Oops!

The wrong illustration appeared with a news story on femtosecond imaging of atomic particles in our May issue ("Synchrotron produces ultrafast pulses," p. 34), for which we apologize. To undo the confusion we here print the correct figure with its caption.

Femtosecond laser pulse interacts with ALS electron beam (green) through resonantly tuned wiggler (a). Bend magnets separate modulated electrons (b). Mirror separates femtosecond synchrotron radiation (c).