The Carrier-envelope Phase Effect On The Population Transfer Of Atoms Illuminated By Sub-cycle Laser Pulses

With the rapid development of ultrafast laser technology, the single-cycle and sub-cycle laser pulse has been implemented in some laboratory at many frequency bands. And the researches about the ultrashort laser pulse and the interaction between laser and atoms have becoming one of the most active researches in strong-field laser physics today. This thesis mainly studies the dependence of the population transfer of the atoms on the carrier-envelop phase of the sub-cycle laser pulse, with numerical simulation results of the time-dependent Schrodinger equation and the density matrix equations.First of all, we analysed the time-domain descriptions of sub-cycle laser pulse and introduced a new vector potential model with analytic envelope. This expression is the self-consistent which doesn’t contain any zero-frequency component and its spectrum is not correlated to carrier-envelope phase. This expression makes the investigation of the laser-matter interaction in the sub-cycle regime possible.With such an expression, we studied the interaction between a two-level atomic system with an intense sub-cycle laser pulse by numerically solving the density matrix equations (neglecting the relaxation effects). The effects of carrier-envelope phase on the population transfer of the atomic system are investigated with various parameters. We found that the initial state of atomic system is crucial to the results. Initially coherent two-level atomic system is much more sensitive to the carrier-envelope phase changes than incoherent one. And the oscillation period of the population transfer about carrier-envelope phase became2π. Apparently, these are two advantages in determining carrier-envelope phase of sub-cycle laser pulse.Finally, for the further verification to the results above, we numerically solve the time-dependent Schrodinger equation for a hydrogen-like atom interacting with the sub-cycle pulses. The dependence of population transfer between ground state and first excited state on the carrier-envelope phase are calculated. The results are similar to the two-level approximation model discussed above. Especially, for initially coherent states, both the enhancement of the population transfer and the change of the oscillation period about carrier-envelope phase have been further confirmed. These results indicate that, the two-level approximation is still applicable in this case.