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.

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Principles and techniques of digital holographic microscopy

We present here the observation of the Talbot effect in digital holography (DH). A self-imaging phenomena is observed by reconstructing the amplitude of the object wavefield by using different distances and different illumination wavelengths. The numerical reconstruction allows to determine the complex field amplitude at different wavelengths while maintaining constant the reconstruction distance. We investigate on the possibility to build a spectrometer based on the Talbot effect. In particular, the spectrometer proposed in this work can cover the whole visible spectrum ranging from 350 nm to 750 nm and, from the FWHM of the spectrograms with a resolution of about 20 nm

A novel interferometric spectrometer obtained by imaging Talbot effect in digital holography

The authors develop a simple method based on holographic interferometry for determining the Poisson's ratio and the Young's modulus for a specimen subjected to four-point flexural testing that evaluates and eliminates the effects of the unwanted rigid-body rotations. In the experimental setup, they use an additional mirror to record the underside and the front surface of the specimen simultaneously. The theoretical analysis shows that it is possible to correlate the holographic fringe pattern of the underside and front surface of the sample. Each rotation angle can be evaluated by counting the fringe orders between two points chosen on the two fringe patterns.

Evaluation of rigid rotations in flexural loading tests by holographic interferometry

A digital holographic microscope (DHM) is employed as non-invasive metrological tool for inspection and 
characterization of a micromechanical shunt switches in coplanar waveguide configuration (CPW) for microwave 
applications. The switch is based on a bridge that can be actuated by using electrodes positioned laterally with respect to 
the central conductor of the CPW. The DHM features, such as speed, contact-less and non-destructivity, have allowed a 
full characterization of an electrical actuated shunt switches. In particular, the out-of-plane deformation of the bridge due 
to the applied voltage has been investigated with high accuracy. DHM inspection allows to investigate the shape of the 
bridge during the actuation, the total warpage due to the actuation, possible residual gap, possible hysteresis, and so on. 
These characterizations have been carried out both in static and in dynamic condition. In full paper the complete 
characterization will be reported together with an accurate description of the optical system employed for the 
investigation.

Non-destructive optical system based on digital holographic microscope for quasi real-time characterization of micromechanical shunt switch

We present and discuss a technique to measure concurrently the temperature dependence of quartz refractive indices in the thermal range 25 degree(s)C - 300 degree(s)C. The magnitude of both indices is found to decrease slightly with increasing temperature in the thermal range considered.

Heterodyne interferometric measurement of the temperature coefficient of birefringence of quartz retardation plates

We report on an interferometric technique based on two-dimensional Fourier fringe analysis for measuring the refractive indices and the thermo-optic coefficients of semiconductor-doped glasses suitable for optical waveguide fabrication The principle of the measurement method is discussed The thermo-optic coefficients of semiconductor-doped Schott glass filters have been determined in the temperature range 25-85 °C

http://iopscience.iop.org/article/10.1088/1464-4258/1/6/308/pdf

Giovanni Pierattini

Papers

A novel interferometric spectrometer obtained by imaging Talbot effect in digital holography

Evaluation of rigid rotations in flexural loading tests by holographic interferometry

Non-destructive optical system based on digital holographic microscope for quasi real-time characterization of micromechanical shunt switch

Heterodyne interferometric measurement of the temperature coefficient of birefringence of quartz retardation plates

Interferometric measurement of the refractive index and the thermo-optic coefficient of semiconductor-doped glasses