High-order harmonics of 248.6-nm KrF laser from helium and neon ions

We report high harmonic generation from a 248.6-nm KrF laser giving harmonic orders up to the 37th (67 {}) in a helium gas jet and the 35th (71 {}) in neon, for laser intensities up to 4 ×{} 10¹⁷ W/cm² in 380-fs pulses. These observations are interpreted using theoretical modeling that identifies the ion species He⁺, Ne⁺, and Ne²⁺ as the sources of the highest harmonics.