Copy tape parameters for thermomagnetic duplication

Thermomagnetic duplication (TMD) of video program material, using mirror master tape with high Curie T. (>500°C) and chromium dioxide copy tape (Curie T. 130°C), was performed at a speed of 4 m/sec using a neodymium YAG laser as heat source to optimize tape parameters for TMD mode, and to study differences between TMD and conventional helical-scan video recording. Optimum TMD copy tape uses CrO2with high Hc, diluted with some non-magnetic pigment in a thin coating. TMD has greater latitude than realtime recording in chroma output and S/N. Dilution (from 50% to 20% by volume) causes 8 dB loss of chroma output in realtime but only 3, 4dB in TMD. The same dilution causes chroma (AM) S/N to drop by 3 dB in realtime, whereas TMD mode maintains a constant value of +4 dB. Very low coverage (30 mg CrO2/dm²or less) copy tapes appear to be within practical reach.