Dynamic light scattering with single-mode receivers: partial heterodyning regime

Flammer, I.; Rička, J.

doi:10.1364/ao.36.007508

Cited by 26 publications

(22 citation statements)

References 13 publications

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“…This procedure compensates for nonidealities of the detectors (dead-time and dark counts [31]) and of the fiber receivers (see Subsection 2.B). A LABVIEW script is used to control the correlator and average the correlation functions.…”

Section: A Multispeckle Setupmentioning

confidence: 99%

Fiber-based multispeckle detection for time-resolved diffusing-wave spectroscopy: characterization and application to blood flow detection in deep tissue

et al. 2007

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We present a technique for the measurement of temporal field autocorrelation functions of multiply scattered light with subsecond acquisition time. The setup is based on the parallel detection and autocorrelation of intensity fluctuations from statistically equivalent but independent speckles using a fiber bundle, an array of avalanche photodiodes, and a multichannel autocorrelator with variable integration times between 6.5 and 104 ms. Averaging the autocorrelation functions from the different speckles reduces the integration time in diffusing-wave spectroscopy experiments drastically, thus allowing us to resolve nonstationary scatterer dynamics with single-trial measurements. We present applications of the technique to the measurement of arterial and venous blood flow in deep tissue. We find strong deviations both of the shape and characteristic decay time of autocorrelation functions recorded at different phases of the pulsation cycle from time-averaged autocorrelation functions.

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Section: A Multispeckle Setupmentioning

confidence: 99%

Fiber-based multispeckle detection for time-resolved diffusing-wave spectroscopy: characterization and application to blood flow detection in deep tissue

et al. 2007

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“…Before fixing the source and detector, the hair was combed away so that the illuminator and detector had good optical contact to the scalp. During both the resting baseline and the task periods, each lasting 100 s, we recorded ten normalized intensity autocorrelation functions, each with a duration of 10 s. To make sure that the amplitude of the measured intensity autocorrelation function was due to the few-mode receiver optics only ͑and not due to contributions of static scattering to the signal 42 ͒, we measured g ͑2͒ ͑r , ͒, using the same setup, from a turbid latex sample immediately before and after the measurements on the subjects.…”

Section: Diffusing-wave Spectroscopymentioning

confidence: 99%

Noninvasive detection of functional brain activity with near-infrared diffusing-wave spectroscopy

et al. 2005

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Abstract. We use near-infrared dynamic multiple scattering of light ͓diffusing-wave spectroscopy ͑DWS͔͒ to detect the activation of the somato-motor cortex in 11 right-handed volunteers performing a finger opposition task separately with their right and left hands. Temporal autocorrelation functions g ͑1͒ ͑r , ͒ of the scattered light field are measured during 100-s periods of motor task alternating with 100-s resting baseline periods. From an analysis of the experimental data with an analytical theory for g ͑1͒ ͑r , ͒ from a three-layer geometry with optical and dynamical heterogeneity representing scalp, skull, and cortex, we obtain quantitative estimates of the diffusion coefficient in cortical regions. Consistent with earlier results, the measured cortical diffusion coefficient is found to be increased during the motor task, with a strong contralateral and a weaker ipsilateral increase consistent with the known brain hemispheric asymmetry for right-handed subjects. Our results support the interpretation of the increase of the cortical diffusion coefficient during finger opposition being due to the functional increase in cortical blood flow rate related to vasodilation.

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“…The decay time of the translational correlation function F t (q, t) = exp[−q 2 D t t] (where q is the magnitude of the scattering vector and D t = k B T /(6πηR) is the translational diffusion coefficient) is independent of the magnetic field strength B 0 , indicating that rotation and translation are indeed decoupled. Correcting g (2) VH (t) for static scattering [12] and Faraday rotation of VV scattered light by the cell walls yields the rotational correlation function g (1) VH (t)/F t (q, t) which is, in this specific geometry, given by…”

mentioning

confidence: 99%

Rotational diffusion in a bistable potential

et al. 2002

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Abstract. -Using depolarized quasielastic light scattering, we have investigated the rotational diffusion of optically anisotropic colloidal particles in a dilute suspension subject to external electric and magnetic fields (E0, B0). The particles were produced by the polymerization of nematic liquid crystal droplets, leading to birefringent colloidal spheres whose frozen orientational order is rigidly coupled to the particle orientation. The torque on the droplet director u(t) originating from the coupling of E0 and B0 to the particles' anisotropy in the refractive index and in the diamagnetic susceptibility, respectively, leads to a suppression of the orientational fluctuations about the direction of the external field. We observe a strong dependence of the measured relaxation rates on the field strength and on the orientation of the field relative to the scattering plane. We explain our findings by a solution of the Smoluchowski equation describing rotational diffusion in a bistable potential V (u) which has two equivalent minima separated by a potential barrier whose height is proportional to (E0, B0) 2 .Colloidal particles in a solvent do not only experience random forces due to the collisions with the surrounding molecules, but are also imparted random torques that lead to fluctuating particle orientations described by a unit vector u(t) also called particle director. If the colloids possess optical anisotropy, e.g., due to intrinsic birefringence or shape birefringence, these orientational fluctuations can be probed by depolarized quasielastic light scattering [1]. For isolated, freely rotating spherical particles in the limit of high solvent viscosity η, the rotational part of the field auto-correlation function g 2 of the scattered depolarized electric field E VH (t) decays exponentially with time t; the corresponding decay rate is proportional to the rotational diffusion constant D r = k B T /(8πηR 3 ), where k B T is the thermal energy and R is the particle radius.This simple situation changes completely when the rotational symmetry is broken by an external field (such as an electric or magnetic field) that couples to permanent or induced (electric or magnetic) dipoles localized on the particle. The orientational distribution then develops a peak around the direction of the external field, and, consequently, the amplitudes

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Dynamic light scattering with single-mode receivers: partial heterodyning regime

Cited by 26 publications

References 13 publications

Fiber-based multispeckle detection for time-resolved diffusing-wave spectroscopy: characterization and application to blood flow detection in deep tissue

Fiber-based multispeckle detection for time-resolved diffusing-wave spectroscopy: characterization and application to blood flow detection in deep tissue

Noninvasive detection of functional brain activity with near-infrared diffusing-wave spectroscopy

Rotational diffusion in a bistable potential

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