Optical properties of Au, Ni, and Pb at submillimeter wavelengths

Measurements of the optical properties, and thus the optical constants, of metals at submillimeter wavelengths are almost nonexistent. We used a nonresonant cavity to measure at ambient temperature the angle averaged absorptance spectra P(omega) of gold, nickel, and lead in the 30-300-cm(-1) wave-number region. The real part of the normalized surface impedance spectrum z(omega) = r(omega) + ix(omega) was determined from P(omega). The r(omega) spectrum was combined with previous measurements by others at higher frequencies, and Kramers- Kronig analyses of the resultant r(omega) spectra provided (omega) =, (1) (omega) + i(2)(omega) and N(omega) = n(omega) + ik(omega) for gold and nickel in the 35-15,000-cm(-1) region and for lead in the 15-15,000-cm(-1) region. We also derived an exact analytical expression for P(omega) of a metal.