  The temporally switchable optical mode conversion is crucial for optical
communication and computing applications. This research demonstrates such
optically switchable mode converter driven by thermo-optic refraction. The MoS2
nanofluid is used as a medium where the thermal microlens is created by a
focused laser beam (pump). The convective thermal plume generated above the
focal point of the pump beam within the nanofluid acts as an astigmatic thermal
lens. It is discovered that mode conversion of the Laguerre-Gaussian (LG) to
the Hermite-Gaussian (HG) beam (vice versa) takes place upon passing through
the thermal lens. The topological charge of the LG beam can be easily
determined using the proposed mode converter. The mode transformation is
explained theoretically as the Fourier components of the LG beam undergoing
different optical paths while propagating through the convective plume.
