ELECTROMAGNETICALLY INDUCED ABSORPTION AND TRANSPARENCY DUE TO RESONANT 2-FIELD EXCITATION OF QUASI-DEGENERATE LEVELS IN RB VAPOR

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. Th e two optical fields resonantly couple Zeeman sublevels, belonging to the same ground-state hyperfine level (GSHL), to an intermediate excit ed state. The SMWR present opposite signs depending on which GSHL part icipates in the interaction with the two optical waves. For both Rb is otopes an increase in the transparency with reduced fluorescence occur s for the lower GSHL while the absorption and fluorescence are increas ed for the upper GSHL. The influence of external magnetic field, polar ization, and intensity of applied optical fields on the SNWR is examin ed. 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 coh erent processes involving ground-state Zeeman sublevels.