Biomedical subjects

A A Chabanov

Publications and source records attributed to A A Chabanov.

7 recordsLinked to original sources

PubMed2005

Statistics of the mesoscopic field.

The measured probability distribution of the microwave field in an ensemble of strongly scattering samples is far from Gaussian. We show, however, that the field in a subensemble with specified total transmission is a Gaussian random variable. This confirms the central hypothesis of random matrix theory of perfect mode mixing and leads to the conclusion that the field and intensity normalized by their respective average magnitudes in a given configuration and the total transmission are statistically independent. This yields a universal form for the intensity correlation function and explains measurements of steady-state and time-resolved transmission in weakly and strongly scattering samples.

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PubMed2004

Dynamic correlation in wave propagation in random media.

Field spectra are analyzed to yield the time-resolved statistics of pulsed transmission through quasi-one-dimensional dielectric media with static disorder. The normalized intensity correlation function with displacement and polarization rotation for an incident pulse of linewidth sigma at delay time t is a function only of the field correlation function, which is identical to that found for steady-state excitation, and of kappa(sigma)(t), the residual degree of intensity correlation at points at which the field correlation function vanishes. The dynamic probability distribution of normalized intensity depends only upon kappa(sigma)(t). Steady-state statistics are recovered in the limit sigma-->0, in which kappa(sigma=0) is the steady-state degree of correlation.

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PubMed2004

Impact of weak localization in the time domain.

We find a renormalized "time-dependent diffusion coefficient," D(t), for pulsed excitation of a nominally diffusive sample by solving the Bethe-Salpeter equation with recurrent scattering. We observe a crossover in dynamics in the transformation from a quasi-1D to a slab geometry implemented by varying the ratio of the radius, R, to the length, L, of the cylindrical sample with reflecting side walls and open ends. Immediately after the peak of the transmitted pulse, D(t) falls linearly with a nonuniversal slope that approaches an asymptotic value for R/L>>1. The value of D(t) extrapolated to t=0 depends only upon the dimensionless conductance g for R/L<<1 and only upon kl(0) for R/L>>1, where k is the wave vector and l(0) is the bare mean free path.

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PubMed2004

Mesoscopic correlation with polarization rotation of electromagnetic waves.

Mesoscopic correlations are observed in the polarization of microwave radiation transmitted through a random waveguide. These measurements, supported by diagrammatic theory, permit an unambiguous decomposition of the intensity correlation function of a vector wave into short, long, and infinite range components. Infinite range correlation that leads to universal conductance fluctuations is measured and found to be in agreement with calculations. The long and infinite range components include nonuniversal frequency-independent terms associated with coupling into and out of the sample.

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PubMed2003

Breakdown of diffusion in dynamics of extended waves in mesoscopic media.

We report the observation of nonexponential decay of pulsed microwave transmission through quasi-one-dimensional random dielectric media signaling the breakdown of the diffusion model. The decay rate of transmission falls nearly linearly in time corresponding to a nearly Gaussian distribution of the coupling strengths of quasinormal electromagnetic modes to free space at the sample surfaces. The peak and width of this distribution scale as L(-2.05) and L(-1.81), respectively.

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PubMed2001

Statistics of dynamics of localized waves.

The measured distribution of the single-channel delay time of localized microwave radiation and its correlation with intensity differ sharply from the behavior of diffusive waves. The delay time is found to increase with intensity, while its variance is inversely proportional to the fourth root of the intensity. The distribution of the delay time weighted by the intensity is found to be a double-sided stretched exponential to the 1/3 power centered at zero. The correlation between dwell time and intensity provides a dynamical test of photon localization.

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PubMed2001

Photon localization in resonant media.

We report measurements of microwave transmission over the first five Mie resonances of alumina spheres randomly positioned in a waveguide. Though precipitous drops in transmission and sharp peaks in the photon transit time are found near all resonances, measurements of transmission fluctuations show that localization occurs only in a narrow frequency window above the first resonance. There the drop in the photon density of states is found to be more pronounced than the fall in the photon transit time above the resonance, leading to a minimum in the Thouless number.

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