A solar sail uses the pressure of sunlight to fly a space probe
through a solar wind. An M2P2 solar sail is made using a powerful
magnetic field which supports a plasma. Could an M2P2 solar sail also
be used to focus or filter sunlight? I am told that the field deflects
particles from the solar wind and that "maybe you could concentrate
more of them into a volume than normal and use them as a lens" and
also that you could "polarize light but not bend it." I pose the
question with regard to a large-scale space telescope, or
focused/directed solar energy.

I think the short answer is no. The M2P2 sail is "blown along" by
charged particles which, under ideal conditions, could be focused. The
solar wind is notorious for being far from ideal, so I doubt that
focusing could be controlled.

Light would be scattered by dust in the sail, and hence polarized, but not focused.

Ian G.