We present a rate-equation theoretical model describing the optical pumping processes on the K D_{1} line and we then discuss their influence on the electromagnetically induced transparency resonance parameters. We present also a comparison with the results of an experiment performed in cells containing pure alkali metal or added with a few torrs of buffer gas. The model shows that, in the last case, the complete Maxwellisation of the atomic population velocity distribution, along with the overlapping Doppler profiles of the transitions from the ground-states typical of K, leads to a partial compensation of optical pumping and a significant increase of the amplitude of the electromagnetically induced transparency resonances.
We present the observation of coherent population trapping resonances on the second resonance line of potassium: 4s^{2}S_{1/2} → 5 p^{2}P_{3/2} with wavelength of 404.4 nm. Moreover, a transfer of the coherent population trapping resonance occurs to the excited 4p^{2}P_{1/2} and 4p^{2}P_{3/2} states of the first resonance line due to cascade transitions. This transfer is evidenced by the observation of narrow resonances at the infrared 4s^{2}S_{1/2} → 4p^{2}P_{1/2} and 4s^{2}S_{1/2} → 4 p^{2}P_{3/2} transitions when alkali excitation is performed at the 404.4 nm violet line.
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