Information recording medium, reproducing device and reproducing method

An information recording medium comprising at least three information recording layers,

• wherein if the readout power of a laser beam in reading information from an nth one L(n) (where n is an integer that is equal to or greater than zero) of the information recording layers, which are counted sequentially from one of the information recording layers that is located most distant from the data side of the information recording medium, is identified by Pw(n), and
• if the readout power of the laser beam in reading information from an (n+a)th one L(n+a) of the information recording layers is identified by Pw(n+a) (where a is an integer that satisfies n+a≧0 and a≠0), and
• if the base thickness between the information recording layers L(n) and L(n+a) is identified by D,
• then the information recording medium satisfies
• 100×Pw(n)/Pw(n+a)≧−0.1238×D2−2.772×D+106.56, and Pw(n)≦Pw(n+a).

A method of making an information recording medium with k information recording layers (where k is an integer that is equal to or greater than three), the method comprising the steps of:

• forming the k information recording layers, from which information is retrievable using a laser beam with a wavelength of 400 nm to 410 nm through an objective lens with a numerical aperture of 0.84 to 0.86, on a substrate with a thickness of 1.1 mm;
• forming (k−1) spacer layers between the information recording layers;
• and
• forming a protective coating with a thickness of 0.1 mm or less on the kth one of the information recording layers as counted from the substrate,
• wherein the step of forming information recording layers includes:
• making either concentric or spiral tracks on one of two groups of the information recording layers that are either odd-numbered or even-numbered as counted from the substrate so that the laser beam scans that group of information recording layers from some outer radial location on the information recording medium toward the inner edge thereof;
• and
• making either concentric or spiral tracks on the other group of the information recording layers that are either even-numbered or odd-numbered so that the laser beam scans that group of information recording layers from some inner radial location on the information recording medium toward the outer edge thereof, and
• wherein if the readout power of the laser beam in reading information from an nth one L(n) (where n is an integer that is equal to or greater than zero) of the information recording layers, which are counted sequentially from one of the information recording layers that is located most distant from the data side of the information recording medium, is identified by Pw(n), and
• if the readout power of the laser beam in reading information from an (n+a)th one L(n+a) of the information recording layers, which are counted sequentially from the most distant information recording layer from the data side of the information recording medium, is identified by Pw(n+a) (where a is an integer that satisfies n+a≧0 and a≠0), and
• if the base thickness between the information recording layers L(n) and L(n+a) is identified by D,
• then 100×Pw(n)/Pw(n+a)≧−0.1238×D2−2.772×D+106.56, and Pw(n)≦Pw(n+a) are satisfied.