A 3.4 μm Quantum Cascade Laser for Photocatalytic Decomposition of Methane

Abstract

Quantum Cascade Lasers (QCLs) are quantum devices that generate mid- to far- infrared light at a specified wavelength via intersubband electronic transitions. In this thesis, we present a high optical power QCL at 3.4 μm, designed for the photocatalytic degradation of methane for hydrogen production, CH4 → C + 2H2. We review the photocatalytic degradation of methane as a promising, low greenhouse gas emission hydrogen production pathway in order to motivate the laser design. We also derive and present essential parameters governing electron physics in a QCL, including the semiconductor band structures and electronic states in multiple quantum wells. The QCL design presented has a calculated emission wavelength of 3.4 μm and period length 25-40% shorter than existing short wavelength QCLs, enabling up to 40% greater optical power. The design is based on the strained Al0.64In0.36As/In0.67Ga0.33As system, and it presents a novel technique for direct coupling of the lower laser level to the injector in order to increase the optical transition energy.