29 June 2001
Vol 292, Issue 5526

About The Cover

Cover image expansion

COVER Femtosecond optical pulses allow coherent operations to be performed on electron spins in semiconductors. A pump pulse excites spins whose precession about a magnetic field is recorded by a probe pulse. A third pulse tips the spins as they precess, inducing changes in the precession amplitude, shown here as a function of probe and tipping pulse time delay. Peaks occur when there is an effective torque between the tipping pulse and the electron spin. 2458 [Image: J. A. Gupta]