Influence of the longitudinal inhomogeneity of the refractive index of a nonlinear crystal on the parametric gain

Abstract

I describe some of the principal landmarks coming up in the medium to long term future of observational extragalactic astronomy. Rather than attempting to compile an exhaustive catalogue, I have instead made a completely biased sample of some of the developments across the electromagnetic spectrum (including x-ray, optical, infra-red, submillimetre and radio) that seemed most exciting to me. Among the 'greatest hits' I have picked are XEUS, GAIA, NGST, OWL, ALMA and SKA.PACS numbers: 9555, 9862, 9880