Undergraduate Honors Theses

Thesis Defended

Fall 2012

Document Type

Thesis

Department

Engineering Physics

First Advisor

Prof. Jason Glenn

Abstract

Anti-reflection coatings are typically applied to a surface to reduce optical reflection at an interface. These coatings are usually in the form of thin lms with matching refractive indices, but only are e cient for a small waveband. This idea can be mimicked by structuring (e.g. cutting parallel grooves) on a surface to change the e ective dielectric constant and can potentially be e cient across a larger band of wavelengths. Surface structuring methods for anti-reflection purposes has been shown to be a viable method at the National Institute of Standards and Technology (NIST) and at the University of Michigan [1]. Two cameras are being developed for CCAT: The Short-Wavelength Camera (SWCam) and the Long-Wavelength Camera (LWCam). SWCam will have a primary band centered at 350 m and LWCam will cover 6 spectral bands from 750 m to 3.3mm. SWCam may also cover secondary bands at 450 and 200 m as well. These bands are too wide for thin lm anti-reflective coatings to be e cient and materials with the appropiate index of refraction do not exist. Silicon is chosen as the lens material due to its low loss in the submillimeter band. The downside to silicon is a high index of refraction which causes an increase in reflection at the air-silicon interface and so a broadband anti-re ection solution must be achieved. I have modeled the physical situation and have used the model to do simulations to verify the performance of anti-re ective structuring. The model allows for multiple layers of structures having di erent depths and widths. We are able to specify wavelength and angle of incidence, allowing one to integrate over full Gaussian beams. We have con dence in the model due to it producing known solutions in limiting cases. Future work entails further simulations to determine what tolerances we must achieve in fabricating the lenses to allow for reflections of less than 1% across the full bandwidth.

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