A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Digital holography is an emerging field of new paradigm in general imaging applications. We present a review of a subset of the research and development activities in digital holography, with emphasis on microscopy techniques and applications. First, the basic results from the general theory of holography, based on the scalar diffraction theory, are summarized, and a general description of the digital holographic microscopy process is given, including quantitative phase microscopy. Several numerical diffraction methods are described and compared, and a number of representative configurations used in digital holography are described, including off-axis Fresnel, Fourier, image plane, in-line, Gabor, and phase-shifting digital holographies. Then we survey numerical techniques that give rise to unique capabilities of digital holography, including suppression of dc and twin image terms, pixel resolution control, optical phase unwrapping, aberration compensation, and others. A survey is also given of representative application areas, including biomedical microscopy, particle field holography, micrometrology, and holographic tomography, as well as some of the special techniques, such as holography of total internal reflection, optical scanning holography, digital interference holography, and heterodyne holography. The review is intended for students and new researchers interested in developing new techniques and exploring new applications of digital holography.

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Principles and techniques of digital holographic microscopy

A thin-film periodically poled lithium niobate waveguide was designed and fabricated which generates entangled photon pairs at telecommunications wavelengths with high coincidences-to-accidentals counts ratio $\mathrm{CAR}g67000$, two-photon interference visibility $Vg99%$, and heralded single-photon autocorrelation ${g}_{H}^{(2)}(0)l0.025$. Nondestructive in situ diagnostics were used to determine the poling quality in 3D. Megahertz rates of photon pairs were generated by less than a milliwatt of pump power, simplifying the pump requirements and dissipation compared to traditional spontaneous parametric down-conversion lithium niobate devices.

High Quality Entangled Photon Pair Generation in Periodically Poled Thin-Film Lithium Niobate Waveguides.

Ferroelectric Crystals for Photonic Applications

Digital Holographic Microscopy (DHM) is a single shot interferometric technique, which provides quantitative phase images with subwavelength axial accuracy. A short hologram acquisition time (down to microseconds), allows DHM to offer a reduced sensitivity to vibrations, and real time observation is achievable thanks to present performances of personal computers and charge coupled devices (CCDs). Fast dynamic imaging at low-light level involves few photons, requiring proper camera settings (integration time and gain of the CCD; power of the light source) to minimize the influence of shot noise on the hologram when the highest phase accuracy is aimed. With simulated and experimental data, a systematic analysis of the fundamental shot noise influence on phase accuracy in DHM is presented.

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Influence of shot noise on phase measurement accuracy in digital holographic microscopy.

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.

In-situ visualization, monitoring and analysis of electric field domain reversal process in ferroelectric crystals by digital holography.

We investigate the effect of the defect-induced internal field on the electro-optic behavior of z-cut congruent lithium niobate crystals. We measure, by a spatially resolved interferometric techn ...

Investigation of electric internal field in congruent LiNbO3 by electro-optic effect

Analysis of moiré fringes for measuring the focal length of lenses

We present a method for in-situ visualization of electric field domain reversal in congruent lithium niobate (LN) through an electro-optic interferometric technique. The crystal refractive index n changes by the linear electro-optic and piezoelectric effects along the z crystal axis, due to the external electric field. This variation depends on the domain orientation so that two adjacent antiparallel domains present a refractive index difference equal to 2Dn which is used for in-situ visualization of the reversed domain pattern during formation. A digital holographic (DH) technique is employed for a two-dimensional (2D) reconstruction of the wavefield transmitted by the sample in amplitude and phase during the process. The corresponding amplitude-map and phase-map movies are presented. The amplitude-map gives qualitative information about the spatial evolution of the domain boundaries while the phase-map provides measurement of the 2D distribution of the phase shift induced along the z axis. The phase-map movies provide unequivocal information about the spatial distribution of the reversed domain regions. This technique can be used as in-situ monitoring method alternative to the measurement of the poling current which provides information only about the amount of charge delivered to the sample, ignoring the spatial distribution of the domain boundaries.

Real-time phase-contrast analysis of domain switching in lithium niobate by digital holography

We investigated the optical birefringence near the wall between two opposite domains in a z-cut congruent LiNbO3 through a full-field polarimetric method. We obtained a measure of domain wall width and determined the direction of the principal axes of stress-induced birefringence. Experimental data show that the principal axes of stress-induced birefringence result to be parallel or perpendicular to the domain wall, according to theoretical predictions. The domain wall width value ranges from 10 to about 50μm, showing a spatial variation that we can appreciate since the used method allows us to obtain two dimensionally resolved measurements.

Marella de Angelis

Papers

In-situ visualization, monitoring and analysis of electric field domain reversal process in ferroelectric crystals by digital holography.

Investigation of electric internal field in congruent LiNbO3 by electro-optic effect

Analysis of moiré fringes for measuring the focal length of lenses

Real-time phase-contrast analysis of domain switching in lithium niobate by digital holography

Investigation of optical birefringence at ferroelectric domain wall in LiNbO3 by phase-shift polarimetry