Cavity-linewidth narrowing in a ring cavity that is due to the high dispers
ion and reduced absorption produced by electromagnetically induced transpar
ency (EIT) in rubidium-atom vapor has been experimentally observed. The cav
ity linewidth with rubidium atoms under EIT conditions can be significantly
narrowed. Cavity-linewidth narrowing was measured as a function of couplin
g beam power. (C) 2000 Optical Society of America.