Influence of magnification on extraction efficiency in laser resonators with non-overlapping beams

The magnification and the Fresnel number determine the mode profile and losses in a bare unstable resonator. Upon inclusion of gain, both the beam pattern and the reflectivity are changed, more than in a stable cavity, because the counter-propagation intensities differ spatially and saturate the amplifier in a way that alters the mode profile, the reflectivity and the conditions of optimal operation. In this paper we present a numerical study of two types of cavities and compute the mode profile and losses in presence of an amplifier that saturates homogeneously. We compare these results with experimental data obtained on a TEA CO2 laser.Fil: González, Martín Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Peuriot, Alejandro Luis. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; ArgentinaFil: Garea, María Teresa. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Santiago, G.D.. Universidad de Buenos Aires. Facultad de Ingeniería; Argentin

Novel achromatic single reflection quarter-wave retarder: design and measurement

In this work, we present an achromatic quarter-wave retarder whose design is based upon the reflection properties of an isotropic-anisotropic interface. In theory, it is possible to obtain a π/2 phase shift by means of a total internal reflection at an isotropic-isotropic interface. However, in order to achieve such a phase shift, it is necessary to use a medium with a particularly high refractive index. We have previously shown that these phase shifts can be achieved by means of a total internal reflection in an isotropic-uniaxial interface, which allows the use of smaller refractive index media. By means of this property, we designed, built, and characterized a novel quarter-wave retarder that makes it possible to obtain circularly polarized light from a linear polarization state. We developed some guidelines that allowed us to obtain a device of competitive performance, low cost, and manageable manufacture.Fil: Veiras, Francisco Ezequiel. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Raffa, G.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Caré, D.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Perez, Liliana Ines. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garea, María Teresa. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentin

A birefringent polarization modulator: Application to phase measurement in conoscopic interference patterns

Conoscopic interferometry for crystal characterization is a very well known technique with increasing applications in different fields of technology. The advantage of the scheme proposed here is the introduction of a polarization modulator that allows the recovery of the phase information contained in conoscopic interferograms. This represents a real advantage since the most relevant physical information of the sample under study is usually contained in the phase of the fringe pattern. Moreover, this technique works successfully even when there are no visible fringes.The setup employed is a simple conoscopic interferometer where the elements under study correspond to two birefringent crystal slabs and a commercial mica wave plate. It allows the crystals to be characterized and the wave plate retardance to be measured as a function of the angle of incidence. The modulator itself consists of a single tiltable crystal plate which, by means of phase shifting techniques, permits the recovery of a phase map for each sample.  It is inexpensive and it can be easily calibrated, so it works with a wide range of phase shifting interferometry algorithms. We show that our scheme is easily adaptable to algorithms that require either a low or high amount of interferograms.Fil: Veiras, Francisco Ezequiel. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garea, María Teresa. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Perez, L. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentin

Aplicaciones de las TICs en el Laboratorio de Física : Análisis de una experiencia con aplicación de sensores de fuerza y posición

El empleo de herramientas informáticas requiere de un trabajo integral de diseño, implementación y evaluación de las estrategias de enseñanza. En el presente trabajo se realiza la evaluación de una experiencia didáctica en la que se aplicaron nuevas tecnologías en el contexto del laboratorio de física. La misma tiene como eje el uso de sensores de posición y fuerza como medio de adquisición de datos y su análisis por medio de programas de computación. Los resultados obtenidos se triangulan a través de una encuesta a alumnos, de los informes de trabajos prácticos presentados por los mismos y de la observación participante de los docentes. El desarrollo de este trabajo se realizó en el primer ciclo de una Facultad de Ingeniería y la temática corresponde a la conservación de cantidad de movimiento y a las fuerzas impulsivas.Red de Universidades con Carreras en Informática (RedUNCI

Aplicaciones de las TICs en el Laboratorio de Física : Análisis de una experiencia con aplicación de sensores de fuerza y posición

El empleo de herramientas informáticas requiere de un trabajo integral de diseño, implementación y evaluación de las estrategias de enseñanza. En el presente trabajo se realiza la evaluación de una experiencia didáctica en la que se aplicaron nuevas tecnologías en el contexto del laboratorio de física. La misma tiene como eje el uso de sensores de posición y fuerza como medio de adquisición de datos y su análisis por medio de programas de computación. Los resultados obtenidos se triangulan a través de una encuesta a alumnos, de los informes de trabajos prácticos presentados por los mismos y de la observación participante de los docentes. El desarrollo de este trabajo se realizó en el primer ciclo de una Facultad de Ingeniería y la temática corresponde a la conservación de cantidad de movimiento y a las fuerzas impulsivas.Red de Universidades con Carreras en Informática (RedUNCI

Distortions of Gaussian pulses transmitted through a transparent isotropic layer

Lasers can operate in two regimes: continuous-wave mode or pulsed mode. In the simplest case, the former mode corresponds to monochromatic beams with Gaussian distribution of amplitudes (beam limited in space); whereas the latter mode corresponds to polychromatic beams with Gaussian distribution of frequencies (pulse limited in time). When the pulsed beams are reflected and refracted in different types of interfaces, they undergo peculiar distortions that bear some parallelism with those found for beams limited in space.  These effects, as shown in a previous work, correspond to time delay (first order) and change of pulse width (second order). The distortions are clearly limited by the principle of causality and their interpretation, while not straightforward, emerges clearly when the associated fields are expressed in magnitude and phase. Since the analytical expressions are not simple even for the case where the pulse is transmitted through a single layer of linear, homogeneous, isotropic and transparent material, it makes it difficult to solve the inverse problem. In this work, we present an alternative analytical development that makes it possible to explicitly determine these distortion effects when a pulse impinges normally on a transparent isotropic layer immersed in a medium of analogous characteristics

Chromatin regulation by Histone H4 acetylation at Lysine 16 during cell death and differentiation in the myeloid compartment

Histone H4 acetylation at Lysine 16 (H4K16ac) is a key epigenetic mark involved in gene regulation, DNA repair and chromatin remodeling, and though it is known to be essential for embryonic development, its role during adult life is still poorly understood. Here we show that this lysine is massively hyperacetylated in peripheral neutrophils. Genome-wide mapping of H4K16ac in terminally differentiated blood cells, along with functional experiments, supported a role for this histone post-translational modification in the regulation of cell differentiation and apoptosis in the hematopoietic system. Furthermore, in neutrophils, H4K16ac was enriched at specific DNA repeats. These DNA regions presented an accessible chromatin conformation and were associated with the cleavage sites that generate the 50 kb DNA fragments during the first stages of programmed cell death. Our results thus suggest that H4K16ac plays a dual role in myeloid cells as it not only regulates differentiation and apoptosis, but it also exhibits a non-canonical structural role in poising chromatin for cleavage at an early stage of neutrophil cell death

Un nuevo método de análisis de los interferómetros de polarización

Fil: Garea, María Teresa. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Ultrasonic Lamb waves detection using an unstabilized optical interferometer with uncalibrated phase shifts

We present an experimental and post-processing scheme that allows ultrasound surface wave detection by means of an unstabilized homodyne interferometric technique. We register interference signals for a set of uncalibrated phase shifts and, from them, we are able to retrieve the normal surface displacement of a thin aluminium plate. The results obtained with this technique are then compared to robust and more traditional phase recovery methods such as the Carré algorithm and the 11-step windowed discrete Fourier transform algorithm. For both algorithms, we found a correlation superior to 99.9%, when compared to the results of the proposed technique. This non-destructive testing scheme represents a simpler and less-expensive alternative to other existing laser ultrasonic techniques.Fil: Alvarez, Natalia Clara. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garea, María Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perez Quintian, Luis Fernando. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Determination of nongeometric effects: equivalence between Artmann’s and Tamir’s generalized methods

This work shows that all first- and second-order nongeometric effects on propagation, total or partial reflection, and transmission can be understood and evaluated considering the superposition of two plane waves. It also shows that this description yields results that are qualitatively and quantitatively compatible with those obtained by Fourier analysis of beams with Gaussian intensity distribution in any type of interface. In order to show this equivalence, we start by describing the first- and second-order nongeometric effects, and we calculate them analytically by superposing two plane waves. Finally, these results are compared with those obtained for the nongeometric effects of Gaussian beams in isotropic interfaces and are applied to different types of interfaces. A simple analytical expression for the angular shift is obtained considering the transmission of an extraordinary beam in a uniaxial–isotropic interface.Fil: Perez, Liliana Ines. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Echarri, Rodolfo Manuel. Universidad Nacional de General Sarmiento. Instituto del Desarrollo Humano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garea, María Teresa. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santiago, Guillermo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin