| 摘要 |
PURPOSE:To decrease and correct the change of the exit angle even if the wavelength of light changes by setting of the Abbe number of the 1st prism of a beam shaping optical system larger than the Abbe number of a 2nd prism. CONSTITUTION:The beam shaping optical system is constituted of the 1st prism 21 and the 2nd prism 22 and the elliptical shape of a light source part 11 is shaped to a circular beam. The Abbe number of the 1st prism material is set larger than the Abbe number of the 2nd prism material. The dispersion of the 2nd prism 22 is, therefore, made larger than the dispersion of the 1st prism 21 and the beam is shifted in the direction where the beam shift by a wavelength change is corrected at the time when the incident collimated beam on the 1st prism 21 is emitted through the 2nd prism 22. The shift quantity is, therefore, decreased even at the time of a wavelength change which arises right after switching at the time of reproducing and recording. |
