Theoretical study on the nonlinear absorption of a strong electromagnetic waves in infinite semi-parabolic plus semi-inverse Squared Quantum Wells (ISPPSISQW) by using quantum kinetic equations for electron in the case of electron-acoustic phonon scattering. Analytical expressions for the nonlinear multi-photon absorption coefficient in the ISPPSISQW are obtained for a specific GaAs/GaAsAl in the case off the absence and the case of the presence of an external magnetic field B. A second- order multi-photon process is included in the result. The dependence of the nonlinear multi-photon absorption coefficient on the intensity
(E0) and the frequency
(Ω) of a strong electromagnetic wave, confinement frequency of ISPPSISQW
(Ω) and the temperature investigated. The numerical computations for a specific ISPPSISQW GaAs/GaAsAl show that the nonlinear multi-photon absorption coefficient decreases rapidly with increasing
ωz or
Ω and the nonlinear multi-photon absorption coefficient increases rapidly
E0 or T. In the case of the presence of an external magnetic field B, numerical calculations indicate the occurrence of magneto-photon-phonon resonances when the resonance conditions are met. As the photon energy changes, the resonance peaks tend to increase with the increase in photon energy.
We have considered one-dimensional organic conjugated polymeric systems to study the two-photon absorption (TPA) processes. The symmetrized density matrix renormalization group (SDMRG) method has been used to compute the low-energy photonic states and the TPA coefficients, for an extended Hubbard model. We find that the TPA coefficients diverge when the ground state of the system changes from the spin-density wave (SDW) state to the charge-density wave (CDW) state. Although in both phases the system is an insulator, the one-photon and two-photon gaps almost become equal near the transition point. The reason for the TPA coefficients to diverge is the near-degeneracy of these photonic states with strong electric dipole couplings at the transition point region. The picosecond scale nonlinear absorption processes observed in charge transfer insulating systems can be explained due to the formation of a triplet band below the lowest optically allowed state, based on our model calculations.