Time-resolved harmonic emission from aligned molecules in orthogonal two-color fields

We study the spectral and temporal properties of high-order harmonic generation (HHG) from aligned molecules in orthogonal two-color laser fields consisting of a strong fundamental field and its second harmonic. Numerical simulations show that the HHG depends strongly on the relative phase between these two colors and the molecular alignment. In particular, for some cases, HHG differs remarkably in consecutive half cycles of the fundamental field. As the emission of harmonics is very strong in a half laser cycle, it is weak in the following half. A simple model related to the molecular structure is proposed to explain these phenomena. Our results suggest a potential approach for generating trains of attosecond pulses with only one pulse per cycle over a wide energy region.