We characterize the electro-phoretic motion of charged sphere suspensions in the presence of substantial electro-osmotic flow using a recently introduced small angle super-heterodyne dynamic light scattering instrument (ISASH-LDV). Operation in integral mode gives access to the particle velocity distribution over the complete cell cross-section. Obtained Doppler spectra are evaluated for electro-phoretic mobility, wall electro-osmotic mobility and particle diffusion coefficient. Simultaneous measurements of differing electro-osmotic mobilities leading to asymmetric solvent flow are demonstrated in a custom made electro-kinetic cell fitting standard microscopy slides as exchangeable sidewalls. Scope and range of our approach are discussed demonstrating the possibility of an internal calibration standard and using the simultaneously measured electro-kinetic mobilities in the interpretation of microfluidic pumping experiment involving an inhomogeneous electric field and a complex solvent flow pattern.freely suspended far off any walls [10,11,12].The standard method to measure the electro-osmotic mobility is the streaming potential [1, 3] but also microscopic determinations of suspension flow-profiles in standard or custom-made microelectro-phoresis cells have been performed [13,14,15]. We here adapt the latter approach but combine a suitable electro-kinetic cell with a recently introduced versatile version of LDV [16]. This is further motivated by the fact that in many technical applications and in particular contemporary micro-fluidic experiments both mobilities are needed simultaneously to interprete the experimental findings. A typical examples are micro-fluidic applications like electrophoretic [17], diffusio-phoretic [18] and osmotic trapping [19] or single particle electro-kinetic experiments of sedimented and optically trapped particles [20,21,22,23 ]. Here often inhomogeneous electric fields are employed which in addition may vary in time. In phoretic micro-swimming and electroosmotic pumping [24,25,26] typical experiments involve locally generated diffusio-electric fields. [27,28]. Also here we are relying on well known values for the electro-kinetic mobilities of substrates and transported particles. The electro-osmotic mobilities of several high purity materials are well documented in literature. However, for many standard materials like glass, quartz, PMMA or PDMS results show a large spread of values depending on cleaning and conditioning conditions. Moreover, in microfluidics and other applications, coated cell walls are frequently used, which introduces additional dependence of µeo on the preparation protocol followed. In this situation, it would be highly desirable to have a fast and reliable characterization method available, which in addition would also yield the particle mobility under exactly the same conditions.Our integral small angle super-heterodyne dynamic light scattering instrument (ISASH-LDV) was designed to determine the electro-phoretic mobilities of charged colloidal spheres in aqueous...

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In this paper we propose a new method for measuring the cross section of low yield nuclear reactions by capturing the products in a cryogenically frozen noble gas solid. Once embedded in the noble gas solid, which is optically transparent, the product atoms can be selectively identified by laser induced fluorescence and individually counted via optical imaging to determine the cross section. Single atom sensitivity by optical imaging is feasible because the surrounding lattice of noble gas atoms facilitates a large wavelength shift between the excitation and emission spectrum of the product atoms. The tools and techniques from the fields of single molecule spectroscopy and superresolution imaging in combination with an electromagnetic recoil separator, for beam and isotopic differentiation, allow for a detection scheme with near unity efficiency, a high degree of selectivity, and single atom sensitivity. This technique could be used to determine a number of astrophysically important nuclear reaction rates.

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We demonstrate a prototype light scattering instrument combining a frequency domain approach to the intermediate scattering function from Super-Heterodyning Doppler Velocimetry with the versatility of a standard homodyne dynamic light scattering goniometer setup for investigations over a large range of scattering vectors. Comparing to reference experiments in correlation-time space, we show that the novel approach can determine diffusion constants and hence hydrodynamic radii with high precision and accuracy. Possible future applications are discussed shortly.