Manipulating harmonic emission with excited states of N₂

Molecular wave functions are used to calculate the harmonic emission of diatomic molecules based on a time-dependent Schrödinger equation. Tunable effects are shown for both magnitudes and molecular-alignment-dependent properties of the harmonic emission with different electronic excited states or mixed states as the initial states. The calculated results are consistent with the experimental results of harmonic signals from N₂ under different rotational temperatures and laser intensities. The molecular-alignment dependence of harmonic signals is rapidly weakened with increasing levels of electronic excited states. Especially when the initial state of N₂ is the first electronic excited state, B³  _g, the magnitudes of the 21st harmonic are significantly changed, and the molecular-alignment dependence of the harmonic shows reverse properties compared to those of the ground state, X¹  , which can be used to manipulate the harmonic emission. ©2010 The American Physical Society