Fig. 3

Dependence of high-harmonic spectrum with carrier-envelope phase of few-cycle pulse. Experimental data for carrier-envelope-phase (CEP) dependence of high-harmonic spectrum from a fused silica and b crystalline quartz at a peak laser field of 2 VÅ⁻¹. The dotted black lines trace the change in photon energy of harmonic peaks with CEP. The amplitude of CEP slope is ~3 eVπ⁻¹. The spectrum of fused silica repeats every π (horizontal axis) while there is a dominant 2π periodicity for crystalline quartz. The spectral minimum of crystalline quartz persists for all CEP settings. We note that the CEP values in the experiments are relative. c, d show the calculated high-harmonic spectrum from a quantum mechanical simulation of multi-level models. The insets show the respective energy levels and the couplings used in the simulations. The simulation results reproduce the periodicity and CEP slope of the experimental results