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Terahertz Conductivity of Copper Surfaces

Terahertz (THz) radiation holds great promise for applications in communications, molecular detection, and imaging. Effective THz system design requires accurate models for the frequency-dependent conductivity of metals and the effect of surface roughness on conduction loss. However, predictive methods are currently unverified in the region between 0.3 and 0.9 THz because few experimental data exist in this regime. In order to address this problem, we have measured the conductivity of copper, of various surface roughnesses, using a semi-confocal open resonator system. This paper describes our measurements of the THz conductivity, dc conductivity, roughness, and microstructure of copper. We show that the classical Drude theory is sufficient for predicting the THz conductivity of copper at room temperature and that dissipation loss enhancement caused by surface roughness is modeled better by the Hammerstad-Bekkadal formula than second-order small perturbation theory.