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In the framework of the perturbation approach to the diffusion equation, an analytical expression is derived to describe the effects on the time-resolved transmittance due to the presence of a spatially varying scattering inclusion hidden inside a diffusive slab. This formula assumes that the reduced scattering coefficient of the inclusion is spatially Gaussian distributed and complements that obtained for the absorptive case. The accuracy and the application range of the perturbed transmittance are investigated through comparisons with the numerical solutions of the time-dependent diffusion equation given by using the finite-element method. The proposed perturbation model is validated through a fitting procedure that determines the relative error in retrieving the scattering perturbation parameter of the inclusion located at the midplane of the slab.

Combining the concept of lateral shear interferometry (LSI) within a digital holography microscope, we demonstrate that it is possible to obtain quantitative optical phase measurement in microscopy by a new single-image-processing procedure. Numerical lateral shear of the reconstructed wavefront in the image plane makes it possible to retrieve the derivative of the wavefront and remove the defocus aberration term introduced by the microscope objective. The method is tested to investigate a silicon structure and a mouse cell line.

We present a new method for numerically reconstructing digital holograms on tilted planes. The method is based on the angular spectrum of plane waves. Fast Fourier transform algorithm is used twice and coordinate rotation in the Fourier domain enables to reconstruct the object field on the tilted planes. Correction of the anamorphism resulting from the coordinate transformation is performed by suitable interpolation of the spectral data. Experimental results are presented to demonstrate the method for a singleaxis rotation. The algorithm is especially useful for tomographic image reconstruction.

We demonstrate experimentally that correct phase imaging without 2pi ambiguity is obtainable in digital holography by using a multiwavelength approach in the microscope configuration. We describe a general approach for removing chromatic aberrations and for controlling the pixel size of the reconstructed phase image in multiwavelength digital holography when the Fourier transform method is adopted for the numerical reconstruction of digital holograms. The retrieved phase is affected by the unavoidable, unwanted chromatic aberration. The correct phase can be obtained by evaluating the phase from the reference holograms reconstructed at different wavelengths to compensate for the chromatic aberration.

In microscopy, high magnifications are achievable for investigating micro-objects but the paradigm is that higher is the required magnification, lower is the depth of focus. For an object having a three-dimensional (3D) complex shape only a portion of it appears in good focus to the observer who is essentially looking at a single image plane. Actually, two approaches exist to obtain an extended focused image, both having severe limitations since the first requires mechanical scanning while the other one requires specially designed optics. We demonstrate that an extended focused image of an object can be obtained through digital holography without any mechanical scanning or special optical components. The conceptual novelty of the proposed approach lies in the fact that it is possible to completely exploit the unique feature of DH in extracting all the information content stored in hologram, amplitude and phase, to extend the depth of focus.

We show the defect dependence of the internal field in Lithium Niobate using a full-field interferometric method and demonstrate that it can be directly measured on some clusters of defects embedded in a stoichiometric matrix. Results show that the value of the internal field grows in proximity of defects and vanishes far from them, which addresses the long-standing issue about its origin in Lithium Niobate crystal.

We demonstrate accurate two-dimensional mapping of the phase retardation induced by the electro-optic effect in lithium niobate crystals. Off-axis digital holography is used to investigate congruent z-cut crystals. The spatially resolved optical path difference is interferometrically measured while a linearly rising voltage ramp is applied to the crystal. This procedure provides information on the uniformity of crystals' electro-optic properties and offers the ability to detect the presence of defects that is of fundamental importance for reliable processing of photonic devices.

We report on the fabrication, by a 26 MHz stretched-cavity femtosecond Ti:sapphire oscillator, of optical waveguides in different glass substrates, and their optical characterization. Operation of these waveguides in the telecom range at 1.55 microm is demonstrated. Digital holography microscopy is used to measure their refractive index profile. The results evidence a strong dependence of the fabrication process on the glass matrix.

We present three-dimensional (3D) image fusion by use of digital holography. We demonstrate experimentally that, through the image fusion technique with multiresolution wavelet decomposition, it is possible to increase the details and contrast of 3D reconstructed images obtained by multiwavelength digital holography. Although there is substantial activity in the fields of image fusion and holography, to the best of our knowledge, this is the first report of 3D image fusion by use of digital holography.

In-situ monitoring of domain reversal in congruent lithium niobate by a digital holographic technique is described. While the ferroelectric polarization is reversed by electric field poling, the two-dimensional distribution of the phase shift, due mainly to the linear electro-optic and piezoelectric effects, is measured and visualized. Digital holography is used to reconstruct both amplitude and phase of the wavefield transmitted by the sample to reveal the phase shift induced by adjacent reversed domains during the poling. The resulting movies of both amplitude and phase maps, for in-situ visualization of domain pattern formation, are shown. The possibility of using the technique as tool for monitoring in real-time the periodic poling of patterned samples is discussed.

A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.

The role of a spatially varying absorptive inhomogeneity located at different depths within a turbid material has been investigated. This inhomogeneity has been characterized by a spatially dependent Gaussian distribution of its absorption coefficient. The present study has been performed calculating the time-resolved contrast function in the framework of the first-order perturbative approach to the diffusion equation for a slab geometry and a coaxial measurement scheme. The model has allowed us to take into account different locations of the inclusion along the source-detector axis. The accuracy of time-resolved contrast predictions has been analyzed through comparisons with results of the finite element method that has been used to numerically solve the diffusion equation. Recovery of the absorption perturbation parameter of the inhomogeneity for different axial positions has also been investigated.

For the first time to the authors' knowledge, the Talbot effect has been observed and investigated in digital holography. By numerical reconstruction of holograms, the Talbot self-imaging phenomenon is observed by reconstruction of the amplitude of the image at different distances and (or) wavelengths. A simple spectrometer based on Talbot self-imaging in digital holography is proposed and demonstrated.

We describe an infrared interferometric technique based on a two-dimensional spatial fringe analysis Fourier method for investigating the characteristic ring diffraction pattern generated by the self-phase-modulation effect induced in nematic liquid crystals (NLCs) by an infrared laser beam and for measuring the nonlinear refractive index of the NLCs. The experimental setup employs a Mach-Zehnder interferometer with a cw CO2 laser emitting at 10.6 microm and a pyroelectric optoelectronic sensor matrix to detect the modulated ring-pattern intensity distribution formed in the far field by a nematic E7 sample. A Fourier-transform-based analysis of the interference fringe pattern allows comparison of the measurements with the theoretical ring-pattern intensity distribution. We show that accurate determination of the nonlinear refractive index can be obtained by analyzing the two-dimensional phase distribution of the modulated ring pattern.

We develop a perturbation model to predict the effect of a spatially varying absorptive inhomogeneities in a diffusing slab. The model is based on a perturbation solution of diffusion equation derived for a refractive index mismatch between the scattering slab and the surrounding medium, through the use of the extrapolated boundary conditions. We show that the model allows to compute the time-dependent relative change in the transmitted signal resulting from the presence of the inclusion. We derive simplified expressions for the perturbed time-resolved transmittance that allows to implement an efficient fitting procedure for obtaining the optical properties of the absorptive inclusion. The accuracy of the predictions of the model was investigated through comparison with the results of the Finite Element Method to solve the time-dependent diffusion equation numerically. The procedure is used to obtain the absorption perturbation parameter of an absorptive inclusion characterized by spatially dependent Gaussian distribution of its absorption coefficient located at the midplane of a scattering slab.

We propose a new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement. Corrected reconstruction distances can be automatically calculated, and well-focused amplitude and phase-contrast images can be obtained for each digitized hologram. The method is demonstrated for inspection of microelectromechanical systems subjected to thermal load. The method can be applied as a quasi-real-time procedure.

A new method for measuring simultaneously the thickness and the refractive index of a transparent plate is proposed. The method is based on a simple, variable lateral-shear, wavelength-scanning interferometer. To achieve highly accurate measurements of both refractive index n and thickness d we use several means to determine these two quantities. We finely tune a distributed-feedback diode laser light source to introduce a phase shift into the detected signal, whereas we make the sample rotate to produce variable lateral shearing. Phase shifting permits precise determination of the optical thickness, nd, whereas refractive index n is obtained from the retrieved phase of the overall interference signal for all incidence angles.

An electro-optic device applied as an optical beam deflector and switch at different wavelengths has been built and tested. The electro-optic device is based on domain-engineered lithium niobate (LiNbO3). In this paper, for the first time, its operation has been visualized by an imaging camera. The device has been characterized both at the visible wavelength (632.8 nm) and at a typical telecom wavelength (1532 nm). Furthermore, the device has been tested as an amplitude modulator in the mid-infrared region as well, at a wavelength of ~4.3 microm, where no Pockels cells are available. A detailed description of this device is given, and the experimental results are discussed.

An approach is proposed for removing the wavefront curvature introduced by the microscope imaging objective in digital holography, which otherwise hinders the phase contrast imaging at reconstruction planes. The unwanted curvature is compensated by evaluating a correcting wave front at the hologram plane with no need for knowledge of the optial parameters, focal length of the imaging lens, or distances in the setup. Most importantly it is shown that a correction effect can be obtained at all reconstruction planes. Three different methods have been applied to evaluate the correction wave front and the methods are discussed in detail. The proposed approach is demonstrated by applying digital holography as a method of coherent microscopy for imaging amplitude and phase contrast of microstructures.

We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling, after patterning by interference lithography. Furthermore we investigate the poling process at an overpoling regime which caused the appearance of submicron dot domains very similar to those induced by backswitch but different in nature. We show the possibility for realizing submicron-scaled threedimensional domain patterns that could be applied to the construction of photonic crystals and in nonlinear optics. We show that high etch-rate applied to such structures allows to obtain pyramidal-like submicron relief structures which in principle could find application for waveguide construction in photonic bandgap devices.

In this paper, we have investigated on the potentialities of digital holography for whole reconstruction of wavefields. We show that this technique can be efficiently used for obtaining quantitative information from the intensity and the phase distributions of the reconstructed field at different locations along the propagation direction. The basic concept and procedure of wavefield reconstruction for digital in-line holography is discussed. Numerical reconstructions of the wavefield from digitally recorded in-line hologram patterns and from simulated test patterns are presented. The potential of the method for analysing aberrated wave front has been exploited by applying the reconstruction procedure to astigmatic hologram patterns.

It is demonstrated for the first time to the authors' knowledge that digital holographic image reconstruction can be applied to correction of image reconstruction in the presence of severe anamorphism and aberrations. It is shown that anamorphism and aberrations can be taken into account and compensated for separately to yield a correct-image reconstruction. Anamorphism and aberrations are introduced by a holographic recording system based on a reflective grating interferometer (RGI). The strong anamorphic behavior of the RGI prevents reconstruction of a correct image unless that behavior is compensated for in the process of numerical holographic reconstruction.

We present a concept of interferometric testing, believed to be novel, that can be applied to measuring aberrations of optical components that have rotational symmetry. The optical configuration uses two coherent, collimated wave fronts that are tilted to impinge upon the optical component being tested such that one beam is on axis and the other is off axis. For small tilt angles the two aberrated wave fronts can be considered to be carrying the same aberrations. Furthermore, the off-axis beam is displaced along a direction orthogonal to the optical axis of the component. Interference between the two aberrated wave fronts produces a fringe pattern that is similar to a lateral shear interference pattern. Moiré fringes are obtained by spatial beating of the interference pattern with a CCD TV camera array. Under such conditions it is possible to subtract most of the linear carrier that is intrinsically present in the resultant fringe pattern owing to the large defocus aberration and tilt.

A third-order aberration analysis for a reflective grating interferometer (RGI) is developed for a noncollimated configuration. In such a configuration the RGI is still a folded and reversing interferometer that is sensitive only to coma aberration, as it is in the collimated configuration. However, for an unaberrated input beam converging on a plane grating, the reflective grating of the interferometer introduces self-aberrations. Consequently, a nonnull fringe pattern is obtained. Nevertheless, a RGI in the noncollimated configuration has the potential to be applied for isolating and measuring coma, and a possible configuration for this application is proposed. As an example of the application, the coma of a large mirror could be isolated and measured by use of a converged configuration to avoid the main limitation in using the RGI in a configuration with a nearly collimated beam.

We present a new, folded reversal interferometer. It is based on the reflective grating interferometer and can be applied for optical isolation and testing of coma aberration. The interferometer has several advantages in respect to other existing optical reversal configurations. A carrier can be easily added for phase retrieval in interferometric fringe patterns for mapping coma aberration. Furthermore, in an asymmetric optical configuration a lateral shear can also be added, transforming it in a reversal shearing interferometer. The principle of operation of the interferometer is described, and the application for measuring the coma aberration of a parabolic mirror used off axis is demonstrated.

Two ideal concentrators with fin absorbers in dielectric rhombuses are described. Expressions for the design, height, and mirror length are derived. The devices have a concentration factor (n/sin ?(M)) that is clearly higher than the traditional air-filled ideal concentrators. They do not require more mirrors or space and, when such easily available dielectrics as glass and water are used, offer useful configurations for purposes such as the collection of solar energy.