Infrared second-order optical susceptibility in InAs/GaAs self-assembled quantum dots

We have investigated the second-order nonlinear susceptibility in self-asse mbled quantum dots. The nonlinear susceptibility associated with intraband transitions in the conduction band and in the valence band is theoretically estimated for lens-shaped InAs/GaAs self-assembled quantum dots. The confi ned energy levels in the dots are calculated in the effective-mass approxim ation by solving the three-dimensional Schrodinger equation. Giant values o f nonlinear susceptibility, about six orders of magnitude larger than the b ull GaAs susceptibility, are predicted. We show that this enhancement resul ts from three key features: (i) the achievement of the double resonance con dition, (ii) the specific polarization selection rules of intraband transit ions that allow both in-plane and z-polarized transitions with large dipole matrix elements to be optically active, and (iii) the small homogeneous li newidth of the intraband transitions. The conclusions of the calculations a re supported by the measurement of the midinfrared nonlinear susceptibility in the valence band. The measurements have been performed using a picoseco nd free-electron laser. Both chi(zzz)((2)) and chi(zxx)((2)) components of the susceptibility tensor are observed. A satisfying agreement is found bet ween theoretical and experimental values.