Giant, triply resonant, third-order nonlinear susceptibility ${\mathrm{\chi }}_{3\mathrm{\omega }}^{\mathrm{}\left(3\right)\mathrm{}}$ in coupled quantum wells

A new coupled-quantum-well semiconductor with triply resonant third-order nonlinear susceptibility ${\mathrm{\chi }}_{3\mathrm{\omega }}^{\mathrm{}\left(3\right)\mathrm{}}$ has been designed and demonstrated using AlInAs/GaInAs heterostructures grown by molecular-beam epitaxy. In order to maximize ‖${\mathrm{\chi }}_{3\mathrm{\omega }}^{\mathrm{}\left(3\right)\mathrm{}}$‖ our structure has been tailored in such a way to maximize the product of the dipole matrix elements of the relevant intersubband transitions while maintaining nearly equal spacing between the electronic bound states of the quantum wells. Experimental values of ‖${\mathrm{\chi }}_{3\mathrm{\omega }}^{\mathrm{}\left(3\right)\mathrm{}}$‖ as high as ≃1×${10}^{\mathrm{-}14}$ (m/V${)}^2$ at 10.7-μm pump wavelength have been obtained, in agreement with theoretical estimates.