Using an effect related to electromagnetically induced transparency, scientists at Harvard University in Cambridge, Mass., have stopped pulses of light in an atomic medium and released them a few microseconds later. The development opens prospects in the manipulation of light, including new types of efficient nonlinear optical processes at very low light levels. An account of the work appears in the Dec. 11 issue of Nature.

Similarly to their experiments in 2001, the researchers prepared a 4-cm-long vapor cell containing ⁸⁷Rb atoms at 90 °C by optically pumping it to the ground state with a Ti:sapphire laser. They then injected a 5-µs-long signal pulse from an extended-cavity diode laser. The atoms store the state of the pulse in atomic spins until it is retrieved by the reapplication of the control laser.

In the new work, a standing wave that was generated by the simultaneous reapplication of counterpropagating beams from the Ti:sapphire laser confined the retrieved signal pulse in the atomic medium. The counterpropagating control fields created the equivalent of a hall of mirrors from which the pulse could not escape until one of the control beams was turned off.