Terahertz quantum cascade laser sources based on intra-cavity difference-frequency generation with grating-assisted vertical light outcoupling

• Applicant: Professor Mikhail Belkin, Ph.D.
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 442667270

The goal of the proposed project is to achieve an order-of-magnitude increase in the key performance metrics, specifically, average terahertz (THz) power output and mid-infrared-to-terahertz conversion efficiency, of room temperature terahertz sources based on intra-cavity difference frequency generation (DFG) in mid-infrared quantum cascade lasers (QCLs). These devices, referred to as THz DFG-QCLs, are currently the only monolithic electrically-pumped semiconductor laser sources of 1-6 THz radiation that can be operated at room temperature. State-of-the-art THz DFG-QCLs can now produce up to 1.9 mW of peak terahertz power output and up to 14 microwatts of continuous-wave terahertz power output at room temperature, with the mid-infrared-to-terahertz nonlinear conversion efficiency in the range of ~0.1-1 mW/W2, depending on the device design. However, our experimental measurements and theoretical analysis show that less than 5% of the generated THz radiation is outcoupled to free space in these devices with the rest being trapped and absorbed inside of the laser chip. The project aims to use efficient grating-assisted surface outcoupling, instead of traditionally-used Cherenkov THz DFG outcoupling scheme, to dramatically improve the outcoupling efficiency of THz radiation in THz DFG-QCLs and achieve an order-of-magnitude increase in their performance. Our preliminary simulations demonstrate that efficient grating-assisted THz radiation outcoupling can indeed be achieved in THz DFG-QCLs using hybrid dielectric-plasmonic double-metal waveguides. The project will focus on theoretical optimization, practical implementation, and experimental verification of high performance of the THz DFG-QCLs with THz grating outcouplers. This project is expected to result in compact surface-emitting THz DFG-QCL sources with low THz beam divergence and an average THz power output close to 1mW at room-temperature. Given their compactness, mass-producibility, and room-temperature operation, the proposed surface-emitting THz DFG-QCL sources are expected to have a major impact on existing THz instrumentation, such as systems for heterodyne detection, spectroscopy, and imaging.

• DFG Programme: Research Grants