Sergio Musazzi

Optical particle sizer based on the Chahine inversion scheme

An optical particle sizer utilizing an iterative procedure, proposed originally by Chahine for the inversion of scattering data, has been developed. The optical scheme is innovative and allows the measuring range to be selected without substitution of the Fourier transform lens. Numerical computer simulations and experimental results are presented to allow both the inversion procedure validity and the instrument performance to be evaluated.

LIBS Instrumental Techniques

The laser induced breakdown spectroscopy (LIBS) is a laser based technique widely used in scientific and industrial applications for the elemental analysis of materials. Because of its very attractive features like e.g. the lack of sample preparation, the ability to perform multi-element real-time analysis and the possibility of in situ analysis, this technique has become very popular during last years. As a consequence a large number of LIBS systems with different experimental configuration have so far been developed. The purpose of this chapter is to provide a description of the basic components of a LIBS system and how their technical specifications as well as their design/configuration may affect LIBS measurements.

Interferometric system for precise submicrometer particle sizing

Following a recently exploited line of thought, we present an interferometric system for particle sizing in the submicrometer region. The phase of the field that results from the interference between the incident and the scattered waves is measured through a heterodyne detection scheme in a Mach-Zehnder-type interferometer. We explored the possibility of extending previous work on this subject to the case of larger particles, i.e., particles larger than 0.5 mum. Experimental results obtained with polystyrene spheres in the range of diameters 0.16-0.71 mum are reported and compared with theoretical predictions. We show that in this range univocal detection of the particle size is not successful because the phase versus particle-size plot exhibits a maximum in correspondence to diameters close to 0.5 mum.

Speckle grain noise in heterodyne techniques for holographic interferometry and speckle photogrammetry

Heterodyne techniques greatly improved the accuracy in readout systems for holographic interferometry and dual plate speckle photogrammetry, since the order of interference fringes is read via phase measurements. The limiting accuracy has been traditionally associated with scintillation noise. We discuss the existence of-an additional intrinsic noise resulting from the random position of the speckles over the detector aperture (speckle grain noise). At variance with the predictions based on the scintillation noise, the accuracy remains finite even for perfectly correlated speckle fields.

Heterodyne readout system for dual plate speckle photography: analysis of error sources and performance evaluation

We describe the design, construction, and testing of a dual plate specklegram heterodyne readout system. The choice of the optical layout and mode of operation is based on the results of a detailed discussion on the sources of error associated both with optical noise and misalignments. Noise analysis includes the conventional scintillation noise and a recently described additional source, the speckle grain noise. Stability and reproducibility tests have been conducted and the accuracy of displacement measurement is 10(-6) of the recorded specklegram size, approximately five times worse than the ultimate noise limited value.

Remote surface contouring using a cross-correlation speckle technique

A new high-resolution technique for remote surface contouring is proposed. Two photographic recordings of the object scene are made on separate plates. Between the two recordings, either the object or the recording camera is shifted laterally with respect to the optical axis by a known amount. The resultant relative relief displacement due to surface height distribution is accurately measured by a cross-correlation speckle technique. It is shown that a surface height resolution of the order of 50 μm is achieved at a distance of 1 m. The principle involved, experimental details, results, resolution of the method, and criteria for attaining better resolution, are discussed.

Period Doubling Bifurcation Route to Chaos

A theory recently formulated by Feigenbaum1,2 predicts that the transition to chaotic behaviour via a sequence of period doubling bifurcations has a universal character. Although at this stage the extent at which the theory is applicable is not entirely clear, it is generally believed that it should hold for a large class of nonlinear systems, provided that phase trajectories remain confined in a phase region of adequately low dimension.

Onset of Chaos in Fluid Dynamics

Forced nonlinear systems exhibit deterministic behaviour when the applied stress is small enough. Let us consider a driven anharmonic oscillation with an x3 restoring force. If the driving force is small, the motion is almost sinusoidal. The spectrum is composed of a sharp peak at the driving frequency and, eventually, smaller peaks at the higher harmonics. As the force is increased, the motion becomes more complicated and additional sharp peaks are introduced in the spectrum. One of course might wonder whether by making the driving force arbitrarily large, the spectrum will continue to be in the form of instrumentally narrow peaks. The answer is no, and this holds true for the simple case we are considering as well as for a large variety of more complex nonlinear systems. Above a given threshold the spectrum will show a continuum in between the remnants of the sharp peaks and one says that the system has reached a “chaotic” state.

A Laser Scanning System for Sag Detection on the Overhead Power Lines: In Field Measurements

The paper describes a new optical system designed for the remote position monitoring of the conductors sag in high voltage aerial electric lines. The principle of operation relies on the detection of the intensity backscattered by the conductor under investigation when it is intercepted by a properly driven scanning laser beam. Results will be presented relevant to measurements carried out on a real power line.

REVIEW OF QUANTITATIVE EVALUATION OF MATERIALS STRESS RESPONSE BY OPTICAL METHODS

Abstract The present paper was written with the aim of using the authors experience to provide a guideline for applying optical methods to the solution of mechanical problems, The question which this paper addresses is: when it is convenient to use optical methods and what kind of results must be expected? The aim is to write an easy to use handbook, hence the text differs from many scientific papers and will be introduced by a detailed flow-chart of the subject.