Two-photon absorption in silicon using the real density matrix approach

Two-photon absorption in indirect gap semiconductors is a frequently encountered, but not well-understood phenomenon. To address this, the real-density matrix approach is applied to describe two-photon absorption in silicon through the excitonic response to the interacting fields. This approach produces an analytical expression for the dispersion of the two-photon absorption coefficient for indirect-gap materials and can be used to explain trends in reported experimental data for bulk silicon both old and new with minimal fitting.