Gold nanostars are theoretically studied as efficient thermal heaters at their corresponding localized surface-plasmon resonances (LSPRs). Numerical calculations are performed through the 3D Green's Theorem method to obtain the absorption and scattering cross sections for Au nanoparticles with star-like shape of varying symmetry and tip number. Their unique thermoplasmonic properties, with regard to their (red-shifted) LSPR wavelentgh, (∼ 30-fold increase) steady-state temperature, and scattering/absorption cross section ratios, make them specially suitable for optical heating and in turn for cancer thermal therapy.

Single metallic nanorods acting as half-wave antennas in the optical range exhibit an asymmetric, multi-resonant scattering spectrum that strongly depends on both their length and dielectric properties. Here we show that such spectral features can be easily understood in terms of Fano-like interference between adjacent plasmon resonances. On the basis of analytical and numerical results for different geometries, we demonstrate that Fano resonances may appear for such single-particle nanoantennas provided that interacting resonances overlap in both spatial and frequency domains. 12 Appendix A. Calculation techniques 12 Appendix B. Details of the fitting of scattering efficiency to Fano-like lineshape 13 References 15

We present a semi-classical analytic model for spherical core-shell surface plasmon lasers. Within this model, we drop the widely used one-mode approximations in favor of fully electromagnetic Mie theory. This allows for incorporation of realistic gain relaxation rates that so far have been massively underestimated. Especially, higher order modes can undermine and even reverse the beneficial effects of the strong Purcell effect in such systems. Our model gives a clear view on gainand resonator-requirements, as well as on the output characteristics that will help experimenters to design more efficient particle-based spasers.Nanoscopic sources of coherent electromagnetic fields are essential elements for different fields in nanooptics, such as nanoplasmonics [1], metamaterials [2], and quantum plasmonics [3]. A surface plasmon laser (spaser) might be such a nanoscopic source [4,5].As compared to a laser, the obvious difference of a spaser is the use of plasmons instead of photons. Plasmons are inherently localized excitations and generally exhibit much smaller (mode) volumes than photonic cavity modes [6]. From an electromagnetic perspective, there is no reason to expect any further principle deviations from well-known (semi-classical) laser physics. For instance, Mie theory [7] completely describes the electromagnetic field for a spherical particle irrespective of the constituent material, i.e., whispering gallery modes of dielectric spheres and localized plasmon modes of metallic spheres are all included. However, as we will detail below, there are certain issues that have to be treated with care.Recently, a number of spaser devices [8][9][10][11][12][13][14] have been characterized and extensive theoretical work has addressed fundamental and device-specific spaser properties [15][16][17][18][19][20]. However, several questions, even of a fundamental nature, remain to be answered. Perhaps the most important of these is related to the rather low spaser efficiency. For instance, previous experiments placed very high demands on the pump (e.g., high laser pulse intensities [10]), the synthesis of the spaser's gain medium (e.g., dense incorporation of fluorophores [8]), and, quite generally, very high demands regarding the material quality [14]. Accordingly, these issues are reflected by the rather small number of publications that address spaser action in fully nanoscopic systems and systems working with organic gain media [8][9][10].Analytic theoretical descriptions have mainly focused on quasi-static analysis, so far [4,[16][17][18][19][20]. Within this framework only a nanoparticle's dipolar resonance or generic numbers of the gain medium's relaxation rate have been considered to describe the spaser. Rather numerical cold cavity analysis of actual devices has been used in order to show (i) correspondence with observed far-field patterns and measured spectra etc. [11][12][13][14], (ii) that the resonator under observation is unable to support ordinary purely optical modes [11][12][13][14], and (iii) to estimate th...