|M.Sc Student||Shalem Guy|
|Subject||Four-Wave Mixing and light Scattering off Metasurfaces|
|Department||Department of Mechanical Engineering||Supervisor||?|
|Full Thesis text|
In the past decade the field of plasmonics has been a fruitful topic of research. Plasmonic characteristic attributes like field-enhancement, slow group velocity and shorter wavelengths compared to photons, were put into use in scanning near-field microscopy, design of very thin optical components and in many other applications. In this work we take advantage of the plasmonic field enhancement and the extra ordinary transmission that is associated with plasmons, to generate a strong nonlinear four-wave mixing response inside nanocavities etched on a thin gold film. In addition, we apply a beam steering technique, made possible by a new type of artificial materials that can manipulate light in ways not possible by materials found in nature - metamaterials. We show theoretically, numerically and experimentally that non-linearly generated light undergoes different beam steering than a linear signal with the same wavelength and we propose an explanation to this phenomenon.
The outline of this dissertation is as follows: In the first chapter we introduce the finite-difference-time-domain algorithm and explain how we can use it to simulate nonlinear four-wave mixing processes. In the second chapter we review the fundamentals of plasmonics which are needed in order to understand the enhancement for fields and the strong transmission through subwavelength-size cavities. The third chapter is dedicated to fundamentals of nonlinear optics. Next we study the nonlinear phenomenon of four-wave mixing in selected metasurfaces. In this chapter we explain the generalized Snell's law, which was predicted and reported in 2011 and apply a theoretical method of coupled modes theory to explain the generation of four-wave mixing in our metasurfaces. We describe simulations to predict beam steering of linear and nonlinear signals from our metasurfaces. Experimental work was done to corroborate the simulations predictions. Wide emphasis is put on the distinction between beam steering due to anomalous refraction via generalized Snell's law versus beam steering via diffraction from a phase grating. We show numerically that there is a difference between the linear- and nonlinear-beam refraction angles but no difference in the diffraction angles.