Surface dominance in high harmonic generation in AlN thin film

We performed measurements using the 17 fs pulses of a Ti:sapphire frequency comb at 108 MHz repetition rate. The beam was focused to a 30-nm-thick AlN (0001) film, grown on sapphire substrate. The on-axis peak intensity of 1.0±0.2 TW/cm 2 was suitable to observe intense 3 rd and 5 th order harmonics in the ultraviolet (267 nm) and vacuum ultraviolet (160 nm), respectively [1] .