Linewidth and coherence properties of scattered light

The holographic recording of light scattered by brownian particles is discussed. It is shown that, due to the finite time of exposure, the record acts as a temporal filter of non-zero bandwidth. As a consequence the holographic recording can be obtained in spite of the frequency change of the scattered light. The experimental results show that, in fact, such a procedure can constitute an alternative way to measure the linewidth of the scattered light.     

The effect of double scattering on critical fluid Rayleigh linewidth measurements

We apply recent work on the intensity correlation function of light double scattered from a system of brownian diffusing balls to the case of a fluid near the critical point. We evaluate the relative intensities and intensity correlation times of the polarized and depolarized components of the double scattered light as a function of k₀ξ. We compare these correlation times to those found for single scattering and find that the more intense polarized component of the double scattered light has a correlation time nearly equal to the singly scattered light in the critical region where $\text{k}{}_0\text{ξ ? 8}$.     

Heterodyne holographic microscopy of gold particles

We report experimental results on heterodyne holographic microscopy of subwavelength-size gold particles. The apparatus uses continuous green-laser illumination of the metal beads in a total internal reflection configuration for dark-field operation. Detection of the scattered light at the illumination wavelength on a charge-coupled-device array detector enables 3D localization of brownian particles in water.     

Photon time-interval statistics of laser light scattered by brownian particles

Measurements are reported and some theoretical expressions are given for half-open photon time-interval statistics of laser light scattered by particles in brownian motion. Expressions in terms of cumulants are shown not to be valid in general.     

Fluctuations in doubly scattered laser light

Fluctuations in laser light, doubly scattered by brownian particles, were analysed by measuring the spectral noise power of the photodetector current. Scattering took place at two spatially separated systems of spherical particles. Analytic expressions for the field and intensity correlations are derived. The analytic expressions for the spectrum of the intensity fluctuations of the doubly scattered laser light demonstrate that the frequency dependence of the spectrum depends strongly of the geometry of the experimental arrangement. This is not the case for singly scattered light where in good approximation the spatial and temporal correlations can be separated analytically.Our measurements show that the noise spectrum of the doubly scattered radiation may have the same frequency dependence as the spectrum of the singly scattered light. However, there are conditions where the frequency dependence of the noise of the doubly scattered light diverges markedly from that of the singly scattered light.     

Fokker-Planck approximation for N-dimensional nonmarkovian langevin equations

The Fokker-Planck approximation for n-dimensional nonmarkovian Langevin equations is discussed through an expansion in powers of the correlation time of the noise. Exact cases are considered and an application to brownian motion is presented.     

Joint probability distribution beyond the Smoluchowski limit for brownian motion in position space

We obtain a time convolutionless partial differential equation for the joint probability distribution in position space of a non-markovian brownian particle under the influence of some potential. We discuss the corrections to the Smoluchowski limit in this context.     

Joint probability distribution of nonmarkovian SDE

We obtain a time convolutionless partial differential equation for the two events joint probability distribution of nonmarkovian processes defined by stochastic differential equations with colored noise. As an example we discuss nonmarkovian brownian motion.     

Fluctuations of time averages for Langevin dynamics in a binding force field

We derive a simple formula for the fluctuations of the time average x(t) around the thermal mean (eq) for overdamped brownian motion in a binding potential U(x). Using a backward Fokker-Planck equation, introduced by Szabo, Schulten, and Schulten in the context of reaction kinetics, we show that for ergodic processes these finite measurement time fluctuations are determined by the Boltzmann measure. For the widely applicable logarithmic potential, ergodicity is broken. We quantify the large nonergodic fluctuations and show how they are related to a superaging correlation function.     

On the relation of two approaches to Rubin's model of brownian particles

The relation between two approaches to Rubin's model of brownian particles is clarified. The Fokker-Planck-like equation for the model is thereby derived.     

Physical kinetics of quantum electrodynamic (1/ω)-noise

The physical kinetics of soft photon emission in electronic quantum brownian motion is invoked to give a simple picture of the quantum electrodynamic sources of “(1/ω)-noise” in conducting systems.     

Cooperative diffusion in one dimensional ionic conductors and soliton brownian motion

It is shown that under simplifying assumptions cooperative diffusion in one dimensional ionic conductors can be approached in terms of soliton brownian motion. At thermal equilibrium the cooperative ionic diffusion coefficient is simply estimated versus the diffusion coefficient of a free ion.     

Heterodyne Detection of Pulsed Co2 Laser Light Scattered from Ion Acoustic Waves in a Plasma

The small angle scattering of light from a pulsed CO2 laser has been used to measure ion acoustic waves excited in a low density plasma. The laser is a hybrid laser consisting of a high pressure TEA discharge and a low pressure continuous discharge. The scattered light is detected by heterodyning, using laser light as the local oscillator. Two methods of providing the laser light local oscillator have been used. The dependence of the scattered light on the ion acoustic wavelength has been measured. The amplitude of the scattered light compared with the amplitude of the waves in the plasma indicates that the heterodyne mixing efficiency is better than 10 percent.     

Migration brownienne de cristallites sur une surface et relation avec l'épitaxie: IV. Mobilité de cristallites sur une surface: Décoration de gradins monoatomiques de surface

The influence of a monoatomic step on the brownian movement of small gold crystallites on (100) KCl has been studied. It is experimentally demonstrated that: (a) the crystallites migrate along a step; (b) a gold decorated step provides an effective barrier for the migrating crystallites on the plane surface; (c) a non-decorated step may effectively capture the incoming crystallites.     

Thomson scattering measurements from a current carrying plasma and the determination of local current density in a Tokamak (T.T.F.2)

Measurements of Thomson scattering in a Tokamak with a component of the scattering vector k along the current direction, give scattered spectra with a red or a blue shift according to the direction of the current. Assuming a displaced Maxwellian electron distribution function it has been possible to determine the local electron drift velocity and hence the local current density. An increase in time of current density on axis, followed by a sudden decrease has been observed: this is probably due to the relaxation following a thermal instability.     

Soliton brownian motion and impurities effects in one dimensional superionic conductors

The scattering of non linear collective excitations by a model impurity potential in one dimensional superionic conductors is treated in terms of S.G. Soliton brownian motion perturbed by an effective potential. The cooperative static and dynamic mobility are derived in some limiting cases and the influence of impurity potential barrier height and shape on soliton mobility, is discussed.     

Nonuniversal nonanalytic density profiles for brownian particles near a partially absorbing wall

We study the stationary density profile of brownian particles near a partially absorbing plane wall. This profile is nonanalytic; the simplest possibility is a variation with a fractional power of the distance. If particles not absorbed are reflected specularly, then the exponent is a continuous function of the absorption coefficient.     

Escape rates in underdamped bistable potentials driven by coloured noise

The brownian motion in a quartic double-well potential driven by coloured noise is investigated in the low-viscosity limit by means of analogue simulation. The dependence of the escape rate on the noise correlation-time τ is determined for the conditions simulated: the escape rate decreases exponentially with increasing τ². The relevant law is derived theoretically in the limit of vanishingly small viscosity and high potential barriers.     

Rigorous diffusion properties for the sawtooth map

We get a rigorous bound for the diffusion constant of the hamiltonian dynamical system generated by a sawtooth map on a cylinder. The momentum variable properly renormalized then behaves almost like a brownian motion in the limit of infinite coupling constants. The strategy of the proof is a rigorous reformulation of the Random Phase Approximation.Supported by Contract CEE n⁰ SC1^*0281     

Laser scattering with a rapidly tuned dye laser

A facility is described for the measurement of the total spectrum produced by laser radiation scattered from a plasma during one laser pulse. The dye laser is electrooptically tuned by a high frequency voltage applied to a modified Lyot filter within its cavity. The scattered spectrum is registrated together with the laser reference signal by a transient recorder and processed afterwards. Both measuring time and inaccuracy could be reduced drastically. Scattering experiments have been accomplished in a H₂ cascade of 5 mm diameter arc at atmospheric pressure, and at 14 and 20 A, respectively. For this arc very precise spectroscopic results are available for checking the accuracy of the scattering measurements. Both the spectroscopic line and continuum experiments yield a temperature which lies between electron and ion temperature if there is no local thermal equilibrium, whereas the pure electron temperature is provided by the scattered spectrum. The agreement between spectroscopic and scattering results within the high error limits is the experimental proof for the applicability of this new scattering technique which requires only about one hundredth of the measuring time, as compared with the usual shot-to-shot registration.