Romanpollock8661

We propose a scheme based on the photorefractive effect to manipulate polychromatic spectra. A sinusoidal phase grating can be obtained by exposing photorefractive material to light, and it is used to diffract monochromatic or polychromatic light. The resultant diffracted spatial intensity distribution for monochromatic light is mapped to spectrum distribution for polychromatic light via the spatial-spectral correspondence relationship for mono-polychromatic light diffraction. Theoretical analyses and numerical examples show that for different detection angles, the diffracted spectrum exhibits different features, and that specific spectral line selection or line filter effects can be achieved. We also discuss the possibility of applying this spectral scheme to detect temperature or the grating's period changes.Two superposed layers of transparent cylindrical lenslet gratings create classical moiré fringes when illuminated from behind. We rely on this observation to conceive special devices made of superposed lenslet gratings that produce compelling beating shapes when tilted against the light. Level-line moirés are created by superposing gratings of cylindrical lenslets of the same period on both sides of a substrate and by locally shifting some of the cylindrical lenses according to the moiré theory. Depending on the illumination and the viewing conditions, constant light intensities or colors move across graphical elements or faces. Such level-line moiré samples have been fabricated and characterized to determine the optimal fabrication parameters. Thanks to their striking visual appeal and their relatively challenging fabrication, moirés created by superposition of lenslets have a high potential for document security, art, and decoration.Except for very particular and artificial experimental configurations, linear transformations of the state of polarization of an electromagnetic wave result in a reduction of the intensity of the exiting wave with respect to the incoming one. PX-12 order This natural passive behavior imposes certain mathematical restrictions on the Mueller matrices associated with the said transformations. Although the general conditions for passivity in Mueller matrices were presented in a previous paper [ J. Opt. Soc. Am. A17, 328 (2000)JOAOD60740-323210.1364/JOSAA.17.000328], the demonstration was incomplete. In this paper, the set of two necessary and sufficient conditions for a Mueller matrix to represent a passive medium are determined and demonstrated on the basis of its arbitrary decomposition as a convex combination of nondepolarizing and passive pure Mueller matrices. The procedure followed to solve the problem also provides an appropriate framework to identify the Mueller matrix that, among the family of proportional passive Mueller matrices, exhibits the maximal physically achievable intensity transmittance. Beyond the theoretical interest on the rigorous characterization of passivity, the results obtained, when applied to absolute Mueller polarimetry, also provide a criterion to discard those experimentally measured Mueller matrices that do not satisfy the passivity criterion.Editor-in-Chief P. Scott Carney congratulates recent awardees and introduces the Journal's newest Topical Editor.Contrast threshold and visual Strehl ratio methods are used to predict visual acuity from wavefront error for a sample population of pre- and post-LASIK patients. Relative error (in logMAR) between predicted and measured visual acuity values are computed for each method and compared using paired t-tests. Differences in aberration data between pre- and post-LASIK eyes are then evaluated. The visual acuity prediction using visual Strehl proved to be more accurate for pre-LASIK patients than contrast threshold. However, both methods are comparable for post-LASIK patients.Diffuse optical tomography (DOT) uses near infrared light for in vivo imaging of spatially varying optical parameters in biological tissues. It is known that time-resolved measurements provide the richest information on soft tissues, among other measurement types in DOT such as steady-state and intensity-modulated measurements. Therefore, several integral-transform-based moments of the time-resolved DOT measurements have been considered to estimate spatially distributed optical parameters. However, the use of such moments can result in low-contrast images and cross-talks between the reconstructed optical parameters, limiting their accuracy. In this work, we propose to utilize a truncated Fourier series approximation in time-resolved DOT. Using this approximation, we obtained optical parameter estimates with accuracy comparable to using whole time-resolved data that uses low computational time and resources. The truncated Fourier series approximation based estimates also displayed good contrast and minimal parameter cross-talk, and the estimates further improved in accuracy when multiple Fourier frequencies were used.The van Trees inequality relates the ensemble mean squared error of an estimator to a Bayesian version of the Fisher information. The Ziv-Zakai inequality relates the ensemble mean squared error of an estimator to the minimum probability of error for the task of detecting a change in the parameter. In this work we complete this circle by deriving an inequality that relates this minimum probability of error to the Bayesian version of the Fisher information. We discuss this result for both scalar and vector parameters. In the process we discover that an important intermediary in the calculation is the total variation of the posterior probability distribution function for the parameter given the data. This total variation is of interest in its own right since it may be easier to compute than the other figures of merit discussed here.We investigate photoacoustic (PA) signal magnitude variation to an absorption coefficient of localized absorbing objects measured by spherically focused ultrasound transducers (US TDs). For this investigation, we develop the PA simulation method that directly calculates Green function solutions of the Helmholtz PA wave equation, considering grid-like elements on absorbing objects and US TDs. The simulation results show that the PA signal amplitude in the PA imaging is nonlinearly varied to the absorption coefficient of localized objects, which are distinct from the known PA saturation effect. For spherical objects especially, the PA amplitude shows a maximum value at a certain absorption coefficient, and decreases even though the absorption coefficient further increases from that point. We suggest conceptual and mathematical interpretations for this phenomenon by analyzing the characteristics of PA spectra combined with US TD transfer functions, which indicates that the combined effect of US TD spatial and temporal filtering plays a significant role in the PA signal magnitude nonlinearity.