Analysis of unconventional optical standing wave patterns outside a metal-substrate supported dielectric microsphere.

Here, we present a theoretical study on the electric field intensity (EFI) and magnetic field intensity (MFI) distributions outside a single dielectric microsphere placed on a metal substrate. For the first time, intense unconventional optical standing wave patterns (UOSWPs) are observed outside the metal substrate-supported microsphere at the resonant wavelengths or wavelengths of whispering gallery modes (WGMs). However, the conventional and reflective photonic nanojets (PNJs) are observed at the non-resonant wavelengths. The minimum separation between the UOSWPs and the microsphere's surface is found to be sensitive to the microsphere's radius (r). The EFI and MFI distributions are analyzed across different planes for transverse electric (TE) and transverse magnetic (TM) polarized light to characterize the UOSWPs. Finally, a comparison is made between UOSWPs observed outside a metal-supported microsphere and conventional optical standing wave patterns (COSWPs) or WGMs observed at the interface of a substrate-free dielectric microsphere. In the case of the substrate-free dielectric microsphere, most of the electric and magnetic fields of WGMs exist inside the microsphere, and only the weak field or evanescent of the WGMs is accessible outside the microsphere for practical applications. In contrast to the WGMs, the intense electric and magnetic fields of the UOSWPs exist outside the microsphere and can enhance the light-matter interaction significantly. Hence, we strongly believe that the UOSWPs will have several potential applications in various research domains.