Quantum Effects Of Rydberg State Excitation In Intense Femtosecond Laser Fields

The interaction of femtosecond intense laser fields with atoms and molecules produce many novel nonlinear physical processes which were induced by strong field tunneling ionization,Rydberg state excitation is considered to be an important complement to the these strong field physical processes.Compared with particle detection,measurement with quantum state discrimination could be realized in the fluorescence spectrum,in the meantime,the time-domain characteristics of the evolution of the Rydberg state and the yield dependence on the laser parameters could be also obtained,which is very helpful for the understanding of the excitation mechanism and quantum state distribution of Rydberg state excitation in intense laser fields.The radiation research provides a new method for the study of the strong field excitation in femtosecond laser fields,and also provides a thought for generating new ultrafast coherent light.This dissertation mainly studied the fluorescence spectrum of Ne atoms in femtosecond laser fields;the intensity and time-domain characteristics of fluorescence were measured as a function of experiment parameters,such as gas pressure,laser intensity and ellipticity.The innovation achievements in this dissertation are as follows:1)The fluorescence spectrum of Ne atoms under different femtosecond laser fields was studied.By measuring the variation of the Rydberg Ne atom yields with the laser ellipticity,and compared with the calculated results of strong field approximation model,the physical mechanism of the Rydberg state excitation under different laser fields was identified.It is found that the Rydberg states produced by different mechanisms have different time domain characteristics.Rydberg states with relative large angular quantum number were produced by frustrated tunneling ionization mechanism,and the intrinsic causes are analyzed combined with semiclassical calculations.2)Combing with the method of real-time monitoring of laser pulse energy,the dependence of fluorescence yield of Ne atoms on the laser intensity was studied,an oscillating structure with a period of 25 TW/cm~2(200 TW/cm~2)was observed in the800 nm(400 nm)laser fields,which is consistent with the channel-closing effect.The results show that obvious quantum effect exists in the strong-field Rydberg state excitation.