Fabrication of photoconductive antenna with mesa structure for terahertz spectroscopy

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Terahertz (THz) electromagnetic waves have frequencies of order 10^12 Hz and wavelengths order 100 um. THz waves are used in THz time domain spectroscopy (THZ-TDS) setups for non-destructive, non-invasive characterization of materials and compounds. It has been shown that many materials including organic materials, explosives, pharmaceutical compounds, and biological agents have distinct signatures in the terahertz frequencies. In this regard, terahertz time-domain imaging (THZ-TDI) and spectroscopy (THZ-TDS) are of great interest not only to scientists but also to industrial stake holders for their unique capabilities in chemical sensing, medical diagnosis, and non-destructive quality control. The potential application and scope of THz-TDS & THZ-TDI systems are largely determined by the THz transmitter and receiver that are both based on photoconductive antenna (PCA) device. Taking the transmitter as an example, state of the art transmitter PCAs and PCA arrays utilize short carrier lifetime semiconductor substrate to generate ultrafast current to produce broadband THz radiation under a femtosecond optical laser pump. In this project we will design, fabricate and characterize three-dimensional mesa-like terahertz PCA that offers higher efficiency than the common planar PCA. The PCA will be integrated into the supporting company's product that measures the individual layer thickness of plastic containers. High performance PCA will enable the measurement of thicker or more absorbing layers, as well as containers having more layers. Moreover, the mesa PCA will work at the telecommunication wavelength (@1550 nm) for the excitation laser, and thus fiber-coupling can be utilized to give an agile and compact THz system.