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EUV-induced plasmas created using intense ionizing radiation pulses from laser-produced plasma sources

In this work two 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) radiation. In experiments a laser-produced plasma source based on a 10 J/ 10 ns Nd:YAG laser system, and a double stream gas puff target, working with a 10 Hz repetition rate was used. The EUV radiation was focused using a ruthenium-plated, grazing incidence, ellipsoidal mirror with a high reflective coefficient in the wavelength range λ>10 nm. 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 various excited states in atoms and ions. Spectra in EUV range were measured using a spectrometer (McPherson Model 251), equipped with a flat-field, 450 lines/mm toroidal grating. In all cases the most intense emission lines were assigned to singly or doubly charged ions, however, lines corresponding to ions with higher charge were also recorded. Apart from the time integrated spectral measurements also spectrally integrated but time-resolved measurements were performed, using a specially prepared detection system. The system was based on a paraboloidal collector and an EUV sensitive photodiode. In all cases the EUV emission time from the EUV-induced, low temperature plasmas was significantly longer comparing to the driving EUV pulse.