Quantitative phase-contrast microscopy by a lateral shear approach to digital holographic image reconstruction.

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.

Recovering correct phase information in multiwavelength digital holographic microscopy by compensation for chromatic aberrations.

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.

Two-dimensional mapping of electro-optic phase retardation in lithium niobate crystals by digital holography.

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.

Optical properties of waveguides written by a 26 MHz stretched cavity Ti:sapphire femtosecond oscillator.

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.

Angular spectrum method with correction of anamorphism for numerical reconstruction of digital holograms on tilted planes.

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.

Two-beam interferometer for measuring aberrations of optical components with axial symmetry.

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.

Correct-image reconstruction in the presence of severe anamorphism by means of digital holography.

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.

Whole optical wavefields reconstruction by digital holography.

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.

Reflective grating interferometer in a noncollimated configuration.

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.

Reflective grating interferometer: a folded reversal wave-front interferometer.

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.