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

Femtosecond laser micromachining can be used either to remove materials or to change a material's properties, and can be applied to both absorptive and transparent substances. Over the past decade, this technique has been used in a broad range of applications, from waveguide fabrication to cell ablation. This review describes the physical mechanisms and the main experimental parameters involved in the femtosecond laser micromachining of transparent materials, and important emerging applications of the technology. Interactions between laser and matter are fascinating and have found a wide range of applications. This article gives an overview of the fundamental physical mechanisms in the processing of transparent materials using ultrafast lasers, as well as important emerging applications of the technology.

Femtosecond laser micromachining in transparent materials

This article describes the principles and major applications of digital recording and numerical reconstruction of holograms (digital holography). Digital holography became feasible since charged coupled devices (CCDs) with suitable numbers and sizes of pixels and computers with sufficient speed became available. The Fresnel or Fourier holograms are recorded directly by the CCD and stored digitally. No film material involving wet-chemical or other processing is necessary. The reconstruction of the wavefield, which is done optically by illumination of a hologram, is performed by numerical methods. The numerical reconstruction process is based on the Fresnel–Kirchhoff integral, which describes the diffraction of the reconstructing wave at the micro-structure of the hologram. In the numerical reconstruction process not only the intensity, but also the phase distribution of the stored wavefield can be computed from the digital hologram. This offers new possibilities for a variety of applications. Digital holography is applied to measure shape and surface deformation of opaque bodies and refractive index fields within transparent media. Further applications are imaging and microscopy, where it is advantageous to refocus the area under investigation by numerical methods.

/pdf/digital-recording-and-numerical-reconstruction-of-holograms-58gz5gqjmd.pdf

Digital recording and numerical reconstruction of holograms

Fringe projection techniques: Whither we are?

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.

/pdf/principles-and-techniques-of-digital-holographic-microscopy-56tmwltigo.pdf

Principles and techniques of digital holographic microscopy

A simple general method is reported for particle tracking and velocity field determination from the reconstruction of holographic images. A preliminary experimental application is reported.

A method for the determination of three-dimensional velocity fields from holographic images

We investigate digital holography method as metrological tool for inspection and characterization of MEMS structures. The efficiency of the digital holography is demonstrated measuring out of plane deformations due to the intrinsic residual stress. Microstructures under investigation are of two different types: the first are made of a single polysilicon layer, whereas the second are bimorph structures with a thin silicon nitride layer over the polysilicon one. These structures exhibit an out-of-plane deformation owing to residual stresses between the different layers. The characterization of these deformations is instrumental to study and understand the effect of residual stress on the deformation of the single microstructures. To this aim digital holography has been applied as metrological tool in order to obtain the profile of the microstructures. These data are employed in analytical and numerical model to evaluate residual stress inside the investigated structures. Moreover, digital holography has been employed to evaluate MEMS behavior when subjected to thermal load. Profile of cantilevers, with dimensions from 1 to 50 μm, has been measured.

Evaluation of residual stress in MEMS structures by digital holography

In this paper we describe an interferometric technique based on high precision 2D spatial fringe analysis Fourier method for measuring the elastic constant of nematic liquid crystals. Since the determination of the elastic anisotropy relies on the measurement of the ratios between the elastic constants, this technique provides a powerful and high accuracy method for characterizing nematic liquid crystals.

Fourier-transform-based interferometric technique for measuring the elastic anisotropy of a dye-doped liquid crystal

In the last years lithium niobate (LN) has become one of the most important optical material in optoelectronics and nonlinear 
optics for its large electro-optics and nonlinear optical coefficients. Ferroelectric materials are employed in several electrooptic, 
acousto-optic, and nonlinear optical devices, as modulator of light, beam deflector, optical frequency converters, or 
tuneable sources of coherent light for spectroscopic applications. Manipulation of ferroelectric domains into gratings, 
matrices, or other shapes is possible. 
Fabrication of new ordered microstructures in LN samples through domain engineering followed by differential etching has 
been developed recently for applications in the fields of optics and optoelectronics. These microstructures have a range of 
applications in optical ridge waveguides, alignment structures, V-grooves, micro-tips and micro-cantilever beams and precise 
control of the surface quality and topography is required of for photonic band-gap structures. Moreover engineering 
ferroelectric domains by an electrical poling technique represent a key process for the construction of a wide range of 
photonic devices. Therefore, a thorough understanding of material properties and of the poling process are crucial issues. We 
will show that interferometric approach based on Digital Holography can provide a very useful tool for investigation and 
characterization of materials and of the engineered structures.

Characterization and engineering of ferroelectric microstructures by interferometric methods

An automated Fourier-transform method of phase retrieval of moire interferometric fringe pattern is presented. The method is shown to provide fast and accurate determination of the phase information by removing the carrier without shifting in frequency domain the filtered Fourier spectrum of the carrier-modulated moire fringe pattern. The principle of the method is described and moire interferometric measurements with submicron sensitivity of the in-plane displacement fields of thick carbon fiber/PEEK composite laminates are analyzed as example of application of the technique.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Giovanni Pierattini

Papers

A method for the determination of three-dimensional velocity fields from holographic images

Evaluation of residual stress in MEMS structures by digital holography

Fourier-transform-based interferometric technique for measuring the elastic anisotropy of a dye-doped liquid crystal

Characterization and engineering of ferroelectric microstructures by interferometric methods

Fringe analysis of moire interferometry for studying micromechanical behavior of composite materials