OPTICAL 2ND HARMONIC-GENERATION FROM LOW-LYING EXCITED-STATES IN POTASSIUM VAPOR

Optical second harmonic generation has been observed on or near the 4s 2S1/2-6s 2S1/2, 4s 2S1/2-np 2P1/2, 3/2(n=5, 6) and 4s 2S1/2-nd 2D5/2, 3/2(n=3, 4) two-photon resonances in potassium vapour, as laser scanning in the 660-940 nm wavelength range. The second harmonic intensities and ionisation currents have been measured as a function of pumping laser detuning from the two-photon resonances. On or near the two-photon resonances, the intensity and vapour-density dependence of second harmonic generation have also been investigated. The saturation of second harmonic generation has been observed. Some calculations and analyses have been made with the chi (3)model. The results have been compared with the measurements. Based on these analyses, the mechanisms for second harmonic generation in isotropic vapours are discussed. © 1990 IOP Publishing Ltd.