Use Odd And Even High-order Harmonics To Probe The Structure Of Polycentric Molecules

The high order harmonic generation(HHG)and ionization of atoms and moleculars in strong laser field are the hot research topic in physics which attract wide attention in theorical and experiment for the past few years.The two research hot spots,ionization and high order harmonic generation that in strong laser field become deeper along with the process of modern science and rechnology.The inrestigation of higher order harmonic generation and ionization in strong laser field enables people to watch the process of electrons movement in the attosecond time scale,which provides an unprecedented condition for the development and improvement of the quantum theory.In recent years,attention has been paid mainly to HHG from two-center molecules,such as H2,N2,HeH2+,CO,and NO.It was revealed that two-center interference are responsible for the suppressed harmonics at certain orders and the minima in harmonic spectra may shift as the intemuclear separation changes.By measuring the interference minima in the HHG spectra,the HHG can also be used to probe molecular instantaneous structures.As attention increasingly turns to polyatomic molecules in intense fields,it would again be useful to start with the simplest system.A few pioneering calculations for mostly the simplified linear configurations in recent years.For multi-center linear asymmetric molecules interest in HHG is increasing.HHG is more complex in the latter cases.In the present paper,by numerically investigating the HHG from multi-center linear molecules such as H32+ and H43+ with different internuclear distances,we find that the position of minima of odd harmonic spectra is largely independent on the internuclear separation.Specifically,when the intemuclear distances between these three nuclei of the molecule have a small change,the odd spectra do not change basically,but the even spectra differ remarkably.But the relative yields of odd-even harmonics at diverse internuclear distance differ significantly from each other.we show that the intersections of odd-even harmonics can be used as a sensitive tool to probe the position of the nuclei of the multi-center linear asymmetric molecules,such as H32+ and H43+.As a result,the relative yields and intersections of odd-even harmonics are characterized by the corresponding orientation angles and molecular bond-length.Our simulations imply that the instantaneous bond-length of different molecular configuration can be reconstructed using odd-even harmonics at different angles by analytical method.With the sensitivity of even spectra to the internuclear distance,a procedure is proposed to probe this distance using the relative yields of odd versus even HHG spectra.