| A subset of compact quasars have exhibited peculiar, distinctive variations in their light curves, whose timescales are so short that they cannot be explained by intrinsic processes. This effect must be due to anomalous propagation through dense plasma lenses in our own Galaxy, which has given rise to the name `Extreme Scattering Event' (ESE). However, the densities required to produce such extreme lensing are wildly inconsistent with our current understanding of gas conditions in the Milky Way.
I will introduce our systematic survey (ATESE) to discover and characterise these events using a novel frequency domain approach, which ideally suits the wideband capabilities of the Australia Telescope Compact Array (ATCA). This survey has already detected 2 candidates and we have triggered a variety of radio and optical followup. I will present the survey technique, our two candidates, and how we are constraining the models of the ESE phenomenon with our data.