MODULATION OF MID INFRARED TO TERAHERTZ NONLINEAR OPTICAL AND THERMAL EFFECTS IN AS₂(SEₓTE₁₋ₓ)₃ AND MOS₂ ASYMMETRIC QUANTUM WELLS VIA EXTERNAL BIASES, PRESSURE, AND TEMPERATURE

Abstract

This dissertation presents a comprehensive computational investigation into the nonlinear optical and thermodynamic properties of stepped quantum well structure. The materials studied here are two low-dimensional materials. The first is a chalcogenide alloy As₂SeTe and second is a two-dimensional MoS₂ monolayer. The study investigates how external fields and material composition change the way these structures interacts with light and thermal energy. To study these interactions we solved one dimensional schrodinger equation using finite element method. We also included Varshini and Kane model in order to see the effects of pressure and temperature on the systems via effective mass. Then we computed the eigenenergies and transition dipole matrices of the system. Then we used these paramters into Density matrix Formulism and canonical partition function to calculated various thermal and optical responses of these systems. We focused to compute linear and nonlinear absorption, refractive index change, second harmonic generation (SHG), and third harmonic generation (THG) for optical studies and Helmholtz free energy, entropy, heat capacity, and the magnetocaloric effect for the thermodynamic studies. This work tries to establish a unified theoretical framework for optimizing next generation electro-optic, thermo-optic and nonlinear photonic applications by systematically analyzing the optical and thermal characteristics of these systems. Understanding how these external fields, thermal environments, and composition affects these materials is critical for developing advanced quantum electronic devices, like wavelength-tunable infrared modulators, frequency convrters, sensors and thermally stable semiconductor lasers.