Coherent population trapping studied through energy transfer and energy-pooling collisions

The coherent population trapping phenomenon in sodium is probed through energy transfer and energy pooling collisions. Quenching of the excited state population (dark resonance) is measured through the detection of the collisional induced fluorescence up to sodium densities as large as 1015 cm−3. Two dark resonances have been studied and a different dependence on the sodium vapor density has been observed. For the first time an enhancement of the upper level population and, hence, of the collisional energy transfer processes has been measured correlated to the double coherent excitation.