Experimental And Theoretical Investigations On Atomic And Molecular Rydberg State Excitation In Strong Laser Fields

The peculiar nature of the Rydberg state of atoms or molecules makes it applicable to many fields of research. It is found that they can exist in many extreme environments, and they are extremely sensitive to extreme environments. With the continuous progress of laser technology, it was found atoms or molecules may also be populated to Rydberg state in the strong laser field. The Rydberg State Excitation(RSE) has become a new phenomenon of interaction between atoms and molecules and high intensity laser field, which attracts a great deal of attention from a lot of researchers.Although there are many research about the rydberg state excitation(RSE) process in intense laser field on theoretical and experimental, a lot of problems need to be solved in further research. Such as the RSE underlying mechanism in intense laser field is still not fully explored; little research about the neutral Rydberg excitation of molecules in strong laser field; the RSE of molecules fragments; the influence with different laser intensity and laser ellipticity; the influence of an additional magnetic field or electric field.In this dissertation, we study the RSE of atomic and molecules with a 800 nm, 50 fs ultrafast laser by applied a delayed static field ionization method to ionize the neutral rydbergs combined with a time-of-flight(TOF) mass spectrometer operated under a pulsed-electricfield mode. First, we measured the RSE yield of He?Ar?Kr atomic as a function of laser ellipticity and compared with the theoretical calculation results of three dimensional semi-classical model and strong-field approximation(SFA). We analyzed the physical mechanism in the RSE. Sencond, we measured the yield of CO?CO2, molucules and their companion atoms Ar in strong field single ionization, non-sequencial double ionization and strong field RSE as a function of laser parameter(laser ellipiticity and intensity) and studied the influence of diffrernt molecules HOMOs orbit on these physical process. Last, based on three dimensional semi-classical model we investigate the RSE of He atomic with an additional magnetic field parallel to the polarization of the laser pulse. The main results as followed:1)We experimentally investigate the ellipticity dependence of the RSE in strong laser fields for different atoms. It is observed that the RSE probability declines as increasing the laser elipticity. For He RSE,both the predications of the SFA model and the semiclassical calculations well reproduce the experimental results.For Ar and Kr, however, the measured RSE probability shows a wider distribution versus ellipticity than that of the SFA model, but closer to that of the semiclassical calculations, indicating the importance of the Coulomb effects in strong field RSE process. Analysis indicates that the decline of the atomic RSE in elliptically polarized laser fields could not be explained in the frame of tunneling-plus-rescattering scenario such as in HHG or NSDI. Instead, it is decrease of electrons with low kinetic energy with increasing laser ellipticity that leads to decrease of the probability of the tunneled electron to be captured in the Rydberg states by the Coulomb potential, indicating tight correlation between the RSE process and the low energy structure in ATI in the strong laser fields.2)We measured the strong field single ionization yield,double ionization yield RSE yield of CO and CO2 which have different HOMO orbit structure as a function of laser parameters,and compared with their companion atom Kr which have the same atomic ionization limit. Experiments revealed;the strong field single ionization yield of CO and CO2 have a similar laser intensity dependence with respect to its companion atom of Ar; there is a intensity dependence of the suppressed double ionization of CO2 with respect to its companion atom of Kr,but not exist in CO;there is a intensity dependence of the suppressed RSE of CO2 and CO with respect to its companion atom of Kr. By comparing with the previous studies we pointed out that the different HOMO orbit structure of CO and CO2 lead to them different photoelectron angular distribution and different two-center interference effect, finally lead to the different physical behavior of the above. In addition, we also observed the neutral fragments(C*?CO*?O*) from CO2 molecule. By measured these fragments as a function of laser ellipticity and intensity and compared with fragment ions we discuss the origin of these neutral fragments. Analysis shows that the neutral fragments produced not only can from the neutral parent dissociation,also their corresponding single ionization ions can capture the a freedom electron to be RSE in the parent molecule dissociation or coulomb explosion.3)Base on 3D semiclassical electron ensemble simulations, we investigate RSE of helium by using an additional magnetic field parallel to the polarization of the laser pulse. Results show that the RSE yield is obvious suppressed with the increase of magnetic field intensity. By analyzing the change of the low energy electron in RSE process, we point out that although the magnetic field can't change the distribution of low energy electron carry energy range(0-0.4 e V), but reduce the production rate of the low energy electrons, thus reducing the rate captured into RSE. Furtherly,we study the influence of magnetic field on the processes of RSE in elliptic polarized light. The calculation results show that when the magnetic field strength is 0.05 a.u., the RSE rate with laser ellipticity is equal to 0.1 is greater than the case in a linearly polarization laser. Analysis shows that through combination of laser polarization with external magnetic field, can effectively control the dynamics of tunneling electron in RSE process.