Diffuse reflecting surfaces for the infrared and far infrared

Efficient random-scattering surfaces for the IR have been fabricated by cementing submillimeter-sized shavings or pellets to a metallic substrate with metal-filled epoxy, followed by deposition of a Ag overcoating. The measured height and lateral spacing distributions for these preparations are both nearly Gaussian. Net surface reflectivities of ≥90% have been measured at 10 µm, and the threedimensional angular intensity distributions agree with the cosine law that defines a perfect uniform diffusing surface to within ~10%. Careful extrapolation of the 10-µm data into the far IR, combined with sample measurements at 90 and 250 µm, indicate that reflectivities of > 96% can be achieved for λ ≥ 90 µm with comparable uniformity of diffusion. These surfaces are intended for use in overmoded resonator cavities excited by continuously tunable, pulsed, far-IR lasers, but they should also find use in other applications where high net reflectivity, uniform diffusion, and ready contrl of the dimensions of the individ scattering elements are important considerations.