Angular Dependence of High-order Harmonic Generation from Nonadiabatically Aligned Molecules

Abstract

We measured the dependence of high-order harmonic generation (HHG) on the angle α between polarization directions of high-intensity femtosecond laser pulses in the pump and probe experiment. The experimental results of N 2 and O 2 are compared with the calculated ones using the theory developed recently to illustrate the characteristic properties of HHG from aligned N 2 and O 2 , and then the excellent agreement is obtained. It is also shown that the observed α-dependent harmonic signal is strongly influenced by the degree of alignment of molecules and is not identical to the harmonic distribution calculated as a function of the angle between the field direction and the molecular axis.

Strong-field ionization of the triplet ground state of O2

“…Only at the highest fluence does the revival pattern resemble the structure familiar from spinless diatomic molecules. For these reasons, earlier experiments on the SFI of oxygen were not sensitive to the triplet nature of its ground state [21,28,29,32].…”

“…Recently, a detail study of rotational wave packets expected to be produced by impulsive alignment in triplet oxygen has been investigated theoretically [23]. However, in most past studies [11,21,22,[24][25][26][27][28][29][30][31][32], these peculiar dynamics were not observed, and O 2 could be approximated as a spinless molecule. In this article, we show that rotational dynamics in ground-state O 2 can be highly nonperiodic when the rotational temperature is kept low and the pump is weak enough to limit the rotational wave packet to small values of rotational angular momentum.…”