Record disk and method for producing the same with constant width groove

In a record disk having a continuous spiral groove opening at a surface thereof with the depth of the groove varying along the latter for representing recorded information;

• the width of said groove at the opening thereof being substantially uniform along the length of the groove regardless of the depth of said groove, and said groove having a cross-section which is symmetrical about the median of the groove with each of the opposite side surfaces of the groove at any location therealong being defined approximately by the equation
• d.sub.x = d.sub.o .multidot. exp [-(x/w).sup.2 ]
• in which d.sub.o is the depth of the groove at said median, w is the distance from said median to the point at each of said side surfaces where the depth of the groove is d.sub.o /e (e being the base of the natural logarithm), and d.sub.x is the depth of the groove at the respective side surface at a distance x from said median.

In the method of optically producing a reproducible recording of information by directing a laser light beam against a substantially flat surface of a positive type photo-resist material on an original recording disk, moving the recording disk and light beam relative to each other for scanning of a spiral track of constant pitch on said recording disk by said light beam, modulating the intensity of said light beam by signals to be recorded, and developing said surface of the photo-resist material after said scanning thereof by the modulated light beam so as to form a continuous spiral groove opening at said surface with the depth of said groove varying therealong in correspondence with said signals to represent said information;

• the improvement of providing said laser light beam, at said surface of the photo-resist material, with substantially a Gaussian distribution of laser light intensity in the direction transverse to said spiral track which is scanned on the recording disk such that said groove which is formed thereby has substantially the shape of a Gaussian distribution curve with a substantially uniform width at the opening thereof regardless of the depth of said groove.

A playable record disk having a continuous spiral groove of constant pitch in a surface thereof with the depth of the groove varying along the latter for representing recorded information;

• said playable record disk being molded in correspondence with an original recording disk which is produced by directing a laser light beam against a layer of positive type photo-resist material on the original recording disk while the latter and said light beam are moved relative to each other for scanning of a spiral track of constant pitch on the original recording disk and while the intensity of said laser light beam is modulated by information signals to be recorded, with the intensity of laser light in said beam at said layer of photo-resist material having substantially a Gaussian energy distribution across said beam, and then developing said layer of photo-resist material to form a continuous spiral groove opening at the surface of said photo-resist material having the shape of a Gaussian distribution curve with a substantially uniform width at said opening thereof regardless of the depth of said groove.