Demonstration of an elliptical plasmonic lens illuminated with radially-like polarized field.

We demonstrate an elliptically symmetric plasmonic lens that is illuminated by a radially-like polarization field. This illumination function is TM polarized with regard to the plasmonic lens, ensuring optimum coupling of the incident light into surface plasmons polaritons. The structure is analyzed theoretically by using the Green function approach, and a finite difference time domain simulation. Both approaches provide similar results. Specifically we calculate and experimentally measure the field distribution on the surface and a few microns above it. The results show strong dependency of the electric field distribution on the eccentricity of the elliptic structure and the illumination wavelength. The interference of surface plasmons generates a structured pattern consisting of distinct peaks distributed inside the ellipse with locations that are wavelength dependent. This pattern can be used in several applications including structured illumination microscopy, particles beam trapping and sensing.

Wavefront reconstruction by spatial-phase-shift imaging interferometry.

Common-path imaging interferometers offer some advantages over other interferometers, such as insensitivity to vibrations and the ability to be attached to any optical system to analyze an imaged wavefront. We introduce the spatial-phase-shift imaging interferometry technique for surface measurements and wavefront analysis in which different parts of the wavefront undergo certain manipulations in a certain plane along the optical axis. These manipulations replace the reference-beam phase shifting of existing interferometry methods. We present the mathematical algorithm for reconstructing the wavefront from the interference patterns and detail the optical considerations for implementing the optical system. We implemented the spatial phase shift into a working system and used it to measure a variety of objects. Measurement results and comparison with other measurement methods indicate that this approach improves measurement accuracy with respect to existing quantitative phase-measurement methods.

Spatial phase-shift interferometry--a wavefront analysis technique for three-dimensional topometry.

We describe a new wavefront analysis method, in which certain wavefront manipulations are applied to a spatially defined area in a certain plane along the optical axis. These manipulations replace the reference-beam phase shifting of existing methods, making this method a spatial phase-shift interferometry method. We demonstrate the system's dependence on a defined spatial Airy number, which is the ratio of the characteristic dimension of the manipulated area and the Airy disk diameter of the optical system. We analytically obtain the resulting intensity data of the optical setup and develop various methods to accurately reconstruct the inspected wavefront out of the data. These reconstructions largely involve global techniques, in which the entire wavefront's pattern affects the reconstruction of the wavefront in any given position. The method's noise sensitivity is analyzed, and actual reconstruction results are presented.

Small-focus integral fiber lenses: modeling with the segmented beam-propagation method and near-field characterization.

Tapered- and straight-core fiber microlenses of hyperbolic shape are studied with the segmented beam propagation method (Se-BPM). This new formulation extends to a large scale the finite-difference time-domain method for calculating propagation of the wave field in guiding systems. It is based on partitioning an entire computational domain into subdomains along the direction of propagation. The Helmholtz equation can be solved directly for each subdomain, and an iterative procedure is used to propagate the field from one subdomain to another. The Se-BPM is compared with other approaches that are commonly used to analyze straight-core fiber microlen devices in the paraxial approximation. We deal mainly with small-spot-size fiber microlenses where this approximation does not apply. We show that the emergent beam is not Gaussian in the far field. Instead of the usual far-field characterization we propose a near-field characterization of the fiber microlens. This is possible with the near-field scanning optical microscopy technique.

Topographic profiling and refractive-index analysis by use of differential interference contrast with bright-field intensity and atomic force imaging.

A methodology is described for phase restoration of an object function from differential interference contrast (DIC) images. The methodology involves collecting a set of DIC images in the same plane with different bias retardation between the two illuminating light components produced by a Wollaston prism. These images, together with one conventional bright-field image, allows for reduction of the phase deconvolution restoration problem from a highly complex nonlinear mathematical formulation to a set of linear equations that can be applied to resolve the phase for images with a relatively large number of pixels. Additionally, under certain conditions, an on-line atomic force imaging system that does not interfere with the standard DIC illumination modes resolves uncertainties in large topographical variations that generally lead to a basic problem in DIC imaging, i.e., phase unwrapping. Furthermore, the availability of confocal detection allows for a three-dimensional reconstruction with high accuracy of the refractive-index measurement of the object that is to be imaged. This has been applied to reconstruction of the refractive index of an arrayed waveguide in a region in which a defect in the sample is present. The results of this paper highlight the synergism of far-field microscopies integrated with scanned probe microscopies and restoration algorithms for phase reconstruction.

Generalized method for wave-front analysis.

We suggest and demonstrate a new method for wave-front analysis based on common-path phase-shift interferometry. We introduce a formalism and an iterative mathematical algorithm in which the wave front is transformed, modified, and inversely transformed. The resulting intensity data are sufficient to reconstruct the entire wave front. In a more restricted case, in which the wave-front modifications are arbitrarily applied over arbitrary spatial regions of the wave front, the wave front is reconstructed semianalytically by use of a model that allows a local solution, followed by an iterative algorithm. Measurement results indicating that the suggested approach has an improved measurement accuracy with respect to existing quantitative phase measurement methods are presented.