G. Tribillon

Biological Activity Measurement on Botanical Specimen Surfaces Using a Temporal Decorrelation Effect of Laser Speckle

Abstract A biological activity phenomenon, the cyclose that occurs in citrus fruits or in seaweed, is analysed by using the temporal correlation of speckle patterns produced when a specimen is illuminated with a laser beam. The experimental verification of the phenomenon as well as a theoretical model of the distribution of the elementary moving particles are given. Specific statistical processing of the digital speckle is applied to the computation of correlation coefficients. Experimental results are given for three kinds of biological samples.

Subpixel Speckle Displacement Measurement Using a Digital Processing Technique

Abstract This paper deals with the optical measurement of deformations and displacements of diffusing rough surfaces using changes in the speckle pattern obtained by laser illumination. A digitized speckle signal is obtained using a linear charge-coupled device photodetector that produces samples of one-dimensional signals of N pixels. A sequential numerical processing procedure is applied to detect the relative displacement of two speckle signals, corresponding to two different states of the surface; the accuracy is better than one micrometre. The principles of the method and the corresponding algorithms are described. Experimental results are given and these include an analysis of the deformation of video structure under directional traction.

Surface profiling by means of double spectral modulation

Double modulation-in frequency and intensity-of the power spectral distribution of a light beam is proposed for interferometric profilometry. The procedure is based on two facts: (1) the continuous spectrum of a light source is frequency modulated by the path difference in an interferometric device, (2) the continuous spectrum of a light source is intensity modulated by the transparency of an object placed in the exit plane of a spectroscopic device. Both procedures can be used to measure the profile of a surface with high precision. Moreover, phase shifting is automatically performed by the continuous wavelength variation along the spectrum, so that no piezoelectric transducers are necessary. The method is adaptable for the analysis of remote surfaces through optical fibers.

Phase-shifting methods for interferometers using laser-diode frequency-modulation

Laser diode interferometers are of particular interest for metrological applications since the optical-frequency dependence on the injection current can be used to produce modulations in the interferometric phase. By this way, the optical path difference can be evaluated accurately without being modulated. However, injection-current variations induce output intensity changes which prevent the direct application of phase-shifting algorithms. In this paper, we show that a corrected fringe pattern can be reconstructed, by considering pairs of output intensities with a relative phase-shift multiple of 2π. Subsequently, the assumption of constant background intensity and fringe visibility is satisfied and any classical phase-shifting algorithm can be applied. Only larger sets of phase-shifted intensities need be considered. The proposed method is validated by the application to experimental data.

Axial resolution of a chromatic dispersion confocal microscopy

An analysis of the axial resolution of a chromatic dispersion confocal microscopy is presented. The system is based on the principle of focus multiplexing by wavelength encoding due to a phase Fresnel lens. The axial resolution is related with the measure of the FWHM value of every spectral response.

The application of fluorescent layers, created by the sol-gel process, in an optical cryogenic temperature sensor

Abstract The sol-gel process is used to elaborate a fluorescent layer containing SrF2:Yb2+ powdered crystal. From this gel, luminescent properties of SrF2:Yb2+ are exploited to realize a cryogenic temperature sensor. Comparative tests with other fluorescent layers using classical binders like glues, show that the gel is a very promising tool for this sensor application.

Laser-diode interferometric heterodyne vibrometer: application to linear motor control

We describe an interferometric heterodyne vibrometer that uses a laser diode with a triangular modulation frequency. This optical sensor is used to probe a vibrating polished surface. As an illustration of the sensor performance, the control of nonuniform velocity of a linear motor is achieved. The technique can be used over a large bandwidth between a few hertz and several tens of kilohertz. Generalization of the technique to the sensing of frequency vibrations is also demonstrated theoretically.

Optical Surface Inspection Using A Transverse Speckle Detection Technique

A method that achieves automatic measurements of the orthogonal components of the motion of optically rough surfaces is described. An optical set-un that implements a speckle rotation is used to extract the components of 2-D displacements, which are obtained from simultaneous data recording performed by a single 1-D CCD line. A temporal analysis of speckle patterns related with a given inspected area of a moving structure is then possible. The movement trajectory is reconstructed. The principle of the method and the experimental set-up are described. Experimental results are shown with a specific application to the deformations of a video film structure under directional traction and dynamic analysis of thermal deformations of mechanical parts.

Optical surface inspection using a transverse speckle detection technique

Abstract A method that achieves automatic measurements of the orthogonal components of the motion of optically rough surfaces is described. An optical set-up that implements a speckle rotation is used to extract the components of 2-D displacements, which are obtained from simultaneous data recording performed by a single 1-D CCD line. A temporal analysis of speckle patterns related with a given inspected area of a moving structure is then possible. The movement trajectory is reconstructed. The principle of the method and the experimental set-up are described. Experimental results are shown with a specific application to the dynamic analysis of thermal deformations of mechanical parts.