Princeton University

School of Engineering & Applied Science

Structured Plasmonic Waveguides and Interface Roughness Scattering for Quantum Cascade Lasers

Akil Word-Daniels
Prof. Gmachl
Engineering Quadrangle B327
Thursday, May 17, 2018 - 4:00pm to 5:30pm

Quantum cascade (QC) lasers are unique devices that provide coherent light with wavelengths from approximately 3 µm to 300 µm. Wavelengths in the range of 8-16 µm are particularly useful for applications such as trace gas detection for the strongest absorption lines of molecular compounds such as the hazardous uranium hexafluoride and benzene. However, despite rapid advancements in QC laser technology over the past two decades since its inception, room temperature, continuous-wave operation for this wavelength range has not been achieved in a standalone system.
The first section of this thesis focuses on creating a new QC laser band structure design and a unique waveguide structure for the 16 µm wavelength. This project stems from improving upon design characteristics found in other high-performance long wavelength QC lasers. It includes the creation a novel mixed air-plasmon waveguide to reduce loss and improve growth parameters for ridge lasers with wavelengths longer than 15 µm. This waveguide design consists of a structured periodic air-plasmon waveguide for the top cladding of the laser.
Next, we explore the effects of interface roughness (IFR) scattering in QC lasers. It was recently found that interface roughness scattering can be the dominant scattering mechanism in QC lasers as opposed to longitudinal phonon scattering. We use this knowledge and present the first QC device designed solely using IFR scattering. This study and design approach has significant implications for how the QC laser community approaches developing and analyzing QC lasers.