Fig. 1. Energy levels and preparation scheme of low excited states (n≤3) of He atoms

Fig. 2. Population transfer from 1s ground state to 2p excited state of He atoms under different laser peak intensities. (a) 4.50×1013 W?cm-2; (b) 8.20×1013 W?cm-2; (c) 1.63×1014 W?cm-2; (d) 3.20×1014 W?cm-2

Fig. 3. Population transfer from 1s ground state to 3p excited state of He atoms under different laser peak intensities. (a) 9.96×1013 W?cm-2; (b) 3.80×1014 W?cm-2

Fig. 4. Population transfer from 2p state to 2s state of He atoms under different laser peak intensities. (a) 7.70×109 W?cm-2; (b) 3.10×1010 W?cm-2

Fig. 5. Population transfers from 1s ground state to 3s and 3p excited states of He atoms under different laser peak intensities. (a) 2.10×1011 W?cm-2; (b) 4.00×1011 W?cm-2

Fig. 6. (a) Wavefunctions of 1s ground and 2p excited states of He atoms; (b) time evolution of electron wavepacket along z axis in a laser field; (c) adopted laser field