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We investigated the spatial and temporal evolution of temperature and electron density associated with femto- and nanosecond laser-produced plasmas (LPP) from brass under similar laser fluence conditions. For producing plasmas, brass targets were ablated in vacuum employing pulses either from a Ti:Sapphire ultrafast laser (40 fs, 800 nm) or from a Nd:YAG laser (6 ns, 1064 nm). Optical emission spectroscopy is used to infer the density and temperature of the plasmas. The electron density (ne) was estimated using Stark broadened profiles of isolated lines while the excitation temperature (Texc) was estimated using the Boltzmann plot method. At similar fluence levels, continuum and ion emission are dominant in ns LPP at early times (<50 ns) followed by atomic emission, while the fs LPP provided an atomic plume throughout its visible emission lifetime. Though both ns and fs laser-plasmas showed similar temperatures (∼1 eV), the fs LPP is found to be significantly denser at shorter distances from the target surface as well as at early phases of its evolution compared to ns LPP. Moreover, the spatial extension of the plume emission in the visible region along the target normal is larger for fs LPP in comparison with ns LPP.

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We investigated the laser wavelength effect on angular atomic and ionic emission from laser-produced Sn plasma, since it is regarded as a viable candidate for an EUV lithography source. For producing plasmas, the fundamental, second and fourth harmonics radiation from a Nd : YAG laser were used. The angular variation of atomic and ionic particle analysis was carried out using quartz crystal microbalance and Faraday cups by moving them in a circular path at a constant distance from the target normal. Along with atomic and ionic emission, we also compared the plasma emission features in the visible and EUV spectral regions. Results indicate strong forward bias in atomic and ionic plasma debris at all wavelengths. Shorter wavelength plasmas are found to generate more atomic particles while ion flux showed a similar trend irrespective of the excitation wavelength.

Laser-produced plasmas (LPP) from Sn targets are seriously considered to be the light source for extreme ultraviolet (EUV) next generation lithography, and optimization of such a source will lead to improved efficiency and reduced cost of ownership of the entire lithography system. We investigated the role of reheating a prepulsed plasma and its effect on EUV conversion efficiency (CE). A 6 ns, 1.06 lm Nd:yttrium aluminum garnet laser was used to generate the initial plasma that was then reheated by a 40 ns, 10.6 lm CO 2 laser to generate enhanced EUV emission from a planar Sn target. The effects of prepulsed laser intensity and delay timings between the prepulsed and the pumping pulse were investigated to find the optimal pre-plasma conditions before the pumping pulse. The initial optimization of these parameters resulted in 25% increase in CE from the tin LPP. The cause of increased EUV emission was identified from EUV emission spectra and ion signal data.

In this work we study the effectiveness of long-wavelength heating in double pulse (DP) LIBS, quantitatively comparing figures of merit with those from traditional single pulse (SP) LIBS. The first laser pulse serves as the source of sample ablation, creating an aerosol-like plume that is subsequently reheated by the second laser pulse. At power densities used, the long-wavelength CO 2 laser pulse does not ablate any of the solid sample in the atmospheric conditions investigated, meaning plasma emission and enhanced signal can be entirely attributed to the reheated plume rather than increased sample ablation. The signal discrimination was improved significantly using long-wavelength DP-LIBS. For bulk elemental analysis, DP-LIBS provided maximum enhancements of about 14 and 15 times for S/N and S/B, respectively, compared to SP-LIBS using the same quantity of ablated sample. For trace elemental analysis, maximum enhancements of about 7 and 4 times for S/N and S/B, respectively, were observed. These improvements are attributed to effective coupling between the second heating pulse and expanding plume and more efficient excitation of plume species than from the single pulse alone. Most significant improvements were observed in the case of low prepulse energy and minimal sample ablation. While bulk elemental analysis observed improvements for all prepulse energies studied, trace element discrimination only significantly improved for the lowest prepulse energy studied.