A new and simple method for pseudo-coloring a photograph in a coherent optical processing system, utilizing a newly developed technique of half-tone screens, is described. By selective spatial filtering of the high diffraction orders in the Fourier plane of a coherent optical system, images with up to ten contours of constant brightness have been generated on a picture from a single half-tone copy of that picture. The pseudo-coloring of the picture is achieved by mixing the high-diffraction-order outputs generated by lasers of different wavelengths. In the experiment described herein, an argon laser and a He-Ne laser were used. The experimental results demonstrate that the method has considerable flexibility. A discussion of the theory, the method, and potential applications is given.
We briefly describe the principle of a completely automatic spectrophotometer which measures optical properties (R, R', T) in the spectral range 2 000-7 000 Å. The results obtained for normal incidence are then used by computer to determine the optical constants (n, k) and thickness d of a thin film.
We first emphasize the original features of our integral formalism and of its numerical applications. We revue the most important results already published for the visible and the near ultraviolet. Then we report new numerical results for the very far ultraviolet and, taking them into account, we discuss the most efficient way to use diffraction gratings in this range of wavelength. A very simple formula is given for the efficiency in the blaze order.
We propose here an experimental set-up allowing a precise measurement of mirror reflectances close to unity. The experimental arrangement is easy to adjust, although it requires the use of multi-paths optical cavity. The method can be applied to spherical mirrors as well as flat ones. The accuracy is up to 5.10−4. Results of measurements for visible and infrared spectral ranges are presented.
Photovoltaic phenomena similar to phototransition effects are induced in ZnS sputtered films by light of energy beneath the band-gap (not more than 0.22 eV). It is advanced that hot electron may escape from the photoionized coulombic centre and moves to some level within shallow traps distribution. Thickness dependent phenomena confirm the existence of a critical thickness in which the density of coulombic centres is higher.
Single exposure, multiple-object holography has been compared with single-exposure, single-object holography. The fringe visibility and hence the diffraction efficiency of single exposure multiplexed hologram decreases rapidly as the number of objects increases. It has been shown that it is possible to record these holograms with the same diffraction efficiency as that of a single-object hologram, if due care is taken for exposure time and number of objects.
We give, in this paper, the analytical expression for the field diffracted by a spatialy limited plane periodic grating. The illumination is first assumed to be completely coherent. The influence of the finite size of the objet on the Fresnel patterns is analysed by means of new « Fourier pseudo-coefficients ». We also analyse the partially coherent illumination case.
The method of scattered light used in a very simple way permitted the observation of isochromatic fringes produced in a plastic model. He-Ne laser radiation was employed in the experiment. Variations of fringe patterns are correlated with the application of stress in normal planes.
An apparatus for image analysis by multiplex optical coding has been designed and built. Two methods were experimented for image decoding: an analogue method and a numerical method, with image visualization in real time. The results obtained confirm the theoretical predictions as regards the « multiplex gain » due to this image analysis method.
The apodization problem is solved analytically for determining the pupil function (amplitude distribution over the exit pupil) which minimizes the second moment of the intensity distribution in the Fraunhofer diffraction pattern of a point object, on the conditions that the central intensity is prespecified to take a certain value less than that for the standard Airy-type optical system without filter and that the optical system is a passive one. The problem is treated for a rotationally symmetric optical system without aberrations. The method used to solve the problem is the calculus of variations of unconventional type involving the constraint of inequalities due to the passivity of the optical system. A detailed derivation of the optimum pupil function is presented and discussion on the resultant pupil function is given.
The visibility of speckle correlation fringes is studied in the case of a longitudinal displacement of the photographic plate between the two exposures. If the two speckle patterns are recorded at a large distance from the ground glass, the fringe visibility varies in the Fourier plane. It is high in the center and at the edge, and very low in the intermediate zone. The same experiment is repeated with the difference that the photographic plate is now quite near the ground glass. In this case the diameter of the central zone of high visibility fringes is related to the angular width of the Fourier spectrum of the ground glass.
We consider a light beam the electric field of which depends only on two dimensions, that case being suited to a linear source. The shift by total reflexion of such a beam depends on the direction, relative to the mean incident plane, of the plane P containing the propagation vectors of the plane waves into which the incident wave may be decomposed. The present work computes this influence, and explains some apparent inconsistancies in the application of the stationary phase method; we confirm the known results in the cases of a plane P coincident with the incidence plane or perpendicular to it.
Several set-ups using coherent light allow the recording of the autocorrelation function as well as of the power spectral density of speckle patterns observed in the image of a diffuse screen or in the scattering beam itself. Results obtained from these experiments conform closely to theoretical expectations [1].
The colour distribution in the Polychromatic Line Spread Function is computed in the case of primary aberrations. Different corrections of longitudinal and transverse chromatism, constant and dispersive cases of spherical aberration, coma and astigmatism have been considered. The calculations have been carried out for source C, and the standard observer, specified by the three sensitivity functions of the human eye CIE 1931.
An object illuminated with partially coherent light is imaged through a square law medium characterized by the dielectric variation (r, z) = 0(1 - α2 r2). We have studied the performance of this medium as an imaging element. An expression for the intensity distribution at the observation plane is derived and is found to be formally identical to the homogenous case. This formal identity is used to obtain an expression for the optical transfer function in the incoherent case. The variation of the degree of coherence at the observation plane is also considered in a special case when the object is incoherently illuminated.
We describe a method of storing a number of real amplitude images on a photographic plate by modulating each image on a different spatial carrier. The signal to be stored is placed in contact with a grid (2 crossed gratings) and this ensemble is imaged on a photographic plate. By choosing a different pair of diffracted orders of the grid, each signal is coded on a different fringe system. The grid remains stationary throughout the operation of storage. Upto eight images have been stored. The signal to noise ratio is calculated and the results are given.
After having discussed the principle of the technique for subtraction of illuminance, based on the use of image holograms, we describe a device employing a Savart plate, placed between an analyser and a polarizer, which enables subtraction directly from a real object rather than its photographed image. The objects are illuminated with quasi-monochromatic spatially incoherent light. We also study the influence of the various parameters on recording and reconstruction of image-holograms. In particular, we show that the orientation adjustments of the analyser and the polarizer do not require great precision. Further more, we determine limitations which must be imposed on the band pass of the recording device and on the slit width of the reconstruction device so that the various orders diffracted by the image hologram do not overlap. Finally, we present results for a three dimensional object, obtained under theoretically determined conditions for the experiment.
We have mentioned state the principle of the optical control of thin films in course of their formation by a prismatic modulator. We have studied the effects of the temperature on the control and we have conclued the utilisations conditions of the device.
A new Fourier spectrometer has been constructed for use in the visible range, where the noise is due to the signal itself. With this instrument it is possible to record in one sweep a spectral range of 10 000 cm-1. The interferograms contain 106 points (corresponding to a resolving power of about 106) and the reproducibility of the measurements of the wavenumbers of recorded lines in emission spectroscopy is 10-7 in relative value; the accuracy of the measurements of the position of the lines, is proportional to line intensity, and is of the order of a few hundreths of mK (1 mK = 10-3 cm-1) for the strongest among them. Finally, the intensity of the weakest measurable line is one thousandth of the intensity of the strongest line of the spectrum. Compared to a conventional grating spectrometer, the Fourier transform spectroscopy has the advantage among others, of maintaining the throughput gain (Jacquinot) constant for all the lines of the spectrum; the multiplex gain (Fellgett) does not disappear entirely; it depends strongly on the intensity of the lines. The work presented here, proves clearly that the extension of Fourier transform spectroscopy to regions where the noise is principally photon-noise, is effectively possible.
An interferometry device has been performed to measure the flexure of the Nice Coude solar refractor. Two small mirrors fixed at the telescope aperture are enlighted with a laser from the focus of the instrument. The system of interference fringes thus obtained is observed by use of a microscope. Any mechanical deformation of the instrument produces a motion of the fringes in the observational plane. This instrument has been checked for differents effects. A temperature stabilization time of about 20 mn has been found, an instrumental buckling during the pointing of the instrument and a continuous instrumental deformation as a function of the hour angle corresponding to a translation of the fringes of about 0.1 arc second by minute of time.
