Thermomagnetic duplication of chromium dioxide video tape

Video program material was duplicated thermomagnetically at copying speeds up to 165 cm/sec, which is 50 times real time for the VHS SP format. Blank chromium dioxide video tape was heated to above its Curie temperature and cooled while in close contact with a master tape bearing a mirror image video signal. The two tapes were held in close contact between a hard transparent polymethyl methacrylate wheel and a slightly deformable elastomeric roll, while heat was supplied by a neodymium YAG laser beam focused through the transparent wheel and the back of the copy tape onto the CrO2coating. The 1.06 μm beam was transmitted by the clear polyester base and efficiently absorbed by the opaque black chromium dioxide coating, raising the CrO2briefly above its 130° Curie temperature. On cooling, the CrO2layer was permanently magnetized in a mirror image of the master tape magnetic pattern. Heating and cooling took place in the 2.5 mm long nip between the two rolls in about two milliseconds, so the heat transferred to the polyester base was insufficient to deform it. The thermal copies had RF outputs approximately equal to real time copies.