Space-resolved extreme ultraviolet emission from laser-produced plasmas

Abstract

We have obtained extreme ultraviolet (XUV) spectra of plasmas created by focusing nanosecond CO2 laser pulses onto massive planar targets of Al, Ti, and CH2. The instrument used to obtain these spectra was a normal incidence extreme ultraviolet spectrograph with the entrance slit removed. The concave spherical grating of such a slitless spectrograph diffracts and focuses the XUV radiation, and the resulting images are recorded on Kodak 101 film. The XUV images are therefore space resolved but time averaged over the lifetime of the plasma. The wavelength range covered in these spectra is 200–500 Å. In this range, the emission lines of aluminum are due to transitions between the 2s22pk, 2s2pk+1, and 2pk+2 configurations within the ions from Al V through Al X. For titanium plasmas, emission lines from Ti VII, Ti XI, and Ti XII have been identified. The prominent images obtained from polyethylene plasma result from 2l-3l′ and 2l-4l′ transitions within the C IV ion. The general morphology of the plasma expansion shows that the most highly ionized species (Al X, Ti XII) expand away from the target surface in well-collimated cylindrical structures. These most highly ionized species also exhibit two component structures; one component expanding along the target normal and the second component expanding parallel to the incident laser direction. The images of the low-ionization stages (Al V, Ti VII) are also cylindrical although their spatial extent is much less than the images from the high-temperature ions and they are not as well collimated. The observations are interpreted in terms of particular temperature structures in such plasmas and the presence of self-generated magnetic fields.