Spatially resolved spectra in semiconductor quantum structures: Spatially averaged spectra compared to far-field spectra

The optical spectra of homogeneous surface systems can display remarkable differences in the near and far zones. The spectral changes occur due to the loss of evanescent modes in the far zone. These changes clearly show that near-field optical spectroscopy and microscopy, besides resolving nanometric structures give also access to excitations that cannot be revealed in the far zone. Are these spectral changes detectable in real systems affected by disorder and imperfections? We address this issue by presenting a theoretical analysis of the local optical properties of semiconductor quantum wells including the effects of interface fluctuations. In particular we compare the far-field absorption spectrum with spatially averaged absorption spectra calculated at different spatial resolutions. We find that summing up local optical spectra does not reproduce the global spectrum in contrast to findings at diffraction-limited resolutions.