Birefringence measurements in gradient-index rod lenses

Stress birefringence can be found in gradient-index (GRIN) materials becaus e they contain a variation in composition. GRIN glass fabricated by ion exc hange may contain stress from two different processes. These include a size difference between the exchange and the diffusing ions and a variation in the thermal-expansion coefficient across the gradient region. The optical p roperties of the stressed material are polarization dependent, and therefor e image quality is directly affected. We examine birefringence in GRIN rod lenses that have lengths more than ten times greater than their diameters. The effects are more easily observed in long rod lenses because of the larg e optical path lengths. (C) 1999 Optical Society of America.