This paper reports the implementation of an optical fiber sensor to measure the refractive index in aqueous media based on localized surface plasmon resonance (LSPR). We have used a novel technique known as photodeposition to immobilize silver nanoparticles on the optical fiber end. This technique has a simple instrumentation, involves laser light via an optical fiber and silver nanoparticles suspended in an aqueous medium. The optical sensor was assembled using a tungsten lamp as white light, a spectrometer, and an optical fiber with silver nanoparticles. The response of this sensor is such that the LSPR peak wavelength is linearly shifted to longer wavelengths as the refractive index is increased, showing a sensitivity of 67.6 nm/RIU. Experimental results are presented.

The generation and manipulation of microbubbles by means of temperature gradients induced by low power laser radiation is presented. A laser beam (λ = 1064 nm) is divided into two equal parts and coupled to two multimode optical fibers. The opposite ends of each fiber are aligned and separated a distance D within an ethanol solution. Previously, silver nanoparticles were photo deposited on the optical fibers ends. Light absorption at the nanoparticles produces a thermal gradient capable of generating a microbubble at the optical fibers end in non-absorbent liquids. The theoretical and experimental studies carried out showed that by switching the thermal gradients, it is possible to generate forces in opposite directions, causing the migration of microbubbles from one fiber optic tip to another. Marangoni force induced by surface tension gradients in the bubble wall is the driving force behind the manipulation of microbubbles. We estimated a maximum Marangoni force of $400nN$ for a microbubble with a radius of 110 μm.

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The most common approach to optically generate and manipulate bubbles in liquids involves temperature gradients induced by CW lasers. In this work, we present a method to accomplish both the generation of microbubbles and their 3D manipulation in ethanol through optothermal forces. These forces are triggered by light absorption from a nanosecond pulsed laser (λ = 532 nm) at silver nanoparticles photodeposited at the distal end of a multimode optical fiber. Light absorbed from each laser pulse quickly heats up the silver-ethanol interface beyond the ethanol critical-point (∼ 243 °C) before the heat diffuses through the liquid. Therefore, the liquid achieves a metastable state and owing to spontaneous nucleation converted to a vapor bubble attached to the optical fiber. The bubble grows with semi-spherical shape producing a counterjet in the final stage of the collapse. This jet reaches the hot nanoparticles vaporizing almost immediately and ejecting a microbubble. This microbubble-generation mechanism takes place with every laser pulse (10 kHz repetition rate) leading to the generation of a microbubbles stream. The microbubbles' velocities decrease as they move away from the optical fiber and eventually coalesce forming a larger bubble. The larger bubble is attracted to the optical fiber by the Marangoni force once it reaches a critical size while being continuously fed with each bubble of the microbubbles stream. The balance of the optothermal forces owing to the laser-pulse drives the 3D manipulation of the main bubble. A complete characterization of the trapping conditions is provided in this paper.

We report the experimental setup of a high power pulsed erbium-doped fiber amplifier. An optical signal at 1550nm emitted by a distributed feedback laser is amplified by two identical stages in reflective configuration using one fiber Bragg grating at each one of those. We demonstrated that for pulses with a frequency of 20kHz and temporal duration of 10, 50, 100, and 500ns, it is possible to obtain output peak powers of 41, 22, 18, and 11W, respectively. We applied our high power amplifier in the characterization of nonlinear optical transmission of single-wall carbon nanotubes deposited on single mode optical fibers end-face by the photodeposition technique. Our results show that the high power system is ideal for carrying out studies of nonlinear effects in optical fibers as well as nonlinear characterization of nanostructured materials deposited on optical fibers

Automatic autofocusing (AF) in digital microscopy is highly dependent on the sample topography variability and also its color distribution. As stated by Qu et al.,¹ different focus criterion functions perform quite differently even for the same sample. The majority of these methods have been addressed to study AF in the context of monochromatic frames.² 3. 4. ^{– 5} Furthermore, many works have been published that present a comparative evaluation of the performance of these kinds of AF techniques.⁶ 7. ^{– 8} Some research has determined that the best AF metric is based on the Brenner function;² other research gives priority to the variance,⁹ Vollath-4,¹⁰ 11. ^{– 12} or the sum-modified-Laplacian,¹³ among other methods.