The conversion efficiency of terahertz radiation produced by the filamentation of two femtosecond laser beams in highly charged noble gases

Optimizing the efficiency of the produced terahertz radiation is the central objective of terahertz research. In this article, we studied the conversion efficiency of terahertz radiation produced by the filamentation of two femtosecond laser beams in highly charged noble gases. In particular, we analyzed the correlation between this efficiency and both the binding energy and ionization level of these gases in order to determine the suitable air plasma structure for efficient terahertz production. In this respect, using a fluid code that refers to the photocurrent model, we numerically evaluated the conversion efficiency of the produced terahertz radiation as a function of the non-relativistic initial input beam intensity period ≈1014∼1017W/cm2 at different ionization levels of selected noble gases of different binding energies (He, Ne, Ar, and Xe). First of all, the numerical results have affirmed the inverse relation between the efficiency and the binding energy of the noble gases; in this case, the gases with lower binding energies were found to attain the highest efficient terahertz radiation at the lowest input intensity. In addition, the obtained results resolved the direct proportionality between efficiency and ionization level, where higher ionization levels considerably enhance the efficiency; for instance, the conversion efficiency of Ar reaches a value that is around 10−5 in the second ionization level, and at the fifth level, this efficiency escalates to an efficiency value that is above 10−4.