Archive: July, 2011

G. Popescu, L. P. Deflores, K. Badizadegan, et al., Fourier phase microscopy for investigation of biological structure and dynamics, 29, 2503 Opt. Lett. (2004).

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Download PDF By use of the Fourier decomposition of a low-coherence optical image field into two spatial components that can be controllably shifted in phase with respect to each other, a new high-transverse-resolution quantitative-phase microscope has been developed. The technique transforms a typical optical microscope into a quantitative-phase microscope, with high accuracy and a path-length […]

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H. Iwai, C. Fang-Yen, G. Popescu, et al., Quantitative phase imaging using actively stabilized phase shifting low-coherence interferometry, 29, 2399, Opt. Lett. (2004).

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Download PDF We describe a quantitative phase-imaging interferometer in which phase shifting and noise cancellation are performed by an active feedback loop using a reference laser. Depth gating via low-coherence light allows phase measurement from weakly ref lecting biological samples. We demonstrate phase images from a test structure and living cells.

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A. Dogariu and G. Popescu, High-resolution spatial and spectral characterization of optical fields, OPN, vol. 13, No. 12, 21 (2002).

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A. Dogariu and G. Popescu, Measuring the phase of spatially coherent polychromatic fields, Phys. Rev. Lett., vol. 89, 243902 (2002).

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Download PDF Realistic optical fields are never completely monochromatic and the interpretation of the concept of phase is not straightforward. It has been pointed out by Wolf that, if a strict condition of spatial coherence is imposed, the statistically averaged behavior of a polychromatic field can be described by an associated monochromatic wave.We show that, […]

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G. Popescu and A. Dogariu, Spectral anomalies at wavefront dislocations, Phys. Rev. Lett., vol. 85, 183902, (2002).

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Download PDF In a recent Letter, Gbur, Visser, and Wolf [Phys. Rev. Lett. 88, 013901 (2002)] predict that remarkable spectral changes can take place in the neighborhood of phase singularities of a diffracted focused wave. We report here the experimental observation of this anomalous spectral behavior and show that this is a general characteristic of […]

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G. Popescu, A Dogariu, and R. Rajagopolan, Spatially resolved microrheology using localized coherence volumes, Phys. Rev. E, vol. 65, 041504 (2002).

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Download PDF We propose an optical technique, based on dynamic light scattering, for investigating the local rheological response of a complex fluid over a frequency range larger than that provided by standard mechanical instrumentation. The low-coherence radiation used in a fiber optics configuration allows the measurements to be confined to a small volume around a […]

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G. Popescu and A. Dogariu, Dynamic light scattering in sub-diffusive regimes, Appl. Optics, vol. 40, 4215 (2001).

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Download PDF For describing the fluctuating signal scattered from a multiple-scattering system, diffusive-wave spectroscopy makes use of a diffusion model that provides the path-length distribution of scattered waves for a specific geometry. Using the recently introduced optical path-length spectroscopy, we show that the diffusion model fails to describe wave propagation in the low-order multiple-scattering regime. […]

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G. Popescu and A. Dogariu, Dynamic light scattering in localized coherence volumes, Opt. Lett., vol. 26, 551 (2001).

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Download PDF We introduce a novel light-scattering technique for investigating the dynamics of random media with a broad range of optical densities. By use of the spatial coherence properties of a single-mode optical fiber and the temporal coherence of a broadband source, the measurement volume is isolated at the end of the optical waveguide. Optical […]

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G. Popescu and A. Dogariu, Ballistic attenuation of low-coherence fields, Appl. Optics, vol. 39, 4469, (2000).

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Download PDF Using a novel experimental geometry, we measured the ballistic attenuation of low-coherence optical fields propagating in multiple-scattering media. The high dynamic range and the angular filtering capability permit detecting the ballistic component through random media thicker than 20 mean free paths. Owing to the accuracy of the technique, we observe deviations from the […]

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G. Popescu, C. Mujat, and A. Dogariu, Evidence of scattering anisotropy effects on boundary conditions of the diffusion equation, Phys. Rev. E, vol. 61, 4523, (2000).

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Download PDF We present experimental evidence that the diffusion process close to the boundary is fundamentally different from the bulk diffusion in the sense that it is affected by the scattering properties of the individual centers. Systematic measurements show a nontrivial behavior of the extrapolation length ratio on the scattering anisotropy of individual particles. The […]

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