Radio Microlensing: Past, Present & Near Future
  Strongly correlated non-intrinsic variability between 5 and 8.5 GHz has been observed in one of the lensed images of the gravitational lens B1600+434. These non-intrinsic (i.e. `external') variations are interpreted as `radio-microlensing' of relativistic micro-arsec-scale jet components in the source at a redshift of z=1.59 by massive compact objects in the halo of the edge-on disk lens galaxy at z=0.41. We shortly summarize these observations and discuss several new observational and theoretical programs to investigate this new phenomenon in more detail. 
L.V.E. Koopmans (1,2,3), A.G. de Bruyn (2,4), C.D. Fassnacht (5), J.   Wambsganss (6), R.D. Blandford (1) and + CLASS collab...