Index variation from field-assisted ion exchange.

Concentration distributions produced from the combined effect of a unidirectional electric field and diffusion are presented for a slab and for a hollow cylinder. A field in the direction such that slow ions follow fast ones results in a stationary distribution that moves with a constant or nearly constant velocity. If the field is in the opposite direction, it tends to mix the ions, and an entirely different distribution that never reaches a steady state is obtained. These results are discussed in the context of the production of graded-index optical materials.