Femtosecond near-field spin microscopy in digital magnetic heterostructures

We have designed a low-temperature femtosecond-resolved near-field scanning optical microscope to study spatiotemporal excitonic spin behavior in magnetic semiconductor heterostructures. Local disorder introduced by focused-ion-beam implantation reduces the otherwise large Zeeman splittings in modest magnetic fields, creating a planar spin-dependent energy landscape for diffusing carriers. Near-field polarization-resolved static and femtosecond measurements map out excitonic spin behavior with similar to 125 nm spatial resolution, revealing spin-dependent diffusion. We demonstrate the applicability of two distinct time resolved techniques in the near held, and discuss Limitations on the measurement of polarized luminescence from semiconductors in the near field. (C) 1996 American Institute of Physics.