THERMOMAGNETIC ANALOG RECORDING.

A thermomagnetic method is described for recording an analog signal on a CrO//2 magnetic tape, using a conventional magnetic head and a laser beam as a heating source. Analog recording is achieved by locally raising the temperature of a small region on the continuously moving tape and applying simultaneously a small external magnetic field which varies with the input signal. Since the coercivity of a part, except for a heated area, is large, the part is not affected by the small applied magnetic field. The local heating was applied by a 3. 0mm diameter He-Ne unmodulated laser beam focused with a microscope objective lens into a spot of 20 mu m in diameter on the coating of the tape. Recording characteristics are shown for 7. 5 mw of laser power. Recording was provided by a magnetic head with an analog signal current flowing through the winding; the head with a 200 mu m gap was in contact with the tape backing. Magnetization of the CrO//2 tape depends in a complicated way on the manner by which heat diffuses into the tape, recording wavelength, the laser power, the intensity of magnetic field, and so on.