Power dependence of the coherent-population-trapping resonances registered in fluorescence and transmission: Resonance-width narrowing effects

The investigation of the coherent-population-trapping (CPT) resonance on the degenerate two-level system of the $({F}_{g}=2\ensuremath{\rightarrow}{F}_{e}=1)$ transition of the $^{87}\mathrm{Rb}\phantom{\rule{0.3em}{0ex}}{D}_{1}$ line by means of a Hanle effect configuration in an uncoated vacuum cell [Opt. Lett. 28, 1817 (2003)] has shown that the measured in fluorescence resonance has a complex shape---a very narrow (about 1 mG) structure superimposed on a broader one (about few tens of mG). In this work, the dependence of the width and amplitude of the CPT resonance structures are measured at different laser power densities when the registration is in fluorescence and transmission. While the narrow resonance width does not change within the limits of the accuracy of our measurements, the wide resonance width dependence is complex and is different in fluorescence and transmission. The origins of the observed resonance width narrowing of the CPT resonance structures registered in fluorescence and transmission are discussed.