Reflective optics for effective collection of x-ray and EUV radiation: use for creation of photoionized plasmas and detection of weak signals

Abstract

In this work different kinds of reflective optical systems were used for creation and investigation of low temperature, photoionized plasmas. The plasmas were created in gases, irradiated with a focused beam of extreme ultraviolet (EUV) or soft X-ray (SXR) radiation, from laser-plasma sources employing 10 Hz Nd:YAG laser systems (0.8 J/ 4 ns and 10 J/ 1-10 ns). In both cases, the EUV radiation was focused using a gold-plated grazing incidence ellipsoidal collector in the wavelength range λ = 9÷70 nm or a gold-plated grazing incidence multifoil collector in the wavelength range λ = 5 ÷ 70 nm. Additionally, in case of the 10 J Nd:YAG laser with the pulse duration 1 ns, a paraboloidal collector optimized for the wavelength range λ ≥ 1 nm was employed. Different gases were injected into the vacuum chamber, perpendicularly to an optical axis of the irradiation system at the focal region, using an auxillary gas puff valve. Irradiation of the gases resulted in ionization and excitation of atoms/molecules. Spectra in SXR/EUV range were measured using a grazing incidence, flat-field spectrometer (McPherson Model 251), equipped with a 450 lines/mm toroidal grating or a home-made spectrograph based on the 5000 l/mm transmission grating. Optical spectra were recorded using the Echelle Spectra Analyzer ESA 4000. In all cases the most intense emission lines were assigned to singly charged ions, however, lines corresponding to ions with higher charge were also recorded. Based on spectral lines originating from ions electron temperature was estimated.