High-$Q$ surface modes in photonic crystal/iron garnet film heterostructures for sensor applications

A novel type of a plasmonic sensor based on a magnetophotonic plasmonic heterostructure with an ultrahigh-$Q$ resonance is considered. A magnetoplasmonic resonance with an angular width of $0.06^\circ$, which corresponds to a $Q$ factor of $700$ and is a record value for magnetoplasmonic sensors, is experimentally demonstrated. It is shown that, owing to the excitation of long-propagation-range plasmons, the transverse magneto-optical Kerr effect is considerably enhanced and, thus, the sensitivity of the magnetoplasmonic sensor to variations in the refractive index increases to $18$ RIU$^{-1}$, where RIU is the refractive index unit. Numerical calculations indicate that the parameters of the magnetoplasmonic structure can be further optimized to attain sensitivities up to $5\times 10^3$ RIU$^{-1}$.