Patent ID: 8830580
Filing Date: 2014-09-09
Classification: G02B,G03B,H04N

Abstract:
1. Imaging optics having reduced susceptibility to thermally-induced stress birefringence for imaging an object plane to an image plane; comprising: an aperture stop positioned between the object plane and the image plane; a first group of optical elements located on the object plane side of the aperture stop; and a second group of optical elements located on the image plane side of the aperture stop; wherein the optical elements in the first and second groups of optical elements that are immediately adjacent to the aperture stop, on both the object plane side and the image plane side, are refractive lens elements fabricated using optical materials having a negligible susceptibility to thermal stress birefringence as characterized by a thermal stress birefringence metric; and wherein the other optical elements in the first and second groups of optical elements, that are not the refractive lens elements immediately adjacent to the aperture stop, are a combination of reflective optical elements and refractive lens elements, the reflective optical elements including non-planar reflective optical elements having optical power, and the refractive lens elements being fabricated using optical materials having a negligible or a moderate susceptibility to thermal stress birefringence as characterized by the thermal stress birefringence metric, at least one of the refractive lens elements being fabricated using a glass having a moderate susceptibility to thermal stress birefringence; wherein the thermal stress birefringence metric includes a factor having the form: where ρ is a coefficient of thermal expansion of the glass, κ is a stress optical coefficient of the glass, α is a light absorption coefficient of the glass, E is a modulus of elasticity of the glass, K is a thermal conductivity of the glass, and μ is a Poisson's ratio of the glass, and wherein the glasses having a negligible susceptibility to thermal stress birefringence satisfy the condition that M 1 ≦0.1×10 −6 W −1 and the glasses having a moderate susceptibility to thermal stress birefringence satisfy the condition that 0.1×10 −6 W −1 ≦M 1 <1.60×10 −6 W −1 .