Abstract
Abstract We introduce two tractable analytical models to describe dynamic effects at resonant light scattering by subwavelength particles. One of them is based on a generalization of the temporal coupled-mode theory, and the other employs the normal mode approach. We show that sharp variations in the envelope of the incident pulse may initiate unusual, counterintuitive dynamics of the scattering associated with interference of modes with fast and slow relaxation. To exhibit the power of the models, we apply them to explain the dynamic light scattering of a square-envelope pulse by an infinite circular cylinder made of GaP, when the pulse carrier frequency lies in the vicinity of the destructive interference at the Fano resonances. We observe and explain intensive sharp spikes in scattering cross-sections just behind the leading and trailing edges of the incident pulse. The latter occurs when the incident pulse is over and is explained by the electromagnetic energy released in the particle at the previous scattering stages. The accuracy of the models is checked against their comparison with results of the direct numerical integration of the complete set of Maxwell’s equations and occurs very high. The models’ advantages and disadvantages are revealed, and the ways to apply them to other types of dynamic resonant scattering are discussed.
Highlights
High-Q resonances are of utmost importance in a wide diversity of problems [1]
We introduce two tractable analytical models to describe dynamic effects at resonant light scattering by subwavelength particles
We show that sharp variations in the envelope of the incident pulse may initiate unusual, counterintuitive dynamics of the scattering associated with interference of modes with fast and slow relaxation
Summary
High-Q resonances are of utmost importance in a wide diversity of problems [1]. It is explained by the fact that to obtain strong resonant effects, the corresponding resonance should have a high amplitude, and a high Q-factor, at least if a spatially bounded system is a concern. The frontier of modern photonics moves toward short and ultrashort pulses Nowadays, currently, these two factors together make a typical situation where the duration of the laser pulse becomes comparable or even shorter than the relaxation time of the resonance effects initiated by this pulse. At the moment, the only possible theoretical description of transient effects at the resonant light scattering by subwavelength particles is made with the help of direct numerical integration of the complete set of Maxwell’s equations. In our case, the mode selection for the approximation and, most importantly, the choice of the values of the model parameters are based on the system in question’s physical properties It reveals the role of different excitations in the system dynamic and sheds light on the physical nature of the system as a whole. Cumbersome details and expressions and several plots illustrating the developed approach are moved to Appendix
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