Towards a Robotically Steerable Laser Ablation Probe.

In this paper, we present a robotically steerable laser ablation probe with application to interstitial thermal therapy. Existing laser interstitial thermal therapy (LITT) methods utilize a straight probe to deliver laser energy around the tip or to the side of the tip. These methods are inadequate to provide effective treatment for large, irregularly shaped tumors.

All-fiber few-mode interference for complex azimuthal pattern generation.

We report on an all-fiber setup capable of generating complex intensity patterns using interference of few guided modes. Comprised by a few-mode fiber (FMF) spliced to a multimodal interference (MMI) fiber device, the setup allows for obtaining different output patterns upon adjusting the phases and intensities of the modes propagating in the FMF. We analyze the output patterns obtained when exciting two family modes in the MMI device using different phase and intensity conditions for the FMF modal base.

Volumetric Temperature Mapping Using Light-Sheet Microscopy and Upconversion Fluorescence from Micro- and Nano-Rare Earth Composites.

We present a combination of light-sheet excitation and two-dimensional fluorescence intensity ratio (FIR) measurements as a simple and promising technique for three-dimensional temperature mapping. The feasibility of this approach is demonstrated with samples fabricated with sodium yttrium fluoride nanoparticles co-doped with rare-earth ytterbium and erbium ions (NaYF:Yb/Er) incorporated into polydimethylsiloxane (PDMS) as a host material. In addition, we also evaluate the technique using lipid-coated NaYF:Yb/Er nanoparticles immersed in agar.

Luminescent Polymer Composites for Optical Fiber Sensors.

Optical fiber sensors incorporating luminescent materials are useful for detecting physical parameters and biochemical species. Fluorescent materials integrated on the tips of optical fibers, for example, provide a means to perform fluorescence thermometry while monitoring the intensity or the spectral variations of the fluorescence signal. Similarly, certain molecules can be tracked by monitoring their characteristic emission in the UV wavelength range.

Experimental and computational model approach to assess the photothermal effects in transparent nanocrystalline yttria stabilized zirconia cranial implant.

Background And Objective: In the last few years, we have been exploring the use of transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) ceramics as a biomedical transparent cranial implant, referred as the "Window to the Brain" (WttB). The WttB aims at providing chronical optical access to the brain for diagnostics and therapeutic procedures and it has shown to provide an effective means to obtain enhanced results from optical imaging techniques. The objective of this work is to explore the photothermal effects of the Wttb produced when it is irradiated by a laser source.

Vernier effect using in-line highly coupled multicore fibers.

We demonstrate optical fiber sensors based on highly coupled multicore fibers operating with the optical Vernier effect. The sensors are constructed using a simple device incorporating single-mode fibers (SMFs) and a segment of a multicore fiber. In particular, we evaluated the performance of a sensor based on a seven-core fiber (SCF) spliced at both ends to conventional SMFs, yielding a versatile arrangement for realizing Vernier-based fiber sensors.

Fiber optic probe with functional polymer composites for hyperthermia.

We demonstrate a fiber optic probe incorporating functional polymer composites for controlled generation of photothermal effects. The probe combines carbon-based and rare-earth composites on the tip of standard multimode fibers, thus yielding a compact fiber optic photothermal probe (FOPP) whose temperature can be measured simultaneously through fluorescent thermometry. We evaluate the thermal features of the probe through experiments and numerical calculations showing that large thermal gradients are obtained within the vicinity of the heating zone.

Photomechanical Polymer Nanocomposites for Drug Delivery Devices.

We demonstrate a novel structure based on smart carbon nanocomposites intended for fabricating laser-triggered drug delivery devices (DDDs). The performance of the devices relies on nanocomposites' photothermal effects that are based on polydimethylsiloxane (PDMS) with carbon nanoparticles (CNPs). Upon evaluating the main features of the nanocomposites through physicochemical and photomechanical characterizations, we identified the main photomechanical features to be considered for selecting a nanocomposite for the DDDs.

Fiber optic interferometric immunosensor based on polydimethilsiloxane (PDMS) and bioactive lipids.

We demonstrate a novel and simple means to fabricate optical fiber immunosensors based on Fabry-Perot (F-P) interferometers using polydimethylsiloxane (PDMS) as support for bioactive lipids. The sensors are fabricated following a straightforward dip-coating method producing PDMS end-capped devices. A biosensing platform is realized by subsequent functionalization of the PDMS cap with a previously characterized bioactive lipid antigen cocktail from , used as a surrogate source of antigens for tuberculosis diagnosis.

Enhanced near infrared optical access to the brain with a transparent cranial implant and scalp optical clearing.

We report on the enhanced optical transmittance in the NIR wavelength range (900 to 2400 nm) offered by a transparent Yttria-stabilized zirconia (YSZ) implant coupled with optical clearing agents (OCAs). The enhancement in optical access to the brain is evaluated upon comparing transmittance measurements of mice native skull and the YSZ cranial implant with scalp and OCAs. An increase in transmittance of up to 50% and attenuation lengths of up to 2.

Fiber optic fluorescence temperature sensors using up-conversion from rare-earth polymer composites.

We demonstrate an optical fiber sensor based on the green up-conversion emission of rare-earth active ions hosted by a polymer matrix. The temperature sensitive composite material is fabricated by simple mixing of the rare-earth ions in powder form (NaYYbErF) with the polymer (polydimethylsiloxane). This fluorescent material is then incorporated on the tip of silica-glass optical fibers to obtain a point temperature sensor probe.

Random laser imaging of bovine pericardium under the uniaxial tensile test.

We demonstrate random laser (RL) emission from within bovine pericardium (BP) tissue. The interest in BP relies on its wide use as a valve replacement and as a biological patch. By imaging the emitting tissue, we show that RL emission is mostly generated inside the collagen fibers.

Scaling photonic lanterns for space-division multiplexing.

We present a new technique allowing the fabrication of large modal count photonic lanterns for space-division multiplexing applications. We demonstrate mode-selective photonic lanterns supporting 10 and 15 spatial channels by using graded-index fibres and microstructured templates. These templates are a versatile approach to position the graded-index fibres in the required geometry for efficient mode sampling and conversion.

Optical trapping and micromanipulation with a photonic lantern-mode multiplexer.

We demonstrate a simple approach based on a photonic lantern spatial-mode multiplexer and a few-mode fiber for optical and manipulation of multiple microspheres. Selective generation of linearly polarized (LP) fiber modes provides light patterns useful for trapping one or multiple microparticles. Furthermore, rotation of the particles can be achieved by switching between degenerate LP modes, as well as through polarization rotation of the input light.

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.

Few layers graphene as thermally activated optical modulator in the visible-near IR spectral range.

We report the temperature modulation of the optical transmittance of a few layers of graphene (FLG). The FLG was heated either by the Joule effect of the current flowing between coplanar electrodes or by the absorption of a continuous-wave 532 nm laser. The optical signals used to evaluate the modulation of the FLG were at 633, 975, and 1550 nm; the last wavelengths are commonly used in optical communications.

Mechanical assessment of bovine pericardium using Müeller matrix imaging, enhanced backscattering and digital image correlation analysis.

Mechanical characterization of tissue is an important but complex task. We demonstrate the simultaneous use of Mueller matrix imaging (MMI), enhanced backscattering (EBS) and digital image correlation (DIC) in a bovine pericardium (BP) tensile test. The interest in BP relies on its wide use as valve replacement and biological patch.

On the Motion of Carbon Nanotube Clusters near Optical Fiber Tips: Thermophoresis, Radiative Pressure, and Convection Effects.

We analyze the motion of multiwalled carbon nanotubes clusters in water or ethanol upon irradiation with a 975 and 1550 nm laser beam guided by an optical fiber. Upon measuring the velocities of the nanotube clusters in and out of the laser beam cone, we were able to identify thermophoresis, convection and radiation pressure as the main driving forces that determine the equilibrium position of the dispersion at low optical powers: while thermophoresis and convection pull the clusters toward the laser beam axis (negative Soret coefficient), radiation pressure pushes the clusters away from the fiber tip. A theoretical solution for the thermophoretic velocity, which considers interfacial motion and a repulsive potential interaction between the nanotubes and the solvent (hydrophobic interaction), shows that the main mechanism implicated in this type of thermophoresis is the thermal expansion of the fluid, and that the clusters migrate to hotter regions with a characteristic thermal diffusion coefficient D(T) of 9 × 10(-7) cm(2) K(-1) s(-1).

Six mode selective fiber optic spatial multiplexer.

Low-loss all-fiber photonic lantern (PL) mode multiplexers (MUXs) capable of selectively exciting the first six fiber modes of a multimode fiber (LP, LP, LP, LP, LP, and LP) are demonstrated. Fabrication of the spatial mode multiplexers was successfully achieved employing a combination of either six step or six graded index fibers of four different core sizes. Insertion losses of 0.

An optopneumatic piston for microfluidics.

We demonstrate an optopneumatic piston based on glass capillaries, a mixture of PDMS-carbon nanopowder, silicone and mineral oil. The fabrication method is based on wire coating techniques and surface tension-driven instabilities, and allows for the assembly of several pistons from a single batch production. By coupling the photothermal response of the PDMS-carbon mixture with optical excitation via an optical fiber, we demonstrate that the piston can work either as a valve or as a reciprocal actuator.

Thermocapillary flow in glass tubes coated with photoresponsive layers.

Thermocapillary flow has proven to be a good alternative to induce and control the motion of drops and bubbles in microchannels. Temperature gradients are usually established by implanting metallic heaters adjacent to the channel or by including a layer of photosensitive material capable of absorbing radiative energy. In this work we show that single drops can be pumped through capillaries coated with a photoresponsive composite (PDMS + carbon nanopowder) and irradiated with a light source via an optical fiber.

Fiber optic Fabry-Perot sensor for surface tension analysis.

We demonstrate a new technique for analyzing surface tension of liquids. This is done upon examining the interference signals reflected from a remnant drop pending at the cleaved end of a single mode optical fiber. The resulting interference patterns are fitted to a multimirror Fabry-Perot model yielding information of the drop size.