Experimental Investigation Of Excitation Dynamics Of High-Lying Rydberg Atoms Surviving The Intense Laser Fields

With the rapid development of laser technology,femtosecond laser pulse becomes an important tool to study the microstructure of matter in the scale of atoms and molecules and ultrafast dynamics of electrons inside.A series of interesting strong field non-linear phenomena have been found for atoms and molecules subject to strong laser fields,such as above-threshold ionization,high-harmonic generation and non-sequential double ionization etc.These phenomena are the hot issues in atomic and molecular physics.Recently,Rydberg atoms surviving strong laser fields have attracted a lot of attention.Although the suggested frustrated tunneling ionization(FTI)mechanism can explain some of the documented experimental results,other numerical calculations and experimental data are beyond the predictions of FTI.Most of the documented experimental data can study only the excited states with principal quantum number less than 30,here,a dedicated experimental procedure is employed to investigate the Rydberg states with principal quantum number equals to or larger than 100 to reveal the physical mechanism behind.The major elements of this thesis are listed below,1.The techniques for laser beam direction stabilization and intensity stabilization have been developed.The laser beam direction and intensity could be influenced by the external environment impact,which may further increase the instability of the measurements.To stabilize the beam direction,a position sensitive detector is employed to measure the position of the light spot.The measured signal will be introduced to a programmed computer,from which another control signal will be sent to a piezoelectric motor to control a mirror,where the beam is reflected.In this way,the feedback signal can be employed to stabilize the beam direction.As for the laser intensity,a similar feedback procedure is applied except that the intensity is controlled through a combination of half waveplate and a polarizer.2.We investigated the excitation dynamics of rare gas atoms subject to strong femtosecond laser field.The cold target recoil ion momentum spectroscopy(COLTRIMS)and 5kHz femtosecond laser system have been applied to measure the photoelectron-photoion-coincident spectrum,where the time dependence of the electron yields and the averaged energy of the ionized Rydberg atoms(AER)can be extracted.The atomic species,intensity,pulse duration,DC electric field strength dependence of the AER has been studied and compared to the semiclasscial calculations to reveal the physical mechanism behind.