| 摘要 |
A lens system having discrete variations of focal length at discrete distances of radius outward from the optic axis for focussing light of plural wavelengths. The lens system which directs a laser beam onto a target for ablation or exposure applications includes one set of lens elements to handle short wavelength light used for ablation or exposure applications, and another set of lens elements to handle long wavelength light used for alignment applications. The lens system which provides for the ablation or exposure functions at short wavelength and for through-the-lens alignment at a longer wavelength and higher numerical aperture consists of three elements. Two outer lens elements are made entirely of fused quartz. An inner element disposed between the two outer lens is composed of any material such as optical glass. The inner lens element has a hole ground through its center.
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