We present the results of a joint experimental and theoretical study of plasma expansion arising from Nd:YAG laser ablation (laser wavelength λ = 1.064 μm) of tin microdroplets in the context of extreme ultraviolet lithography. Measurements of the ion energy distribution reveal a near-plateau in the distribution for kinetic energies in the range 0.03-1 keV and a peak near 2 keV followed by a sharp fall-off in the distribution for energies above 2 keV. Charge-state resolved measurements attribute this peak to the existence of peaks centered near 2 keV in the Sn 3+ -Sn 8+ ion energy distributions. To better understand the physical processes governing the shape of the ion energy distribution, we have modelled the laser-droplet interaction and subsequent plasma expansion using two-dimensional radiation hydrodynamic simulations. We find excellent agreement between the simulated ion energy distribution and the measurements both in terms of the shape of the distribution and the absolute number of detected ions. We attribute a peak in the distribution near 2 keV to a quasi-spherical expanding shell formed at early times in the expansion.

We present results from a combined experimental and numerical simulation study of the anisotropy of the expansion of a laser-produced plasma into vacuum. Plasma is generated by nanosecond Nd:YAG laser pulse impact (laser wavelength [Formula: see text]) onto tin microdroplets. Simultaneous measurements of ion kinetic energy distributions at seven angles with respect to the direction of the laser beam reveal strong anisotropic emission characteristics, in close agreement with the predictions of two-dimensional radiation-hydrodynamic simulations. Angle-resolved ion spectral measurements are further shown to provide an accurate prediction of the plasma propulsion of the laser-impacted droplet.

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Abstract. We investigate synchrony breaking bifurcations in neuronal networks. These bifurcations occur from synchronous steady-states. In the mutual dyad and a three-neuron feed-forward chain we show that the generic bifurcation behaviour can be derived from the physical modelling parameters, in particular from the sign of the interaction between neurons. Each neuron is equipped with a simplified FitzHugh-Nagumo model and the coupling is based on synaptic coupling. An inhibitory or excitatory coupling can determine if the bifurcation is 'soft' (supercritical) or 'hard' (subcritical). For the analysis of the three-neuron feed-forward chain we follow the work of Rink and Sanders (2013): we can relate excitatory and inhibitory coupling to a 'soft' and a 'hard' transition, respectively. For the mutual dyad system we make use of a centre manifold reduction to find the type of pitchfork bifurcation. As we find an expression in terms of physical parameters, we can state whether the bifurcation is subcritical or supercritical in the weak coupling limit, and for slow and fast input.1. Introduction. We will consider neuronal networks as dynamical systems with a network structure. The nodes of the network model the neurons. Real life neuronal networks are immensely complex but in this paper we will consider small networks. Such small networks are called 'motifs' and are often present as sub-networks of large neuronal networks. In this paper we consider the mutual dyad and a feedforward chain. The mutual dyad contains two identical neurons, mutually coupled by identical coupling. The feed-forward chain contains three identical neurons with a specific feed-forward coupling. These two motifs are shown in figures 1.1 and 1.2.

The light source in extreme ultraviolet (EUV) lithography tools is a hot and dense laser-driven plasma. We will give an overview of our recent work on modeling the radiative and expansion characteristics of these plasmas.

State-of-the-art nanolithography machines employ extreme ultraviolet (EUV) light to pattern nanometer-scale features on silicon wafers for the production of integrated circuits. This radiation is generated in a laserproduced plasma formed on tin microdroplet targets. In this contribution, we give an overview of our recent experimental and theoretical studies on the properties of tin plasmas driven by short-wavelength lasers and the subsequent tin fluid dynamics. First, we will present a comprehensive characterization of the properties of laserproduced tin plasmas driven by lasers with wavelengths in the 1–10 µm range. Second, we present absolutely calibrated, charge-state-resolved measurements of the ion kinetic energy distribution recorded under multiple detection angles. Through extensive radiation-hydrodynamic simulations of the plasma formation, growth and expansion, we demonstrate that a single-fluid approach accurately reproduces the angular dependence of the ion energy distribution. Moreover, we identify the origin of a high-energy peak in the distribution as a high-speed shell generated at early times in the expansion. Finally, we show that the time evolution of the droplet target morphology is entirely determined by the early-time plasma-driven pressure impulse on the droplet.

We characterize the properties of extreme ultraviolet (EUV) light source plasmas driven by laser wavelengths in the [Formula: see text] range and laser intensities of [Formula: see text] W cm−2 for [Formula: see text]. Detailed numerical simulations of laser-irradiated spherical tin microdroplet targets reveal a strong laser-wavelength dependence on laser absorptivity and the conversion efficiency of generating in-band EUV radiation. For [Formula: see text] irradiation, the increase in in-band radiation with increasing laser intensity is offset by only a minor reduction in conversion efficiency. Radiative losses are found to dominate the power balance for all laser wavelengths and intensities, and a clear shift from kinetic to in-band radiative losses with increasing laser wavelength is identified. Yet, with increasing laser intensity, such a shift is absent. We find that the existence of a maximum conversion efficiency, near [Formula: see text], originates from the interplay between the optical depths of the laser light and the in-band EUV photons for this specific droplet-target geometry.