Abstract

Electromagnetically induced transparency (EIT) has been the subject of many experimental and theoretical studies over recent years.¹ Most recently, substantial experimental and theoretical work in this area has been focused on the use of EIT to give ultraslow group velocities for light in both ultracold atomic gas² and hot atomic vapors.^3-5 Much of this interest is based on the fact that slowing the group velocity of a laser pulse down to the speed of sound in the same material can produce strong coupling between acoustic waves and electromagnetic field.⁶ It has been suggested that a giant nonlinearity obtained by this method might be utilized for efficient multi-wave mixing and quantum nondemolition measurements.⁷ Slow light might also allow a very efficient nonlinear interaction between laser pulses of extremely low (down to a single photon) energies.⁸ Here, we report the first direct observation of an ultraslow group velocity of light down to 45 m/s in a solid, well below the speed of sound in the medium.

© 2001 Optical Society of America