Enhancement of Two-Photon Absorption in Quantum Wells for Extremely Nondegenerate Photon Pairs.

We recently demonstrated orders of magnitude enhancement of two-photon absorption (2PA) in direct gap semiconductors due to intermediate state resonance enhancement for photons of very different energies. It can be expected that further enhancement of nondegenerate 2PA will be observed in quantum wells (QWs), since the intraband matrix elements do not vanish near the band center, as they do in the bulk, and the density of states in QWs is larger near the band edge. Here, we present a perturbation-theory-based theoretical description of nondegenerate 2PA in semiconductor QWs, where both the frequency and the polarization of two incident waves can vary independently. Analytical expressions for all possible permutations of frequencies and polarizations have been obtained, and the results are compared with the degenerate 2PA in QWs along with the degenerate 2PA and the nondegenerate 2PA in bulk semiconductors. We show that using QWs in place of bulk semiconductors with both the beams in the transverse magnetic-polarized mode leads to an additional order of magnitude increase in the nondegenerate 2PA. Explicit calculations for GaAs QWs are presented. [ABSTRACT FROM AUTHOR]