This paper addresses developments in the understanding of intra-cavity elements in ion lasers using sol-gel prepared silica. Growing interest centres around the generation of coherent light in the near u.v. spectrum. Sol-gel silica offers unprecedented levels of purity and homogeneity for critical intra-cavity applications and may well solve the problem of creating colour-centre free Brewster windows for use in the u.v.

We also report new work which makes use of the porous phase of such material and show how it is directed at one of the early bastions of photographic science – Lippmann's photography.