Terahertz Radiation and Detection
The terahertz (THz) region of the electromagnetic spectrum (1012 Hz), between infrared- and micro- waves, has the potential to enhance homeland security, medical imaging, pharmaceutical analysis, chemical/biological detection, semiconductor monitoring, and quality control surveillance for a multitude of industries. Unfortunately, THz radiation sources have traditionally been cumbersome and expensive to produce, limiting their proliferation in commercial applications. An attractive method of THz generation takes advantage of conductivity modulation of a semiconductor due to an incident electromagnetic wave; this is called a photoconductive THz source (PCT). PCTs include an interdigited contact array that harnesses photo-generated carriers, which in turn drive a THz antenna. Inherent problems with PCTs include shadowing of the semiconductor by the metallic grid, and the requirement that low-lifetime materials be used to allow modulation in the THz range; both of these contribute to low power and quantum efficiencies.
Plasmonic Photoconductive Terahertz Source
The Terahertz Electronics Laboratory, part of the department of electrical engineering and computer science (EECS) at the University of Michigan, has designed, simulated and experimentally verified a plasmonic photoconductive THz source. Through the use of optimized metallic contacts that exploit plasmon resonances, or collective electronic cloud oscillations, the shadowing effect of traditional PCTs has been effectively eliminated. Additionally, the plasmonic field-enhancement near the contacts provides efficient carrier collection within the modulation time, negating the necessity of a low-lifetime material. These benefits hold promise for increasing both the power and quantum efficiency of photoconductive terahertz sources to help escalate their proliferation in commercial applications.
Applications and Advantages
- Medical imaging
- Pharmaceutical dose, structure and chemical analyses
- Semiconductor manufacturing
- Explosive detection for airport security
- Chemical/Biological detection and analysis
- Quality control of food, pharmaceuticals, plastics, etc.
- Shading effect of contact has been minimized
- Carrier generation near contact negates need for low-lifetime semiconductors
- Higher expected efficiency and power than traditional photoconductive generation
- Operates at 1550 nm driving wavelength for ease of integration