observed at ρ=2.15×10 22 cm −3 . The observed behaviour shows good agreement with the results of previously published molecular dynamics simulations.

Kramers-Kronig relations for an interferometer

Abstract The treatment in the literature of the transfer functions for interferometers does not allow for a proper use of the Kramers-Kronig (KK) relations between amplitude and phase. We will present a systematic description of transfer functions. We show that if the full frequency dependence of all the optical parameters, including the complex index of refraction, is properly taken into account KK relations do exist. The modification of KK relations for amplitude and phase due to zeros of transfer functions is described. As an example, numerical results for the phase calculated from the amplitude of light reflected from a Gires-Tournois interferometer are presented.

Orientational relaxation times of Rhodamine 700 in glycerol-water mixtures

We determined orientational relaxation times for rhodamine 700 dye in glycerol-water mixtures using time-resolved fluorescence depolarization. It appears that the orientational relaxation time varies linearly with the viscosity of the solvent between 1 and 60 cP, in accordance with the Perrin-Stokes-Einstein model with stick boundary conditions. Previously others have found that for two anionic dyes in glycerol-water and a cationic dye in glycerol-ethylene glycol mixtures, the orientational relaxation time becomes less sensitive to the viscosity at very high viscosities (>25 cP at least). We discuss the influence of dye and solvent on the relation between orientational relaxation time and viscosity, which suggests that the relaxation time as a function of viscosity can be scaled on a common curve.

Examination of a Theoretical Model of Streaming Potential Coupling Coefficient

Seismoelectric effects and streaming potentials play an important role in geophysical applications. The key parameter for those phenomena is the streaming potential coupling coefficient, which is, for example, dependent on the zeta potential of the interface of the porous rocks. Comparison of an existing theoretical model to experimental data sets from available published data for streaming potentials has been performed. However, the existing experimental data sets are based on samples with dissimilar fluid conductivity, pH of pore fluid, temperature, and sample compositions. All those dissimilarities may cause the observed deviations. To critically assess the models, we have carried out streaming potential measurement as a function of electrolyte concentration and temperature for a set of well-defined consolidated samples. The results show that the existing theoretical model is not in good agreement with the experimental observations when varying the electrolyte concentration, especially at low electrolyte concentration. However, if we use a modified model in which the zeta potential is considered to be constant over the electrolyte concentration, the model fits the experimental data well in a whole range of concentration. Also, for temperature dependence, the comparison shows that the theoretical model is not fully adequate to describe the experimental data but does describe correctly the increasing trend of the coupling coefficient as function of temperature.

Depolarization of femtosecond laser pulses in disordered media

Abstract Depolarization of coherent light waves in disordered media has been studied directly in the time-domain with femtosecond time resolution. The experimental results are compared with recent results from calculations for Rayleigh scattering in random media.