Freeform shaping of fused silica substrates via viscous deformation induced by a laser patterned, stressed film.

Freeform optics enable improved optical solutions but their fabrication usually requires complicated precision machining processes. We report on an approach for freeform shaping of optical surfaces via a stress-induced viscous deformation of glass plates. We studied the deformation of fused silica substrates covered by specifically laser patterned films of substoichiometric silicon oxide during annealing at about 1100 °C in an oxidizing ambient. The obtained large deformation of the substrates can be understood by a mostly viscous deformation but can be described in analogy to a purely elastic deformation. Our results demonstrate the feasibility of a method for freeform shaping of individual optical substrates that only requires the preparation of a flat surface.