Above-threshold ionization was first observed in 1979.
Notes on verification
Confirmed by multiple independent high-quality sources including the original 1979 Physical Review Letters discovery paper by Agostini et al., a PNAS paper, a Europhysics News article on the 2023 Nobel Prize, a ScienceDirect review, and an OSTI/DOE report. All sources consistently date the discovery to 1979.
Sources
- Above-threshold ionization (en.wikipedia.org)
- https://www.sciencedirect.com/science/article/abs/pii/0370157391901315 (sciencedirect.com)
- https://www.pnas.org/doi/10.1073/pnas.1719481115 (pnas.org)
- https://www.europhysicsnews.org/articles/epn/pdf/2023/05/epn2023545p8.pdf (europhysicsnews.org)
- https://www.osti.gov/servlets/purl/1801056 (osti.gov)