High-harmonic generation sources can produce coherent, broadband radiation at extreme-ultraviolet and soft-x-ray wavelengths. The wavefronts of the generated high-order harmonics are influenced by the incident laser field, the generation conditions, and geometry. These influences depend on harmonic wavelength, which may result in wavelength-dependent focusing properties and spatiotemporal couplings that can affect attosecond physics experiments. We experimentally demonstrate and characterize these chromatic effects in high-harmonic generation by measuring the spectrally resolved high-harmonic wavefronts as a function of generation conditions. We find that the high-harmonic generation process can have significant intrinsic chromatic aberration, particularly for converging incident laser fields. Furthermore, we identify regimes where chromatic effects can be minimized, and show that analytical single-atom models allow accurate predictions of harmonic wavefronts produced by a specific driving field.

ERC , NWO , European Union's Horizon 2020
Phys. Rev. Res.
EUV Generation & Imaging

Liu, X., Pelekanidis, A., Du, M., Zhang, F., Eikema, K., & Witte, S. (2023). Observation of chromatic effects in high-order harmonic generation. Phys. Rev. Res., 5(4), 043100: 1–9. doi:10.1103/physrevresearch.5.043100