Photoionization-assisted resonant high-order harmonic generation from Sn iii states
Phys. Rev. A 113, 033518 – Published 16 March, 2026
DOI: https://doi.org/10.1103/hxfy-t2b8
Abstract
We observe experimental results that support photoionization-assisted resonant high-order harmonics from laser-ablated tin. Experiments were performed using pump lasers with wavelengths of 800, 1750, and 1780 nm. At 800 nm laser wavelength, we observe the splitting of the 17th-order harmonic into multiple components due to the presence of strong Sn iii transitions at 26.83 eV and 27.14 eV, in addition to the well-known strong Sn ii transition at 26.27 eV that generates single-harmonic enhancement as per the four-step model. For driving laser wavelengths of 1750 nm and 1780 nm, we observe multiple harmonic enhancements between 26 eV and 30 eV, where several strong transitions of Sn iii are identified. Despite the appearance of harmonics due to Sn iii transitions, the harmonic cutoff is similar to the values observed in previous studies in which Sn ii was the main harmonic emitter. These observations reveal that Sn iii does not directly participate in the harmonic generation process through the tunnel ionization of its valence shell electron, but rather appears in the harmonic spectra through the photoionization of the autoionization state of Sn ii.
