Interaction of intense nanosecond pulses of extreme ultraviolet (EUV) with gases and solids (Conference Presentation)

Abstract

In this work investigations concerning interaction of intense, nanosecond EUV pulses with matter were performed. Various laser-produced plasma radiation sources were employed for creation of the driving EUV pulses. The sources were based on two different laser systems with pulse energies ranging from 0.8 J to 10J and pulse duration 4 ÷ 10 ns. They were equipped with the EUV collectors for focusing of the radiation. This way radiation fluence up to 0.5 J/cm2 in the interaction region was obtained. In our experiments solid material samples or gases injected into the vacuum chamber synchronously with the EUV pulses were irradiated. Irradiation of the gases resulted in ionization and excitation of atoms and molecules forming low temperature plasmas with a relatively high electron density. Emission spectra obtained from these plasmas, contained spectral lines corresponding to radiative transitions in atoms, molecules, atomic or molecular ions. For analysis of the EUV spectra numerical simulations were performed, using a collisional-radiative PrismSPECT code. For computer simulations of the molecular spectra measured in the UV/VIS range a LIFBASE and Specair codes were employed. This way ionization states together with various thermodynamic parameters were deduced. Irradiation of solid samples resulted in melting of a thin near-surface layer or, in some cases its ablation or even conversion to a low temperature plasma. It depended on physico-chemical properties of the material and its thickness. In case of organic polymers, usually ablation connected with fragmentation of the polymer molecules, took place. In case of thick samples of inorganic solids, a thin near surface layer was heated up to a high temperature exceeding melting or even boiling point. In most cases different kinds of micro- or nanostructures were created, modifying the surface morphology. Except the EUV interaction with solid materials, simultaneous EUV and the EUV induced plasma treatment was investigated. Plasmas were created in gases injected close to the exposed surface. Part of the EUV radiation was absorbed in the injected gas forming the low temperature plasma near the surface, while the other part of radiation, that was not absorbed, interacted with the surface material. This way additional atoms could be incorporated into the molecular structure of the exposed material, or reactive etching took place. Especially interesting results were obtained using molecular gases for creation the reactive plasmas.