N-type resonances in Cs D2 lines are investigated in optical cell for different detuning of the fixed coupling transition frequency. Using two independent DFB lasers makes it possible to observe high contrast and subnatural-width N-resonances without magnetic field shielding of an optical buffer gas cell with sub-centimeter dimensions. According to the detuning of the coupling laser frequency, an N-resonance with frequency higher or lower than this of the coupling transition frequency is registered. In the first case the N-resonance is in absorption, but in the second case, an inverse N-resonance (enhanced transparency) is measured. A theoretical simulation of the line shape, which is based on solution of optical Bloch equations and considers the interaction of both coupling and probe radiations with the atomic system is done. The simulation leads to N-resonance peaks in agreement with the observed peaks for different positions of the coupling frequency. The presented approach is of importance for further study and optimization of the three-photon and magneto-optical resonances, as well as for miniaturization of optical sensors based on spatially restricted hot alkali vapor.

We present the first experimental observation of narrow dips in the fluorescence profiles of completely closed hyperfine transitions in Rb vapor at high atomic density, which is attributed to the depolarization of the excited state. Moreover, at low atomic density, a narrow peak on the top of the fluorescence profile is demonstrated, centered at the completely closed transition within the D2 line of Cs. Experiments are performed in thin (700 µm) alkali cell by single light beam spectroscopy. The cell is filled with Cs containing a small portion of Rb.