Atomic spectral detection of tunable extreme ultraviolet pulses

A novel method of detecting the spectral width and wavelength of extreme ultraviolet (XUV) pulses with a minimum number of experimental tools is demonstrated. The method relies on the photoionization probability of an atom as a function of the electric field. A tunable laser source in the XUV is used that is based on higher-harmonic generation of the frequency-doubled output of a ~50-fs Ti:sapphire laser. The bandwidth and the wavelength of the seventh harmonic 57 nm are detected with Ne, and the resolving power is l / D l =10⁵.