Comparison of field correlations in multiply scattered quasi-monochromatic light

An experiment is described that directly compares the degradations, with the number of scattering mean free paths, of two field correlations that may be used to form gates for imaging techniques in scattered light: the correlation of the scattered wave with an unscattered reference wave and the correlation of two wave-vector components of the scattered wave itself. Results for 20-mum polymer spheres show that the latter correlation is consistently larger well into the multiple-scattering regime (up to 10 mean free paths) for wave-vector separations less than at least 50 mm(-1) and that the two correlations tend to merge in this scattering regime for larger wave-vector separations.     

Fourier analysis of light scattered by elongated scatterers

Biological stimulation of living cells is sometimes associated with morphological changes. A practical method is developed to monitor cell stimulation by means of their conformational changes through interpretation of the pattern of light scattered from a cell population. For this purpose a mathematical model is suggested that predicts the power spectrum from a population of elliptic objects with a given eccentricity. A computer simulation of that model is presented together with supporting experimental results of the simulation. The predicted and the measured spectra are in good agreement. This technique was applied to elongated cells that become circular on exposure to a human hormone, indicating the potential applicability of the method in biology and medicine. The method and the apparatus presented in this study could be applied to bioassays of cell systems that respond to a variety of stimulants and to trace quantitatively the structural changes that occur during biological processes.     

Higher moments of scattered light fields by heterodyne analysis

In heterodyne detection (such as in coherent lidar) the optical local oscillator defines a single mode of the incoming-signal light field; this single-mode selectivity has been previously predicted to preserve the full fluctuation character of scattered light. This is in contrast with direct-detection schemes, as in photon-correlation spectroscopy, where aperture averaging usually reduces the range of fluctuations. Examples of Gaussian and non-Gaussian statistics in laser light scattered from a moving ground-glass screen have been studied. This simple laboratory experiment has several advantages over equivalent direct-detection schemes and has been shown to yield experimentally the theoretically predicted factorial intensity moments (up to the seventh order) that result from zero-mean, circulo-complex Gaussian statistics.     

Fractal dimension analysis of time-resolved diffusely scattered light from turbid samples

To improve quantification of optical properties in highly scattering and absorbing samples, time-correlated single photon counting measurements were analyzed using quantities related to the correlation dimension. Photon time-of-flight (TOF) distributions were collected in reflection and transmission optical configurations from samples made of cream and water-soluble dye (0 < mu(a) < 0.05 mm(-1); 100 < mu(s) < 250 mm(-1)). It was found that absorption and scattering properties of samples could be accurately quantified from information used to determine the correlation dimension. Scattering coefficients were estimated with less than 4% error for both optical configurations. Absorption estimates were made with CVs of 7.5 and 9.6% for reflection and transmission, respectively. Overall, fractal dimension analysis of TOF distributions provides a simple method of determining the optical properties of a sample.     

Angular distribution of light scattered from a sinusoidal grating

The angular distributions of light scattered by gold-coated and aluminum-coated gratings with amplitudes of ~90 nm and periods of 6.67 mum were measured and calculated for light incident from a He-Ne laser at an angle of 6 degrees . Experimental results are compared with predictions of Beckmann's scalar theory and Rayleigh's vector theory. The measured scattering pattern has a background of scattered light due mainly to residual surface roughness. Also the power in the higher-order peaks is larger by several orders of magnitude than the computed one, which can be attributed mainly to the low-order contributions of the harmonics in the profile.     

Near-field intensity correlations of scattered light

We show that the two-point correlation function in the near field of scattered light is simply related to the scattered intensity distribution. We present a new, to our knowledge, optical scheme to measure the correlation function in the near field, and we describe a processing technique that permits the subtraction of stray light on a statistical basis. We present experimental data for solutions of latex spheres, and we show that this novel technique is a powerful alternative to static light scattering.     

Intensity distribution of light scattered by a turbulent jet flow

Results are presented of a computation of the farzone distribution of the intensity of radiation scattered by a turbulent nonisothermal air jet.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 1, pp. 95–98, January, 1991.     

Surface characterization from doubly scattered light

When a translucent diffuser is illuminated by a speckle pattern, a new speckle pattern is produced. We show that the decorrelation of this intensity pattern by displacement of the diffusing surface is related to the standard deviation of the slope's distribution when the illuminating speckle grain is chosen appropriately small. The experimental results are compared with those obtained by measuring the angular distribution of the mean scattered intensity, and they show good agreement with each other.     

Polarimetry of scattered light using heterodyne detection

Abstract

Heterodyne detection has been used to measure the polarization state of light back-scattered from various targets (including flame-sprayed aluminium, sandpaper and painted surfaces). The samples are illuminated with a linearly polarized single-frequency continuous-wave CO₂ laser operating at a wavelength of 10.6 μm. The back-scattered co-polarized and cross-polarized components are both coherently detected by beating with an optical local oscillator. This process allows the relative amplitudes and phases of the two components to be measured and hence the light's polarization state can be evaluated. When the target undergoes movement, the scattered light demonstrates the usual properties of dynamic speckle, and the technique allows observation of the time evolution of the polarization ellipse.     

Image estimation from scattered field data

The purpose of this paper is to reappraise the linearizing methods frequently used to solve inverse scattering problems. We describe inversion algorithms based on the Born and the Rytov approximations and the nature of the distortions obtained in the reconstructions when using them. We present extensions of these methods, namely, the distorted-wave Born and the distorted-wave Rytov approximations, which incorporate prior knowledge about part of the scattering structure. A method for inverting scattered field data using these distorted-wave approximations is described, which retains the computational simplicity of the Born and the Rytov techniques. Some examples of their use with simulated and real data are given. A further extension of our distorted-wave formalism, which leads to improvements of the reconstructed image, is suggested. This entails a spectral estimation procedure also based on the incorporation of prior knowledge about the scatterer. This spectral estimation procedure can be useful for interpolation of scattered field data as well as resolution enhancement.     

Influence of intraocular scattered light on lightness-scaling experiments

Following Munsell's bisection procedure [J. Opt. Soc. Am. 23, 394 (1933)], we established a nine-step gray scale in which each step is an equal increment in lightness. We calculated retinal illuminances after intraocular scatter by using the point-spread function of Vos et al. [Vision Res. 16, 215-219 (1976)]. After this correction for intraocular scatter, we find a logarithmic relationship between retinal illuminance and achromatic lightness scales that are determined by the bisection method. Additional bisection experiments with a series of different backgrounds corroborate this result. We find that lightness depends linearly on the logarithm of scatter-corrected retinal illuminance, with different slopes for backgrounds of different lightness. This study also highlights the importance of using scatter-corrected illuminance in any quantitative model of lightness.     

Separation and analysis of forward scattered power in laboratory measurements of light beam transmittance through a turbid medium

In laboratory measurements of the transmittance of a light beam through a diffusing medium (water plus latex spheres), a distinction between the attenuated beam power and the received forward scattered power was made possible by the use of a transmissometer whose receiver has a variable field of view. The dependence of the received scattered power on the FOV angle and on the medium optical depth was analyzed. The deduced separated contributions of first- and second-order scattering, as well as the total received scattered power, were compared to the results of calculations.     

Effective suppression of multiply scattered light in static and dynamic light scattering

The evaluation of conventional light-scattering experiments in turbid media is often highly complicated because of the presence of multiple scattering contributions. The three-dimensional (3-D) cross-correlation method presented provides an effective and handy method to suppress the influence of multiply scattered light. As the time dependence of the 3-D cross-correlation function is determined solely by the singly scattered light, the evaluation of the decay constant yields reliable values for the effective diffusion coefficient and the hydrodynamic particle size of the suspended particles. Furthermore, analysis of the amplitude of the 3-D cross-correlation function permits the determination of the differential scattering cross section even for highly turbid suspensions.     

Improved interferometric detection of scattered light with a 4f imaging system

We analyze the performance of three imaging systems to detect near-forward scattered light interferometrically by using a Mach-Zehnder geometry. The alignment of each system is demonstrated by measurement of the heterodyne efficiency and correlation of the angular width and field 1/e radius measurements of the sample beam. Measurements of angular-scattering data demonstrate the range of angles over which each system is effective. Of the three systems analyzed, the 4f imaging system is determined to be most effective, because it accurately reproduces both the phase and the amplitude of the scattered field at the detector.     

A study of atom localization in an optical lattice by analysis of the scattered light

Abstract

We present an experimental study of a four-beam optical lattice using the light scattered by the atoms in the lattice. We use both intensity correlations and observations of the transient behaviour of the scattering when the lattice is suddenly switched on. We compare results for three different configurations of the optical lattice. We create situations in which the Lamb–Dicke effect is negligible and show that, in contrast with what has been stated in some of the literature, the damping rate of the ‘coherent’ atomic oscillations can be much longer than the inelastic photon scattering rate.     

Temperature field of a two-layered plate with time-varying heat-transfer conditions

The investigation results have shown that the solution to the heat conduction problem in a double-layer plate with time-variable boundary conditions may be obtained numerically if the solutions to the problem at constant boundary conditions are known. It is also shown that the method [8] is applicable for solving the problem on a nonstationary temperature field of the system of bodies at time-variable boundary conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 9, No. 6, pp. 1094–1099, December, 1970.     

Two-fiber spectroscopic probe with improved scattered light rejection

Our angled two-fiber probe design for in situ spectroscopic measurements (e.g., fluorescence, phosphorescence, or Raman) through a sapphire window has been modified to provide improved rejection of scattered excitation light while maintaining good efficiency of collection of the desired signal. The improvement is achieved by changing the probe axis to an off-normal configuration to minimize back reflection from window surfaces while maximizing the overlap of the light cones of the excitation and collection fibers at the outer window surface where the sample is in contact with the window. The results of laser-induced fluorescence measurements on phenol solution and sand samples, demonstrating the improved performance of the new probe, are reported. Up to 90-fold improvement in the fluorescence/scattered light ratio has been observed with the new probe.     

Transmitted scattered light from a thin film with shallow random rough interfaces

The transmitted scattered energy of plane electromagnetic waves from a thin metallic film with shallow rough interfaces bounded by two semi-infinite media is calculated. Both interfaces are modeled as independent stationary random processes with a Gaussian roughness spectrum. Scattering of light is calculated for both TM (p) or TE (s) polarizations for normal and oblique angles of incidence. An integral equation is obtained for the transmitted field based on the Rayleigh method and their solution involves Fourier coefficients, depending on the roughness profiles. We present some results for the case of a single thin metallic film in the attenuated total reflection configuration for s and p polarization around the angle of the excitation of surface-plasma waves θ(sp). The transmitted scattered intensity shows a maximum at the resonant angle θ(sp) in the case of p polarization.