טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYuval Lamhot
SubjectNanofluids Optical Interactions
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor ? 18? Segev Mordechai
Full Thesis textFull thesis text - English Version


Abstract

My M.Sc. research focuses on complex nonlinear interactions between light and nanofluids (suspensions of nanoparticles inside a liquid). I have studied these interactions in order to explore new nonlinear dynamical processes which could facilitate new types of optofluidc systems. In my work which was both experimental and theoretical, I explored these interactions and have shown that they rely on long range thermal changes. These enable the systems to be altered in a tunable and continuous manner, thereby creating unique phenomena capable of much functionality. My M.Sc. research encompasses primarily of the following two topics: Optical Control of Thermo-Capillary Effects in Complex Nanofluids, and Self-Trapping of Optical Beams through Thermophoresis.

In the first part of my research, I study the strong coupling of light and nanoparticle suspensions, with surface-tension effect in capillaries. I show that increasing the intensity of a narrow laser beam, passing through capillary results in a significant decrease in the fluid level. The fluid capillary system exhibits the ability to control the fluid height optically, from afar, and tune the height continuously by varying the beam power. The physical mechanism behind the process is based on the particles absorbing light and transferring the heat to the liquid, thereby creating a thermal profile. The light-induced temperature distribution changes the local nanoparticle concentration via thermophoresis. Thermophoresis is a reaction to temperature gradients which causes particles to drift either parallel or antiparallel to the temperature gradient. This effect produces a new concentration profile in the capillary thereby changing the local absorption capability. The final level of the fluid is determined by the beam power and the interaction between light-induced heat diffusion and light-induced thermopohersis.

In the later part, I show that self-channeling of optical beams in fluidic suspensions via thermal effects can be achieved through negative thermophoresis and concentrating particle suspension around the beam. A beam propagating in a fluid with nanoparticles gives rise to a refractive index profile that guides the beam. If the particles have a refractive index higher than that of the liquid, under negative thermpphoresis they increase the refractive index at the beam center, thereby creating a waveguide. Hence, this mechanism can serve as a means to concentrate nanoparticles with light, and arrange them at prescribed structures within the liquid. Such nonlinear optofluidic interaction could be utilized to control chemical and biological reactions, to separate between particles, to arrange molecules and many other aspects.