| This dissertation examines two types of mid-infrared semiconductor nanostructure: quantum cascade (QC) lasers and optical metamaterials. These lasers and metamaterials are both composed of stacks of nanometer-thin semiconductor layers, and each has unique functionality in the mid-infrared portion of the spectrum. QC lasers have application in areas such as medical diagnostics, environmental sensing, homeland security, and infrared countermeasures. Optical metamaterials have fundamentally novel interactions with light and have potential for applications in areas such as sub-wavelength imaging, solar energy collection, and optical cloaking.;In this work, we explore several new approaches to the design of QC laser gain regions, with an emphasis on improving their wall-plug efficiency (WPE). Short injector, low-voltage defect QC lasers achieve high performance with a voltage defect of only 19 meV, overturning previously held assumptions about QC laser design. These devices operate with the highest voltage efficiency ever reported in QC lasers. Lasers with ultra-strong coupling between the injector and the upper laser level attain 50% WPE---a major accomplishment for QC technology. Furthermore, a thermoelectric effect is measured for the first time within QC lasers, informing decisions about how to design and fabricate devices for optimal temperature performance.;We describe two major efforts to improve important properties in strongly anisotropic mid-infrared metamaterials. The bandwidth and dispersion properties are improved through the use of multiple-metamaterial stacks, where the doping level and total thickness of each stack are tailored to produce a broader and flatter spectral region of negative refraction. This work demonstrates that these materials can be engineered to take on specified behavior according to design, a basic tenant of transformation optics. Preliminary work is reported in which QC gain regions are incorporated into the structure of these metamaterials, in an effort to actively reduce their optical absorption loss.;The dissertation concludes with a focus on QC lasers for specific applications. QC lasers are developed for use in sensing trace amounts of CO2 isotopes in the atmosphere. These lasers show single mode emission in continuous wave operation at 4.32 mum and are tunable over strong optical absorption lines for 12CO2, 13CO2, and 18OCO. The economic and policy implications of improved CO2 isotope measurements are considered for applications such as CO2 storage reservoir leakage monitoring, and a quantitative economic model is used to analyze the value of such measurements. We also collaborate to examine QC laser applications in non-invasive tissue measurements, miniature inter-planetary sensors, high-resolution C60 spectroscopy, and directional infrared countermeasures. |
