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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.

The mechanical stress in thin films can have a deleterious effect on the quality of optical components by deforming the underlying substrate. In addition, the substrate might be deformed by gravity or stress induced by mounting. We suggest a method to compensate the substrate deformation by laser generated tensile stresses in the backside of the substrate. We show results for irradiation of the borosilicate glass Schott D263M with an ArF excimer laser. We measured the integrated stress in dependence of the laser fluence and corrected a sample for the deformation by a chromium coating. We show that also antibiaxial plane stress components can be induced. For precise corrections a scheme for stabilization of the generated surface stresses still needs to be developed.

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