Optical six-wave mixing via two forbidden transitions in the potassium atom

Optical six-wave mixing via two forbidden transitions has been studied in the potassium atom by resonant interaction with two tunable dye lasers. Despite the two quadrupole resonances, one in excitation and one in emission, the non-linear optical susceptibility responsible is significantly enhanced. Comparison is made with other forbidden non-linear schemes, realized by the same two-wavelength resonant excitation.