Optics Communications 420 (2018) 52–58 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom Effect of plasmonic coupling on photothermal behavior of random nanoparticles Vahid Siahpoush *, Sohrab Ahmadi-kandjani, Arash Nikniazi Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz 51665-163, Iran ARTICLE INFO Keywords: Plasmonics Plasmonic coupling Thermoplasmonics Photo-thermal Coupled dipoles ABSTRACT In this paper, the effect of plasmonic coupling on the photothermal behavior of a random distribution of silver nanoparticles is investigated. The spatial profiles of the temperature increase for illuminated nanoparticles have been computed by means of discrete dipole approximation method and thermal Green’s function. Our results show that in a random assembly of nanoparticles the effects of plasmonic coupling with other nanoparticles and thermal accumulation lead to a photothermal behavior for nanoparticles which is different from the one with an isolated single nanoparticle. The separate contributions of plasmonic coupling and thermal accumulation effects to temperature increase of nanoparticles assembly have been determined qualitatively. Based on obtained results, for wavelengths far from the plasmonic resonance of a single nanoparticle, the plasmonic coupling between clustered nanoparticles can heat up nanoparticles to significant high temperature which it cannot be expected for the case where the plasmonic coupling is assumed to be ignored (where nanoparticles only can interact due to the thermal accumulation). On the other hand, at the plasmonic resonance wavelength of a single nanoparticle, plasmonic coupling between clustered NPs causes the temperature increase to be lower in comparison with the case which the clustered nanoparticles are assumed as an assembly of individual non-coupled nanoparticles. Our results help to have a better understanding of the physics of photo heating of random nanoparticles in biological applications. 1. Introduction A noble metal nanoparticle (NP) under illumination at its plasmonic resonance, which can be tuned from the visible to the infrared frequency ranges, strongly absorbs the light energy. The absorbed energy is converted to heat which raises the temperature of nanoparticle and its immediate surrounding media [1–5]. For a long time, heat generation in metallic NPs, induced by light absorption, has been considered as the side effects in plasmonics appli- cations that had to be minimized. Recently, metallic NPs have been used as nanoscale sources of heat which it emerges a new promising field that could be named thermo-plasmonics [1,6–8]. In recent years, thermo-plasmonics found a wide range of applica- tions in nanotechnologies especially in biology and medicine such as photothermal cancer therapy [9,10], drug delivery [11], nanosurgery [12,13] and photothermal imaging [14]. Almost in all the applications, we encounter with a random dis- tribution of many NPs. In the case of low concentration, where NPs are far enough from each other and the interaction between them can be ignored, the photothermal behavior of the distribution can * Corresponding author. E-mail address: v_siahpoush@tabrizu.ac.ir (V. Siahpoush). be considered as the summation of the response of individual non- interacting NPs [15]. In general, when the NPs interact, the photothermal behavior of each NP in the distribution can be very different in comparison with a single isolated NP. In fact, in an assembly of NPs, two different effects determine the photothermal properties of each NP; the effect of plasmonic coupling with the other NPs and thermal accumulation effect. While extensive studies made on plasmonic coupling for a pair of nanoparticles [16–22], there is much less effort being expended on the ensemble of random NPs. The important question that arises about the effect of plasmonic coupling on the photothermal behavior of random NPs is that will plasmonic coupling work in favor of the application, because of the field enhancement? Or will it work against it, because it shifts the plasmonic resonance wavelength? The main concern of this paper is to find the answer of this question. In this paper, we use the discrete dipole approximation (DDA) method and thermal Green’s function [7,8] to investigate the effects of plas- monic coupling and thermal superposition on temperature increase of randomly distributed nanoparticles. To the best of our knowledge, this is https://doi.org/10.1016/j.optcom.2018.03.021 Received 21 December 2017; Received in revised form 13 February 2018; Accepted 8 March 2018 0030-4018/© 2018 Elsevier B.V. All rights reserved.