Angular-scattering characteristics of ferroelectric liquid-crystal electro-optical devices operating in the transient-scattering and the extended-scattering modes

The angular distribution of forward-scattered light in transient-scattering-mode (TSM) and extended-scattering-mode (ESM) ferroelectric liquid-crystal (FLC) devices was evaluated by use of circularly polarized incident light. For both modes the intensity and the distribution of forward-scattered light depended primarily on the FLC birefringence, spontaneous polarization, and the cell path length. In the FLC materials examined, the forward-scattering intensity under ESM drive conditions increased with longer FLC pitch lengths, whereas under TSM conditions stronger forward scattering was observed with increasing FLC spontaneous polarization. Although both TSM and ESM drive conditions displayed a similar angular distribution for forward-scattered light, the intensity of ESM scattering over a 0 degrees -6 degrees range was considerably smaller than that observed in earlier experiments with linearly polarized incident light.     

Full angular profile of the coherent polarization opposition effect

We use the rigorous vector theory of weak photon localization for a semi-infinite medium composed of nonabsorbing Rayleigh scatterers to compute the full angular profile of the polarization opposition effect. The effect is caused by coherent backscattering of unpolarized incident light and accompanies the well-known backscattering intensity peak.     

All-optical controlling of the focal intensity of a liquid crystal polymer microlens array

The current work demonstrates a liquid crystalline polymer microlens array (LCP MLA) with an all-optically tunable and multistable focal intensity through photochemical phase transition. The operational mechanism of the optical tuning is associated with the photoisomerization effect. The proposed LCP MLA device has a focusing unit based on a birefringence LCP and a tuning unit with a light responsive material to control the polarization state of the incident probe beam. The optically variable refractive indices of LCP enable a positive or negative MLA that can control the polarization of incident light to be realized.     

Retrieval of the scattering and microphysical properties of aerosols from ground-based optical measurements including polarization. I. Method

A method has been developed for retrieving the scattering and microphysical properties of atmospheric aerosol from measurements of solar transmission, aureole, and angular distribution of the scattered and polarized sky light in the solar principal plane. Numerical simulations of measurements have been used to investigate the feasibility of the method and to test the algorithm's performance. It is shown that the absorption and scattering properties of an aerosol, i.e., the single-scattering albedo, the phase function, and the polarization for single scattering of incident unpolarized light, can be obtained by use of radiative transfer calculations to correct the values of scattered radiance and polarized radiance for multiple scattering, Rayleigh scattering, and the influence of ground. The method requires only measurement of the aerosol's optical thickness and an estimate of the ground's reflectance and does not need any specific assumption about properties of the aerosol. The accuracy of the retrieved phase function and polarization of the aerosols is examined at near-infrared wavelengths (e.g., 0.870 mum). The aerosol's microphysical properties (size distribution and complex refractive index) are derived in a second step. The real part of the refractive index is a strong function of the polarization, whereas the imaginary part is strongly dependent on the sky's radiance and the retrieved single-scattering albedo. It is demonstrated that inclusion of polarization data yields the real part of the refractive index.     

Polarization effects on scatterer sizing accuracy analyzed with frequency-domain angle-resolved low-coherence interferometry

Angle-resolved low-coherence interferometry (a/LCI) enables us to make depth-resolved measurements of scattered light that can be used to recover subsurface structural information such as the size of cell nuclei. Endoscopic frequency-domain a/LCI (fa/LCI) acquires data by using a novel fiber probe in a fraction of a second, making it a clinically practical system. However, birefringent effects in fiber-based systems can alter the polarization state of the incident light and potentially skew the collected data. We analyze the effect the polarization state of the incident light has on scattering data collected from polystyrene microsphere tissue phantoms and in vitro cell samples and examine the subsequent accuracy of the determined sizes. It is shown that the endoscopic fa/LCI system accurately determines the size of polystyrene microspheres without the need to control the polarization of the incident beam, but that epithelial cell nuclear sizes are accurately determined only when the polarization state of the incident light is well characterized.     

Angle- and size-dependent characteristics of incoherent Raman and fluorescent scattering by microspheres. 2. Numerical simulation

The results of numerical simulation of inelastic scattering by microspheres with the use of a dipole model are presented. The formulas that are derived speed up the computation, thereby permitting larger-sized microspheres to be studied. The angular scattering cross section and depolarization are calculated for a wide range of size parameters as well as for different orientations of incident wave polarization. Calculations performed with small incremental changes in size permit the influence of morphology-dependent resonance (MDR) on the power and angular distribution of scattered radiation to be studied. TM and TE types of MDR produce enhanced scattering of the incident wave with vertical and horizontal polarization; the corresponding shape of the phase function becomes oscillatory. Special attention is paid to the simulation of backward scattering by water droplets, which is important for Raman lidar applications.     

Angular distribution of diffuse reflectance in biological tissue

We measured angular-resolved diffuse reflectance in tissue samples of different anisotropic characteristics. Experimental measurements were compared with theoretical results based on the diffusion approximation. The results indicated that the angular distribution in isotropic tissue was the same as in isotropic phantoms. Under normal incidence, the measured angular profiles of diffuse reflectance approached the Lambertian distribution when the evaluation location was far away from the incident point. The skewed angular profiles observed under oblique incidence could be explained using the diffuse model. The anisotropic tissue structures in muscle showed clear effects on the measurements especially at locations close to the light incidence. However, when measuring across the muscle fiber orientations, the results were in good agreement with those obtained in isotropic samples.     

Optical properties of a retroreflecting sheet

The power reflection and polarization properties of a close-packed array of retroreflectors are modeled, and a commercially available sheet is measured to verify the predictions. The modeling technique is conceptually simple and applicable to a wide range of structures of this type. The close-packed sheet retroreflects over a range of angles of incidence of approximately -40 to 40 deg in both directions and returns the polarization that illuminates it largely unchanged. Predictions of returned power are within 10% for light incident within 15 deg of normal and within 20% for angles less than 20 deg. Angles of polarization rotation are predicted to within 10 deg over a similar range of input angles. The model predicts the angular aperture of the sheet and the major features of the angular response. Future research will focus on design of structures with wider angles of acceptance and responses optimized for specific applications.     

Point Group Symmetry Determination via Observables Revealed by Polarized Second-Harmonic Generation Microscopy: (1) Theory

We present a methodology based on polarization-controlled second-harmonic generation microscopy that allows one to determine the point group symmetry of noncentrosymmetric structures in situ and in vivo in complex systems regardless of the occurrence of periodicity. Small, randomly oriented structures suffice for the analysis, which is based on simple recognition of observables in four tests. These can be performed in any standard SHG-microscope that allows polarization control of the incident and detected light. The method is resilient to birefringence and light dispersion.     

Electromagnetic field for a focused light sheet incident on a plane surface

A solution procedure is developed for the determination of the electromagnetic field that results from the interaction of a focused light sheet with a plane surface. The effects of angle of incidence, relative index of refraction, polarization, and incident light sheet profile on the resulting electromagnetic field distribution are demonstrated.     

Two-dimensional point spread matrix of layered metal-dielectric imaging elements

We describe the change of the spatial distribution of the state of polarization occurring during two-dimensional (2D) imaging through a multilayer and in particular through a layered metallic flat lens. Linear or circular polarization of incident light is not preserved due to the difference in the amplitude transfer functions for the TM and TE polarizations. In effect, the transfer function and the point spread function (PSF) that characterize 2D imaging through a multilayer both have a matrix form, and cross-polarization coupling is observed for spatially modulated beams with a linear or circular incident polarization. The PSF in a matrix form is used to characterize the resolution of the superlens for different polarization states. We demonstrate how the 2D PSF may be used to design a simple diffractive nanoelement consisting of two radial slits. The structure assures the separation of nondiffracting radial beams originating from two slits in the mask and exhibits an interesting property of a backward power flow in between the two rings.     

Polarization changes at Lyot depolarizer output for different types of input beams

Lyot depolarizers are optical devices made of birefringent materials used for producing unpolarized beams from totally polarized incident light. The depolarization is produced for polychromatic input beams due to the different phase introduced by the Lyot depolarizer for each wavelength. The effect of this device on other types of incident fields is investigated. In particular two cases are analyzed: (i) monochromatic and nonuniformly polarized incident beams and (ii) incident light synthesized by superposition of two monochromatic orthogonally polarized beams with different wavelengths. In the last case, it is theoretically and experimentally shown that the Lyot depolarizer increases the degree of polarization instead of depolarizes.     

Focal shifts in focused nonuniformly polarized beams.

We present a simple formula to evaluate the relative focal shift in a circular-aperture lens system illuminated by a nonuniformly polarized (NUP) light wave. Specifically, it is shown that the relative focal shift is determined by the effective Fresnel number. The effective Fresnel number is equal to the product of the Fresnel number of the lens aperture and the parameter sigma, which describes the uniformity of the polarization distribution of the NUP beam across the lens aperture. Some examples are given to illustrate the use of this approach. The influence of the polarization distribution of the incident NUP light wave on the polarization distribution in the axial points of the focused field is also presented.     

Localizable imaging study for the noninvasive diagnosis of lesions with the backscattering polarized light

The asymmetry appearing in the degree of polarization (DOP) distribution of the backscattering polarized light from tissues is investigated by using polarized Monte Carlo simulation. When the incident point is close to the boundary of the lesion inside the tissue, high asymmetry emerges regardless of the polarized direction of the incident light. A noninvasive method based upon the DOP asymmetry of the backscattering light is proposed to locate lesions hidden in live tissues by scanning a point light source. Imaging of the front projection on complicated lesion structures is demonstrated with this method. Its transverse resolution, which is affected by the wavelength of incident light and the size of the scattering particle, can reach the diameter of the lesion scattering particle theoretically while the best longitudinal detection depth can be achieved by choosing a suitable incident wavelength according to the scattering characters of the tissue.     

Modal dynamics in multimode fibers

The dynamics of modes and their states of polarizations in multimode fibers as a function of time, space, and wavelength are experimentally and theoretically investigated. The results reveal that the states of polarizations are displaced in Poincaré sphere representation when varying the angular orientations of the polarization at the incident light. Such displacements, which complicate the interpretation of the results, are overcome by resorting to modified Poincaré sphere representation. With such modification it should be possible to predict the output modes and their state of polarization when the input mode and state of polarization are known.     

Effect of laser-radiation polarization on the nonlinear scattering of light in nanodiamond suspensions

The effect of laser radiation polarization on the nonlinear scattering of light in aqueous suspensions of detonation nanodiamonds (DNDs) in a regime of optical power limiting (OPL) has been studied. It is established that the nonlinear transmission coefficient of DND suspension in the OPL regime in a field of nanosecond laser pulses with a wavelength of 532 nm is independent of the polarization of incident radiation. The nonlinear scattering of light observed at an angle of 90° in the plane perpendicular to the plane of polarization of the incident radiation depends on the polarization angle in accordance with a trigonometric law. It is shown that the ratio of the signals of scattered radiation for the vertical and horizontal polarizations exhibits nonmonotonic dependence on the laser-beam power density. The results are explained by the Rayleigh-Mie scattering and a change in the size of scattering centers as a result of the effect of a laser upon the DND suspension.     

The Effects of Optical Properties on Thin Films on Polarization and Intensity of Light Diffracted through Wide Angles

The effect of the edge material and the wavelength on wide-angle diffraction was investigated with a sensitive photomultiplier photometer. Measurements of as little as 10^?8 fraction of the incident light at an angle of 70° showed the effect on the intensity and polarization of the diffracted light due to the nature of the edge material and depending on the wavelength used.     

可见光区一维光子晶体纳米膜偏振带通滤波器的设计

应用一维时域有限差分方法研究各种条件下一维二元光子晶体的偏振带通滤波特性,具体数值分析了掺杂层位置、厚度、电磁参数、入射角度四种因素对偏振滤波特性的影响.数值结果表明传统意义上的光学多层膜是一维二元光子晶体在光学厚度满足四分之一波长时的特例;可见光区的偏振滤波器的窄带滤波特性与掺杂层的位置有关,掺杂层在整个膜中间位置时偏振分离效果好,掺杂层的厚度与周期层厚度相差越大则分离效果越好,两组元折射率相差越大越易形成禁带,入射角越大禁带越窄,偏振的分离度越好.特别是P偏振局域模更多;在线度参数相同的情况下介质电磁参数对禁带有较大影响,禁带只有在两组元折射率相差越大才能形成,介质损耗同样是不可忽略的因素;光源的入射角对禁带有重大影响.本文的研究对光子器件的设计有一定的指导作用.     

Model of light scattering that includes polarization effects by multilayered media

We present a model for calculating the angular distribution of light, including polarization effects from multilayered inhomogeneous media, with an index of refraction mismatch between layers. The model is based on the resolution of the radiative transfer equation by the discrete ordinate method. Comparisons with previous simpler models and examples of simulations are presented.