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(a) The input face of the coaxial transmission line showing the outer tube with outside diameter and inside diameter, the PTFE (Teflon) dielectric, and the diameter plated inner conductor. The cable was from Coax Co., Ltd. Yokohama, Japan with Part No. SC-033/50, design impedance , and maximum single mode frequency . (b) the output face shows the central conductor extended outside of the line for biasing. The optoelectronic antenna is also shown; (c) the experimental schematic shows the SOS excitation plate in contact with the input face of the coaxial line, shown in cross section. The biasing is shown together with the positioning of the insulating film, the SOS antenna and the additional sapphire plate, used to extend the time between the transmitted and reflected THz pulses. The dielectric is shown cross-hatched.
Measured output THz pulses (a)–(c) for the coaxial transmission line lengths of 15, 44, and , respectively. The arrows indicate the truncated pulses used to obtain the simplified Fourier transforms.
(a)–(c) Corresponding amplitude spectra of the THz pulses shown in Figs. 2(a)–2(c) respectively. The heavy dashed line spectra are for the truncated pulses of Figs. 2(a)–2(c). The light vertical dashed lines indicate the cut-off frequency of the mode.
Measured total amplitude absorption coefficient (, dots) and (, open circles) compared to the theoretical absorption . The theoretical absorption coefficient of the coaxial line and the measured Teflon are also shown. For comparison the theoretical absorption is shown for the air-spaced, PPWG. (Ref. 5).
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