Stopping power and Cherenkov radiation in photonic crystals

Electron energy loss spectroscopy (EELS) induced by fast electrons in electron microscopes are used to probe photonic structures. Some of the loss features are shown to be associated to the excitation of radiative modes in the samples (Cherenkov radiation), from where information on photonic bands is extracted. The case of a 1D crystal is qualitatively discussed to explain the physics behind Cherenkov radiation in photonic crystals. For an electron beam collimated on one of the pores of 2D crystal consisting of a porous alumina film with 100-nm lattice constant, theory predicts a Cherenkov feature at around 6-9 eV, which is in excellent agreement with experiment. Finally, the features of the loss spectra are shown to be strongly correlated with the density of photonic states, suggesting the potential application of this technique to probe the quality and actual performance of photonic crystals.