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ABSTRACT: Second-harmonic cross-correlation operates a selection in time-phase among the randomly dephased contributions to an optical
field that propagated through a scattering medium. It can thus be used to selectively detect the weak contribution remaining
coherent with the incident field.
The European Physical Journal D 04/2012; 8(1):111-116. · 1.48 Impact Factor
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ABSTRACT: We present a method based on the optical theorem that yields absolute, calibration free estimates of the optical thickness of scattering particles. The thickness is determined from the phase delay of the zero angle scattered wave. It uses a heterodyne scattering scheme operating in the Raman-Nath approximation. The phase is determined by the position of Talbot-like modulations in the two dimensional power spectrum S(qx, qy) of the transmitted beam intensity distribution. The method is quite insensitive to multiple scattering. It is successfully tested to provide quantitative verification of the optical theorem. Exploratory tests on soft matter samples are reported to suggest its wide applicability to turbid samples.
Physical Review Letters 11/2010; 105(19):193901. · 7.37 Impact Factor
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ABSTRACT: We present a novel Dynamic Depolarized Scattering method based on a tight confocal, zero scattering angle, heterodyne scheme. The method is highly immune from parasitic multiple-scattering contributions, so that it can operate with non-index-matched samples presenting large turbidity. It provides measurements of both rotational and translational diffusion coefficients, the latter via number fluctuation spectroscopy. In addition, the amplitude ratio between the two baselines for the fast rotational mode and the slow translational mode can be used to determine the particles intrinsic birefringence.
The European Physical Journal E 01/2010; 31(1):69-72. · 1.94 Impact Factor
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ABSTRACT: We present a novel method to map the two-dimensional transverse coherence of an x-ray beam using the dynamical near-field speckles formed by scattering from colloidal particles. Owing to the statistical nature of the method, the coherence properties of synchrotron radiation from an undulator source is obtained with high accuracy. The two-dimensional complex coherence function is determined at the sample position and the imaging optical scheme further allowed us to evaluate the coherence factor at the undulator output despite the aberrations introduced by the focusing optics.
Physical Review Letters 11/2009; 103(19):194805. · 7.37 Impact Factor
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ABSTRACT: The technique heterodyne near field scattering (HNFS), originally developed for low-angle static light scattering, has also been implemented for carrying out dynamic light scattering. While the classical dynamic light scattering method measures the intensity-intensity correlation function, dynamic HNFS gives directly the field-field correlation function, without any assumption on the statistical properties of the sample, as the ones required by the Siegert relation. The technique has been tested with calibrated Brownian particles and its performances compared to those of the classical dynamic light scattering method.
Applied Physics Letters 06/2008; 92(24):241101-241101-3. · 3.84 Impact Factor
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Nature Physics. 01/2008; 4:238-243.
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ABSTRACT: We review the technique named heterodyne speckle velocimetry and present two applications for testing the method with a fluid moving under the conditions of Poiseuille flow. The fluid was seeded with small tracking particles (diameter 300 nm) and fluxed between the two parallel planes of a cell with constant or variable cross section. In the first case the velocity distribution was constant along the direction parallel to the planes and was in excellent agreement with the expected Poiseuille profile along the orthogonal direction. In the second case, where velocity gradients were present also along the planes, the technique was able to reconstruct both the orthogonal Poiseuille profile and the in-plane two dimensional mapping of the velocity vectors, with the possibility of measuring the fluid flux within an accuracy of 1%.
Journal of Applied Physics 10/2007; 102(7):073113-073113-8. · 2.17 Impact Factor
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ABSTRACT: We present a simple method for fluid velocimetry based on the velocity of the heterodyne speckles generated by tracking particles illuminated with coherent light. It works in real time and provides instantaneous two-dimensional velocity mappings in the direction orthogonal to the optical axis, independently of the particle concentration and size, also for subwavelength particles. It also provides the velocity distribution of the fluid over the entire sample thickness. The method has been quantitatively tested by using the motions of rigid diffusers and applied for mapping the flow of a confined fluid.
Applied Physics Letters 05/2006; 88(19):191101-191101-3. · 3.84 Impact Factor
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ABSTRACT: We show that the time evolution of near-field scattering speckles, originated by a fluid suspension of particles, provides information about the velocity field in the fluid. This information can be extracted from a statistical analysis of speckle fields taken at different times, either by measuring their cross-correlation function or by recovering the power spectrum corresponding to the difference between the two speckle fields. Experimental data are in accordance to the expected behaviors. The results are independent of the scatterer's size, allowing one to exploit the technique also with sub-wavelength tracking particles.
Optics and Lasers in Engineering 01/2006; 44:722-731. · 1.84 Impact Factor
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ABSTRACT: We implemented the heterodyne near-field scattering (HNFS) technique [Appl. Phys. Lett. 81, 4109 (2002)]], showing that it is a fairly valid alternative to traditional elastic low-angle light scattering and quite suitable for studying complex fluids such as colloidal systems. With respect to the original work, we adopted a different data reduction scheme, which allowed us to improve significantly the performance of the technique, at levels of sensitivity and accuracy much higher than those achievable with classical low-angle light scattering instrumentation. This method also relaxes the requirements on the optical/mechanical stability of the experimental setup and allows for a real time analysis. The HNFS technique has been tested by using calibrated colloidal particles and its capability of performing accurate particle sizing was ascertained on both monodisperse and bimodal particle distributions. Nonstationary samples, such as aggregating colloidal solutions, were profitably studied, and their kinetics quantitatively characterized.
Physical Review E 11/2004; 70(4 Pt 1):041405. · 2.26 Impact Factor
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ABSTRACT: Summary form only. Second-harmonic (SH) cross-correlation is a substantially new method for wave-field transformation that shares many properties with holographic methods. In this case the reconstructed wave-field is formed by the frequency-doubled radiation, while both fields impinging on the SH crystal, which acts as the holographic plate, are at the fundamental frequency
Lasers and Electro-Optics Europe, 2000. Conference Digest. 2000 Conference on; 10/2000
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ABSTRACT: Second-harmonic generated holograms result from the
second-harmonic crosscorrelation in a thin crystal of the optical field
diffused by an object with a reference field. The SH field reconstructs
a virtual holographic image in real time
Nonlinear Optics: Materials, Fundamentals, and Applications, 2000. Technical Digest; 02/2000
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ABSTRACT: We present a novel technique for particle sizing based on recent studies about the statistical information contained within the light intensity distribution close to a disordered sample. We show that it is much simpler and more robust than the traditional light scattering methods and any imaging technique. Applications to optical diagnostics, process monitoring and pollution monitoring are expected. In principle, since the basic phenomenon is wavelength independent, radiation other than visible light can be used.
Nuclear Physics B - Proceedings Supplements.
