  We have measured the scintillation properties of 151 young, energetic pulsars
with the Parkes radio telescope and have identified two extreme scattering
events (ESEs). Towards PSR J1057-5226 we discovered a three-year span of
strengthened scattering during which the variability in flux density and the
scintillation bandwidth decreased markedly. The transverse size of the
scattering region is ~23 au, and strong flux density enhancement before and
after the ESE may arise from refractive focusing. Long observations reveal
scintillation arcs characteristic of interference between rays scattered at
large angles, and the clearest arcs appear during the ESE. The arcs suggest
scattering by a screen 100-200 pc from the earth, perhaps ionized filamentary
structure associated with the boundary of the local bubble(s).
  Towards PSR J1740-3015 we observed a "double dip" in the measured flux
density similar to ESEs observed towards compact extragalactic radio sources.
The observed shape is consistent with that produced by a many-au scale
diverging plasma lens with electron density ~500cm$^{-3}$ . The continuing ESE
is at least 1500 d long, making it the longest detected event to date.
  These detections, with materially different observational signatures,
indicate that well-calibrated pulsar monitoring is a keen tool for ESE
detection and ISM diagnostics. They illustrate the strong r\^ole au-scale
non-Kolmogorov density fluctuations and the local ISM structure play in such
events and are key to understanding both their intrinsic physics and their
impact on other phenomena, particularly fast radio bursts.
