Donna Strickland, special speaker at the Physics Department's general seminar.

Capturing images ever more rapidly in order to study the unfolding of natural phenomena in ever greater detail is a scientific and technical challenge with a long history. Donna Strickland is one of its leading figures. This Canadian physicist, professor at the University of Waterloo and winner of the 2018 Nobel Prize in Physics, was the guest speaker at the general seminar of the École Polytechnique Physics Department.

While working on her thesis at the University of Rochester with Gérard Mourou, Donna Strickland discovered the CPA (Chirped Pulse Amplification) laser amplification technique, which produces pulses that are both ultrashort and very intense. It consists in temporally stretching a laser pulse before amplifying it and then recompressing it. 

To observe a fast-moving phenomenon, you need to be able to capture images or signals in less time than the total duration of the process. This is far from easy to achieve in practice, when these phenomena last barely a few femtoseconds - a millionth of a billionth of a second - typically the scale involved in molecular vibrations, or even a few attoseconds, a duration a thousand times shorter. At these scales, where cameras no longer function, only ultrashort laser beams can illuminate and capture the scene. 

To create such laser pulses, you need a physical process capable of generating light over a wide frequency range, and you also need to ensure that all these light waves are in phase. Donna Strickland's current research, detailed in this seminar, is fundamental to understanding the physics of such a process, multi-frequency Raman generation. 

The video of this seminar will soon be available on the Physics Department website.