Femtosecond laser excitation of mixed Ar/Kr clusters: peculiarities of K-line x-ray production from nanoplasma under varied fraction of initial gas components

摘要

For the first time, we defined the range of krypton fraction (C-Kr) in an initial binary Ar-Kr gas mixture that provides the production of large (N similar to 10(6) atoms/cluster) mixed Ar/Kr clusters under co-expansion of the mixture at room temperature and the stagnant pressure of 25 bar. Mixed Ar/Kr clusters exist at the krypton fraction of 3-15%. The presence of mixed clusters is detected by the simultaneous generation of both x-ray K alpha lines of argon (E = 3.1 keV) and krypton (E = 12.7 keV) from nanoplasma originating as a result of femtosecond nonlinear laser excitation with intensity about 5.10(17) W cm(-2). It was shown that the amplitude of lines in dual-energy x-ray spectrum can be controlled by proper selection of the fraction of initial gas mixture components. Maximal laser energy conversion efficiency to krypton x-ray line is achieved for pure krypton clusters (i.e. C-Kr = 100%) and reaches 2.10(-7) at laser intensity of 5.10(17) W cm(-2). The laser energy conversion efficiency to argon x-ray line reaches the maximal value of 3.10(-6) at C-Kr = 0%.