We study the correlation between photons in the fluorescence light scattered from an atom driven by an intense bichromatic field having one strong and one weak component, with or without the use of frequency filters in front of the photodetectors. Depending on the filters used and on the spectral components selected, we predict signals corresponding either to bunching or to antibunching, and modulations at the driving field Rabi frequencies as well as at their sum and difference. In contrast with the case of monochromatic driving, the antibunching can occur between photons emitted into different (as well as the same) lines of the fluorescence spectrum.
New methods for recognition of range images based on correlation are presented. The techniques allow the detection of a range image of a tridimensional pattern whatever its position along the x, y and z axes. The first method uses the phase-coding of the range image in order to obtain invariance along the z-axis in the correlation process. The second method uses the sine-coding of the range image in order to obtain better discrimination than that obtained with phase-coding. The third method is a hybrid one that makes use of sine-coding for the input scene and phase-coding for the reference image, so both the full translation invariance and high discrimination abilities are obtained. Computer simulations are presented. Also, an experimental implementation of the method has been carried out showing good agreement with theoretical predictions.
In interferometry, spatial heterodyning is performed by multiplying the optical phase to be determined by a reference phase. Thus the spatial frequency spectrum corresponding to the signal investigated is better identified and manipulated. We propose a holographic interferometry method that is spatially heterodyned by deliberate rigid-body movement of the object investigated. The object deformation is calculated from the fringe pattern corresponding to two different positions of the object. This work is aimed at a quantitative deformation analysis of highly dynamic objects through pulsed holographic interferometry.
The aim of this paper is to determine the best value of the signal-to-noise ratio (SNR) for a non-guided optoelectronic link with minimum electrical power consumption by the emitter. Transmitter structures have been analysed and optimized as a function of the bit error rate {BER} of the link in order to give either the highest autonomy or a lower number of emitter components. The application requirement for the transmitter is consequently to offer a flexible and secure communication solution. The transmitter provides non-guided infrared communication inside a limited cell size. The thermal effects, the rise and fall times of the optical power output of the emission and the characteristics of component devices have been taken into consideration in order to evaluate the SNR. We demonstrate that, for a given electrical consumption, the emitted optical power of the transmitter circuit increases with the logarithm of the total number of light emitting diodes.
A phase-shift expander has been designed for distance measurements with a low-frequency phase-shift laser rangefinder using two coherent indirect frequency synthesizers. Using such a set-up, a theoretical analysis shows that the resolution of the phase-shift measurements can be improved. The main error source due to the output voltage, which is a frequency-modulated signal, is then analysed. Other error sources, such as the output frequency stability and the cross talk between the two channels, are evaluated. The intrinsic resolution is estimated as a function of the frequency drift of oscillators and an improved circuit is proposed. Experimental results are presented for a 16 and 32 expansion factor of the phase shift. Le dispositif propose a pour but d'augmenter la resolution d'un telemetre par dephasage fonctionnant a une basse frequence. Des generateurs synthetises utilisant des boucles a verrouillage de phase permettent de multiplier par une constante N les dephasages des signaux de frequence intermediaire. La principale source d'erreur provient d'un residu de modulation de frequence que l'on observe en sortie. On doit aussi prendre en compte la derive en frequence des VCO et la diaphonie presente entre les voies `signal' et `reference'. On propose une solution qui donne une valeur optimale du gain de boucle de chaque PLL en fonction de la derive des oscillateurs. Des resultats experimentaux sont presentes pour une multiplication du dephasage par 16 et 32.
A novel transmission structure for holographic colour filters is proposed. The colour filters utilize two identical transmission photopolymer hologram structures, laminated on both sides of a transparent substrate. The incoming white light is normally incident onto the device. Three different R, G, B beams are separated normally and coupled out due to the optical reciprocity. The simulation shows that the three peak wavelengths are at 460, 550 and 630 nm, consistent with the experimental results. The colorimetric properties are compatible with efficient R, G, B separation of white light. Keywords: Holographic optical elements, diffraction optics, colour filters, holographic technology Resume. On propose une nouvelle structure pour des filtres holographiques colores operant par transmission. Les filtres utilisent deux structures identiques d'hologrammes par transmission de photopolymeres deposes sur les deux faces d'un substrat transparent. La direction de la lumiere blanche incidente est normale au dispositif. Trois differents faisceaux R, G, B sont separes et couples a cause de la reciprocite optique. La simulation montre que les trois longueurs d'onde des maximums sont 460, 550 et 630 nm en bon accord avec les resultats experimentaux. Les proprietes colorimetriques sont compatibles avec une separation efficace R, G, B de la lumiere blanche. Mots cles: Element optique holographique, optique diffractive, filtres colores, technologie holographique
A non-contact sensor using the self-mixing interference inside a CW single-mode laser diode has been designed to measure displacements. By using an appropriate signal processing based on the interpretation of the interfringe of the sawtooth-like optical power variations, a resolution of lambda/12 has been obtained for displacements up to several micrometres even in the case of hysteresis in the laser characteristics.
In this paper, an electric-field-dependent 2 x 2 bypass-exchange photorefractive switch based on the high angular selectivity of a photorefractive volume phase grating is discussed.
We analyse the behaviour of a focus wave mode incident on a dielectric plane. The Descartes-Snell law is valid for the reflected beam but the refracted beam undergoes a Goos-Hanken shift and propagates in the direction of the incident focus wave mode. The Fresnel coefficients do not depend on the angle of incidence.
We show that Hillion's claim (Hillion P 1997 J. Opt. 28 130) that a Tellegen material can be distinguished from an isotropic dielectric-magnetic material by putting both materials in motion, is not true. Furthermore, his analysis holds for nondispersive media only, but such media are unphysical.
We show that Hillion's claim (Hillion P 1997 J. Opt. 28 130) that a Tellegen material can be distinguished from an isotropic dielectric-magnetic material by putting both materials in motion, is not true. Furthermore, his analysis holds for nondispersive media only, but such media are unphysical.
A one-channel optical hit-miss transform processor is proposed, which is based on incoherent correlation with a polarization-encoding method to code the input image and structuring element pair and electronic thresholding. The polarization-encoding-based rank-order hit-miss transform, which yields better performance in the presence of noise and clutter, can be carried out by using variable levels. Experimental results are also given.
Profilometry is a technique which measures the shape of a surface. This method provides the height z of every point of a surface above a reference plane. A pattern of bright and dark parallel stripes is obliquely projected onto the object which acts as a screen and the pattern of lines is distorted if the object is not a plane. The distorsion is related to the shape of the surface. The presented system uses the spatial phase-stepping technique which allows shape determination from a single video frame, so that it is possible to study a living subject. It is a non-invasive optical technique which allows non-contact measurements. As examples, the method is applied to observations of a hand and of a forefinger.
Two kinds of laser source interferometer (polarizing and absorbing beamsplitter) used for the accurate measurement of the optical path difference of a Fourier transform spectrometer are described and compared. The two interferometer configurations have been used with aircraft- and balloon-borne far-infrared spectrometers for atmospheric limb-sounding measurements, SAFIRE-A and IBEX. A comparison of the two implementations is described in this paper, and the relative performances and merits are compared.
in a photorefractive LiNbO3 crystal, two-mode polarization-controlled optical switches are proposed. These normally on and normally off switches are based on the polarization-sensitive property of the diffraction efficiency. Depending on the Kogelnik theory, we find, for o- and e-polarized readout beams, the diffraction efficiency ratio can range between 80% and 90%, and thus a switching arrangement exists.
An optical system permitting modulation of the repartition of the energy of a laser beam in real time has been investigated starting from the theory of Fourier optics. Comparisons of the results obtained theoretically and experimentally were made. The thermal effects induced during the surface treatment have also been simulated.
In this work we have studied the damaging effect of laser light on cell membranes using single bilayer liposomes as a model system. Liposomes, because of their structural similarities to membranes of biological cells, are the best model systems used for the investigation of the effect of laser radiation on biomembranes. Samples of liposomes were routinely prepared and stained in our laboratory For efficient localized heating of the membrane by laser light, we stained liposomes with a membrane dye with strong absorption at the laser wavelength. Irradiated by the laser beam, the membrane breakdown occurred at a particular laser power for samples of stained liposomes. The laser-induced damage was detected with the use of a photon correlation technique. The power threshold for this damage was measured.
A new design of fully integrated time counter is presented for application in laser ranging systems with 3 cm resolution. The counter is implemented on a single FPGA chip with amorphous antifuse structures. The counter contains two time-to-digital converters, each having 200 ps resolution least-significant bit (LSB) within a 10 ns range and a 32-bit, 100 MHz real-time counter. The control software and a versatile user interface, developed with the aid of the Delphi tools, are also described. At an ambient temperature of +20 degrees C we achieved a random error of 129 ps or 0.65 LSB. This is equivalent to a random error in the distance measurement equal to about 2.1 cm. The power consumption of the integrated counter is 5.2 mW when the clock is disconnected, which rises to about 390 mW in the active mode.
