Chirality driven effects in multiphoton excited whispering gallery mode microresonators prepared by a self-assembly technique

Organic microresonators are highly attractive for numerous applications including biosensing, optical switching and metrology. Adding chiral materials to resonators can enhance their sensing properties due to the appearance of chiroptical effects. Here we study experimentally resonant multiphoton processes in spherical microresonators with the diameter of 2-12 m made of 1,1'-bi-2-naphthol derivatives by a self-assembly technique. Using nonlinear single-particle microscopy, we demonstrate that these microspheres provide excitation of whispering gallery modes (WGMs) in two- and three-photon excited luminescence with a Q-factor of up to 300. We also demonstrate that the nonlinear circular dichroism is enhanced due to the WGM excitation and reaches 7.7% and 11% in the two- and three-photon absorption, respectively. Pronounced modulation of the WGMs spectrum due to the mode's splitting is observed in coupled binol-based microresonators, which opens a path for the control over their resonant response and makes them suitable for nonlinear optical sensing applications.