Experimental study of volume speckle in four-wave mixing arrangement

We study a high frequency modulated speckle pattern in a four-wave mixing arrangement. The three-dimensional nature of the speckles is considered in the phase conjugate reflectivity evaluation which implies to analyze its dependence on the average speckle size. Also, the reflectivity is analyzed in terms of the external applied field, the probe beam ratio, and the pupil aperture diameter of the imaging system that generates the subjective speckle beam

Pseudocoloring with BSO crystals

A new pseudocoloring technique is proposed using pho torefractive BSO crystals biased under the influence of an externally applied electric field with coherent or incoherent illumination

Experimental study of volume speckle in four-wave mixing arrangement

We study a high frequency modulated speckle pattern in a four-wave mixing arrangement. The three-dimensional nature of the speckles is considered in the phase conjugate reflectivity evaluation which implies to analyze its dependence on the average speckle size. Also, the reflectivity is analyzed in terms of the external applied field, the probe beam ratio, and the pupil aperture diameter of the imaging system that generates the subjective speckle beam.Material digitalizado en SEDICI-CIC Digital gracias al Centro de Investigaciones Ópticas (CIOp).Centro de Investigaciones ÓpticasFacultad de Ingenierí

Efecto Talbot no paraxial en una red unidimensional de periodo comparable a la longitud de onda

The Talbot effect is a diffractive phenomenon which was found since its inception in the Gaussian optics, but when the period of the object is comparable with the wavelength is considered entering its non-paraxial regime. There, it has attracted interest for its applications related to the design of objects and their restorative effects posing in damaged gratings on this scale. In this contribution a study of this phenomenon at level non-paraxial (metaxial) is presented by using scalar diffraction theory in plane waves representation for periodic transversal fields. To this end, a one-dimensional amplitude grating of period p is used which is illuminated by a monochromatic plane wave of wavelength λ where p ranges between 1,5 λ and 4,2 λ.El efecto Talbot es un fenómeno difractivo ubicado desde su origen en la óptica Gaussiana, pero cuando la longitud de onda es comparable con el periodo del objeto se considera que este efecto entra en su régimen no paraxial, el cual nuevamente ha despertado el interés por su volumen de aplicación relacionado con el diseño de objetos y sus efectos curativo que presenta en redes averiadas a esta escala En esta contribución presentamos un estudio de este fenómeno a nivel no paraxial (metaxial),usando la teoría escalar de difracción en representación de ondas planas para campos periódicos transversal. Para ello se utiliza como objeto periódico una red de amplitud unidimensional de periodo p, iluminada con una onda plana monocromática de amplitud unitaria y longitud de onda λ, donde p se encuentra entre 1,5 λ y 4,2 λ.Centro de Investigaciones Óptica

Efecto Talbot no paraxial en una red unidimensional de periodo comparable a la longitud de onda

The Talbot effect is a diffractive phenomenon which was found since its inception in the Gaussian optics, but when the period of the object is comparable with the wavelength is considered entering its non-paraxial regime. There, it has attracted interest for its applications related to the design of objects and their restorative effects posing in damaged gratings on this scale. In this contribution a study of this phenomenon at level non-paraxial (metaxial) is presented by using scalar diffraction theory in plane waves representation for periodic transversal fields. To this end, a one-dimensional amplitude grating of period p is used which is illuminated by a monochromatic plane wave of wavelength λ where p ranges between 1,5 λ and 4,2 λ.El efecto Talbot es un fenómeno difractivo ubicado desde su origen en la óptica Gaussiana, pero cuando la longitud de onda es comparable con el periodo del objeto se considera que este efecto entra en su régimen no paraxial, el cual nuevamente ha despertado el interés por su volumen de aplicación relacionado con el diseño de objetos y sus efectos curativo que presenta en redes averiadas a esta escala En esta contribución presentamos un estudio de este fenómeno a nivel no paraxial (metaxial),usando la teoría escalar de difracción en representación de ondas planas para campos periódicos transversal. Para ello se utiliza como objeto periódico una red de amplitud unidimensional de periodo p, iluminada con una onda plana monocromática de amplitud unitaria y longitud de onda λ, donde p se encuentra entre 1,5 λ y 4,2 λ.Centro de Investigaciones Óptica

Modulated speckle simulations based on the random-walk model

The random-walk model is employed to simulate modulated speckle patterns. We demonstrate that the geometrical image approximation fails to describe the modulated speckle pattern. A new approach to analyzing this phenomenon is proposed. The validity of the approximations employed is verified by comparison of the simulation with the experimental results. Speckle metrological applications and phase measurement techniques could be improved by taking advantage of this model

Single-random phase encoding architecture using a focus tunable lens

We propose a new nonlinear optical architecture based on a focus tunable lens and an iterative phase retrieval algorithm. It constitutes a compact encryption system that uses a single-random phase key to simultaneously encrypt (decrypt) amplitude and phase data. Summarily, the information encoded in a transmittance object (phase and amplitude) is randomly modulated by a diffuser when a laser beam illuminates it; once the beam reaches a focus tunable lens, different subjective speckle distributions are registered at some image plane as the focal length is tuned to different values. This set of speckle patterns constitutes a delocalized ciphertext, which is used in an iterative phase retrieval algorithm to reconstruct a complex ciphertext. The original data are decrypted propagating this ciphertext through a virtual optical system. In this system, amplitude data are straightforwardly decrypted while phase data can only be restored if the random modulation produced in the encryption process is compensated. Thus, an encryption-decryption process and authentication protocol can simultaneously be performed. We validate the feasibility of our proposal with simulated and experimental results.Centro de Investigaciones Óptica

Phase-object analysis with a speckle interferometer

We describe the characteristics of a double-exposure specklegram obtained through a double-aperture system, by introduction of a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and visibility of the interferometric fringes in the Fourier plane are analyzed. An alternative interferometric technique for phase-object detection is proposed

Modulated speckle simulations based on the random-walk model

The random walk model is employed to simulate modulated speckle patterns. We demonstrate that the geo metrical image approximation fails to describe the modulated speckle pattern. A new approach to analyzing this phenomenon is proposed. The validity of the approximations employed is verified by comparison of the simulation with the experimental results. Speckle metrological applications and phase measurement tech niques could be improved by taking advantage of this model.Facultad de Ingenierí

Speckle photography with different pupils in a multiple-exposure scheme

The use of different multiple aperture pupils for recording each image in speckle photography is proposed. The introduction of suitable spatial frequency carriers, by internally modulating imaged speckles, allows one to selectively isolate or combine the spectral content of different images into spatially separated regions in the Fourier plane. Theoretical and experimental results extend the speckle photography technique to the depic tion of several specklegrams of multiple uniform in plane displacements. In this case, because different pu pils are considered for recording, the cross correlation functions for the amplitudes and intensities in the image plane are calculated on the basis of the statistical properties of the object. Also, the ensemble average inten sity in the Fourier plane is analytically derived, and fringe visibility is investigated