Speckle Wave Research Articles

Stochastic dual-plane on-axis digital holographic imaging on irregular surfaces.

An imaging method based on dual-plane on-axis digital holography is proposed for the situation in which an object is on the irregular surface of a transparent medium. Light propagation of the object on the uneven surface of the medium is analyzed and simulated. The diffracted pattern of the object is deformed or destroyed by the refracted light of the medium. Dual-plane on-axis digital holography is used to eliminate the twin image. In order to retrieve the information lost in the reconstructed image due to destructive interference, the object is illuminated by a stochastic beam that is a speckle wave produced by a ground glass. Simulated and experimental results are presented, to demonstrate that the proposed method can be used for imaging on the irregular surface of a transparent medium.

Full-field and single-shot quantitative phase microscopy using dynamic speckle illumination

We developed an off-axis quantitative phase microscopy that works for a light source with an extremely short spatial coherence length in order to reduce the diffraction noise and enhance the spatial resolution. A dynamic speckle wave whose coherence length is 440 nm was used as an illumination source. To implement an off-axis interferometry for a source of low spatial coherence, a diffraction grating was inserted in the reference beam path. In doing so, an oblique illumination was generated without rotation of the wavefront, which leads to a full-field and single-shot phase recording with improved phase sensitivity of more than a factor of 10 in comparison with coherent illumination. The spatial resolution, both laterally and axially, and the depth selectivity are significantly enhanced due to the wide angular spectrum of the speckle wave. We applied our method to image the dynamics of small intracellular particles in live biological cells. With enhanced phase sensitivity and speed, the proposed method will serve as a useful tool to study the dynamics of biological specimens.

Twisted speckle entities inside wave-front 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.

Digital speckle pattern interferometry using spatial phase shifting: influence of intensity and phase gradients

Spatial phase shifting technique in digital speckle pattern interferometry (DSPI) and digital shearography (DS) provides the phase information due to the object displacement from two images, one stored before and other after loading. The technique needs a carrier fringe system. The double aperture mask in front of the imaging system is one of the methods for introducing the spatial carrier frequency for phase evaluation. The size of the apertures and their separation are important criteria to obtain appropriate phase shift/column within the desired size of the speckle for phase retrieval. The assumptions of constant intensity and phase on adjacent pixels of the camera while calculating phase in spatial phase shifting (SPS) are not met as the speckled object wave contains intensity and phase gradients, resulting in distortions in the calculated phase profiles. In this paper we discuss a strategy to overcome these problems. The contrast of the correlation fringe obtained using this approach is much improved. It also eliminates the distortion in the unwrapped phase map like wave ripples. The experimental results on an edge clamped circular plate loaded at the center are presented.

Enhanced angular selectivity in volume holograms with speckle reference waves

A speckle-multiplexing scheme with enhanced angular selectivity for holographic storage is proposed. Angular selectivity in the proposed holographic storage system is theoretically and experimentally investigated. We find the effect of speckle reference wave on angular selectivity strongly depends on the techniques to perform multiplexing for holographic storage. Angular selectivity of a holographic storage system can be effectively enhanced as long as angular deviation of reading wave induces a lateral displacement of the speckle pattern on the hologram plane. When angular deviation of reading wave only induces a speckle wavefront tilt on the hologram plane, the speckle wave is not helpful to enhance the angular selectivity and the angular selectivity becomes to depend on material thickness (Bragg condition) only.

Adaptive Correlation Filter Based on Dynamic Reflection Hologram Formed in Photorefractive Bi12TiO20 Crystal

An experimental and theoretical study of adaptive processing of non-stationary speckled waves by a dynamic reflection holographic grating formed in photorefractive (100) cut BTO crystal without applying external electrical field is presented.

Phase conjugation of speckle-inhomogeneous radiation in a holographic Nd:YAG laser with a short thermal hologram

A model of the so-called short hologram, which does not exhibit in-depth diffraction deformation of the fine speckle pattern of the recording fields, is studied. The investigation is performed by the example of a thermal hologram recorded by two speckle waves, which is the output mirror of a ring laser produced as a result of this recording. It is shown that the ability of this short hologram to select a wave conjugated to a speckle signal in the mode of the holographic laser depends both on the degree of mutual mixing of the speckles of recording beams in the hologram volume and on the effects of its saturation by the beams. The maximum accuracy of phase conjugation of speckle radiation in the holographic Nd:YAG laser achieved upon the best selection of the conjugate wave by the short thermal hologram was 93%.

Implementation and comparative evaluation of various architectures of ultrasonic photorefractive sensors

A novel optical sensor for the detection of ultrasonic motion has been recently developed. It allows to reach 25 μm displacement sensitivity with a large frequency range bandwidth 100 MHz. We will present a comparative study between various architectures of this ultrasonic detection system we have implemented. It uses InP:Fe or CdZnTe:V holographic crystals and operates with CW laser at 1.06 μm. Two configurations called the direct detection and the anisotropic diffraction configurations work with either plane or speckled waves. A third discussed configuration works with depolarized speckled waves. We measured their relative detection limits as a function of the applied electric field that governs photorefractive efficiency of the materials. Experimental results are well described by theory, using photorefractive models relevant to the used crystals

Electronic speckle pattern interferometry with thin beam illumination of miniature reflection and transmission speckling elements for in-plane deformation measurements

A new method of electronic speckle pattern interferometry (ESPI) for in-plane deformation measurements is presented. Unlike usual ESPI methods used for in-plane deformation measurements with two symmetrical smooth illuminating waves, we introduce miniature speckling elements and thin laser beam illumination of them. The minia- ture elements serve for generating two symmetrical speckled waves. These miniature speckling elements are produced as reflection or trans- mission holograms. Nonholographic speckling elements were also tested. We present a family of flexible electronic speckle pattern interfer- ometers for in-plane deformation analysis based on our method. Due to their simplicity, compactness, and low cost, the devices are ideally suited for industrial automated inspection. Experimental results obtained with the novel ESPI devices are given. © 1998 Society of Photo-Optical Instrumenta- tion Engineers. (S0091-3286(98)01508-6)

Speckle intensity and phase gradients: influence on fringe quality in spatial phase shifting ESPI-systems

Spatial phase shifting (SPS) is a good method to exclude time-dependent phase variations from interferometric phase measurements, since the phase shifted data are acquired simultaneously but from different points. This leads to problems when SPS is applied to electronic speckle pattern interferometry. The speckled object wave contains a multitude of phase and intensity gradients that violate the assumption of constant object intensity and phase on adjacent data points, from which most phase reconstruction formulas are derived. Based on today's knowledge of second-order properties of speckle fields, some phase retrieval algorithms specially adapted to SPS are proposed that improve the phase maps obtained. Quantitative experimental results are given to estimate the amount of improvement.

Spatial-Angular Selectivity of 3-D Speckle-Wave Holograms and Information Storage

The properties of volume holograms recorded with speckle reference wave are of interest because they allow high-density information multiplexing and its coding and processing. The results of theoretical and experimental study of angular selectivity for this type of hologram are presented in this article. Several mechanisms are interacting in this case as a result of the joint action of cross modulation grating (diffraction on cross grating) and intermodulation structure (locally recorded speckle pattern). The conditions are determined when the value of the angular selectivity depends either on the cross grating spacing or on the speckle pattern parameters. The strong angular selectivity of the speckle-wave hologram can be observed by its angular detuning in any arbitrary direction. It is demonstrated that observed peculiarities in the character of angular selectivity of the hologram with reference speckle wave can be very efficient for multiple holographic image recording in thick media.

Selection of a wave phase-conjugated to an input speckled beam in an FWMF-oscillator with a “short” hologram

The possibility and conditions of providing phase conjugation (PC) of high fidelity for speckled beams in the scheme based on Four-Wave Mixing with Feedback (FWMF) have been studied. The selective capabilities of a “short” hologram, which thickness is less than the lengths of the longitudinal correlation of the recording speckled waves have been investigated. The average-statistical parameters of the base mode of an FWMF resonator have been calculated theoretically. The experimentally obtained PC fidelity in the scheme on Nd glass with nonlinearity of gain saturation has amounted to 80%.

Coherent image synthesis from wave-front sensor measurements of a nonimaged laser speckle field: a laboratory demonstrations

We report what are to our knowledge the first coherent images recovered in the laboratory from measurements made with a Shack-Hartmann wave-front sensor of the phase and amplitude of a laser speckle wave front. We discuss the design of our wave-front sensor, which can obtain the phase and amplitude of an optical field with a single intensity measurement, and we point out a particular type of phase jump that cannot be detected by the Shack-Hartmann sensor. We also discuss implementations of this technique that may permit near-diffraction-limited imaging through turbulent media.

Multiply Scattered and Diffusing Ultrasound: Applications, Experiments, Theory

ABSTRACTThe study of ultrasonic waves in random media in a strong multiple scattering limit is becoming increasingly relevant to applied techniques of nondestructive characterization of material microstructures. This paper reviews the state of that art within the context of engineering applications and also reviews the evidence for the Anderson Localization of ultrasound.While ultrasound has long been employed as a nondestructive probe of material microstructure, it has usually been the rapidly attenuated coherent wave, and in particular, its speed and attenuation, which has been scrutinized for that purpose. The theory of such waves is discussed here. However, recent experiments and theory are increasingly addressing the diffuse speckle wave field. This small but growing body of work is also reviewed.While there has been much work recently on optical and microwave realizations for the study of the Anderson localization of classical waves, there has been little such investigation with sound waves. Recent work demonstrating the Anderson Localization of Ultrasound in two dimensions may be the first such for any classical waves in dimension greater than one.

Measurement of small displacements by speckle holography

A speckle holography technique is discussed for measuring small displacements of objects. It is based on the sensitivity of the diffracted light intensity from a mutual shift between the hologram and the reconstructed speckle wave. The proposed method allows the measurement of both an object's lateral and longitudinal displacement without changing the arrangement of the apparatus. This set-up allows continuous measurements to be taken.

Calculation of cross noise in a volume holographic corrector

The problem of a volume hologram converting a reference speckle field into a plane wave is considered. The angular distribution and the total intensity of a plane wave are calculated for distortions which appear because of the amplitude inhomogeneity of cross gratings and which propagate close to the plane wave direction. The total intensity is found to be proportional to the product of the angle between the signal and reference waves and the divergence of the reference speckle wave.

The Speckled Wave Front of Light

IN view of Sir J. J. Thomson's suggestion (quoted by Reiche, “Quantentheorie,” p. 25) that the wave front of light may have a speckled structure, it may be asked whether anything peculiar happens when two specks, belonging to different waves, collide. They might, for example, be deviated from their courses. If so, one light wave would cause some scattering of another wave with which it collided, and the direct light in the second wave would be dimmed. This effect, if it exists at all, must be small or it would have been noticed. Evidence as to its existence might be obtained in the following way. The supposed dimming of the second ray would be likely to depend on the angle between it and the first ray. On this supposition the brightness of a star lying on the ecliptic would vary slightly with the angle between it and the sun, as seen from the earth. Russell (Astrophys. Journ., vol. xliii., 1916) has shown that the brightness of the moon does so vary, but that has been explained otherwise.