Space-resolved spectra of laser-produced plasmas in the XUV

Abstract

Monochromatic images of laser‐produced plasmas have been obtained in the 200–550‐Å region using a slitless normal‐incidence spectrograph. The plasmas were produced by subnanosecond 10¹⁶ W cm⁻² irradiation of thick and thin targets containing a wide variety of elements. The XUV emission is observed to extend several millimeters from the target surface. Secondary regions of emission were frequently observed 2–3 mm from the target. The regions of plasma emission usually lie along the direction of the incident laser pulse. The ions present in the spectra are formed at electron temperatures that range from ∼7×10⁵ to ∼7×10⁶ K. Density‐sensitive spectral line ratios are used to show that the plasma electron density decreases by no more than an order of magnitude over a few millimeters. Similar spectra were observed on both sides of 7‐μm Fe foil irradiated with a 100‐psec pulse, implying a penetration velocity on the order of 10⁷ cm sec⁻¹. It was deduced from spectra of thin foils that the penetration of the laser pulse used is about 10 μm of iron. A technique is proposed for obtaining time‐ and space‐resolved spectra over time intervals of a few tens of picoseconds. The imaging properties of the slitless spectrograph and a method of improving the spatial resolution of the instrument are discussed in the Appendix.