Formation and direct writing of color centers in LiF using a laser-induced extreme ultraviolet plasma in combination with a Schwarzschild objective

摘要

In order to generate high-energy densities of 13.5 nm radiation, an extreme ultraviolet (EUV) Schwarzschild mirror objective with a numerical aperture of 0.44 and a demagnification of 10 was developed and adapted to a compact laser-based EUV source. The annular spherical mirror substrates were coated with Mo/Si multilayer systems. With a single mirror reflectance of more than 65percent the total transmittance of the Schwarzschild objective exceeds 40percent at 13.5 nm. From the properties of the EUV source (pulse energy 3 mJ at 13.5 nm and plasma diameter approximately 300 (mu)m), energy densities of 73 mJ/cm~(2) at a pulse length of 6 ns can be estimated in the image plane of the objective. As a first application, the formation of color centers in lithium fluoride crystals by EUV radiation was investigated. F_(2), F_(3), and F_(3)~(+) color centers could be identified by absorption spectroscopy. The formation dynamics was studied as a function of the EUV dose. By imaging of a pinhole positioned behind the plasma, an EUV spot of 5 (mu)m diameter was generated, which accomplishes direct writing of color centers with micrometer resolution.