Terahertz Wave Radiation Of Helium Atom Driven By Intense Two-color Laser Fields

Under normal conditions,a terahertz wave which frequency within the range of0.1¹0THz(1 THz=10¹² Hz)is a special electromagnetic radiation,its wavelength was located between 0.03⁰.3 mm.The THz wave has many unique properties,for instance the lower quantum energy and blackbody temperature,wide frequency band,good coherence and strong penetrability etc.Therefore,THz wave has been widely used in many fields,such as physics,biology,chemistry,materials,medicine,information science and so forth.However,there is no widely used high power continuous THz source,so how to obtain stable and reliable THz wave source is one of the hotspots in the field of strong field physics in recent years.The main contents of this thesis are that:By solving the two dimensional time-dependent Schrodinger equation of a helium atom in a strong laser field,we studied the characteristics of the THz radiation of a helium atom interacting with a two-color intense laser in two dimensional case,the numerical results show that:the phase difference of two-color fields has a significant modulation effect on the yields of THz wave.Under the intense laser driver,the maximum yield of THz wave is obtained when the phase differences are equal to-5.0?and.055?,which is consistent with the results obtained from the photocurrent model.Compared with the quantum mechanical method and the photocurrent model,it is shown that the Coulomb field of the atomic core has little effect on the formation of currents by the free electrons for helium atom driven by intense laser field.In addition,the phase difference of the two-color field can be adjusted to obtain a half-cycle waveform with a pulse width of less than 30 femtosecond in time domain based on emission terahertz spectra.