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Abstract

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.ltoreq.[(D.sub.max -D.sub.min)/D.sub.avg ].times.100(%).ltoreq.200(1) wherein D.sub.max, D.sub.min and D.sub.avg 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 D.sub.max, D.sub.min and D.sub.avg 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 '(F.sub.max -F.sub.min)/F.sub.avg ' is maintained within the range of 0.01 to 100, wherein F.sub.max, F.sub.min and F.sub.avg 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.

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