Theory of enhanced second-harmonic generation by the quadrupole-dipole hybrid exciton

We report calculated substantial enhancement of the second harmonic generation (SHG) in cuprous oxide crystals resonantly hybridized with an appropriate organic material (DCM2:CA:PS 'solid-state solvent'). The quadrupole origin of the inorganic part of the quadrupole-dipole hybrid provides inversion symmetry breaking and the organic part contributes to the oscillator strength of the hybrid. We show that the enhancement of the SHG, compared to bulk cuprous oxide crystal, is proportional to the ratio of the DCM2 dipole moment and the effective dipole moment of the quadrupole transitions in the cuprous oxide. It is also inversely proportional to the line-width of the hybrid and bulk excitons. The enhancement may be regulated by adjusting the organic blend (mutual concentration of the DCM2 and CA part of the solvent) and pumping conditions(varying the angle of incidence in case of optical pumping or populating the minimum of the lower branch of the hybrid in case of electrical pumping).