Jorge Luis Flores

Design of a diluted aperture by use of the practical cutoff frequency

We analyze the imaging performance of a number of diluted-aperture configurations, using the modulation transfer function. We select a single figure of merit, the practical cutoff frequency, rather than the traditional cutoff frequency, as the more useful frequency for the detection of details. Using this new parameter, we compare the performance of a number of published aperture configurations. On the basis of this analysis a new configuration is proposed for the Polar Stratospheric Telescope primary.

Effects of misalignment errors on the optical transfer functions of synthetic aperture telescopes

A segmented or diluted aperture optical system will undergo phase errors as a result of errors in the positioning of the segments. The errors associated with a segmented primary mirror limit the image quality obtainable with synthetic aperture telescopes. Here we study the effects of segmentation errors on image quality, considering both the phase angle and the amplitude of the optical transfer function (OTF). We show that, in these kinds of telescope, phasing and alignment errors among segments reduce the amplitude and distort the phase angle of the OTF.

Optimal aperture configuration for a segmented and partially diluted extremely large telescope

Abstract We analyse the feasibility of replacing hexagonal mirror segments with circular segments in very large telescopes, requiring approximately the same performance in the spatial frequency domain. The potential advantages of circular segments are that they are easier to fabricate and there is a decreased amount of stray light contribution from the edges.

Variable sensitivity of vectorial shearing interferometer

A vectorial shearing interferometer with variable sensitivity based in the rotation of a pair of wedge prisms is discussed. The prism rotations incorporates differential and extended wavefront controlled displacements, combining the advantages of high sensitivity of conventional interferometers and low sensitivity of traditional shearing interferometers. The vectorial shearing interferometer allows the optimization of the measurement parameters for wave reconstruction algorithms. The reliable directional sensitivity of this interferometer has been experimentally demonstrated in spherical and aspherical surfaces. We also show the regularization technique to estimating the wavefront shearing interferometric patterns generated in vectorial shearing interferometry.

Phase reconstruction from undersampled intensity pattern(s) : Underdetection

We analyze the problem of recording and detection of high density fringe patterns with finite pixel size. Two detrimental consequences of the pixalation are identified, both increasing the difficulty of phase reconstruction. First, the intensity information is undersampled for the large pixel center-to-center separation. Second, the intensity distribution, averaged over a pixel of about the same size or larger than the fringe width, significantly decreases the detected fringe visibility. In the limiting case that the pixel width is equal to that of a fringe and with a proper registration, no phase information is recorded: a condition we call the moire limit. Neither the intensity, nor contrast, nor phase reversal effects are seen in the simulations. We show that the high-density fringe detection may not be characterized with the modulation transfer function.

Diluted-aperture mirror with the performance equivalent to that of the Keck

We analyze the imaging performance of synthetic-aperture optical systems (diluted-aperture, and segmented-aperture) using the modulation transfer function. We select a single figure-of-merit, the functional cutoff frequency, over the traditional cutoff frequency, as the most useful one for assessing the optical performance of an instrument for detection of small details. On the basis of this analysis, a simplified layout of the Keck telescope is proposed with an equivalent performance, but employing a smaller number of segments.

Interferometric layouts for extrasolar planet detection

We use the point spread function and the modulation transfer function as the most appropriate measures to analyze the performance of the multi-aperture interferometric configurations. We design non-redundant interferometric layouts that provide satisfactory coverage of the spatial frequencies. We compare our designs with the previously proposed configurations.

Diluted-aperture mirror with a constraint on the cut-off frequency

We analyze the optical performance of a number of diluted- aperture configurations using the modulation transfer function. We select a single figure of merit, the practical resolution limit, over the traditional one, the cut-off frequency, as the most useful one for the detection of small sources. We compare the performance of a number of published configurations, using the practical resolution limit. A new design of a POST configuration is proposed on the basis of this analysis.

Shock-wave pressure decay in aluminum – model development

A laser shock wave is a pressure wave in a gigapascal range propagating at speeds above the speed of sound in a medium, induced by a high-power density laser pulse. Its duration is of the order of magnitude of nanoseconds. When the shock wave propagates in a solid, some materials characteristics in the area where laser beam is incident, change due to the application of compressive residual stress. These may be hardness, corrosion resistance, stress-fatigue resistance, to name a few. The shock wave has been found useful for working materials in diverse application fields such as aeronautics, defense, material science, and micro-components. The shock wave pressure decreases drastically as it propagates inside the solid, making it difficult to obtain experimental data when the shock wave propagates in solids with a thickness greater than one millimeter. We employ finite element method for the solution of shock wave propagation problems. Its primary benefit is that wave pressure and velocity may be determined upon modeling for thicknesses greater than one millimeter. We demonstrate a non-linear relationship between the material thickness and the shock wave that decreases with increasing slab thickness. In addition, the relationship between thickness and shock wave velocity is found. We estimate the material thickness by obtaining the attenuation ratio of the shock wave pressure.

Trans-illumination of ballistic photons through 3 tissues and an occlusion

We describe a novel method of optical diagnostics of tissues with ballistic photons. They are selected by detecting them in an interferometric setup, further using heterodyning to increase the signal size. Three strategically placed apertures select the beam diameter for spatial resolution in scanning, and the angle within which the partially scattered photons might be collected. We model inclusion inside a bone-like object as a treelayer tissue that includes the skin, the muscle, and the bone. We calculate the size of detected inclusion as a function of limiting signal to noise ratio.