Exploration of Below-Threshold Harmonic Generation Mechanisms of Cesium Atoms in Intense Mid-Infrared Laser Pulses

摘要

We present a non-perturbative quantum study of high-order harmonic generation (HHG) of Cesium atoms in intense mid-infrared laser pulses. An accurate angular-momentum-dependent model potential is constructed for the high-precision description of the Cs atom electronic structure. The three-dimensional time-dependent Schrodinger equation is solved accurately and efficiently by means of the time-dependent generalized pseudospectral methods (TDGPS) [Tong and Chu, Chem Phys 217(2-3), 119-130 (1997)].Besides the expected odd harmonics, the calculated HHG power spectra show additional structures due to the strong 6s-np couplings. The spectral and temporal characteristics of the HHG are further explored through the wavelet transformation [Tong and Chu, Phys Rev A 6102(2), 21802 (2000)]. As a result, we can investigate the prevailing mechanisms in different energy regimes, especially those contributing to the below- and near-threshold harmonics [Power et al., Nat Photon 4(6), 352-356 (2010); Soifer et al., Phys. Rev. Lett. 105(14), 143904 (2010); Yost et al., Nat Phys 5(11), 815-820 (2009)].