Abstract

Manipulating the group velocity of light has resulted in many advances, including slowing light to a car’s pace, stopping light and even forcing pulses to propagate faster than the speed of light in a vacuum. While the group velocity is equal to or less than the speed of light in a vacuum (<i>c</i>) when propagating through a medium exhibiting normal dispersion, anomalous dispersion allows the group velocity to be greater than <i>c</i>, or even negative. Strangely, the peak of a pulse propagating with a negative group velocity through a medium appears to exit the medium before entering it. This is a result of interference from spectral components of a pulse propagating with different phase velocities in the medium.

© 2012 Optical Society of America