Contents

04 June 2010
Vol 328, Issue 5983

About The Cover

Cover image expansion

COVER Multiple images of an object located between two nearly parallel mirrors illustrate the principle of superradiant emission of x-rays. If an ensemble of atoms between two mirrors is resonantly excited by synchrotron radiation, the atoms interact collectively to emit a fast x-ray photon pulse that exhibits a redshift of its frequency, known as the collective Lamb shift. See page 1248. Photo: Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany/Boris Kumicak