DEVELOPMENT OF A WATER-WINDOW X-RAY SOURCE USING A LIQUID-NITROGEN JET

Abstract

As a source for a soft X-ray microscope, a liquid-nitrogen jet has been developed and its radiation characteristics have been investigated for various laser Parameters, such as the laser pulse energy and duration. The effects of pre-pulse and multiple pulses have also been studied. The focus has been the N VI 1s2-1s2p transition at 2.88 mu m. The investigation shows that the laser intensity for the maximum conversion efficiency scales as I(m) alpha 1/tau(alpha), where alpha = 0.9 +/- 0.15. The study of the pre-pulse effect on the conversion efficiency shows that a pre-pulse of only 2 mJ enhances the conversion efficiency by 10 - 15 times for the main pulse of 15 - 60 mJ at a delay of 3 - 6 ns. The photon flux is 1.2 x 10(12) photons / (pulse sr) at a delay of 4 ns for a main pulse of 60 mJ with a pre-pulse of 4 - 8 mJ. The study of the multiple pulse effect was done in the 4-pulse configuration. The enhancement of the radiation compared to the accumulation of the radiation intensity of each pulse was observed at a certain delays between 4 pulses, implying that there exists a proper pulse structure for maximum radiation.