G. Schirripa Spagnolo

Propagation of axially symmetric flattened Gaussian beams

Flattened Gaussian beams are characterized by a waist profile that passes in a continuous way from a nearly flat illuminated region to darkness. The steepness of the transition region is controlled by an integer parameter N representing the order of the beam. Being expressible as a sum of N Laguerre–Gauss modes, a flattened Gaussian beam turns out to be very simple to study as far as propagation is concerned. We investigate the main features of the field distribution pertaining to a flattened Gaussian beam throughout the space and present experimental results relating to the laboratory production of this type of beam.

Generalized Bessel-Gauss beams

In this paper we describe a superposition model for Bessel-Gauss beams, in which higher orders are included. An analogous model leads to a different class of beams, namely the modified Bessel-Gauss beams. Then a generalized set of beams, containing the previous beams as particular cases, is introduced. The behaviour of these beams upon propagation is investigated, both analytically and numerically.

Displacement measurement using the Talbot effect with a Ronchi grating

In this study the Talbot effect with a Ronchi grating is applied to measurement of shift. It is shown that by using a measurement procedure based on the Fourier transform a cosine grating can be replaced by a Ronchi grating. Two different methods for data reduction and some experimental results are given.

High-precision digital automated measurement of degree of coherence in the Thompson and Wolf experiment

We propose a high-precision digital automated quantitative determination of the modulus of the complex degree of coherence. The Thompson and Wolf experiment is repeated, using a CCD and a measurement method based on the fast Fourier transform. The experimental results agree very well with the predictions of the theory.

A new method for measuring the diffusivity of liquid binary mixtures using DSPI

A simple and compact digital speckle pattern interferometer is proposed to measure the isothermal diffusion coefficient in transparent mixtures. The diffusion constant is determined directly from the skeletonized video correlogram. An example of diffusion coefficient measurement of a binary liquid mixture demonstrates the usefulness of the method.

Study of free-convective onset on a horizontal wire using speckle pattern interferometry

Abstract The onset and development of heat convection from a suddenly heated thin horizontal wire in air has been studied experimentally by an optical technique, named dynamic electronic speckle pattern interferometry, which allows the acquisition of qualitative and quantitative data. Attention is focused in providing temperature field visualizations and data about the temporal behavior. The heat-rate-based Rayleigh number, Ra ∗ , ranges from 0.069 to 0.67, a region of parameters poorly covered by previous investigations. Experimental results are compared with previous data. The extent, at which existing correlations can be used for wires of 0.2 and 0.4 mm in diameter, is outlined. A new correlation is proposed.

Electro-optic correlation for in situ diagnostics in mural frescoes

A method based on the properties of local correlation of speckle patterns, scattered by the surface when it is illuminated by a laser, is used for in situ evaluation of the state of conservation of mural frescoes. Some experimental results are presented.

Image decorrelation for in situ diagnostics of wooden artifacts

Local decorrelation of speckle patterns scattered by a surface is used for nondestructive evaluation of the state of conservation of wooden artifacts. Some experiments have been carried out on models with simulated internal flaws and on real, ancient, wooden panel paintings. The setup is very simple and can easily be used by nonoptically skilled operators.

Experimental determination of the size of a source from spectral measurements

We show how spectral changes measurements in a Young interferometer can be used to determine the dimension of an incoherent source. The experimental results confirm the theoretical predictions.

Fast Fourier transformed electronic speckle contouring for diffuse surfaces profilometry

Abstract A method of contouring three-dimensional objects using an out-of-plane sensitive ESPI apparatus with optical fibers is presented. The contour map is obtained by shifting the object illumination beam. A Fourier transform method is suggested for automatic quantitative analysis of specklecorrelograms in terms of phase. An example of application is presented.