| 摘要 |
A three slit interferometric focus control device capable of focal positioning accuracies on the order of 300 angstroms. The device includes a zero path Michelson interferometer with reference and movable legs comprising, respectively, an annular reference mirror and the surface to be brought into position of best focus. A three slit plate positioned between the beamsplitter and energy detection device allows interference of light reflected off the movable and reference surfaces, creating an amplitude modulation signal. The energy detection device will measure a minimum energy intensity at the position of best focus.
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