Reinher Pimentel-Domínguez

Microbubble generation using fiber optic tips coated with nanoparticles

We show that fiber optic tips can be used as microbubble generators in liquid media. Using standard single-mode silica fibers incorporating nanoparticles (carbon nanoparticles and metallic powders), bubbles can be generated with low optical powers owing to the enhanced photothermal effects of the coating materials. We provide details about the hydrodynamic effects generated in the vicinity of the fiber tip during the coating process, bubble generation and growth. Flow visualization techniques show that thermal effects lead to bubble formation on the tip of the fibers, and coating optimization is crucial for optimal performance of the probes.

Laser induced deformation in polydimethylsiloxane membranes with embedded carbon nanopowder

We demonstrate optically induced micron-range deformation of polydimethylsiloxane (PDMS) membranes with embedded carbon nanopowder. The mechanical deformation can be controlled by low power laser irradiation of the samples and the resulting surface modifications are analyzed via dynamic speckle measurements. Photothermal effects due to optical absorption by the nanopowder are shown to deform the polymer samples leading to localized mechanical stresses induced via thermal expansion of the PDMS.

Photothermal Effects and Applications of Polydimethylsiloxane Membranes with Carbon Nanoparticles

The advent of nanotechnology has triggered novel developments and applications for polymer-based membranes with embedded or coated nanoparticles. As an example, interaction of laser radiation with metallic and carbon nanoparticles has shown to provide optically triggered responses in otherwise transparent media. Incorporation of these materials inside polymers has led to generation of plasmonic and photothermal effects through the enhanced optical absorption of these polymer composites. In this work, we focus on the photothermal effects produced in polydimethylsiloxane (PDMS) membranes with embedded carbon nanoparticles via light absorption. Relevant physical parameters of these composites, such as nanoparticle concentration, density, geometry and dimensions, are used to analyze the photothermal features of the membranes. In particular, we analyze the heat generation and conduction in the membranes, showing that different effects can be achieved and controlled depending on the physical and thermal properties of the composite material. Several novel applications of these light responsive membranes are also demonstrated, including low-power laser-assisted micro-patterning and optomechanical deformation. Furthermore, we show that these polymer-nanoparticle composites can also be used as coatings in photonic and microfluidic applications, thereby offering an attractive platform for developing light-activated photonic and optofluidic devices.

Optically driven deposition of nanostructures on optical fiber end faces

We present a simple and inexpensive way to incorporate nanostructures in optical fibers based on optically driven transport of nanoparticles. The technique has been previously used to incorporate carbon nanotubes in fiber laser systems and relies on the deposition of nanostructures driven by the optical radiation propagating in the fiber. We demonstrate that this technique allows for incorporating graphite nanotubes and nanoparticles on the tip of the fibers and fiber connectors. Flow visualization techniques and thermal analysis of the deposition process show experimental evidence of the thermophoretic and pressure gradients involved in the incorporation of nanostructures onto optical fibers. Furthermore, we demonstrate the formation of micron sized bubbles on the tip of the fibers coated with nanostructures and show that this technique could render useful for developing micro bubble generators and mixers for micron sized structures.

Integration of multiple SiO2 nanoparticles on a tapered fiber through evanescent wave

We present a simple method to incorporate SiO2 nanoparticles on the surface of tapered optical fibers exploiting optically driven transport of SiO2 nanoparticles. Changes in the transmission spectrum are registered during particle deposition

Photothermal lesions in soft tissue induced by optical fiber microheaters

Photothermal therapy has shown to be a promising technique for local treatment of tumors. However, the main challenge for this technique is the availability of localized heat sources to minimize thermal damage in the surrounding healthy tissue. In this work, we demonstrate the use of optical fiber microheaters for inducing thermal lesions in soft tissue. The proposed devices incorporate carbon nanotubes or gold nanolayers on the tips of optical fibers for enhanced photothermal effects and heating of ex vivo biological tissues. We report preliminary results of small size photothermal lesions induced on mice liver tissues. The morphology of the resulting lesions shows that optical fiber microheaters may render useful for delivering highly localized heat for photothermal therapy.

Microbubble Generation Using Carbon Nanostructures Deposited onto Optical Fibers

We present an easy, fast and inexpensive method to produce micron-sized bubbles using a low power laser diode operating in CW mode. The technique is based on light absorption by a thin layer of carbon nanostructures (nanotubes and nanoparticles) deposited on the tip of an optical fiber. Through flow visualization techniques and thermal imaging, we have observed evidence of the thermal and pressure gradients that appear in this process. With this method, micron-sized bubbles can be generated. These effects might be of significance for cavitation studies as well as for laser surgery.

Fiber Optic Micro-Bubble Generator

A simple method to incorporate carbon nanotubes onto optical fibers is to immerse its tip in a solution of nanostructures dispersed in ethanol. Laser light guided by the fiber attracts the nanostructures thus forming deposits on the optical fiber tip. After deposition, micron-sized bubbles can be formed on the tips of the optical fibers owing to light absorption by the nanostructures.

Nanoparticle coated optical fibers for single microbubble generation

The study of bubbles and bubbly flows is important in various fields such as physics, chemistry, medicine, geophysics, and even the food industry. A wide variety of mechanical and acoustic techniques have been reported for bubble generation. Although a single bubble may be generated with these techniques, controlling the size and the mean lifetime of the bubble remains a difficult task. Most of the optical methods for generation of microbubbles involve high-power pulsed laser sources focused in absorbing media such as liquids or particle solutions. With these techniques, single micron-sized bubbles can be generated with typical mean lifetimes ranging from nano to microseconds. The main problem with these bubbles is their abrupt implosion: this produces a shock wave that can potentially produce damages on the surroundings. These effects have to be carefully controlled in biological applications and in laser surgery, but thus far, not many options are available to effectively control micron-size bubble growth. In this paper, we present a new technique to generate microbubbles in non-absorbing liquids. In contrast to previous reports, the proposed technique uses low-power and a CW radiation from a laser diode. The laser light is guided through an optical fiber whose output end has been coated with nanostructures. Upon immersing the tip of the fiber in ethanol or water, micron-size bubbles can be readily generated. With this technique, bubble growth can be controlled through adjustments on the laser power. We have obtained micron-sized bubbles with mean lifetimes in the range of seconds. Furthermore, the generated bubbles do not implode, as verified with a high-speed camera and flow visualization techniques.