  We demonstrate extremely narrow resonances for polarization rotation in an
atomic vapor. The resonances are created using a strong control laser on the
same transition, which polarizes the atoms due to optical pumping among the
magnetic sublevels. As the power in the control laser is increased,
successively higher-order nested polarization rotation resonances are created,
with progressively narrower linewidths. We study these resonances in the $D_2$
line of Rb in a room-temperature vapor cell, and demonstrate a width of $0.14
\, \Gamma$ for the third-order rotation. The explanation based on a simplified
$\Lambda$V-type level structure is borne out by a density-matrix analysis of
the system. The dispersive lineshape and subnatural width of the resonance
lends itself naturally to applications such as laser locking to atomic
transitions and precision measurements.
