| 摘要 |
PURPOSE:To form an isotropic spot by a simple optical system by providing a beam converting prism in an optical system leading a beam from a semiconductor laser element to an information recording medium. CONSTITUTION:A beam having an expansion angle, emitted from one end face of a semiconductor laser element 1 passes through a coupled lens 2, a prism 7 and an objective 3, and forms a spot 5 on a disk 4. When angles at e<-2> in the horizontal direction and the vertical direction of an emitted light distribution in a distant view field image of the beam from the laser element 1 are denoted thetaH and thetaV, and a hemihedral angle made by the laser 1 and the lens 2 is denoted as theta, a numerical aperture of the lens 2 is selected so as to satisfy theta<thetaH<=thetaV, the prism 7 is formed so as to satisfy a prescribed condition, and the horizontal direction of expansion of the beam is expanded and made to coincide with expansion in the vertical direction, by which an isotropic spot is obtained by a simple optical system. |
