Analysis of polarization speckle for imaging through random birefringent scatterer

Method of generating a vortex array embedded in a partially coherent beam is proposed and experimentally demonstrated. The vortex array exists in the complex coherence function of a random field arising due to interference of three independent coherence functions with appropriate phase profiles. Existence of the vortex array is confirmed by presenting amplitude and phase distributions of the complex coherence function. The phase structure of the complex coherence function, embedded with a vortex array, is obtained by interfering it with an independent fourth coherence function known as a reference and applying the Fourier fringe analysis technique to the cross-covariance of the intensity of the resultant random field.

Complex self-coherence function determination using geometric phase techniques

Light propagation in anisotropic random media is studied in the steady-state and time domains. Solutions of the anisotropic diffusion equation are compared to results obtained by the Monte Carlo method. Contrary to what has been reported so far, we find that even in the "diffusive regime" the anisotropic diffusion equation does not describe correctly the light propagation in anisotropic random media.

We demonstrate an optimized two-step procedure for measuring the full complex coherence function. The measurement relies on a wavefront shearing interferometer that permits characterizing nonstationary fields over an extended angular domain. The accuracy of the coherence measurement was demonstrated by excellent agreement with theoretical predictions.

Turbulence coherence in complex wind field: Focusing on its on-site characteristics based on multi-point clustering

We propose a new analysis method of microtremor circular arrays for detecting phase velocities of Rayleigh waves in microtremors, aiming to conduct the microtremor array observations with fewer restriction of seismometer arrangement than the spatial autocorrelation (SPAC) method. The method is based on the complex coherence function (CCF) of the Rayleigh waves formulated by Shiraishi and Matsuoka (2005) to study the relationship between wave sources and observation points on an array. In this method, the values of the Bessel function J0 (kr) (k: wave number, r: distance between observation points) that generate phase velocities are obtained as a solution of the simultaneous equations of CCFs, while they are calculated from the directional average of CCFs in the SPAC method. Therefore, our method allows observation points not equally spaced on the circumference.From theoretical studies of this method for a circular array, it was found that seismometers on the circumference could be set at almost any place with the condition of symmetrical seismometer arrangement. Moreover, a field experiment have confirmed that the phase velocity obtained from the proposed method agreed with that of the SPAC method.

We review the principle of coherence dynamics proposed recently to explain the origin of coherence vortices, which are the phase singularities in a complex coherence function. Some properties associated with coherence vortex, such as the coherence current describing the circular contrast flow close to a vortex core and conservation laws of coherence, are investigated both theoretically and experimentally.

The optimal microphone array includes two processing blocks ‐ minimum variance distortionless response (MVDR) beamformer and the single‐channel Wiener filter, which acts as post‐filter. The main drawback of MVDR beamformer is the cancellation of the desired speech signal and its degradation in multi‐path wave propagation environment. To make the adaptive algorithm robust against room reverberation and to prevent desired signal cancellation, an estimation of the unknown desired speaker's transfer function was proposed. The estimation is based on the imperfect signal and the interference covariance matrices estimated from available microphone signals during speaker activity and pause of speech respectively. As MVDR beamformer suppresses coherent interference, post‐filter has to reduce diffuse acoustic noise. The post‐filter proposed in this paper is developed under assumption that complex coherence function is unknown but time invariant. The additional improvement of the post‐processing algorithm on low frequencies is obtained by combining a priori noise power attenuation factor for diffuse noise field with estimated one. The proposed algorithm is tested on simulated room with reverberation, and compared with some known post‐processing algorithms with rather good results.

We investigate the possibility of interferometric optical field sensor with DMD forming a series of sampling interferometers in the pupil of an optical system. Our preliminary experiment validates the feasibility of our approach for the field reconstruction in the case of coherent field. We believe that this approach can be extended to sensing of speckle patterns and even incoherent fields, by analyzing not only the intensity and phase, but also the amplitude and the visibility of the interference patterns. Such analysis would yield the complete complex amplitude and/or coherence function, making the approach directly applicable to a wide range of inverse source problems in optics.

We combine a telescopic imaging system with a common-path, lateral-shearing interferometer and use phase-shifting interferometry to measure the complex spatial coherence function (or mutual intensity) of a linearly-polarized optical field. Our telescopic design increases the numerical aperture of the system without distorting the shape of the wave front, and therefore without changing the phase difference between lateral positions in the optical field. Our method of generating lateral-sheared images introduces no additional astigmatism. To demonstrate the use of the interferometer we extract the information contained in the complex spatial coherence function to reconstruct the amplitude and phase of a coherent optical field, and we also show how the spatial coherence function evolves from a coherent field to a partially coherent one as light traverses a random multiple-scattering medium.

Compensation Based Displacement Measurement Using Objective Laser Speckles

Light propagation in stratified anisotropic media with arbitrary orientation of optic axes smoothly varying from layer to layer is considered. In the WKB approximation, a general expression for the field is obtained. For the case of a uniaxial medium, the normal waves are found and specific features of the light propagation are analyzed. General conditions are obtained that determine the turning points and forbidden zones. It is shown that the developed approach allows one to find trajectories of rays in anisotropic media with arbitrary layered structure.

We consider the propagation of light in an anisotropic medium with a topological line defect in the realm of geometrical optics. It is shown that the effective geometry perceived by light propagating in such medium is that of a spacial section of the cosmic string spacetime.

Influence of small-scale heterogeneity on upward CO2 plume migration in storage aquifers

Crystals are widely applied in laser systems and they play important roles as polarization manipulators. A simple uniaxial crystal plate with a certain thickness may serve as a linear/circular polarizer. A uni/biaxial crystal with a proper orientation may work as a polarization beam splitter/combiner. A biaxial crystal at conical refraction may be used to generate radially polarized light or help form a Bessel beam. To design a laser system including crystal component(s), or to optimize the performance of such a system, simulation techniques which models the light propagation through crystals is required. We present a full-vectorial and electromagnetic method that enables the modeling of crystal components with general laser fields, based on the angular spectrum of plane waves. Propagation of general field within anisotropic media and the reflection and transmission at a planar interface between isotropic/anisotropic and anisotropic/anisotropic media are discussed. We demonstrate examples on how crystals are used to manipulate the polarization state of laser beams.