Coherent hole-burnings induced by a bichromatic laser field

In a Doppler-broadened three-level Λ-type system driven simultaneously by a coupling laser and two equal-amplitude saturating laser fields with a frequency difference 2δ, the absorption spectrum of a weak probe laser exhibits multiple deep spectral holes through coherent hole-burning CHB with controllable numbers, widths, depths, and positions. More significant, changing δ or lasers directions, CHBs can degenerate into narrower and deeper spectral holes where the slope of the refractive index is very steep. The multiple narrow spectral holes in a single absorption profile are expected to have potential applications in high density storage, optical information processes, and slow-light.