Properties of axicon systems for collecting foil-excited accelerator beam spectra.

We describe properties of a particular kind of light-collecting system used for spectroscopy of light emitted by foil-excited accelerator beams. This system, built to test the possibility of obtaining narrow lines from such sources, has as its basic optical element an axicon, a conical reflector with its axis coincident with that of the accelerator beam. We consider the properties of an axicon followed by a lens and aperture and point out some criteria that are appropriate to the design of optical systems using such devices. Experimentally we find that scattering of the accelerator beam by the foil contributes significantly to spectral linewidths.