In this paper we describe an interferometric process using a polychromatic light source and a spectroscopic detection system. This method is used for surface metrology or for bulk optical components characterisation (dispersion for example). As classical monochromatic interferometry, it consists in comparing a reference wave front with one issued from the component to be tested. However this measurement is assumed by determination of the spectral dispersion induced upon the various frequencies of the light source spectrum. The aim of this work is both dispersion measurements and characterisation of aspherical surfaces
Optical Coherent Tomography (OCT) technique is based on an interferometric device bringing to the inter-correlation between a short reference pulse and the signal issued from the medium. This correlation is obtained by mechanical length modulation of the interferometer reference arm. We propose here an original technique using the SISAM (“Spectroscope Interferentiel a Selection par l’Amplitude de la Modulation”: Interferential Spectrometer by Selection of Amplitude Modulation) correlator, which allows to obtain directly without length modulation, the inter-correlation signal between the reference and the tests waves. With a large spectral bandwidth light source, the temporal depth of the original pulse is short compared to the signal diffused in the complex medium, and the inter-correlation function may be reduced to the impulse response of the structure to be studied. This temporal analysis could be very interesting to obtain both amplitude and phase parameters on the waves propagated in the medium, and could induce significant data on the medium and its structure. We will present the experimental SISAM device and results obtained in imaging through turbid media with this technique. We will also discuss about efficiency of this method in terms of accuracy and of ability to characterize complex structures and media.
The Vectorial Modulation Transfer Function (VMTF) calculation will be used for the explanation of diffraction patterns obtained with Brewster ellipsometers. The method used to study these phenomena lays on protection of the incident monochromatic distribution on a basis constituted of monochromatic plane wave components. The first point examined is how the plane wave spectrum could be propagated through a polarizing pate considering the polarization distortions introduced by diffraction. The same calculation is realized for the whole system in order to establish the expression of the whole VMTF. Paraxial approximations are used in order to analyze more easily the reflected beam pattern and to compare it with experimental results. The good agreement between experimental results and model allows a quantitative valuation of index measurement accuracy as a function of the interface mean surface roughness of the experimental sample considering the specular reflection on the homogeneous plane interface. Taking into account the amount of light scatter by the interfaces irregularities it is then possible to specify the theoretical uncertainties limits affecting as well refractive index and refractive index gradients measurements.
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