Singularities in Speckled Speckle

Speckle patterns produced by random optical fields with two (or more) widely different correlation lengths exhibit speckle spots that are themselves highly speckled. Using computer simulations and analytic theory we present results for the point singularities of speckled speckle fields: optical vortices in scalar (one polarization component) fields; C points in vector (two polarization component) fields. In single correlation length fields both types of singularities tend to be more{}-or{}-less uniformly distributed. In contrast, the singularity structure of speckled speckle is anomalous: for some sets of source parameters vortices and C points tend to form widely separated giant clusters, for other parameter sets these singularities tend to form chains that surround large empty regions. The critical point statistics of speckled speckle is also anomalous. In scalar (vector) single correlation length fields phase (azimuthal) extrema are always outnumbered by vortices (C points). In contrast, in speckled speckle fields, phase extrema can outnumber vortices, and azimuthal extrema can outnumber C points, by factors that can easily exceed $10^{4}$ for experimentally realistic source parameters

Twisted speckle entities inside wavefront reversal mirrors

The previously unknown property of the optical speckle pattern reported. The interference of a speckle with an oppositely moving phase-conjugated speckle wave produces a randomly distributed ensemble of a twisted entities (ropes) surrounding optical vortex lines. These entities appear in a wide range of randomly chosen speckle parameters inside the phase-conjugating mirrors regardless to an internal physical mechanism of the wavefront reversal. These numerically generated interference patterns are relevant to a Brillouin $\bf PC$-mirrors and to a four-wave mixing $\bf PC$-mirrors based upon laser trapped ultracold atomic cloud.Comment: 4 pages,3 figures, Accepted to Physical Review

Progress in high temperature speckle-shift strain measurement system

A fast, easy to use speckle tracking system is under development for the speckle-shift strain measurement technique. Preliminary correlation tests on wire specimens show strong correlations of well-developed speckle patterns. Stable cross-correlations were obtained from a tungsten filament at 2480 C. An analysis of the optical system determines the minimum required sampling frequency of the speckle pattern to be 2.55 pixels per speckle

Speckle Reduction Using Multiple Tones of Illumination

The occurrence and smoothing of speckle are studied as a function of the line width for a highly collimated illuminating source. A general theory is presented for speckling in the image of a partially diffuse, phase type of object, which has a variable number of random scattering centers per resolution element. Then, an expression is derived for the wavelength spacing required to decouple the speckle patterns arising from two monochromatic tones in an imaging system, thereby establishing that it is feasible to smooth speckle using multicolor illumination. This theory is verified in a series of experiments using both laser illumination and band-limited light from a carbon arc. With highly collimated sources, we show that speckle appears laserlike for an imaged diffuser even up to line widths of 5 Å. Then, smoothing of speckle is demonstrated in the imaging of a diffuser and for a section of an optic nerve when the illumination is provided by six narrow lines spread over 1500 Å. Since with color-blind, panchromatic viewing the speckle smooths, a direct extension of this method to holographic microscopy, using a multitone laser, should permit one to record and reconstruct holograms of diffraction-limited resolution that are essentially speckle-free