Omar Ormachea

Nonlinear formation of dynamic holograms and multiwave mixing in resonant media

The schemes of light beam transformations by volume dynamic holograms in resonant media revealing the fifth- or higher-order nonlinearities have been theoretically analyzed. N-wave mixing has been realized by changing of the propagation direction or frequency of the read-out wave in the solution of Rhodamine 6G and polymethine 3274U dyes. It has been demonstrated that the experimental results are in good agreement with the theoretical data obtained for a three-level medium model with due regard to absorption from the excited singlet level.

Frequency up-conversion of coherent images by intracavity nondegenerate four-wave mixing

This work presents theoretical and experimental studies of the processes of light field transformations upon frequency-nondegenerate fourwave mixing (NFWM) in a nonlinear Fabry-Perot interferometer (FPI). The principal aims are the development of a theory for intracavity four-wave mixing in complex molecular media in conditions of scattering from dynamic gratings and resonator feedback; determination of a mechanism of light field transformations in dynamic holograms, and also by nonlinear interferometers; working out and introduction of novel nonlinear-optical methods to control the characteristics of light beams. High diffraction efficiency (up to 13.5%) with simultaneous infrared-to-visible frequency conversion of coherent images has been experimentally obtained by intracavity NFWM.

Development of a portable low-cost LIBS system

This article reports the construction of a portable, low-cost LIBS (Light Induced Breakdown Spectroscopy) system for use in the Bolivian mining industry for the qualitative and quantitative analysis of the composition of mineral samples. The device consists of a portable laser, a medium-resolution spectrometer and an optomechanical light collection system. The laser developed for the device is a YAG:Nd+++ with an estimated power output of 10 MW/cm2. Weighing approximately 3 kg and powered by lithium ion batteries, it is easily carried and can be used in remote locations. The spectrometer has a resolution of 0.3 nm allowing the detection fine spectral features, while its range of 80 nm is broad enough to simultaneously show many of the principal spectral lines of the element of interest. A monochromatic CCD camera was used as the detector of the spectrometer and was fitted with an external trigger to coordinate the camera frames with the firing of the laser. The light emitted by the plasma is collected with a photographic objective and is transmitted to the spectrometer via a fiber optics cable. A mechanical system was incorporated to make, both the laser beam and the receptor positionable. In the preliminary tests of the prototype, a LIBS spectrum of a Bolivian copper coin was obtained. Analysis showed that the spectral lines obtained coincide with those of a copper reference spectrum and demonstrate the capacity of the device to perform qualitative analysis of materials.

Analysis of a semiconductor semimagnetic microcavity for optical amplification and wavelength conversion applications

The importance of nonlinear optical devices is increasing due to their hopeful characteristics such as small size, high speed or even low power consumption. These devices integrated in all-optical systems achieve the best results because of the elimination of optoelectronic or electro optic conversions that imply great reductions in these advantages. Therefore the main effort should be directed to make as many functions as possible by optical means. Among these functions, wavelength conversion or amplification seem to be likely to implement with a nonlinear device. In this work a structure called Semiconductor Semimagnetic Microcavity (SSM), for optical amplification and wavelength conversion, is introduced and studied. This study requires a suitable method for nonlinear series devices. It must take into account each wave and its relationship with the others. An Extended Yeh matrix is appropriate for the characterization of this structure. The method reveals that if the microcavity is exposed to an input signal and a pumping input signal and also matches the conditions of degenerate four-wave mixing, another wave at a different wavelength appears. What is more, the original input signal becomes greatly amplified depending on the pumping input signal. The process of obtaining these results with the Extended Yeh matrix applied to a SSM is shown. Optical wavelength conversion and optical amplification in a microcavity is demonstrated by means of this matricial method.

Formation of the Nonlinear Dynamic Hologram in Clear Organic Fluids

The recording of dynamic holograms during multiwave interactions in clear organic fluids (ethanol, acetone, dioxan, etc.) is investigated. It is shown that the fifth-order nonlinearities and higher become activated along with the cubical nonlinearity under the intense laser excitation (∼100 MW cm−2) in the near-IR spectral range, which allows visualization of the IR images using different orders of diffraction.

Polarization recording of dynamic holograms in saturable absorbers

The potentialities of diffraction methods for wavefront transformations may be considerably widened due to the use of nonlinear recording of dynamic holograms enabling multiwave mixing in media with the fifth and higher order nonlinearities. There is a great variety of such media including the resonant ones for which the presence of higher order nonlinearities is conditioned by the absorption saturation effect and transitions between different excited states of the molecules. However, in the majority of previous studies of multiwave mixing the resonant medium approximation has been used disregarding the induced anisotropy effect. This work presents a theoretical model and experimental studies of the energy efficiency of multiwave mixing in complex molecular media exhibiting higher order nonlinearities, in two cases: when the nonlinear cavity is introduced in the Fabry-Perot interferometer (IFP), and without it. Owing to the use of different combinations of mutually aligning polarizations for interacting waves, one is enabled to determine the contribution into the interaction efficiency by various dynamic gratings and nonlinearity mechanisms. The role of polarization gratings resultant from spatial modulation of the light field polarization state at the orthogonal polarization of the hologram recording waves has been established. Comparisons between the contributions of the above gratings and “normal” gratings recorded by identically polarized light beams into the process of multiwave mixing have demonstrated that the relation of these contributions is dependent on the intensity of interacting waves, and also it has been found that polarization of the diffracted wave is dependent on the diffraction order.

Polarization dynamics and control of anisotropic nonlinear interferometer

In this work a theoretical study of the interaction between a light beam and an anisotropic nonlinear interferometer has been considered and methods to control the transmission of the microcavity using optical and magnetic fields have been developed. It has been demonstrated that anisotrophy of intracavity media determines the differences in transmission functions for various polarization modes and produces polarization instability. Varying spectroscopic parameters of the resonant medium and parameters of the anisotropic element, different types of intensity self-oscillations for different polarization modes can be obtained. To control the characteristics of nonlinear interferometer, it is proposed to use an additional light beam whose frequency is tuned into the absorption band from the excited level. The propagation characteristics of periodic magento-optical and dielectric multilayer films made of alternating layers of these materials having a symmetric periodicity with the center of the structure under a magnetic field is analyzed. The magnetic induction on this type of materials is temperature dependent and modifies the transmission and reflection characteristics of these structures. This kinds of structures, gives us the possibilities for an additional controlling of the characteristics of nonlinear interferometer.

Four-wave mixing in nonlinear interferometer Fabry-Perot with saturable absorbers

In this work the different schemes of propagation and interaction of the light beams in nonlinear Fabry-Perot interferometer have been studied theoretically and experimentally. Degenerate and non-degenerate four-wave mixing have been realized in the cavity of Fabry-Perot type using Rhodamine-6G dye and polymethine dye 3274U solution as saturable absorber. The diffraction efficiency of intracavity dynamic grating has been studied in dependence on intensity of interacting beams and parameters of resonator. The theoretical model of the processes of intracavity degenerate and non-degenerate four-wave mixing has been developed and applied to the analysis of the efficiency of light beams conversion by mean of Bragg diffraction from intracavity dynamic gratings. For theoretical description of typical experimental situations we used the round-trip model of nonlinear interferometer adapted for the geometry of degenerate four-wave mixing, which can be realized in the scheme of symmetrical oblique incidence of pump, signal and probe beams to the front and back mirrors of cavity.

Dynamic hologram magnification with incoherent optical pumping

In the present work consideration is given to theoretical and experimental analysis of the possibilities for improving the efficiency of multiwave mixing in the process of dynamic hologram recording in solutions of complex organic compounds with additional irradiation of resonant medium at a frequency falling within the absorption band from the excited level. Three- and seven-fold increase in the diffraction efficiency has been realized in Rhodamine 6G dye for four- and six-wave missing, respectively.

DESARROLLO DE UN MICROSCOPIO DE EPIFLUORESCENCIA DE BAJO COSTO

La microscopia de epifluorescencia es una tecnica poderosa con altos niveles de sensibilidad y resolucion microscopica que se utiliza en varias areas, particularmente en el campo biomedico. En este articulo se presenta el diseno y desarrollo de un microscopio de epifluorescencia de bajo costo basado en una fuente laser de excitacion, un filtro barrera simplificado, y un sistema embebido (hardware y software) para la visualizacion y el control digital. El prototipo desarrollado utiliza un filtro barrera por absorcion, basado en una solucion de Rodamina 6G en alcohol etilico que absorbe de manera efectiva la radiacion del laser de excitacion y deja pasar la senal fluorescente de la muestra de interes. El poder de aumento del microscopio desarrollado es 100X aproximadamente y permite identificar particulas fluorescentes del orden del 10 m. Los resultados obtenidos con el prototipo desarrollado, muestran su viabilidad para un potencial uso en aplicaciones biomedicas.