High-order harmonic generation of 1-nonene under linearly polarized laser pulses

High-order harmonic generation of the long-chain molecule 1-nonene (C9H18) under a few-cycle linearly polarized laser field was studied using time-dependent density-functional theory. The efficiency and the cutoff frequency of the C9H18 harmonic spectrum are significantly higher than those of the BF molecule irradiated by the same laser pulse. By analyzing the time-frequency behavior of the harmonic and the classical simulation of electron, it is found that the C9H18 harmonics near the cutoff energy are caused by the recombination of electrons from one atom to others of the parent molecule. In addition, the high-order harmonic generation of the long-chain molecule 1,3-Butadiene (C4H6) is also investigated. The harmonics generated by this mechanism can be applied to produce high-intensity isolated attosecond pulses.