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Low thermal stress birefringence imaging lens

  • US 9,069,105 B2
  • Filed: 10/01/2013
  • Issued: 06/30/2015
  • Est. Priority Date: 05/21/2010
  • Status: Active Grant
First Claim
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1. A lens system having reduced susceptibility to thermally-induced stress birefringence for imaging an object plane onto an image plane comprising;

  • a plurality of lens elements arranged to image the object plane onto the image plane,wherein the lens element that experiences a highest optical power density from transiting light when the lens system is used to image the object plane onto the image plane is fabricated using a glass having a negligible susceptibility to thermal stress birefringence as characterized by a thermal stress birefringence metric;

    wherein the other lens elements are fabricated using glasses having a negligible or a moderate susceptibility to thermal stress birefringence as characterized by the thermal stress birefringence metric, at least one of the other lens elements being fabricated using a glass having a moderate susceptibility to thermal stress birefringence;

    wherein the thermal stress birefringence metric has the form;


    M1

    κ

    α

    E
    /(K·

    (1−

    μ

    ).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 the negligible susceptibility to thermal stress birefringence satisfy the condition that M1

    0.1×

    10

    6
    W

    1
    and the glasses having the moderate susceptibility to thermal stress birefringence satisfy the condition that 0.1×

    10

    6
    W

    1


    M1<

    1.6×

    10

    6
    W

    1
    .

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