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

Abstract

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 (QW's) since the intraband matrix elements do not vanish near the band center as they do in the bulk, and the density of states in QW's is larger near the band edge.Here we present a perturbation-theory based theoretical description of nondegenerate 2PA in semiconductor QW's, where both frequency and 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 degenerate 2PA in quantum wells along with degenerate and nondegenerate 2PA in bulk semiconductors. We show that using QW's in place of bulk semiconductors with both beams in the TM-polarized mode leads to an additional order of magnitude increase in the nondegenerate 2PA. Explicit calculations for GaAs QW's are presented.

Nondegenerate two- and three-photon nonlinearities in semiconductors

“…Thus, the largest enhancement occurs when the photon energies are very different from one another, so called extremely nondegenerate (END) enhancement. Similar enhancement is investigated here theoretically for semiconductor quantum wells [17], as well as for three-photon absorption in bulk semiconductors. This nondegenerate enhancement also applies to nonlinear refraction (NLR).…”

“…The ND-2PA in QW's is expected to be enhanced more near the band edge as the density of states and the transition matrix elements exceed those of bulk semiconductors [17]. Since QW's are anisotropic, the 2PA selection rules differ for the electric field polarized in the plane of the QW's (TE) and light polarized perpendicular to the plane of the QW's (TM).…”

“…Thus, TM-TM 2PA transitions are interband-intersubband, as shown in Figure 3(c). For the ND-2PA, an analytic expression is derived using second order perturbation theory both for TE-TE and TM-TM polarizations [17], which assumes an infinite QW. The ND-2PA coefficient for the TE-TE polarized case is …”

Nondegenerate two-photon absorption in GaAs/AlGaAs multiple quantum well waveguides

“…This form exhibits two improvements over that in Refs. [18] and [19], viz. M z jn,im = /(m j P ) χ j jn |p z |χ j jm .…”

“…Pasquarello and Quattropani [17] relaxed some of Shimizu's approximations and extended the analysis to nondegenerate photon pairs, predicting large enhancements as one photon energy neared an intersubband resonance. Pattanaik et al [18] quantitatively examined these nondegenerate resonance enhancements, expanding upon a six-band theory developed by Khurgin [19].…”