| 摘要 |
PURPOSE:To optionally decide an interval between two spots independent of an optical path difference. CONSTITUTION:A beam from a light source 6 is reflected by a recording medium 10, and after the reflected beam is transmitted through a beam splitter 20 forming a wave front division coating on the slope of a prism, is detected by an optical sensor 21. For instance, an auxiliary prism 19 with a rectangular shape is jointed on the slope of the prism, and a part of the beam, e.g. the beam of P polarization is reflected by the coating to emit the first beam 22. Further, the beam of e.g. S polarization transmitting through the coating is reflected plural times in the auxiliary prism, emitted as a second beam 24, and made away from the first beam by a prescribed interval DELTA in parallel. At this time, the interval between the first and second beams, that is, the interval of the spots formed by these beams is independent of the optical path difference of both beams. |
