Emission From Neutral Excited Neon Atoms In Strong Laser Fields

The atom excitation in the laser field is one of the frontier topics in the field of strong field physics research,which has been favored and valued by a large number of scientific research workers.At present,most of the methods for the excitation process of atoms in strong field are neutral excitation method and field ionization method.In this paper,the radiation characteristics of the inert gas Ne atom at 800 nm and 50 fs intense laser field are studied by using the fluorescence detection technique.The excited state of the Ne atom in the strong laser field is identified with the existing spectral knowledge.The influence of the laser parameters(light intensity,polarization state)on the fluorescence yield was studied.The physical mechanism of the Ne atom excitation process in the intense laser field was analyzed and compared with the results of pulsed ion field ionization-time of flight mass spectrometry.The main conclusions are as follows:(1)The emission fluorescence of the neutral excited state Ne atom is observed in the strong laser field with the pulse width of 50 fs and the wavelength of 800 nm.It is found that the fluorescence decay curve of excited state of the Ne atom can be decomposed into a fast decay process with a lifetime of less than 400 ns and a slow decay processwith a lifetime to the order of microseconds.(2)Through the fitting of the fluorescence decay curve,the lifetime of spontaneous emission of different excited states in the two processes is obtained.By referring to the known atomic spectrum data,we find that the fast process of fluorescence is a direct radiationfrom the excited state of low(n = 4-7)to 3p or 3s,while the slow process is anindirect process: higher Rydberg state(n > 7)relaxes to the n = 6-7 state and then radiates the fluorescence to the 3p or 3s.(3)We found that the fast process and slow process fluorescence yield dependence on the laser parameters are completely different.The dependence of the slow process fluorescence on the laser parameters is consistent with the results of the mass spectrometry measurements inspired by the strong field Rydberg state,indicating that the excitation state is generated by tunneling ionization induced by the Rydberg state.Further experimental study should be necessary to investigate the physical mechanism behind the fast fluorescence.