| 摘要 |
An objective lens is described, which is switchable between a far-field mode and a near-field mode. The objective lens comprises a lens, an optical element having a variable refractive index and a solid immersion lens, which are disposed on a common optical axis, wherein the optical element is arranged at a convex side of the solid immersion lens and has a top and a bottom surface arranged adjacent to each other in a direction of the optical axis, the bottom surface having a concave shape that is adapted to the shape of the convex side of the solid immersion lens and the top surface having a curvature that is lower than a curvature of the convex side of the solid immersion lens, and wherein a difference between a refractive index of the optical element and the solid immersion lens is small in the far-field mode so that the solid immersion lens and the optical element act substantially as a single optical element in the far-field mode, whereas the difference is large in the near-field mode so that the optical effect of the solid immersion lens is significant in the near-field mode.
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