A laser flash lasts a few femtoseconds — imagine a single instant stretched into a million parts. Such a flash mixes many colors, from red to violet. Instruments that measure the pulse shape often err: they see some colors well and others poorly, blurring the picture.

The authors propose a simple fix. The pulse's light is passed through color filters, like colored glass slides. Each filter lets through only a narrow band of colors, which the instrument measures accurately. Then the bands are carefully stitched into a single overall picture. This technique is called spectral filtering and stitching.

The method was tested on three different measurement devices. One is the most common type; the other two are newer. In all cases, measurement accuracy improved markedly. Physicists will now be able to better control ultrashort laser pulses used in medicine, materials processing, and scientific experiments.