G. O'Sullivan

Colliding laser-produced plasmas as targets for laser-generated extreme ultraviolet sources

Colliding plasmas produced by neodymium-doped yttrium aluminium garnet (Nd:YAG) laser illumination of tin wedge targets form stagnation layers, the physical parameters of which can be controlled to optimise coupling with a carbon dioxide (CO2) heating laser pulse and subsequent extreme ultraviolet (EUV) production. The conversion efficiency (CE) of total laser energy into EUV emission at 13.5u2009nmu2009±u20091% was 3.6%. Neglecting both the energy required to form the stagnation layer and the EUV light produced before the CO2 laser pulse is incident results in a CE of 5.1% of the CO2 laser energy into EUV light.

Optimizing an EUV source for 13.5 nm

The emission spectra of laser produced plasmas of pure tin targets are dominated by recombination continuum emission throughout the entire EUV spectral region with intense structure due to line emission dominating the spectra in the 13 - 14 nm region. This feature arises from resonant 4p64dn - 4p54dn+1 + 4p64dn-14f emission lines that are generally concentrated in a narrow band, 5 - 10 eV wide, which overlaps considerably in adjacent ion stages to form an intense unresolved transition array (UTA). Such plasmas are optically thick; the strongest lines are attenuated and frequently appear in absorption. However, if tin comprises a few percent of a predominantly low-Z matrix, the recombination is suppressed and the plasmas can become optically thin to resonance radiation. Under these conditions, resonance line emission can dominate the spectra. The application of a collisional radiative (CR) model, combined with ab initio atomic structure calculations, allows one to estimate the laser plasma parameters that will optimize the UTA as efficient narrow bandwidth emitters of EUV radiation. The dependence on laser power density of both in-band emission and debris generation from pure tin targets is presented. The influence of a pre-pulse on the plasma output is also investigated.

4d → 5p transitions in the EUV photoabsorption spectrum of Ba IV, Ba V and Ba VI

The photoabsorption spectra of La V, La VI and La VII have been recorded in the 85–96 eV region using the dual laser plasma technique. 4d → 5p transitions from their ground configurations were observed and identified with the aid of Hartree–Fock with configuration interaction calculations. The excited states were found to decay by autoionization involving 5s or 5p electrons and rates for the different processes and resulting linewidths were calculated and compared with experiment.

Investigation of ions emitted from a tin fuelled laser produced plasma source

In this work ions emitted from a laser produced plasma created from a solid tin target have been analyzed using a spherical sector energy analyzer (ESA). Employing time of fiight analysis, the ESA allows determination of ion energy and charge stage as a function of ion emission angle. Ions of charge Sn+1 - Sn+9 with energy to charge ratios of 0.22 - 3.2keV have been investigated over a range of emission angles from 20 - 80 degrees, relative to the target normal, for three distinct laser pulse energies

4d photoabsorption in Sn III

The 4d photoabsorption spectrum of Cd I-like Sn III has been recorded in the 25-50 eV region using the dual-laser plasma (DLP) technique. Transitions from the 4d105s2 ground state dominate the Sn III spectrum with some contribution from the metastable 3P2 and 3P0 levels of the excited 4d105s5p configuration also observed. Transitions were identified with the aid of multiconfiguration Hartree-Fock calculations.

EUV Emission from Laser Produced Plasmas of Bismuth, Lead and their Alloys

Extreme ultraviolet (EUV) spectra from laser produced plasmas of Bi, Pb and Bi-Pb-Sn alloy were recorded in the 10-16 nm spectral region using an 8-ns Nd: YAG laser operating at different laser power densities. The theoretical Bi spectra were calculated and shown in the form of binned scatter plots.

Laser-Produced Heavy Ion Plasmas as Efficient Soft X-Ray Sources

We demonstrate extreme ultraviolet (EUV) and soft x-ray sources in the 2to 7 -nm spec‐ tral region related to the beyond extreme ultraviolet (BEUV) question at 6.x nm and a wa‐ ter window source based on laser-produced high-Z plasmas. Strong emissions from multiply charged ions merge to produce intense unresolved transition array (UTA) to‐ ward extending below the carbon K-edge (4.37 nm). An outline of a microscope design for single-shot livecell imaging is proposed based on a high-Z UTA plasma source, cou‐ pled to x-ray optics. We will discuss the progress and Z-scaling of UTA emission spectra to achieve lab-scale table-top, efficient, high-brightness high-Z plasma EUV-soft x-ray sources for in vivo bio-imaging applications.

Characteristics of extreme ultraviolet emission from high-Z plasmas

We demonstrate the extreme ultraviolet (EUV) and soft x-ray sources in the 2 to 7 nm spectral region related to the beyond EUV (BEUV) question at 6.x nm and the water window source based on laser-produced high-Z plasmas. Resonance emission from multiply charged ions merges to produce intense unresolved transition arrays (UTAs), extending below the carbon K edge (4.37 nm). An outline of a microscope design for single-shot live cell imaging is proposed based on high-Z plasma UTA source, coupled to multilayer mirror optics.

Efficient "water window" soft x-ray high-Z plasma source

Unresolved transition array (UTA) is scalable to shorter wavelengths, and we demonstrate a table-top broadband emission water window soft x-ray source based on laser-produced plasmas. Resonance emission from multiply charged ions merges to produce intense UTAs in the 2 to 4 nm region, extending below the carbon K edge (4.37 nm). An outline of a microscope design for single-shot live cell imaging is proposed based on a bismuth (Bi) plasma UTA source, coupled to multilayer mirror optics.

Recent results on the development of extreme ultraviolet sources for lithography and metrology at 6.x nm

Recent increases in reflectance at 6.x nm of La/B4C multilayer mirrors has led to the adoption of this wavelength for the development of future sources for lithography. The emission from laser produced plasmas of Gd and Tb emit strongly in this wavelength region. The transitions responsible and the optimum plasma conditions for optimum emission have been identified both theoretically and experimentally.