  A new configuration for observation of magneto-optical subnatural-linewidth
resonances of electromagnetically induced absorption (EIA) in alkali vapor has
been verified experimentally. The configuration includes using two
counter-propagating pump and probe light waves with mutually orthogonal linear
polarizations, exciting an open optical transition of an alkali atom in the
presence of a buffer gas. The main advantage of the novel observation scheme
consists in the possibility of obtaining simultaneously high-contrast and quite
narrow nonlinear signals. Here a 2.5-cm long rubidium-87 vapor cell filled with
Ar buffer gas is used, and the excited optical transition is the F$_g$=2 $\to$
F$_e$=1 of the D$_1$ line. The signals registered reach a contrast of 57.7%
with a FWHM of 7.2 mG. The contrast with respect to a wide Doppler pedestal
well exceeds 100%. To our knowledge, to date this is the best result for EIA
resonances in terms of contrast-to-width ratio. In general, the results
demonstrate that the new magneto-optical scheme has very good prospects for
various applications in quantum metrology, nonlinear optics and photonics.
