We investigate the dependence of the ionization probability of ${\mathrm{N}}_2$ in an intense laser field on the angle between the laser polarization direction and the molecular axis by recording the yield of ${\mathrm{N}}_2^{+}$ as a function of both the time delay between the pump and probe laser pulses and the polarization angle $\left(\mathrm{\Theta }\right)$ between the pump and probe laser polarization directions when the rotational wave packet of ${\mathrm{N}}_2$ is created by the pump pulse and ${\mathrm{N}}_2$ is ionized by the probe pulse. The Fourier transform of the delay dependence of the ${\mathrm{N}}_2^{+}$ yield exhibits peaks at the energy differences of the rotational levels of ${\mathrm{N}}_2$ with $J+2$ and $J$, with $J$ being the rotational quantum number of ${\mathrm{N}}_2$, and the polarization dependences of the amplitudes of these peaks are mainly given by the Legendre polynomial $P_2(cos\mathrm{\Theta })$. From the comparison with the analytical formula of the polarization dependent Fourier transform spectra, we partly determine the angular dependence of the ionization probability of ${\mathrm{N}}_2$ without estimating the molecular axis distribution of ${\mathrm{N}}_2$ prepared as the ensemble of the rotational wave packets. The resultant angular dependence of the ionization probability suggests the ionization induced by the photoelectron emission from the lower-lying $1{\pi }_{\mathrm{u}}$ orbital of ${\mathrm{N}}_2$ in addition to the highest occupied $3{\sigma }_{\mathrm{g}}$ orbital.

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• Multiphoton or tunneling ionization & excitation
• Rotational states
• Strong field ionization & excitation
• Ultrafast phenomena