Silicon as a standard material for infrared reflectance and transmittance from 2 to 5 μm

We have investigated the specular reflectance and transmittance of polished, high-resistivity single-crystal Si in the spectral range from 2 to 5 μm. Measurements were performed with a nearly collimated (≈0.7° divergence) beam at angles of incidence from 12° to 80°, and a spectral resolution of 16 cm⁻¹. The measured values agree with the expected values obtained from the published index of refraction of Si to within 0.002. This represents a substantial reduction in experimental uncertainty compared to previous results and demonstrates the usefulness of Si as a standard material for infrared reflectance and transmittance.