Importance

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Abstract

A substrate for an information recording medium has a microwaviness average height Ra' not greater than 0.05 microinch as measured by a contactless laser interference technique for measurement points within a measurement region of 50 .mu.m.quadrature.-4 mm.quadrature. on a surface of the substrate. The microwaviness average height Ra' is given by: ##EQU1## where xi represents a measurement point value of each measurement point, x representing an average value of the measurement point values, n representing the number of said measurement points. Alternatively, the substrate has a waviness period between 300 .mu.m and 5 mm and a waviness average height Wa of 1.0 nm or less as measured by the contactless laser interference technique for measurement points in a measurement region surrounded by two concentric circles which is spaced from a center of a surface of the substrate by a predetermined distance. The waviness average height Wa is given by: ##EQU2## where Xi represents a measurement point value of each measurement point, X representing an average value of the measurement point values, n representing the number of said measurement points.

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First Claim