Feasibility study of broadband efficient “water window” source

Abstract

We demonstrate a table-top broadband emission water window source based on laser-produced high-Z plasmas. Resonance emission from multiply charged ions merges to produce intense unresolved transition arrays (UTAs) in the 2–4 nm region, extending below the carbon K edge (4.37 nm). Arrays resulting from n=4-n=4 transitions are overlaid with n=4-n=5 emission and shift to shorter wavelength with increasing atomic number. An outline of a microscope design for single-shot live cell imaging is proposed based on a bismuth plasma UTA source, coupled to multilayer mirror optics.

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

“…As a result, the bulk of the emission, especially from regions of "1" and "4", was associated with the recombining phase of the expanding plasma plume. We evaluate for comparison spectra calculated for steady-state electron temperatures of 180 and 700 eV, while the higher temperatures were required to produce the emission in the region of "2", the calculations verify that both the longer and shorter wavelength features were consistent with much lower plasma electron temperatures [26].…”

“…Therefore, for an optimized source, we should produce a plasma at high electron temperature of around 1 keV. The emission intensity of the Bi plasma was compared with 2.48-nm nitrogen line emission from a Si 3 N 4 planar target, in the same experimental setup, and was observed to be 1.2 times higher within a bandwidth of 0.008 nm (FWHM) even though the plasma electron temperature was much lower than the optimum value [26]. …”

“…Neither the emission spectra nor the plasma electron temperatures, however, have been optimized, as shown below. However, the emission intensity of the n = 4−n = 5 transitions was compared with that of the n = 4−n = 4 transitions of the UTA emission [26].…”

“…In order to achieve high resolution in the recorded image, we should also replace the recording device from the x-ray CCD camera to the sensitive EUV resist to overcome the resolution limitation of the CCD pixel size, coupling with the Schwarzschild optics, consisting of Sc/Cr multilayer mirrors. Although our proposal is based on a simple microscope construction, the key component is the UTA emitted from a hot dense Bi plasma point source, combined with Sc/Cr MLMs and sensitive EUV resists based on the photochemical reaction [26].…”

Gd plasma source modeling at 6.7 nm for future lithography

“…Self-absorption due to lower ionic charge states and neutral vapor in the expanding Gd plasmas will reduce the intensity at wavelengths greater than 6.8 nm. The resonant emission at 6.76 nm is therefore not absorbed by lower ion stages and is essentially unattenuated [20].…”