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(ω) of gold, nickel, and lead in the 30–300-cm−1 wave-number region. The real part of the normalized surface impedance spectrum z(ω) = r(ω) + ix(ω) was determined from P(ω). The r(ω) spectrum was combined with previous measurements by others at higher frequencies, and Kramers-Kronig analyses of the resultant r(ω) spectra provided ∊(ω) = ∊1(ω) + i∊2(ω) and N(ω) = n(ω) + ik(ω) 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(ω) of a metal.