Abstract. We illustrate an iterative method for retrieving the internuclear separations of N 2 , O 2 and CO 2 molecules using the high-order harmonics generated from these molecules by intense infrared laser pulses. We show that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. For linear molecules the internuclear separations can also be retrieved from harmonics generated using isotropically distributed molecules. By extracting the transition dipole moment from the high-order harmonic spectra, we further demonstrated that it is preferable to retrieve the interatomic separation iteratively by fitting the extracted dipole moment. Our results show that time-resolved chemical imaging of molecules using infrared laser pulses with femtosecond temporal resolutions is possible.

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Abstract. By numerically solving the time-dependent Schrödinger equation, we calculate the ionization probability of a vibrating H + 2 exposed to ultrashort intense laser fields. The results show that the ionization probability increases by time and gets a saturation value. We also find that with some first vibration levels, the ionization probability from a higher vibration level is larger than that from a lower one. However, with higher vibration levels, at a certain level the ionization probability will take maximum and decrease with next levels.

A new method of extracting interatomic separation of CO 2 is proposed based on using the dipole moment extracted from high-order harmonic generation (HHG) spectra. For this method, we show that the Bragg's equations related to the electron interference effect can be obtained from the zero-points of the dipole moment. Using not only HHG with parallel polarization but also HHG with perpendicular one we discover an error-compensation effect which means that the errors of interatomic separation extracted from the two components of dipole moment are always opposite in the sign. Therefore, the final result of the interatomic separation obtained by the proposed method has a very high accuracy with the systematic error less than 1%.

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