Isolated Attosecond Pulses

Hentschel et al.'s 2001 "Attosecond metrology" reported the first isolation and measurement of a single (not a train of) attosecond light pulse -- a distinct, harder technical achievement from observing a pulse train, achieved the same year by a different group. Modeled as a sibling of the Attosecond Pulse Trains Observation node (both build on the same 1996 theoretical framework but achieve different specific milestones), not a restatement of it. This is the pairing that is genuinely cited for the 2023 Nobel Prize (Krausz, L'Huillier, Agostini) -- the source list's "2023" year is the Nobel year, not the discovery year, same pattern as several other corrections in this dataset.