A simple instrument to find spatiotemporal overlap of optical/X-ray light at free-electron lasers.

A compact and robust diagnostic to determine spatial and temporal overlap between X-ray free-electron laser and optical laser pulses was developed and evaluated using monochromatic X-rays from the Linac Coherent Light Source. It was used to determine temporal overlap with a resolution of ∼10 fs, despite the large pulse energy fluctuations of the monochromatic X-ray pulses, and covers a wide optical wavelength range from ultraviolet to near-infrared with a single configuration.