Optical reading and recording device containing a radiation source which has a substantially constant mean heat dissipation during reading and recording

摘要

A radiation beam is generated by a radiation source such as laser. An optical system focuses the radiation beam at a recording layer (in a disc-shaped carrier) of a type in which an optically detectable change is caused to take place if the recording layer is heated to above a write temperature. The recording layer is scanned by the radiation beam by means of a motor. A control circuit feeds the radiation source with electric power which is converted in the radiation source partly into heat and partly into radiation for the radiation beam. The control circuit operates in a read mode in which the power supplied to the radiation source has a value at which the rise in temperature of the recording layer caused by the radiation beam is insufficient to cause an optically detectable change to take place. The control circuit also operates in a write mode in which the radiation source is intermittently fed with power pulses having a strength at which the rise in temperature of the recording layer caused by the radiation beam is sufficiently large to cause an optically detectable change to take place. The power pulses generated in the write mode have a strength and a duration for which the corresponding mean heat dissipation in the radiation source is substantially equal to the mean heat dissipation in the radiation soure in the read mode. As a result, the wavelengths of the generated radiation in the read mode and write mode are equal, thereby avoiding problems with a wavelength dispersion in the optical path of the optical system.