Linear and Nonlinear Optical Effects in High Carrier Concentration Oxides and Nitrides at Epsilon-Near-Zero
Doctor of Philosophy
Electrical & Computer Engineering
Nonlinear optics has been an important method for achieving ultrafast light manipulation. Recently, ENZ material have gained interest due to inherent advantages such as slow light, improved confinement, and ideal relaxation times, the nonlinear response of these materials, such as the intensity-dependent-refractive-index, are ultra-large yet remain ultra-fast. This experimental discovery of epsilon-near-zero enhancement has thus opened new avenues in nonlinear optics research in recent years, and while experiments have continued to progress a theoretical understanding of the processes and origins of nonlinear optical enhancement at epsilon-near-zero has lagged.
To fill this gap, the work herein focuses on uncovering the mechanisms that drive the nonlinear interactions of Drude-based epsilon-near-zero materials. This framework utilizes knowledge of a given material’s electronic band structure in energy-momentum space to understand the kinetic motion of free electrons under intense optical irradiation, realizing a fully feed-predictive simulator without fitting parameters. From this, two types of nonlinearities are elucidated, intra- and inter-band, whose overall effect on the optical properties are rooted in the non-parabolic dispersion of energy bands. Moreover, these effects are shown to induce opposing changes on the optical permittivity leading to distinctively different outcomes that can be used individually or together to sculpt the material’s optical properties in time and space.
Experimentally, both intraband and interband nonlinearities are interrogated through these methods with the first known multi- beam deflection studies in epsilon-near-zero materials.
Through this holistic study, improved prediction power is available for finding the ideal nonlinear films, and effects can be explored to optimize them.
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