  We present a novel cathodoluminescence spectroscopy technique which combines
a 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 new technique for the
characterization of photonic structures with deep subwavelength dimensions.
