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.

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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

Digital holography is proposed as a non-contact method for the inspection and characterization of MEMS. The method can be useful for assessing the fabrication process and the functionality as well as the reliability of micromachined structures.

Digital holography for characterization and testing of MEMS structures

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.

On the origin of internal field in Lithium Niobate crystals directly observed by digital holography.

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.

Talbot self-image effect in digital holography and its application to spectrometry.

Liquid refractometer based on interferometric fringe projection

We report a new method to generate an optical dipole potential with a null intensity region surrounded in all directions by light walls. This is achieved with a simple scheme based on a conical lens. Applications to optical trapping of neutral atoms are discussed.

Giovanni Pierattini

Papers

Digital holography for characterization and testing of MEMS structures

On the origin of internal field in Lithium Niobate crystals directly observed by digital holography.

Talbot self-image effect in digital holography and its application to spectrometry.

Liquid refractometer based on interferometric fringe projection

Single-beam optical bottle for cold atoms using a conical lens