Engineering The Spectral Reflectivity Of Multilayer Thin Films Multilayer Thin Films

Achieving a high reflectance over the infrared bands has attracted interest due to potential applications in lasers and thermophotovoltaic devices. Additionally, structures that operate across multiple bands and provide spectrally selective broadband reflectivity are under investigation for various applications. Moreover, there has been a growing interest in recent years in studies aimed at achieving switchable radiation properties for thermal management, particularly in space applications. Distributed Bragg Reflectors are commonly used in applications that require high reflectivity, consisting alternating high-index and low-index dielectric thin films. They can be specifically designed for multi-band functionalities. In this study, the reflectivity of multilayer thin film structures was first examined separately for single band ap plications. The performance of Bragg Reflectors was enhanced through Tandem Approaches and optimization techniques. Both the Transfer Matrix Method and Finite Difference Time Domain methods were employed, allowing for the evaluation of the reliability of these design tools. Optimization studies were conducted using Impedance Mismatch-Based Optimization, a physics-based method which aims equalizing the absolute value of complex reflectivity to unity. The broadband reflectivity of thin multilayer thin films was assessed, and spectrally selective reflectance was pursued through further optimization. Finally, conical VO2 structures were employed to achieve tunable spectral reflectance, leveraging the phase change prop erties of VO2. The effects of geometric parameters—such as height, radius, and periodicity of the conical structures—on the optical response were investigated.