Photoresponse of condensed matter over the entire range of excitation energies: Analysis of silicon

Methods for the analysis of experimental data to determine the photorespons e of condensed-matter systems over the entire spectral range are considered in light of sum-rule constraints imposed by quantum mechanics, causality, and linear-response theory. We outline an extension to elemental semiconduc tors of the self-consistent Kramers-Kronig method for constructing composit e sets of optical constants developed in the 1980s for metals. Several new sum rules relating the refractive index at infrared wavelengths to moments of the absorption spectrum are derived and illustrated for silicon.