We have observed strong and unexpected subnatural width resonances of enhanced absorption in Rb vapour under particular experimental conditions. The resonances are polarisation dependent and appear to require a long atomlight interaction time.
Abstract Magneto-optical subnatural-linewidth resonances of electromagnetically-induced absorption (EIA) in an alkali vapour cell have been experimentally studied. The observation configuration includes using two counter-propagating pumps and probe light waves with mutually orthogonal linear polarizations, exciting an open optical transition in the 87 Rb D 1 line in the presence of argon buffer gas. The EIA signals registered in a probe-wave transmission reach an unprecedented contrast of about 135% with respect to the wide ‘Doppler’ absorption pedestal and 29% with respect to the level of background transmission signal. These contrast values correspond to a relatively small resonance full width at half maximum of about 7.2 mG (5.2 kHz). The width of the narrowest EIA resonance observed is about 2.1 mG (1.5 kHz). To our knowledge, such a large relative contrast at the kHz-width is the record result for EIA resonances. In general, the work has experimentally proved that the magneto-optical scheme used has very good prospects for various quantum technologies (quantum sensors of weak magnetic fields, optical switches and other photonic elements).
Velocity selective optical pumping effects in electromagnetically induced absorption for 85Rb atoms: polarization dependences
The paper report an experimental observation of the electromagnetically induced transparency (EIT) in the D 2 line of 85 Rb atoms. When a coupling laser for 5S 1/2 ,F=3→5P 3/2 ,F′ is Raman resonant to the probe laser in 5S 1/2 ,F=2→5P 3/2 ,F′ , EIT peaks apparently appear. Under certain conditions, absorption enhancement due to the electromagnetically induced absorption (EIA) was also recorded together with the EIT. A lambda coupling scheme with two strong lasers (a coupling laser and a pumping laser) was realized, the spectrum of the probe laser exhibits more complex structure, revealing rich quantum coherence interactions.
Positive and negative subnatural-width resonances (SNWR) were observed in the absorption and fluorescence of rubidium vapor under excitation by two copropagating optical waves with variable frequency offset. The two optical fields resonantly couple Zeeman sublevels, belonging to the same ground-state hyperfine level (GSHL), to an intermediate excited state. The SNWR present opposite signs depending on which GSHL participates in the interaction with the two optical waves. For both Rb isotopes an increase in the transparency with reduced fluorescence occurs for the lower GSHL while the absorption and fluorescence are increased for the upper GSHL. The influence of external magnetic field, polarization, and intensity of applied optical fields on the SNWR is examined. The narrowest observed resonance has a width of 10 kHz (full width at half maximum). The origin of the SNWR is discussed in terms of coherent processes involving ground-state Zeeman sublevels.