Broadband THz frequency comb generation in quantum cascade lasers

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The scientific objective of this proposal is to create terahertz (THz) frequency combs based on quantum cascade laser sources operating at room-temperature. The research will focus on innovative designs of the quantum cascade laser to produce hundreds of evenly-spaced THz emission lines. Based on these laser sources, the PI intends to demonstrate a prototype spectroscopic system using the frequency-comb emission lines. The proposed devices could lead to room-temperature spectroscopic instrumentation for security and industrial applications based on mass-producible semiconductor components. This project is a multidisciplinary activity that offers a unique educational environment for graduate and undergraduate students involved in the project. At least one graduate student and several undergraduate students will be involved in this research program. The PI will endeavor to recruit these students from underrepresented minorities and will interact with students at the K-12 level through the NSF-sponsored UTeachEningeering program.The objective of this proposal is to attain the necessary knowledge to create room-temperature quantum cascade lasers having THz frequency combs spanning the entire 0.5-5 THz range. The research will focus on creating quantum cascade laser active region design that provides broadband mid-infrared laser gain, giant third-order optical nonlinearity for efficient mid-infrared frequency comb generation, and giant second-order nonlinearity for efficient down-conversion of mid-infrared frequency comb to THz spectral range. The laser waveguide will be designed to enable low group velocity dispersion for mid-infrared TM00 laser modes and efficient terahertz radiation generation and out-coupling via Cherenkov difference-frequency generation. A subtle interplay of three- and four-wave mixing processes in mid-infrared quantum cascade lasers will be investigated, linewidth measurements of terahertz frequency comb emission from the lasers will be performed, and novel low group-velocity-dispersion quantum cascade laser waveguide designs will be optimized via iterative design-fabrication-measurements process. A prototype frequency comb spectroscopic system based on quantum cascade laser sources and a heterodyne detector, such as room-temperature Schottky-diode or cryogenically-cooled superconducting or hot-electron bolometer, is to be demonstrated.