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We study the phenomenon of electromagnetically induced transparency andabsorption (EITA) using a control laser with a Laguerre-Gaussian (LG) profileinstead of the usual Gaussian profile, and observe resonances with width up to20 times below the natural linewidth. Aligning the probe beam to the centralhole in the doughnut-shaped LG control beam allows simultaneously a strongcontrol intensity required for high signal-to-noise ratio and a low intensityin the probe region required to get narrow resonances. Experiments with asecond-order LG beam show that transit time and orbital angular momentum do notplay a significant role. This explanation is borne out by a density-matrixanalysis with a radially varying control Rabi frequency. We observe theseresonances using degenerate two-level transitions in the $D_2$ line of Rb in aroom temperature vapor cell. We show that the linewidth is reduced by about afactor of 4 compared to the use of a Gaussian control beam, which should proveadvantageous in all applications of EITA and other kinds of pump-probespectroscopy.

Narrowing of resonances in electromagnetically induced transparency and absorption using a Laguerre-Gaussian control beam