Ejected material from neutron star mergers give rise to electromagnetic emission powered by radioactive decays of r-process nuclei, which is so called kilonova or macronova. While properties of the emission are largely affected by opacities in the ejected material, available atomic data for r-process elements are still limited. We perform atomic structure calculations for r-process elements: Se (Z = 34), Ru (Z = 44), Te (Z = 52), Ba (Z = 56), Nd (Z = 60), and Er (Z = 68). We confirm that the opacities from bound-bound transitions of open f-shell, Lanthanide elements (Nd and Er) are higher than those of the other elements over a wide wavelength range. The opacities of open s-shell (Ba), p-shell (Se and Te), and d-shell (Ru) elements are lower than those of open f-shell elements and their transitions are concentrated in the ultraviolet wavelengths. We show that the optical brightness can be different by > 2 mag depending on the element abundances in the ejecta such that post-merger, Lanthanide-free ejecta produce brighter and bluer optical emission. Such blue emission from post-merger ejecta can be observed from the polar directions if the mass of the preceding dynamical ejecta in these regions is small. For the ejecta mass of 0.01 M ⊙ , observed magnitudes of the blue emission will reach 21.0 mag (100 Mpc) and 22.5 mag (200 Mpc) in g and r bands within a few days after the merger, which are detectable with 1m or 2m-class telescopes.

Extreme ultraviolet (EUV) radiation from laser-produced plasma (LPP) has been thoroughly studied for application in mass production of next-generation semiconductor devices. One critical issue for the realization of an LPP-EUV light source for lithography is the conversion efficiency (CE) from incident laser power to EUV radiation of 13.5-nm wavelength (within 2% bandwidth). Another issue is solving the problem of damage caused when debris reaches an EUV collecting mirror. Here, we present an improved power balance model, which can be used for the optimization of laser and target conditions to obtain high CE. An integrated numerical simulation code has been developed for the target design. The code agrees well with experimental results not only for CE but also for detailed EUV spectral structure. We propose a two-pulse irradiation scheme for high CE, and reduced ion debris using a carbon dioxide laser and a droplet or a punch-out target. Using our benchmarked numerical simulation code, we find a possibility to obtain CE up to 6–7%, which is more than twice that achieved to date. We discuss the reduction of ion energy within the two-pulse irradiation scheme. The mitigation of energetic ions by a magnetic field is also discussed, and we conclude that no serious instability occurs due to large ion gyroradius.

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We report conclusive evidence of an efficient cooling mechanism via the electronic radiative transitions of hot small molecular anions isolated in vacuum. We stored C6(-) and C6H(-) in an ion storage ring and observed laser-induced electron detachment with delays up to several milliseconds. The terminal hydrogen atom caused a drastic change in the decay profiles. The decay of photoexcited C6H(-) is slow and nonexponential, which can be explained by depletion cooling, whereas that for C6(-) occurs extremely fast, on a time scale below 0.1 ms and can only be explained by electronic radiative cooling via low-lying electronic excited states.

Atomic processes in Sn plasmas are investigated for application to extreme-ultraviolet (EUV) light sources used in microlithography. We develop a full collisional radiative (CR) model of Sn plasmas based on calculated atomic data using Hebrew University Lawrence Livermore Atomic Code (HULLAC). Resonance and satellite lines from singly and multiply excited states of Sn ions, which contribute significantly to the EUV emission, are identified and included in the model through a systematic investigation of their effect on the emission spectra. The wavelengths of the 4d−4f+4p−4d transitions of Sn5+ to Sn13+ are investigated, because of their importance for determining the conversion efficiency of the EUV source, in conjunction with the effect of configuration interaction in the calculation of atomic structure. Calculated emission spectra are compared with those of charge exchange spectroscopy and of laser produced plasma EUV sources. The comparison is also carried out for the opacity of a radiatively heated Sn sample. A reasonable agreement is obtained between calculated and experimental EUV emission spectra observed under the typical condition of EUV sources with the ion density and ionization temperature of the plasma around 1018 cm−3 and 20 eV, respectively, by applying a wavelength correction to the resonance and satellite lines. Finally, the spectral emissivity and opacity of Sn plasmas are calculated as a function of electron temperature and ion density. The results are useful for radiation hydrodynamics simulations for the optimization of EUV sources.

We have detected visible photons emitted from the thermally populated electronic excited state, namely recurrent fluorescence (RF), of C_{6}^{-} stored in an electrostatic ion storage ring. Clear evidence is provided to distinguish RF from normal fluorescence, based on the temporal profile of detected photons synchronized with the revolution of C_{6}^{-} in the ring, for which the time scale is far longer than the lifetime of the intact photoexcited state. The relaxation (cooling) process via RF is likely to be commonplace for isolated molecular systems and crucial to the stabilization of molecules in interstellar environments.

Extreme ultraviolet emission spectra of multiply charged Sn ions were measured in the wavelength range 5-38 nm, following electron capture into the excited states of slow Sn q+ (q = 5-21) ions passing through He and Xe gas targets. Identification of the transitions was carried out by comparison with calculations using the Hebrew University Livermore Laboratory Atomic physics Code. The target and the charge-state dependences of 4d-n (n = 4f, 5p and 5f) and 4p-4d transitions were observed.

Inverse internal conversion followed by recurrent fluorescence was observed as a fast decay (10 μs range) in the time profile of neutral yields from photo-excited C4(-) molecular ions. We also elucidated the contribution of such electronic radiative cooling to the C4(-) ions with internal energy far below the detachment threshold by an alternative novel approach, observing the laser wavelength and storage time dependence (ms range) of the total yield of the photo-induced neutrals.