Mr. Omar Garcia Medel Profile

Omar Garcia Medel

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Proceedings Article | 4 March 2019 Paper

Solvent effect in extra-cavity pulses by thermo-cavitation in natural dyes

S. Afanador-Delgado, José Omar García Medel, V. Marañón Ruíz, R. Sevilla-Escoboza, R. Chiu

Proceedings Volume 10903, 109030M (2019) https://doi.org/10.1117/12.2507054

KEYWORDS: Cavitation, Nonlinear optics

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Optical cavitation is the formation of vapor cavities in a liquid when a pulsed laser is focused over highly absorbent liquid; however, when a continuous laser is used, the phenomenon is called thermo-cavitation. Recently, thermocavitation has been studied in different materials^1–3. In this work, we present the analysis of extra-cavity pulses generation by thermo-cavitation induced by a CW laser beam focused into solutions of Hibiscus Sabdariffa in ethanol and Hibiscus Sabdariffa in methanol. Due to the high absorption of the natural dye and the low boiling point of the solvents (< boiling point of the water), heating is produced which gives origin and implosion of bubbles. The process of explosion and implosion of the bubbles acts as an obturator allowing the pulses formation of the light passing through the sample. The characterization of the pulses was performed by moving the sample around the focus of the lens, we observe a modification in the thermo-cavitation time, an analysis of the changes in the frequency rate and the amplitude of pulses was performed. The frequency rate, the amplitude, and the full width half maximum (FWHM) of the pulses were measured. We found that the average frequency decreases, and the average amplitude increases when we move the sample at a distance from the focus. The temporary response of the pulses obtained in both solutions, change as a consequence of the difference between the boiling point of the methanol and ethanol.

Proceedings Article | 20 February 2019 Paper

Light propagation in turbid media: an approach of interpolation in the optimal phase matrix

José Omar García Medel, S. M. Afanador Delgado, R. Chiu

Proceedings Volume 10886, 108860W (2019) https://doi.org/10.1117/12.2507269

KEYWORDS: Wavefronts, Signal to noise ratio, Spatial light modulators, Algorithm development, Speckle pattern

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To control the light propagation in turbid media, it is necessary to reconstruct the output wavefront. In 2007 Vellekoop et al.¹, developed an iterative algorithm that divides the input wavefront in N x N channels called segments, after passing through turbid media, the output wavefront is reconstructed by measuring the intensity at a desired point, and then the phase of each channel is updated, the final N x N phase is called optimal phase matrix. The interpolation technique is capable of transforming a N x N matrix into a second 2N x 2N matrix, where, the 50 percent of the resulting matrix elements correspond to the homogeneous distribution of the original matrix values and the remain values are generated by interpolating the neighbors. Our proposal uses the optimal phase matrix obtained by an iterative algorithm, and then the number of segments is increased by interpolation. We analyze the circularity, the signal to noise ratio (SNR), the Full Width at Half Maximum (FWHM) and the correlation for different output wavefronts obtained by the optimal phase matrix and the interpolation optimal phase matrix. Our results show that, Circularity, SNR, and FWHM parameters do not change significantly and the acquisition time of the optimal phase matrix decreases compared with a similar matrix obtained by the iterative algorithm; therefore, our proposed technique that consists in the combination of interpolation and iterative algorithm is useful to study the light transmission in turbid media when a high resolution is needed in the transmission matrix, for example, phase holograms transmission through turbid media.

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