Signatures of field-induced intramolecular quantum interference in high-order harmonic generation by laser-irradiated homonuclear diatomics

We report about the results of our theoretical study of the strong-field phenomenon of high-order harmonic generation (HHG) in homonuclear diatomics $H_{2}^{+}$ and$ H_{2}$ irradiated by a high-intensity laser field of mid-infrared wavelengths corresponding to intermediate values of the so-called \textit{Keldysh parameter} ($\gamma \le $1). The problem is addressed within the \textit{length-gauge} (LG) formulation of \textit{strong-field} \textit{approximation }(SFA) [1] additionally exploiting the \textit{density-functional-theory} (DFT) method for numerical composition of initial (laser-free) molecular state using the routines of GAUSSIAN-03 code [2]. The results of our present LG-VGA calculation well reproduce a pronounced interference-related minimum arising in high-frequency region of respective molecular HHG spectra and suggesting clear signatures of the field-induced \textit{intramolecular} interference [3] corresponding to photoelectron emission to intermediate continuum states from different atomic centers.\\[4pt] [1] M. Lewenstein \textit{et al.} \textit{Phys.Rev.A }\textbf{49}, 2117 (1994)\\[0pt] [2] M. J. Frisch and J. A. Pople. \textbf{Gaussian-03, Revision A.1} (Gaussian, Inc., 2003 Pittsburgh, PA)\\[0pt] [3] J. Itatani \textit{et al. Nature (London) }\textbf{432~}, 867 (2004); J. P. Marangos, ibid. \textbf{435}, 435 (2005); T Kanai \textit{et al. } ibid. \textbf{435~}, 470 (2005).