Unstable Bessel beam resonator

We examine the properties of a Bessel-Gauss resonator design studied previously, and explain the bell-shaped modulation imposed on its lowest-order mode in terms of an equivalent linear cavity. We propose an unstable cavity to eliminate this effect, and obtain modes whose intensities resemble a true Bessel function along the diameter of the defining aperture of the resonator. (C) 2003 Published by Elsevier B.V.