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The experiment involving Ferenc Krausz combined a subfemtosecond soft-X-ray pulse with a few-cycle visible electric field. Its delay-dependent krypton photoelectron spectra tested the field-controlled response. The reported pulse duration was $650\pm 150$ attoseconds. Changing delay compared the emitted electron distributions at different reference phases; the spectral-width trace supplied a further duration-sensitive observable.^[ref]

The distinction from RABBITT is the measurement regime and reconstruction, rather than merely calling one trace a clock. The attosecond streaking momentum map is a limiting model; a finite-duration wave packet requires a quantum transition calculation. Inferring an emission delay also requires separating the illuminating pulse's spectral phase from the target response. The measurement supports time-dependent photoionization in a specified model, with no unique classical electron trajectory inside an atomic orbital implied.

Ferenc Krausz coauthored a 2001 demonstration of attosecond timing using photoionization. A synchronized visible electric field changes the energy distribution of photoelectrons released by a soft-X-ray optical pulse. Scanning their relative delay converts an otherwise inaccessible time interval into a measured electron spectrum. The report inferred a soft-X-ray duration of $650\pm 150$ attoseconds and demonstrated an instrument for probing electron dynamics on that scale.^[ref]

A physicist who leads research in attosecond physics.^[ref]

An experimental optical physicist who coauthored attosecond pulse measurements. Combining a short extreme-ultraviolet excitation with a synchronized optical field lets emitted photoelectrons carry information about the pulse's timing. This makes a subfemtosecond optical event measurable through an electron-energy distribution rather than by an electronic stopwatch.^[ref]