Nonlinear Excitation of Ideal Anapoles

Anapoles are nonradiating states of light, in which optical fields are trapped by destructive interference of outgoing radiation. They have recently attracted significant interest due to their potential in resonant nanoscale light confinement, which could be used in lasers, sensors, quantum computers and other areas of light-based research and technology. However, ideal anapoles have never been experimentally achieved, because making them perfectly decoupled from external radiation would prevent their excitation and observation. The proposed project will resolve the above issues. Advanced theoretical modeling tools will be used to design the ideal anapoles that can be excited through second-harmonic generation. In this process, the incident light would illuminate the anapolar nanoresonators and nonlinearly induce local optical fields matching the anapole's excitation at twice the incident light frequency. Second-harmonic optical fields may form configurations that can not be induced through linear interactions with external optical fields, hence allowing these local fields to be fully decoupled from external radiation. These local nonradiating fields will then induce photoluminescence at optical wavelengths detuned from the anapole's resonance. Detecting this photoluminescence will enable probing the anapole excitation. To demonstrate this concept in experiments, resonant photonic samples will be fabricated in the silicon nitride (Si3N4) material platform, integrated with molibdenium disulfide (MoS2) monolayers which can simultaneously support efficient second-harmonic generation and photoluminescence. The samples will be excited by time-controlled ultrashort laser pulses, enabling investigation of the temporal dynamics of the anapole's local optical fields and retrieving their Q factors. Demonstration of the ideal anapoles is an ambitious and challenging goal with breakthrough potential for the research on confined states of light and their possible applications.