An experimental evidence of electromagnetically induce narrowing of an absorption line is presented. The width of this resonance is sub-Doppler and subnatural and it is confined between two closely spaced electromagnetically induced transparency windows.
A method is presented for obtaining sub-Doppler and subnatural narrowing and increased absorption of a spectral line. The ultranarrow spectral line is confined between two closely spaced electromagnetically induced transparency windows in a nearly degenerate tripod atomic system formed by an ${F}_{g}=1\ensuremath{\rightarrow}{F}_{e}=0$ transition, split by a magnetic field. The system is driven by a $\ensuremath{\sigma}$-polarized pump and probed by a tunable $\ensuremath{\pi}$-polarized laser. It can be used to measure small magnetic fields and also as a magneto-optic switch.
We demonstrate experimentally the effect of a three-photon electromagnetically induced transparency in hot 85Rb atomic vapor driven by two coherent electromagnetic fields. The narrow transparency window is observed on the background of high-contrast Doppler-free subnatural absorption resonance. Our analytical calculations and numerical simulations are in good agreement with the experimental data. Both the transparency and the absorption resonances can find applications in high-precision metrology.