The present work consists on the development of an adaptive control system to compensate the reduction of the contrast
in interferograms caused by mechanical vibrations present in a Mirau based interference microscopy system. The control
generates random signals that are injected during the integration time of the camera through a piezoelectric device in
order to change the phase of the interferometer. Each obtained image has different control signals injected during the
integration time. The contrast is evaluated and if the contrast is improved, the signal injected is adjusted to seek for a
better improvement. The best signals collected are added to the control signal, which is applied to the system after the
adaptation process is over. The control scheme implemented is capable of finding signals to compensate the main
frequency noisy components of the system.
We present a phase shifting interferometry system for the study of the early adhesion process for osteoblast-like cells,
through an interference microscope. Optical phase maps from the cells are obtained experimentally as a function of cell
adhesion time. The process is carried out on surfaces of metallic materials relevant to the development of bone implants.
The surfaces were subjected to various levels of mechanical polishing and their roughness was measured using the same
experimental technique mentioned before. Morphological changes of the cell can be measured over their optical phase
maps while the cell adhesion process is accomplished. The experimental technique shows a suitable feature as to the
observed time scale, and also shows a high stockiness and precision for the determination of the optical phase.
We present a method for measuring weak absorption in optical materials, using a new diferential
interferrometry technique. Both thermal shift phase and thermal characteristic time may be determined by
fitting the observed time-resolved interferometric signal.
Although a variety of surfactant based processes of technological importance occur in the presence of temperature gradients, very little information is available on the thermal diffusion of these macromolecules in solution. In this work optical interferometry is applied to the study of photothermal properties of aqueous solutions of surfactants. This technique allows to visualize spatio-temporal changes of the refractive index of the samples produced by the local heating of the solvent and the solute redistribution set up by thermal diffusion. We present preliminary results on the photothermal response to absorption of cw laser radiation of aqueous solutions of ionic and nonionic surfactants in the presence of trace amounts of the malaquite green dye.
A new method for real-time obtention of the dispersion behavior n=n(λ) of a transparent media is presented. The procedure stands on the analysis of the hybrid bidimensional fringe pattern obtained at the exit plane of a spectrometer which performs the spectral analysis of a white light interferogram. The phase of the signal depends both on a spatial coordinate and the chromatic variable wavenumber σ=λ-1. Taking profit of the dispersion behavior of the sample the phase of the signal can be forced to become stationary at certain points of this hybrid plane. The line which connects the stationary phase points can be experimentally obtained through an appropriate numerical fitting. It stores the parameters of a Cauchy approximation for the refractive index.
In this paper we study the axial absorption in thermal lenses with a standard interferometric technique, using a novel technique for phase retrieving: the Wavelet Transform. This recently developed technique is very robust and shows both relative speed of calculus and excellent accuracy in phase determinations.
Spectrally Resolved White Light Interferometry (SRWLI) is used for precise measurements of both the sample width and the differential refractive index, attaining precision of about 10-6 in the refractive index. This is achieved through the experimental simulation of a thin virtual cell about 40μm wide.
In this paper we present a different point of view of phase measurements performed in interferometry, image processing and intelligent vision using Wavelet Transform. In standard and white-light interferometry, the phase function is retrieved by using phase-shifting, Fourier-Transform, cosinus-inversion and other known algorithms. Our novel technique presented here is faster, robust and shows excellent accuracy in phase determinations. Finally, in our second application, fringes are no more generate by some light interaction but result from the observation of adapted strip set patterns directly printed on the target of interest. The moving target is simply observed by a conventional vision system and usual phase computation algorithms are adapted to an image processing by wavelet transform, in order to sense target position and displacements with a high accuracy. In general, we have determined that wavelet transform presents properties of robustness, relative speed of calculus and very high accuracy in phase computations.
Spectrally Resolved White Light Interferometry is used for real-time high-precision measurement of differential refractive index of low concentration solutions. Dispersion behavior of low concentration solutions is similar to that of their solvents, so that the differential refractive index is non-dispersive. White light provides redundant information which yields high precision results. Moreover, white light provides information about the absolute fringes' order, which allows to improve precision.
The evolution of the spatial profile of a thermal lens induced by a cw low power laser beam in an absorbing dye solution is directly visualized in real time using glow- coherence light interferometry. Both spatial characteristics and response times of the lens are measured. Preliminary comparisons between experimental result and thermal diffusion theory are presented. The accuracy of measured refractive index in the thermal lens profile is better than 10-6.
The frequency-modulation continuous wave (FMCW) interferometry is used in combination with a reference technique by measuring the linear thermal expansion coefficients in metallic bars. Unlike other methods, the technique shown provides results in real time with a very good accuracy, and fulfills the requirements of absolute distance and displacement measurement. First results yield uncertainties of about 50 microns over a 0.1 - 10 cm dynamic range.
Spectrally resolved white light interferometry (SRWLI) is applied to 1-D profilometry. The technique allows us to deal with discontinuous profiles without any ambiguity. Experimental results show good agreement with phase shifting profilometry; nanometric resolution is attained. In order to extend the method to 2-D samples, double spectral modulation (DSM) is applied using a new experimental set-up which enhances luminosity.
The purpose of recent developments of profilometry by using white light interferometry is to provide new tools for the analysis of rough samples which when studied by monochromatic phase-shifting interferometry, may cause phase calculation ambiguities. The usual way to perform depth measurements by white light interferometry is to analyze the coherence-limited interference fringes while the optical path difference is scanned. The method proposed here does not use optical path difference scanning. A spectroscopic device is used instead to separate the interference intensities associated to each spectral component of the light source. Phase variations due to wavelength change are proportional to the optical path difference and allows depth measurement to be performed without axial scanning. The profile of one line of the inspected sample is obtained from only one 2D interferogram. In this 2D interferogram one direction corresponds to the inspected direction of the surface while the other one is the chromatic axis which allows phase to change with wavelength. Experimental results show the ability of the proposed method to obtain the profile of 1D surface with nanometric resolution.
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