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

Abstract

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.