Fig. 1. Dielectric and SPP propagation properties for Au and Al at terahertz frequencies based on published data, assuming εd=1. (a) Real component of the dielectric constant based on a Drude model fit. (b) Real component of the dielectric constant based on a Drude model fit. (c) 1/e propagation length, Lx, along the x axis. (d) 1/e spatial extent, Lz, along the z axis.

Fig. 2. Schematic diagram of the excitation and detection scheme for measurement of the SPP propagation and sample dielectric properties. Broadband terahertz radiation is normally incident on a 2 cm long rectangular cross-sectional groove that is 300 μm wide×100  μm deep. The groove is used to couple normally incident freely propagating broadband terahertz radiation into SPP waves that propagate along the sample surface. A 〈110〉 ZnTe crystal that can be freely positioned anywhere above the sample surface is used to measure the z component of the terahertz electric field via electro-optic sampling.

Fig. 3. SPP propagation and dielectric properties for Au. (a) Measured terahertz time-domain waveforms for two positions separated by 10 cm on the Au-coated metal sheet. The time shift arises from the difference in propagation velocities between the terahertz SPP and the optical probe pulses. (b) Corresponding amplitude and phase spectra. (c) Extracted values of n and κ using the Eq. (5). (d) Calculated values of εmr and εmi using Eq. (6). (e) Comparison between the 1/e propagation length along the x axis computed from εm (solid line) with εd=1 and values obtained by taking measurements along the x axis. (f) Comparison between the 1/e decay length along the z axis computed from εm (solid line) with εd=1 and values obtained by taking measurements along the z axis.

Fig. 4. SPP propagation and dielectric properties for Al and stainless steel. (a) and (b) Extracted values εmr and εmi. (c) and (d) Comparison between the 1/e propagation length along the x axis computed from εm (solid line) and values obtained by taking multiple measurements along the x axis. (e) and (f) Comparison between the 1/e decay length along the z axis computed from εm (solid line) and values obtained by taking measurements along the z axis. Note the differences in the y axes values between aluminum and stainless steel.