Abstract: The optical limiting effect was analyzed in two oils of vegetable origin, extra virgin olive oil and virgin avocado oil; which are materials that have a large amount of organic components and excellent physicochemical characteristics. In multiple works, organic materials have been shown to be effective as optical limiting devices, presenting a good response in materials that show two-photon absorption and saturable absorption. On the other hand, between the two configurations in which the optical limiting phenomenon can be analyzed (dispersion and transmission), the optical limiting study by transmission was carried out for both oils, where olive oil manifested a more limited region wide compared to avocado oil. Nevertheless, avocado oil showed saturation power and a lower limiting threshold. Important characteristics in the manufacture and search for materials used in optical limitation devices.

Abstract Two-photon transitions from ground state to excited and ionized states are studied. The energy levels and radial matrix elements of an impenetrable spherically confined hydrogenic atom embedded in plasma environment are evaluated using accurate Bernstein-polynomial (B-polynomial) method. Transition probability amplitudes, transparency frequencies and resonance enhancement frequencies for various transitions, namely, 1s - 2s, 1s - 3s, and 1s - 3d are evaluated for various values of confining Debye potential parameter. The effect of spherical confinement is studied and explained.

O objetivo deste trabalho é demonstrar a confecção de um obturador de feixe óptico a partir de um disco rígido de computador. O controle de corrente do dispositivo é feito por modulação de largura de pulso (Pulse width modulation - PWM), uma técnica que permite variar níveis de tensão/corrente por meio do ajuste da largura de pulso de um sinal digital. Este controle é feito de forma a minimizar a potência dissipada no dispositivo, aumentando assim sua vida útil. O núcleo do circuito de controle de corrente é o Arduino Uno, uma placa de microcontrolador de baixo custo e de fácil programação, amplamente utilizado como plataforma para prototipagem eletrônica. Por fim, a título de ilustração, apresentamos o uso do obturador de feixe óptico desenvolvido em um sistema de microfabricação via fotopolimerização por absorção de dois fótons, no qual ele tem papel fundamental.

This work demonstrates the development of an optical shutter from a computer hard disk. The electrical current control of the device is made by pulse width modulation, a technique that allows varying current/voltage levels by adjusting the pulse width of a digital signal. This control is made in order to minimize the power dissipated into the device, thus raising its lifetime. The main unit of the control circuit is Arduino Uno, a low cost and ease of programming microcontroller board, extensively used as a platform for electronic prototyping. As an example, we present the use of an optical shutter developed in a microfabrication setup via two-photon polymerization, in which it plays an important role.

Collagen is the most abundant structural protein found in organs and is responsible for providing tissues with structure and function. In order to investigate in canine uteri the potential effect of medroxyprogesterone acetate (MPA) on the changes in collagen deposition were grouped as nulliparous (n=11), multiparous (n=11) and treated with MPA (n=11; nulliparous with two treatments; 5 mg/kg; i.m.). The amount of collagen was studied in the fold and basal regions of the endometrium and myometrium using second harmonic generation with a two-photon spectral confocal microscope, quantified using ImageJ software with a color segmentation plugin, was expressed as fraction area (%) and analyzed by ANOVA (p<0,05). No differences were observed between groups in the fold (p=0,3995) or base (p=0,7392) of the endometrium and myometrium (p=0,1781). In conclusion, our data demonstrate that two doses of MPA (5 mg/kg; i.m.) do not affect the total collagen deposition in canine uteri undergoing contraceptive treatment.

El colágeno es la proteína estructural más abundante presente en órganos y es responsable de proporcionar la sostén y función a los tejidos. Para investigar en caninos el efecto potencial del acetato de medroxiprogesterona (MPA) sobre cambios en el depósito de colágeno en útero, éstos fueron agrupados como nulíparos (n = 11), multíparos (n = 11) y tratados con MPA (n = 11, nulíparos con dos tratamientos 5 mg/kg, im). El colágeno fue evaluado en el pliegue y regiones basales del endometrio y en miometrio utilizando la Generación de un Segundo Harmónico con un microscopio confocal espectral y dos fotones y cuantificado utilizando el software ImageJ a partir de la segmentación de colores. Los resultados fueron expresados y analizados como fracción de área (%; ANOVA; p<0,05). No se observaron diferencias entre los grupos en el pliegue (p = 0,3995) y base (p=0,7392) del endometrio y tampoco en miometrio (p=0,1781). En conclusión, nuestra evidencia demuestra que dos dosis de MPA (5 mg/kg, i.m.) no afectan el depósito total de colágeno en úteros caninos expuestos a tratamiento anticonceptivo.

The design and construction of an experimental system for studying two photon spectroscopy processes in atomic rubidium is presented. It is designed to measure absorption and polarization rotation induced by any of the two laser beams and also the visible fluorescence that results from decay of the excited states. Two home-built diode lasers are used to produce the optical fields that later interact with room temperature rubidium atoms. Using counterpropagating beams allows velocity selection of the groups of atoms that interact with both laser beams. The system was tested in the 5 S → 5 P3/2 → 5 Dj ladder energy level configuration of atomic rubidium. Blue fluorescence (420 nm) that results from decay of the intermediate 6Pj states is filtered and then measured with a photomultiplier tube. Absorption and fluorescence spectra provide mutually complementary information about the interaction between the rubidium atoms and the two optical fields.

Novel materials have been developed to meet the increasing mechanical, electrical and optical properties required for technological applications in different fields of sciences. Among the methods available for modifying and improving materials properties, femtosecond laser processing is a potential approach. Owing to its precise ablation and modification capability, femtosecond laser processing has already been employed in a broad range of materials, including glasses and polymers. When ultrashort laser pulses are focused into a transparent material, the intensity at the focus can become high enough to induce nonlinear optical processes. Here, we report on femtosecond (fs) laser microfabrication in special glasses and polymers. Initially, we describe fs-laser micromachining on the surface of copper doped borate and borosilicate glasses. Subsequently, we present results on two-photon induced polymerization to fabricate microstructures containing fluorescent dyes for manufacturing optical microcavities. Both approaches are promising for designing optical and photonics micro/nanodevices.

The theories of quantum entanglement between two distant particles, which clearly confirm the non-local nature of Quantum Mechanics, are applied to naturally produced particles in astrophysical objects. We study the production and reception of the cases of optical quantum entanglement most feasible to be observed: the two-photon spontaneous transition of the hydrogen 2 ²S1/2 metastable level, which is known to be one of the components of the continuous spectra of ionized regions. We obtain the two-photon emission rate for four astrophysical objects: the Orion Nebula, two nearby planetary nebulae IC 2149 and NGC 7293, and the solar corona. The production of entangled pairs per second is 5.80 × 10(48), 9.39 × 10(45), 9.77 × 10(44), and 1.46 × 10(16) respectively. The distribution of the propagation directions of both emitted photons does not vanish at any angle; therefore it is possible to observe the entangled pair at angles θ ≈ 0°. Because the number of two-photon coincidences goes as the fourth power of the ratio between the detector size and the distance from the astrophysical object, coincidences are scarce; for its detection we require receivers much larger than those currently available.

Las teorías del entrelazamiento cuántico entre dos partículas lejanas, que claramente confirman la naturaleza no local de la Mecánica Cuántica, se aplican a las partículas producidas naturalmente en los objetos astrofísicos. Estudiamos la producción y la recepción del caso de entrelazamiento cuántico más factible de observarse: la transición espontánea de dos-fotones del nivel metastable 2 ²S1/2 del hidrógeno, componente conocido del espectro del continuo de las regiones ionizadas. Obtenemos la tasa de emisión de dos-fotones para cuatro objetos astrofísicos: la Nebulosa de Orion, dos nebulosas planetarias cercanas IC 2149 y NGC 7293, y la corona solar. La producción de pares entrelazados por segundo es de 5.80 × 10(48), 9.39 × 10(45), 9.77 × 10(44) y 1.46 × 10(16), respectivamente. La distribución de las direcciones de propagación de ambos fotones emitidos no se anula para ningún ángulo; por lo que es posible observar el par entrelazado a ángulos θ ≈ 0°. Debido a que el número de coincidencias de dos-fotones va como el cociente entre el tamaño del detector y la distancia al objeto astrofísico elevado a la cuarta potencia, las coincidencias son escasas; para su detección se requiere de receptores de un tamaño mucho mayor que los que existen en la actualidad.

The two-photon absorption process is a nonlinear phenomenon that shows very low optical efficiency in bulk semiconductors. For this reason the detection of these processes becomes very difficult from the experimental point of view. Nevertheless, when dealing with semiconductor QD's with few nanometer radii, these transitions are enhanced and the detection is possible. In this contribution we present analytical calculations for the absorption coefficient in CdSe spherical QD's subjected to these second order processes, as a function of the characteristic dot parameters. The intensities of the absorption peaks, as well as the statistical treatment involving QD's ensembles, are also reported.

Two-photon absorption is theoretically analyzed within the semiclassical formalism of radiation-matter interaction. We consider an ensemble of inhomogeneously broadened three-level atoms subjected to the action of two counterpropagating fields of the same frequency. By concentrating in the limit of large detuning in one-photon transitions, we solve perturbatively the Bloch equations in a non-usual way. In this way we derive an analytical expression for the width of the two-photon resonance that makes evident sub-Doppler two-photon spectroscopy. We also derive an analytical expression for the Stark shift of the two-photon resonance.

Se analiza teóricamente la absorción de dos fotones dentro del formalismo semiclásico de la interacción entre la radiación y la materia. Consideramos un conjunto, con ensanchamiento inhomogéneo, de átomos de tres niveles sometido a la acción de dos campos contrapropagantes de igual frecuencia. Resolvemos perturbativamente las ecuaciones de Bloch del sistema de una forma no usual concentrándonos en el límite de alta desintonía de las transiciones a un fotón. De esta forma obtenemos una expresión analítica para la anchura de la resonancia a dos fotones en la que se pone de manifiesto la posibilidad de espectroscopía sub-Doppler a dos fotones. También obtenemos una expresión analítica para el desplazamiento Stark de la resonancia a dos fotones.

In this work, we present the design and construction of a femtosecond laser pulse autocorrelator, based on the two-photon absorption process in a light emitting diode (LED). Compared with traditional autocorrelators based on nonlinear crystals, this autocorrelator has the advantages of lower cost and greater ease of alignment. The intensity and interferometric autocorrelation traces obtained with this device for a titanium-sapphire laser with pulses that are less than 100 fs long, are also presented.

En este trabajo se presentan el diseño y la construcción de un autocorrelador de pulsos de láser de femtosegundos, basado en el proceso de absorción de dos fotones en un diodo luminiscente (LED). Comparado con los autocorreladores tradicionales basados en cristales nolineales, este autocorrelador presenta las ventajas de un costo reducido, así como de una mayor sencillez en su uso y alineación. Se presentan las trazas de autocorrelación de intensidad e interferométrica obtenidas con este dispositivo para un láser de titanio:zafiro con pulsos de menos de 100 fs de duración.

We discuss the production of hadronic resonances in very peripheral heavy ion collisions, where the ions collide with impact parameter larger than twice the nuclear radius and remain intact after the collision. We compare the resonance production through two-photon and double Pomeron exchange, showing that when we impose the condition for a peripheral interaction the <FONT FACE=Symbol>gg</FONT> process dominates over the Pomeron interaction, due to the short range propagation of this last one. We also discuss the observation of light resonances through the subprocess <FONT FACE=Symbol>gg</FONT> ->R <FONT FACE=Symbol>®gg</FONT> , which is a clean signal for glueball candidates as well as one way to check the existence of a possible scalar sigma meson.

We report on an experiment showing that the wavelength of a biphoton is clearly dependent onthe measurement scheme and on the way it is defined. It is shown that it can take any value, depending on the control of the interferometer phase differences. It is possible to identify the interference of the single and two-photon wavepackets as particular cases of the most general interference process. The variable wavelength has no implication on the energy of the individual photons neither on the total energy of the biphoton.