  Light-matter strong coupling (LMSC) is intriguing state in which light and
matter are coherently hybridized inside cavity. It has been gaining widespread
recognition as an excellent way for controlling material properties without any
chemical modification. Here we show the LMSC is a powerful state to manipulate
and improve a chiral nonlinear optical (NLO) effect through the investigation
of second harmonic generation circular dichroism. At the upper polaritonic band
in LMSC, in addition to an enhancement of SHG intensity by more than one order
of magnitude, the responsivity to the handedness of circular polarized light is
largely modified, where sign inversion and increase of dissymmetric factor is
achieved. Quarter wave plate rotation analysis reveals that the LMSC clearly
influence the coefficients associated with chirality in NLO process and it also
contributes to the enhancement of nonlinear magnetic dipole interactions. This
study demonstrates that LMSC serves as a novel platform for control of chiral
optoelectronics and magneto-optics.
