He transformed chemistry from a science of "before and after" into a science of "during." Because of Zewail, we no longer have to imagine the dance of atoms—we can watch it.
Zewail's work led to the birth of femtochemistry, a field that seeks to understand the dynamics of chemical reactions at the femtosecond timescale. His research group at Caltech developed innovative techniques, such as pump-probe spectroscopy, to study the ultrafast dynamics of chemical reactions. These techniques enabled Zewail and his colleagues to visualize the transition states of chemical reactions, providing unprecedented insights into the mechanisms of chemical transformations.
In the late 1980s, Zewail developed a technique using ultra-short laser pulses. Imagine a strobe light at a disco so fast that it freezes water falling. Zewail’s laser "strobe light" fired pulses lasting just a few femtoseconds. He would fire one pulse (the "pump") to start a chemical reaction, and then fire a second, delayed pulse (the "probe") to take a snapshot of the molecules in that exact moment.