| 摘要 |
A light returning target for a photometer. The light returning target comprises a ball lens, and a cradle. The cradle has a hemispherical receptacle in which the lens is intimately received. Preferably, the lens is formed of fused silica, the receptacle is polished sufficiently to reflect, more than it scatters, light, and at least the surface of the receptacle is formed of a material that absorbs, more than it reflects, light.
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