Light scattering

About: Light scattering is a research topic. Over the lifetime, 37721 publications have been published within this topic receiving 861581 citations.

Measuring cellular structure at submicrometer scale with light scattering spectroscopy

Abstract: We present a novel instrument for imaging the angular distributions of light backscattered by biological cells and tissues. The intensities in different regions of the image are due to scatterers of different sizes. We exploit this to study scattering from particles smaller than the wavelength of light used, even when they are mixed with larger particles. We show that the scattering from subcellular structure in both normal and cancerous human cells is best fitted to inverse power-law distributions for the sizes of the scattering objects, and propose that the distribution of scattering objects may be different in normal versus cancerous cells.

Non-reciprocal interband Brillouin modulation

Abstract: Non-reciprocal light propagation is essential to control optical crosstalk and back-scatter in photonic systems. However, realizing high-fidelity non-reciprocity in low-loss integrated photonic circuits remains challenging. Here, we experimentally demonstrate a form of non-local acousto-optic light scattering to produce non-reciprocal single-sideband modulation and mode conversion in an integrated silicon photonic platform. In this system, a travelling-wave acoustic phonon driven by optical forces in a silicon waveguide spatiotemporally modulates light in a separate waveguide through linear interband Brillouin scattering. This process extends narrowband optomechanics-based schemes for non-reciprocity to travelling-wave physics, enabling large operation bandwidths of more than 125 GHz and up to 38 dB of non-reciprocal contrast between forward- and backward-propagating optical waves. The modulator operation wavelength is tunable over a 35-nm range by varying the optical drive wavelength. Such travelling-wave acousto-optic interactions provide a promising path toward the realization of broadband, low-loss isolators and circulators within integrated photonics. Non-reciprocal single-sideband modulation and mode conversion are realized in a low-loss integrated silicon waveguide, enabling >125 GHz operation bandwidths and up to 38 dB of non-reciprocal contrast between forward- and backward-propagating waves.

Single‐pulse coherent anti‐Stokes Raman scattering

Abstract: A new technique for use in coherent anti‐Stokes Raman scattering experiments allows the simultaneous generation of an entire Q‐branch spectrum of the anti‐Stokes radiation from a molecular gas using a single laser pulse. With this technique the stringent requirements of the previous techniques concerning laser linewidth and frequency stability are significantly relaxed. The excellent temporal resolution (20 nsec) makes the technique very attractive for temperature and concentration measurements of molecular gases, even in nonstationary media.

Rearrangements in hard-sphere glasses under oscillatory shear strain.

Abstract: We investigate particle rearrangements in colloidal glasses subjected to oscillatory shear strain by the technique of light scattering (LS) echo. LS echo directly follows the motion of the particles through peaks (echoes) in the intensity autocorrelation function; the height of the peak measures the reversible motion in the sample. Polydisperse hard-sphere poly-methylmethacrylate particles were used to avoid crystallization under shear. The yielding behavior is monitored through irreversible particle rearrangements at several volume fractions in the glass phase region. At high volume fractions the glasses are found to yield at strains as high as 15% while the irreversible rearrangements have a more gradual onset with strain for low volume fraction glasses. The behavior of high order echoes at long times is related to the effects of shear on the frozen-in fluctuations of the glass.

Theory of lasing in a multiple-scattering medium

Abstract: In several recent experiments, isotropic lasing action was observed in paints that contain rhodamine 640 dye molecules in methanol solution as gain media and titania particles as optical scatterers. These so-called paint-on laser systems are extraordinary because they are highly disordered systems. The microscopic mechanism for laser activity and the coherence properties of light emission in this multiple-light-scattering medium have not yet been elucidated. In this paper we derive the emission intensity properties of a model dye system with excited singlet and triplet electronic energy levels, which is immersed in a multiple-scattering medium with transport mean free path l * . Using physically reasonable estimates for the absorption and emission cross section for the singlet and triplet manifolds, and the singlet-triplet intersystem crossing rate, we solve the nonlinear laser rate equations for the dye molecules. This leads to a diffusion equation for the light intensity in the medium with a nonlinear intensity-dependent gain coefficient. Using this model we are able to account for nearly all of the experimentally observed properties of laser paint reported so far when l *@l0, the emission wavelength. This includes the dependence of the peak intensity of amplified emission on the mean free path l * , the dye concentrationr, and the pump intensity characteristics. Our model recaptures the collapse of the emission linewidth at a specific threshold pump intensity and describes how this threshold intensity varies with l * . In addition, our model predicts a dramatic increase in the peak intensity and a further lowering of the lasing threshold for the strong scattering limit l *→l0. This suggests a striking enhancement of the characteristics of laser paint near the photon localization threshold in a disordered medium. @S1050-2947 ~96!07510-5#