Alignment And Orientation Of Linear Molecule In Laser Field

The oriented and aligned molecules are very useful for in a variety of fields ,such as molecular reaction,nanoscale design, quantum information,etc.In this thesis, we focus on the theory for the interaction of linear molecule with laser field ,we are interested in orientation and alignment,especially.We based on the numerical calculation for a quantum mechanical treatment of molecules and their interaction with the external field,using the software of Matlab,carrying through the research of molecular orientation and alignment.At first, we describe molecular system in qutanum theory, particular we give a fundamental theoretical description of molecular rotation properties. In this case, we calculated the wave function of the system , combining Four Order Runge-Kutta Method,and then we received the alignment and orientation of typical molecule CO, N2O in laser field later.Moreover, we only study the alignment by polarized interaction under the nonresonant laser field because the dipole interaction can be quenched,we can attain certain alignment through polarization effect by Raman excited. Molecular orientation is more difficult than alignment as an additional spatial symmetry breaking scheme has to be involved.In particular ,the half-cycle(HCP),serve as powerful tool to realize molecular orientation under field-free condition.Because of it's highly asymmetric in its positive and negative field strengths.In this thesis, we investigate the alignment of CO and N2O, the orientation of the molecule N2O in a half cycle field.The results show that for a short-pulse, there will be more or less alignment or orientation effects left after the laser pulse turned off, and even the recurrences periodly .An intermediate case that occurs for a pulse between long and ultrafast pulsed laser,when laser turned on pendular states appear just like molecules in long pulsed laser and when laser turned off recurrences periodly as that in ultrafast pulsed laser case, but the coherence is weak and period of is poor and irregular. Under a HCP,the of small polar molecular recurrences periodly and faint,the max.only exceed 0.2.when we strengthen the intensity of electric field ,it's improved littly,i.e.the in fluence of intension to the orientation degree.So we have to find other methods to improve the orientation. Because it's moment is little ,that the molecule is not sensitive to the external fields. As a result,we advise people to introduce HCPs or combination ofωand 2ω.In conclusion,the orientation and alignment of molecule have luciferous future, require us to do futher research.