Quantum Cascade Terahertz Emitters for Subsurface Defect Detection

The transmission and penetration capability of electromagnetic waves with terahertz frequencies promises nondestructive subsurface inspection capabilities using low energy, non‐harmful radiation. The development of compact and portable terahertz frequency radiation sources and detectors is crucial to the practical implementation of future terahertz based nondestructive evaluation tools for aerospace, medical, security, and electronic industries. Recent progress in the bandstructure engineering of multi‐quantum well heterostructures offers the potential to design miniature, efficient, high power, and direct terahertz emitters using standard semiconductor materials and fabrication techniques. Using a recently developed terahertz spectrometer, combined with near and mid‐infrared spectroscopy data, we report on the transmission characteristics of aerospace coatings over a broad spectrum from near‐infrared to terahertz frequencies. The design of quantum cascade emitters based on the obtained transmission data is presented.