Electromagnetically induced transparency and optical switching in a rubidium cascade system

Electromagnetically induced transparency is observed in a mismatched-wavelength cascade system with a room-temperature rubidium vapor cell. A cw probe laser beam monitors the 5S(1/2) ? 5P(3/2) transition while another cw laser couples the 5P(3/2) state to a higher excited state. The ratio of the observed Rabi frequencies for coupling to the 5P(3/2) ? 8D(3/2), (5/2) transitions agrees well with that predicted by use of the transition oscillator strengths. Optical switching is demonstrated with an 80-mW coupling laser beam modulated up to 1 MHz.