Angle-resolved cathodoluminescence spectroscopy
We present a cathodoluminescence spectroscopy technique which combines deep subwavelength excitation resolution with angle-resolved detection capabilities. The cathodoluminescence emission is collected by a paraboloid mirror (effective NA = 0.96) and is projected onto a 2D CCD array. The azimuthal and polar emission pattern is directly deduced from the image. As proof of principle, we use the technique to measure the angular distribution of transition radiation from a single crystalline gold surface under 30 keV electron irradiation. We find that the experiment matches very well with theory, illustrating the potential of this technique for the characterization of photonic structures with deep subwavelength dimensions.