| 摘要 |
A magnetic recording medium having a substrate disc with microscopic bumps formed by focusing a laser beam, wherein spacings D between adjacent bumps in the circumferential direction of the disc are varied so that formula (1) is satisfied:1</=[(Dmax-Dmin)/Davg]x100(%)</=200(1)wherein Dmax, Dmin and Davg are the maximum, minimum and average spacings, respectively, as determined by a method wherein 2.5% of the total number of spacings D, having the largest dimensions, and 2.5% of the total number of spacings D, having the smallest dimensions, are excluded; and Dmax, Dmin and Davg are measured on the remaining 95% of the total number of spacings D. The variation of bump spacings is attained, for example, by (i) modulating the pulse repetition frequency F of laser beam so that the ratio of "(Fmax-Fmin)/Favg" is maintained within the range of 0.01 to 100, wherein Fmax, Fmin and Favg are the maximum, minimum and average values, respectively, of the F of laser beam; (ii) by transmitting the laser beam through a mask having perforations, wherein spacings between adjacent perforations in the mask are varied, i.e., not constant; or (iii) by reflecting the laser beam by mirrors working at a continuously varied reflection angle.
|
