Search PubMed⌕ Search

PubMed · 11531479

Angle-resolved second-harmonic light scattering from colloidal particles.

Abstract

We report angle-resolved second-harmonic generation (SHG) measurements from suspensions of centrosymmetric micron-size polystyrene spheres with surface-adsorbed dye (malachite green). The second-harmonic scattering profiles differ qualitatively from linear light scattering profiles of the same particles. We investigated these radiation patterns using several polarization configurations and particle diameters. We introduce a simple Rayleigh-Gans-Debye model to account for the SHG scattering anisotropy. The model compares favorably with our experimental data. Our measurements suggest scattering anisotropy may be used to isolate particle nonlinear optics from other bulk nonlinear optical effects in suspension.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

N Yang, W E Angerer, A G Yodh. 2001-08-16. Angle-resolved second-harmonic light scattering from colloidal particles.. https://doi.org/10.1103/physrevlett.87.103902

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Measurement of circular birefringence and circular dichroism of the single crystals of lambda-(+)589- and delta-(-)589-tris(ethylenediamine)cobalt(III) triiodide monohydrate by the extended HAUP method.

We have achieved measuring four optical parameters simultaneously, namely, linear birefringence (LB), circular birefringence (CB), linear dichroism (LD), and circular dichroism (CD), of single crystals of Lambda-(+)(589)- and Delta-(-)(589)-tris(ethylenediamine) cobalt(III) triiodide monohydrate (1) along the <001> plane at the fixed wavelength (514.5 nm). Such measurements are possible only when the High Accuracy Universal Polarimeter (HAUP) is employed; it is called the extended HAUP method. Our experimental results showed that both LB and LD of the Lambda-(+)(589)-(1) crystal have the same magnitude as those of the Delta-(-)(589)-(1) crystal. It was also revealed for the first time that the CB data of crystals of Lambda-(+)(589)-(1) and Delta-(-)(589)-(1) are almost of the same magnitude, but are of opposite sign, reflecting their opposite absolute configurations. On the other hand, although the CD data obtained for Lambda-(+)(589)-(1) is almost three times larger than that for Delta-(-)(589)-(1,) these CD data are also opposite in sign, as expected from the opposite chirality of crystals. .

Anisotropy↗

Anisotropic small amplitude Peptide plane dynamics in proteins from residual dipolar couplings.

The effect of small amplitude anisotropic peptide plane motion on residual dipolar couplings (RDC) measured in proteins has been investigated. RDC averaging effects in the presence of GAF (Gaussian axial fluctuation) motions are found to vary strongly depending on the peptide plane orientation. Even low amplitude dynamics can significantly affect derived alignment tensor parameters if this motion is not taken into account. An analytical description of averaged N-(N)H RDCs is introduced that includes basic GAF-like motion. The averaging depends on the orientation of the peptide plane (alpha, beta, gamma) in the alignment frame and on the motional amplitude (sigma). This expression is used to investigate the presence of anisotropic reorientational dynamics in proteins by incorporating sigma as an additional parameter into the alignment tensor analysis. Average GAF amplitudes (sigma(av)) are determined for secondary structural elements from single experimental N-(N)H RDC data sets from five different proteins, in combination with high-resolution structural models. This yields statistically significant improvement over the static description, and detects sigma(av) values ranging from 14.4 to 17.0 degrees for the different proteins. A higher value of sigma(av) = 20 degrees from loop regions was found using two independent sets of N-(N)H RDC in the protein lysozyme, for which a very high-resolution structure is available. Comparison of fitting behavior over 13 structures from lysozyme of crystal diffraction resolution ranging from 0.9 to 2.1A indicates a small spread of motional amplitudes, demonstrating that the method is robust up to this level of resolution. A combined definition of (alpha)C-C' and N-(N)H RDC under the influence of GAF motions allows simultaneous fitting of both RDC. Application to three proteins leads to similar sigma(av) values and a more significant improvement with respect to the static model. Using the GAF model to describe conformationally averaged RDC is important for two reasons: a more accurate definition of the alignment tensor magnitude can be derived, and the method can be used to detect average small amplitude motions in protein backbones from readily accessible data, on time scales not easily sampled by other NMR techniques.

Anisotropy↗

Electromagnetic response of a dipole-coupled ellipsoidal bilayer.

We derive an expression for the polarizability of an ellipsoidally shaped cell-like structure at field frequencies where membrane molecular resonances (vibrational and electronic) are important. We first present analytical results for the dielectric function of a flat, dipole coupled, bilayer consisting of molecules with one prominent resonance frequency. Due to the nature of the dipole coupling the dielectric function is different for the field being parallel or perpendicular to the bilayer normal with two new resonance frequencies omega=omega;(0 parallel) and omega=omega;(0 perpendicular ). We then combine this anisotropic bilayer dielectric function with the analytical solution of Gauss equation for an ellipsoid with an anisotropic coating (the coating dielectric function being different parallel and perpendicular to the coating normal) in order to find the polarizability of an ellipsoidal bilayer membrane. In particular, we find that for a thin-walled (compared to the size of the cell) membrane the resonance frequencies of the polarizability are the same as for a flat bilayer (independent of the cell shape). However, our analytic result for the geometric weights for the oscillator strengths is sensitive to the shape; the geometric weight for the omega=omega;(0 perpendicular ) (omega=omega;(0 parallel)) peak is largest when the external field is along the largest (smallest) axis. The geometric weights are shown to be constrained by three sum rules.

Anisotropy↗