High-Energy Photoexcitation in Solids

We formulate an expression for the single-electron photoexcitation cross section, $\sigma \left(\omega \right)$, exploiting the orthogonality of the final electron eigenstate to the occupied states of the excited solid. We find that $\sigma$ depends significantly on the final-state angular momentum. The predictions of a simple model calculation correspond closely with experimental photoabsorption in several metals, as shown explicitly for the $K$ shell in Li and the $K$ and $L$ shells in Al.