7th International Conference on Inertial Fusion Sciences and Applications
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英文:
Bordeaux
アブストラクト
Discharge produced plasma (DPP) is a promising tool to generate effective extreme ultraviolet (EUV) light. Hydrogen-like nitrogen is one of good candidates to get photons at 13.4 nm with an optical allowed atomic transition from n=3 to 2 (Balmer-alpha), where n stands for a principal quantum number. To get an optimum condition for the generation of 13.4 nm laser light, we focus on the properties of population inversion between n=3 and 2 in recombining phase. Population inversion is calculated in the framework of population kinetics and an inversion factor F is estimated.
So far, the competition between the increase in F and the reduction of the duration of the population inversion tau at higher plasma density was found, and it seems to be very critical to get enough GL, where G is a gain at 13.4 nm, and L is created plasma length. The higher plasma density is up to 10^19 cc ^-1, the higher F can be obtained and the shorter becomes tau. Since L can be estimated by ~c x tau, where c is a speed of light, tau is one of essential factors to determine the lasing property. In this scheme, nitrogen must be fully stripped and rapidly cooled, resulting in the large drop of plasma temperature.
In this study, dielectronic-capture ladderlike (DL) processes are considered [1]. These processes implicitly include autoionizing states, and enhance the population of the excited states of hydrogen-like nitrogen with n=3. Since nitrogen do not have to be fully stripped in ionizing phase to get the excited states, the necessary temperature drop may
be reduced. In the presentation, discussion will be devoted to the contribution of the DL processes to the creation of the population inversion.
[1] T. Fujimoto and T. Kato, Phys. Rev. A 32, 1663 (1985).
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