A simple and inexpensive method to measure vibrations in mechanical structures is presented by means of Fabry-Perot interferometry and Doppler effect. The sensor consists of a transparent hydrogel sphere attached to an single-mode optical fiber from a 50:50 fiber coupler, laser light with a wavelength of 658 nm, and a photodetector which is connected to an oscilloscope. The vibrometric sensor works in the time domain by detecting the number of interference fringes. The tip of the prototype is composed of mechanical couplings that join the fiber with the hydrogel sphere. The sensor allows knowing the vibration frequency at which a mechanical part is oscillating. The analysis presented in this work shows several advantages over conventional methods, such as low cost, real-time measurement, and simplification in experimental setup. The sensor system is capable of capturing vibrations of up to 5000 Hz.
We present the generation and 3D manipulation of microbubbles by thermal gradients, induced by low power nanosecond pulsed laser in non-absorbent liquids. Light absorption at photodeposited silver nanoparticles on the optical fiber tip heat up the surrounding liquid, which leads to optothermal effects. With each laser pulse a microbubble is detached from the optical fiber end, creating a microbubbles-stream. The microbubbles move away from the optical fiber end driven by non-spherical cavitation until they coalesce creating a main-bubble which is attracted towards the optical fiber end by Marangoni force. In addition, the main-bubbles are under the influence of buoyancy and gravity forces, which act upwards and downwards, respectively. The balance of these forces allows the 3D manipulation of the main-bubble. The main-bubble position can be controlled by careful control of the pulse energy. To our knowledge this is the first time that 3D manipulation of microbubbles using pulsed lasers is demonstrated.
Generation and 3D manipulation of microbubbles by means of temperature gradients induced by low power laser radiation is presented. Photodeposited silver nanoparticles on the distal end of two optical fibers act as thermal sources after light absorption. The temperature rises above liquid evaporation temperature generating a microbubble at the optical fibers end in non-absorbent liquids. Alternatively, switching the thermal gradients between the fibers, 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
An optical method to obtain a colloidal solution starting from a mixture of silver nanopowder and ethanol is presented. The particles of the silver nanopowder do not exhibit a specific shape, however in the colloidal solution are spherical. This method is carry out when the mixture is irradiated with a pulsed laser at 532 nm via optical fiber. Due to a stronger absorption of the laser light by silver nanoparticles arise both photofragmentation and photomelting processes. The photomelting process starts when the laser energy is 5 mJ/cm2, inducing an enlargement of nanoparticles whereas the photofragmentation occurs when the laser energy is 25 mJ/cm2 causing a reduction on their sizes (the higher energy is, the smaller nanoparticles are). Results show that it is possible to obtain a colloidal silver solution and to control the particle size by adjusting the laser energy. Experiments were performed at 5 and 25 mJ/cm2, and the results are presented.
There are many studies focuses on self-assembled films characterization, photochromic material (spiropyran) had been electrosattached to different enzymes, and in this work we used these spiropyran characteristics to immobilized glucose oxidase. The aim of this work is establish a protocol to build an optical device that shows absorption changes when an enzyme is immobilized and characterized the devise through FTIR and UV/Vis spectroscopy and Atomic Force and Scanning Electron Microscopy. We use different methods such as self-assembled monolayers and the activation reaction by carbodiimide. Corning of quartz was used as matrix, clean solution (1:1 MeOH:HCl, H2SO4) was used to prepared the matrix, 1% silane solution was prepared to functionalized the surface, and a solution prepared with spiropyran (C19H18N2O3), EDC (C5H11N=C=NC6H11), NHS (C4H5NO3), HEPES (C8H18N2O4S) and glucose oxidase from Aspergillus niger was the last step to immobilized this enzyme. Three steps to build it, the first step was cleaned the matrix, the next step was functionalized the surface with silane material, this step allows to modified the surfaces, to prepared to attach the spiropyran. The bonds found from the FTIR spectra to silanized step and the functionalized step (spiropyran attached). That indicated that FTIR and AFM techniques are available to characterized and identify absorption, morphology of a devise modified with spiropyran, that allows attach some biological material, in this case glucose oxidase, the absorption changes and morphological changes are the evidence of immobilization successful.
The radiation pressure forces for Au nanoparticles in the Rayleigh regime under the influence of a coherent source of infrared light from 0.7-1.5 μm of a Gaussian beam with fundamental mode corresponding to the TEM00 mode are studied. An intensity distribution of the source in terms of the spot size and power are considered to analyze the gradient, scattering and absorption forces on a sphere located arbitrarily on a Gaussian beam. The results have shown, through an analysis stability, the optical manipulation is better suited for longer wavelengths, small particles, and a beam waist significantly reduced.
By using the Hot Filament Chemical Vapor Deposition (HFCVD) technique tungsten thin films were deposited on
amorphous quartz substrates. To achieve this, a tungsten filament was heated at 1300 °C during 30 minutes maintaining
a constant pressure inside the chamber at 460 mTorr and substrate at 700 °C. Transition from tungsten oxide deposits to
tungsten thin films, by varying the substrate temperature, were characterized by means of Scanning Electron Microscope
(SEM), Atomic Force Microscope (AFM), X-Ray Diffraction and, micro-Raman spectroscopy. The SEM micrographs
reveal that the tungsten films have no more than 200 nm in thickness while XRD show evidence of the films crystallize
in the á-tungsten modification. On the other hand, AFM shows that the tungsten thin films exhibit a uniform and smooth
surface composed with semi-spherical shapes whose diameters are below than 50 nm. Furthermore, to the naked eye, the
as-deposited tungsten films exhibit a high mirror-like appearance.
A study of optically induced Zn/ZnO nanoparticles selective deposition using a coherent light source on single-mode
fiber optic end is presented. In the numerical studies, Zn/ZnO spherical nanoparticles are considered dissolved in
isopropyl alcohol with different diameters under the influence of a Gaussian beam with fundamental mode and linear
polarization. The results of this study show that the gradient force is not sufficient to move Zn nanoparticles toward
optical fiber end face, but it is sufficient to move ZnO nanoparticles of a certain diameter. In the experimental studies,
Zn/ZnO nanoparticles were mixed with isopropyl alcohol and subsequently deposited on the fiber end face using an
infrared laser. The results obtained by atomic force and optical microscopy show a good uniform distribution of
nanostructures deposited on the core of the fiber end face.
Experimental studies of titania nanotubes (TiO2) and tungsten oxide nanospheres (WO3) as devices of saturable
absorption for a fiber laser in ring configuration to optical short-pulse generation are presented. A deposition technique,
based on optical pressure radiation generated from a coherent source at 1550 nm is used to deposit the nanostructured
materials. Since this nanomaterials can be deposited directly on the optical fiber, this proposal results very interesting for
applications of saturable absorbers. Experimental results, by using nanotubes TiO2 and nanospheres deposited on the
fiber as a saturable absorption device, show that the TiO2 nanotubes exhibit better saturable absorption properties than
WO3 nanospheres, generating pulses with a wavelength of 1550 nm, frequency of 10 MHz, temporally width of 4.5 ps
and an output power of 1 mW.
In this paper we show numerically how a Gires-Tournois etalons (DGTE) is used to flatten
the gain spectrum of an erbium-doped fiber amplifier. A broadband amplifier with uniform
gain over 40-nm with a residual gain <2-dB is presented.
Thermocavitation is a mechanism induced by a focused CW laser beam into a high absorbing solution. As a result an
overheated region is created followed by explosive phase transition and consequently the formation of an expanding
bubble. Once the bubble reaches a cooler region it collapses very rapidly crating a shock wave. Thermocavitation can be
a useful tool for the generation of ultrasonic waves and controlled ablation with the important difference compared with
pulsed lasers that low power lasers are required. In particular, the above mentioned pressure waves may be capable of producing damage to substrates, for example, in metallic and dielectric thin films. In this work, we present an application of the thermocavitation phenomena which consist in the formation of micro-holes on thin films of titanium and Indium Tin Oxide (ITO) deposited on glass substrate. The micro holes can be employed as a micrometer light sources or spatial filters.
The nonlinear optical loop mirror (NOLM) is used in application like optical switching and demultiplexing, all-optical active mode locking, passive mode locking, pedestal suppression, pulse shaping, etc. This device offers a versatile way to obtain a nonlinear transmission behavior through the nonlinear differential phase shift between the two interfering beams due to the self-phase modulation. Recently we discussed a NOLM device using a symmetrical coupler, highly twisted fiber, and a quarter-wave (QW) retarder introducing the polarization asymmetry in the loop. We have shown high contrast operation, flexibility of characteristics, and stability in time. In this report we analyze theoretically and study experimentally the transmission behavior for different input polarization considering as well different output polarizations. We propose a simple description of the NOLM transmission for right- and left-hand circular output polarization at different output polarization states. The nonlinear characteristics depend on the QW retarder plate angle, but also on the polarization state at the NOLM input. Experiments were carry out with the NOLM consisted of a 500-m length SMF-28 fiber with twist rate of 7 turns/meter. Experiments show a good agreement with our theoretical approach. Appropriate choice of the input and output polarizations allows very high contrast, at least higher than 5000. Our measurements were restricted by sensitivity of our detection system to measure low power pulses at conditions when theoretically transmission must be equal zero. Experiments show flexibility and stability of characteristics. Adjustment of the QW retarder and input polarization allows tuning the critical power over a wide range.
We present experimental measurements and a corresponding theoretical analysis of a novel NOLM device made using a symmetrical (50/50) coupler, highly twisted fiber, and a quarter-wave (QW) retarder plate in the loop. The physical mechanism for the nonlinear properties is the polarization rotation of the counter-propagating optical fields. We also experimentally demonstrate that the nonlinear polarization rotation analysis is correct by controlling the transmission behavior as the QW retarder plate is rotated. We propose a simple description of the NOLM behavior, showing that nonlinear switching is obtained through the polarization asymmetry generated by the QW retarder plate. The proposed NOLM design is very attractive for applications like pedestal suppression and amplitude regularization of optical signals, since it operates stably without day-to-day drifting. We experimentally demonstrate the efficiency of the NOLM for high-order amplitude regularization of an optical pulse train subject to amplitude modulation, as an overall suppression of about 20 dB of the modulation was obtained over all frequencies. An environmentally stable NOLM will enable a wide range of applications, such as, optical switching and demultiplexing, all-optical active and passive mode-locking, and pedestal suppression.
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