Juan M. Simon

Transparent heat mirrors: influence of the materials on the optical characteristics

Transparent heat mirrors of the antireflecting metal type with a dielectric/metal/dielectric structure are studied. It is found that dielectrics of lower refractive index give a higher cutoff wavelength, but the transition becomes more gradual. The angular behavior of these mirrors is also analyzed. The optimum mechanical efficiency obtainable with a plain collector and a carnot engine is given for different concentrations and refractive indices. Moreover it appears that using Al instead of Ag introduces appreciable absorption losses (~25-35%).

Localization of Interference Fringes.

If one considers the interference of two extended sources and if one is able to observe fringes only at certain points in space one says that the fringes are localized on those points. As an example we show how the localized fringes may be found in a device used to observe Newton’s rings. Moreover we give a proof of the general method used to determine the localized fringes position. This proof is suitable for undergraduate optics courses. We also analyze the visibility of fringes.

Fringe localization depth

We calculate the complex degree of coherence for any interferometer in which there is amplitude division and simple interference. We consider the exact optical path length differences between both branches. We find that, when there is a localization surface, this degree of coherence is equivalent to the complex optical disturbance at the image of an aberrated isoplanatic optical system. Moreover, we show that the radius of the central lobe at the diffraction pattern of this equivalent system is the distance between rays when visibility is zero. This distance enables us to evaluate localization depth and adjustment tolerance.

Measurements of free-surface profile in transient flow with a simple light-slicing method.

A simple light-slicing technique for the direct measurement of the free-surface shape h(x) in onedirectional transient liquid flows is studied. The method is used to determine h(x) with a precision of the order of 10(-2) mm along a line several centimeters long, allowing for height differences of some millimeters. It is useful for transient flows in rectangular channels in which capillarity and liquid adhesion at walls perturb lateral observations; the method can also be used for nondiffusive fluids in cases in which it is not advisable to add diffusive particles.

Measurement of the slope of an unsteady liquid surface along a line by an anamorphic schlieren system

We describe and test a simple quantitative schlieren method for measuring the slope of an unsteady free liquid surface along a straight segment. The optical system, based on an anamorphic element placed at the focal plane of a standard objective, forms a distorted image of the illuminated segment on a screen. The abscissa of the resulting bright curve is proportional to the coordinate along the segment and the ordinate to the longitudinal slope at the corresponding coordinate, provided that the transverse slope component is negligible. The method is useful to probe axisymmetric flows along a diameter or flows in straight channels along the axis.

Interferometers: equivalent sine condition

The parallelism we have previously drawn between an interferometer and an equivalent optical system enables us to study both systems similarly. The constant contrast condition along the localization surface is equivalent to the condition of isoplanatism at the system image. As the sine condition is necessary for a system to be isoplanatic, a relationship we call the equivalent sine condition must hold if the contrast is constant. Some classic interferometers do not satisfy this condition and we here analyze the Michelson interferometer. Moreover, we find that, for the record of interference fringes to be a pseudohologram, this condition must be unfulfilled.

Phase shift in dielectric reflection.

The phase shifts in external dielectric reflection were analyzed as a function of the incident angle. The contrast of the interference fringes formed between the incident and the reflected beams was considered. For the parallel mode the phase shift disappears between 45 degrees and the Brewster angle. Experimental results are shown which demonstrate the contrast inversion in this region.

Elliptic polarization in grating spectrographs.

It is well known that a metallic diffraction grating has a different efficiency for light with the electric vector polarxad ized parallel to the grooves of the grating than that for the electric vector normal to those grooves.For natural inxad cident light this gives rise to linear polarization which is strongly dependent on the diffraction order and the wavexad length. We find that if the incident beam is polarized the phase difference φ for both components (parallel and perxad pendicular to the grooves) becomes important and can produce elliptical polarization. This may be important for solar magnetographs or other cases in which the polarxad ization of the incident beam is investigated. The measurements were made with the Ebert spectroxad graph of the Observatorio Nacional de Fîsica Cósmica in San Miguel described by Greco et al. The spectrograph

Diffraction in high numerical aperture systems: polarization effects

In high numerical aperture systems polarization effects should be taken into account; hence it is necessary to use a vectorial diffraction theory to describe them. We develop a computational model to study image formation in a high numerical aperture microscope objective by simulating images of self-luminous, non-polarized point objects. We compare the predictions made by scalar and vectorial theories of diffraction. In the last case we also consider an analyzer placed behind the objective to study the polarization effects. We find that vectorial theory predicts a larger diffraction pattern and, when an analyzer is used, an enlargement along the transmission axis of the analyzer. We also study the resolution of the system, finding that the true resolution predicted for vectorial theory is approximately 10% lower than that usually expected for scalar theory.

The Mach-Zehnder interferometer: examination of a volume by non-classical localization plane shifting

The Mach-Zehnder interferometer can be used as is customary in optical testing but, to examine different layers of a volume, the procedure of either readjusting the interferometer or displacing the specimen can be avoided, employing an incoherent periodic source. In this case, leaving the specimen in a fixed position and without readjusting the interferometer, the different layers can be analysed, shifting a non-classical localization plane by a change in the source period. In this paper experimental interferograms, obtained by varying this period to map the disturbances present on either one or both faces of a phase object, are shown.