Optical detection of magnetic data using magnetooptic indicators with   in-plane magnetization
  We investigate detection of magnetic data using magnetooptical indicators with in-plane magnetization. A simple model for the magnetooptical detection system is presented. We find that the signal to noise ratio changes strongly with the bit size, the polarization noise and the distance between the magnetic carrier and the indicator. In particular, it is found that within our model a signal to noise ratio of 30 is possible for a bit size of 200 nm. We also estimate the resolution of the system, and find that a spot size of $\sim 200$ nm can be obtained using a suitably designed solid immersion lens. Finally, we discuss detection of several magnetic tracks simultaneously. 
L.E. Helseth, E.I. Il'yashenko, M. Baziljevich and T.H. Johansen