Efficient x-ray line production from laser excited CF_2Cl_2 clusters. Mixed cluster formation and control of the x-ray line yield

摘要

We report on effective x-ray generation under excitation of clusters of polyatomic CF_2Cl_2 molecules by femtosecond laser radiation of moderate intensity I ≈ 5 × 10~(15) W cm~(-2) (E ≈ 5 mJ). The maximal laser energy conversion efficiency to chlorine x-ray lines (E = 2.6-2.8 keV) reached 2 × 10~(-5) when the CF_2Cl_2 clusters were formed in the presence of the carrier gas helium. It was demonstrated that the spectrum of laser-induced x-rays can be used to detect mixed clusters, appearing in a 3% mixture of CF_2Cl_2 with Ar. We proposed adding a light thermalizing gas to the mixture, i.e., using a ternary mixture CF_2Cl_2-Ar-He, to control the fraction of components that the mixed clusters are composed of. We have given the first demonstration of a dual-energy x-ray source with a tunable line amplitude that is controlled by the helium fraction in the mixture.