| 摘要 |
1509495 Disc record SONY CORP 8 April 1976 14397/76 Heading G5R In a disc record having a spiral groove of constant pitch and with the depth of groove varying with recorded signal, the groove has an inverted bell shaped cross-section of substantially the shape of a Gaussian distribution curve, which varies with groove depth to maintain the groove width at the record surface substantially constant. The signal recorded can be video information. The record is formed from a disc master 28 including a glass base 30 and a layer of photoresist material 29 in which a modulated spiral groove (or modulated spiral ridge with negative photo-resist material) is formed by developing the layer after exposure by a modulated light beam from a laser light source whilst rotating the disc and moving it in the direction of arrow 32. In order to produce the required groove shape a laser source is used which has a beam with a substantially Gaussian distribution of light intensity in the direction transverse to the spiral track formed in the master. As shown in Fig. 6 increasing depth of groove results in little change in track width. In order to prevent the amount of light per unit area impinging on the disc increasing as the scanning beam moves towards the record centre, the light intensity is reduced by a compensating filter 26 in the form of a grey scale which is moved in synchronism with movement of the beam along the disc radius.
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