Propagation of photons in homogeneous magnetic fields: index of refraction

The index of refraction associated with the vacuum polarization induced by homogeneous magnetic fields is calculated for two cases: high energy photons traversing fields weak compared with the critical field, H/sub cr/ = m$sup 2$c$sup 3$/eh approximately 4.41 x 10$sup 13$ G; and low energy photons in fields of arbitrary intensity. Some implications for the physical optics of intense magnetic fields are briefly discussed. (auth)