 The time it takes for electrons in atoms and molecules to react to intense lasers is measured using a calibrated clocking technique. The technique is based on measuring the difference in time between two separate ionizations caused by the same laser pulse. By comparing these times, the researchers are able to determine how long it takes for the electrons to react to the laser pulse. This article was authored by Jiayin Che, Chao Chen, Xiong Wang, and others.