STUDY OF THE 5P(3 2)-4S(1/2) EMISSION IN K UNDER 2-PHOTON 4S(1/2)-6S(1/2) EXCITATION/

It is shown that by proper use of the excitation spectra, the emission spectra of the 5P(3/2)-4S(1/2) transition and the far-field patterns it is possible to distinguish between competing processes involved in the two-photon excitation to the 6S state of potassium, namely: (a) re sonant fluorescence emission associated with the cascading spontaneous emission (ASE) and (b) the four-wave mixing parametric process. The e ffect of the buffer gas on the intensities of the spectra of the radia tions emitted is discussed. Conical emission and spatial instabilities of the excitation radiation and the 5P(3/2)-4S(1/2) emission were als o observed for high excitation and high vapour pressure of potassium.