The photoabsorption spectra of Te I-Te IV have been recorded and analysed in the XUV spectral region using the dual laser produced plasma technique. Photoexcitation from the 4d subshell is the dominant process in the 35-150 eV energy region. For photon energies between 35-45 eV discrete structure corresponding to 4d-np (n>4) transitions were obtained. Above the 4d ionisation threshold the spectra of Te I-Te III were found to be dominated by a 4d-ef shape resonance, which peaks at ~88 eV in each case. A transfer of oscillator strength from the resonance to discrete 4d-nf (n>3) transitions with increasing ionisation is clearly evident, and the 4d-4f transitions are the strongest features in the Te IV spectrum. Hartee-Fock with configuration interaction and time dependent local density approximation calculations successfully account for this behaviour and permit identification of the discrete features. The use of a prepulse to maximise the brightness of a tungsten continuum emitting plasma was also investigated.
The search for a source of EUV radiation for photolithography in the 13.5 nm region has been narrowed down to laser produced or pulsed discharge plasmas containing either xenon or tin. Higher conversion efficiencies can however be obtained with tin based plasmas within this wavelength regime. It is known that EUV photoabsorption by the lower ion stages of xenon reduces the photon flux from a xenon source. This is due to shape resonances from 4d-epsilonf transitions within Xe I-IV. The corresponding resonances for Sn I-IV have been obtained by means of the dual laser plasma (DLP) technique. It is also found that above the 4d ionisation threshold the spectra of Sn I-IV are dominated by a 4d-epsilonf shape resonance which peaks at close to 65 eV in each case. A transfer of oscillator strength from the shape resonance to pseudo-discrete 4d→nf transitions with increasing ionisation is clearly evident. Hartree-Fock with configuration interaction and relativistic time dependent local density approximation calculations successfully account for this behaviour and also permit identification of the discrete features.