Abstract: A description is given of an optical information carrier comprising a substrate (1), a thin reflective layer (5), a dielectric layer (7), a phase-change recording layer on the basis of GeTeSe (9), a dielectric layer (11), an opaque metal reflective layer (13) and a protective layer (15). The information carrier can be inscribed, erased and read by means of a laser-light beam a and, in the inscribed state, complies with the CD-industrial standard. The recording layer (9) comprises an alloy having the composition Ge.sub.x Te.sub.y Se.sub.z, in atom %, wherein47.ltoreq.x.ltoreq.5317.ltoreq.y.ltoreq.4112.ltoreq.z.ltoreq.30andx+y+z.gtoreq.96 and, preferably, equal to 100.

Abstract: An optical reader for record carriers of a two types adapted for scanning with radiation beams. The information structures of the respective types are arranged in tracks. The structure of the second type has a phase structure in which effect areas alternate with intermediate areas, and is adapted for scanning with radiation of a wavelength longer than that for the first type. This reader scans both types with radiation of the first wavelength. An analog read signal is detected from radiation received from a scanned track. For reading the second type, first and second comparators supply respective detection signals if the differences between values of the read signals, separated by a given time interval, are greater than a given positive threshold or more negative than a given negative threshold. A signal recovery circuit derives a binary information signal from the first and second detection signals.

Abstract: An optical information carrier comprising a substrate, an auxiliary layer bounded by dielectric layers, a thin reflection layer, a dielectric layer, a phase-change layer, a dielectric layer, a tight metal reflection layer and a protective layer. The information carrier is recordable and erasable by a laser-light beam and can be played in a conventional CD player. The auxiliary layer consists of selenium or AlGaAs, and has the property that the absorption increases substantially at temperatures above 70.degree. C. An information carrier comprising this auxiliary layer can be recorded with a lower laser power as compared to information carrier which does not comprise the auxiliary layer.

Abstract: A device in which a radiation source generates a radiation beam of a first wavelength. The scanning spot 7 generated by this radiation beam follows the centerline 13 of a track 8 to be scanned on a first type of record carrier designed for this wavelength. When a second type of record carrier is being read, in which the information is stored in a phase structure designed for a wavelength which is longer than the first wavelength, the read spot 7 follows the edge of a track 38 to be read instead of the centerline 18. In this way it is possible to generate a satisfactory information signal not only from the first type of record carrier but also from the second type of record carrier.