  We demonstrate the manipulation of transmitted light through an optical
Fabry-Perot cavity, built around a spectroscopy cell containing enriched
rubidium vapor. Light resonant with the $^{87}$Rb D$_{2}$ ($F=2/F=1$)
$\leftrightarrow F'$ manifold, is controlled by transverse intersection of the
cavity mode by another resonant light beam. The cavity transmission can be
suppressed or enhanced depending on the coupling of atomic states due to the
intersecting beams. The extreme manifestation of cavity mode control is the
precipitious destruction (negative logic switching) or buildup (positive logic
switching) of the transmitted light intensity, on intersection of the
transverse control beam with the cavity mode. Both the steady state and
transient response are experimentally investigated. The mechanism behind the
change in cavity transmission is discussed in brief.
