Probing ~100 AU Intergalactic Mg II Absorbing ``Cloudlets'' with Quasar Microlensing

Intergalactic Mg II absorbers are known to have structures down to scales ~10^2.5 pc, and there are now indications that they may be fragmented on scales <~10^-2.5 pc according to Hao and coworkers. When a lensed quasar is microlensed, the microimages of the quasar experience creation, destruction, distortion, and drastic astrometric changes during caustic crossings. I show that quasar microlensing can effectively probe Mg II and other absorption ``cloudlets'' with sizes ~10<sup>-4.0</sup> to 10<sup>-2.0</sup> pc by inducing significant spectral variability on timescales of months to years. With numerical simulations, I demonstrate the feasibility of applying this method to Q2237+0305, and I show that high-resolution spectra of this quasar in the near future would provide a clear test of the existence of such metal-line absorbing ``cloudlets.''