Reproduction of sound from old disks by the laser diffraction method

A laser diffracton method was developed as a noncontacting nondestructive means of reproducing the sound from old disk-type records. In the method, the sound signals encoded in the sound grooves are converted to the direction of the linear structure in the diffraction patterns which are produced by the reflection of a laser beam from the sound grooves. The tracking is performed using a variation of the intensity distribution of the diffraction pattern when the sound grooves deviate from the illuminating spot. The properties of the reproduced sound are discussed in comparison with those reproduced by the laser-beam reflection method [Appl. Opt. 25, 597 (1986)] developed for wax phonograph cylinders and by traditional phonographs.