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2 Optica Applicata

2 2011

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Acousto-optic method for liquids refractometry

Ferria K., Laouar N., Bouaouadja N.

Optica Applicata

2011

Vol. 41, nr 1

109--119

Various methods of liquids refractive index measurements were previously developed by others. They differ however in the measurement accuracy, the used light wavelength, the measurement range and the sensitivity to the temperature and pressure. In this work, we present and discuss an acousto-optic technique for measuring the index of refraction of transparent liquid materials. In the proposed technique, a diffraction pattern produced by an acousto-optic interaction is imaged by a liquid lens placed between an optical flat glass and a convergent glass lens. The diffraction pattern consists of two symmetrical dots that are digitized by a CCD camera. The focal shift, which is induced by the liquid sample, produces changes in the position of the diffracted orders. The spatial frequency measurement of the diffractive pattern leads to determine the sample refractive index. The current method presents the advantage to have an adjustable measurement range and can be easily interpreted geometrically.

A new spherical aberration coefficient C4 for the Gaussian laser beam

Bencheikh A., Bouafia M., Ferria K.

Optica Applicata

2011

Vol. 41, nr 4

855--861

Laser beam quality is related to the aberration effect. Quartic phase aberration, more commonly known as spherical aberration, can result from aberrated optical components such as beam expanding telescopes, focusing or collimating lenses, or other conventional optical elements. In general, any kind of quartic aberration will lead to increased far field beam spread, degraded laser beam focusability and increased values of the beam quality. Currently, a well established quality parameter for laser beams is the M2 factor which is proportional to the coefficient of quartic phase aberration denoted C4. In many recent papers, authors used C4 given in geometrical optics approach to evaluate the laser beam quality M2 which belongs to the Gaussian beam optics and the two disciplines are not to be confused. In this paper, we present a new mathematical set for the spherical aberration coefficient C4, especially for Gaussian beams in the context of Gaussian beam optics. A numerical analysis of a set of lenses is done to show the importance of the new C4.