New Method Measures Super-Fast, Free Electron Laser Pulses Using photoionization as an ultrafast, optical shutter, slow visible-light cameras can measure femtosecond extreme ultraviolet laser pulses New research shows how to measure the super-short bursts of high-frequency light emitted from free electron lasers (FELs). By using the light-induced ionization itself to create a femtosecond optical shutter, the technique encodes the electric field of the FEL pulse in a visible light pulse so that it can be measured with a standard, slow, visible-light camera. “This work has the potential to lead to a new online diagnostic for FELs, where the exact pulse shape of each light pulse can be determined. That information can help both the end-user and the accelerator scientists,” said Pamela Bowlan, Los Alamos National Laboratory’s lead researcher on the project. The paper was published April 12, 2021 in Optica. “This work also paves the way for measuring x-ray pulses or femtosecond time-resolved x-ray images.”