I GREATLY regret that in a note of mine on a “new mode of using the concave diffraction grating,” in the “Astronomical Column” of March 22 (p. 501), I wrongly interpreted a sentence of Prof Rizzo's ...

Scientists have made the first experimental observation of matter wave diffraction in a short-lived electron-positron atom.

It is widely assumed that diffraction places a limit on the smallest features that can be produced by light-based fabrication techniques, such as photolithography. This limit is typically about ...