1. Field of the Invention
This invention relates to mixtures of platinum dithiolene dyes and their use in optical recording elements.
2. Background of the Invention
In optical recording processes generally a laser beam is modulated, e.g., pulsed corresponding to a pattern of information, and focused onto the surface of a recording layer of a recording element.
The recording layer absorbs sufficient energy at the wavelength of the laser beam to cause small portions of the layer to burn, evaporate or otherwise deform. Generally, there is continuous relative motion between the laser and the layer so that, as the laser is pulsed or modulated, discrete pits or holes of varying length are created in the layer. The length and spacings of these holes constitute the encoded information.
The resulting recorded information is generally read back by turning down the power of the writing laser or by using another laser to which the layer is transparent, thereby precluding the reading laser from further physically altering the recorded layer. The reading beam is disposed to follow the same path as the recording beam. When the read beam is significantly absorbed by the recording, an optical density difference is detected between recorded and unrecorded areas. When the read beam is transmitted by the layer, light scattering caused by the recorded and unrecorded areas are detected as an optical density difference.
This density difference is detected by a photodetector positioned to receive laser radiation reflected from the underlying support where holes have been formed in the recording layer (in the case of a transmissive support). The detected density variations are converted back into electrical signals corresponding to the information recorded.
Optical recording elements comprising a binderless layer of a single platinum dithiolene dye as the recording layer are known. It is also known to coat a platinum dithiolene dye with a binder to form an optical recording layer. However, in each instance upon incubation crystallization of the dye occurs. Crystallization has a negative affect upon the carrier-to-noise ratio of amorphous recording layers. Moreover, experiments have shown that it is extremely difficult to dissolve sufficient amounts of such dyes in conventional coating solvents to make optical recording layers having the desired sensitivity.