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Abstract

Apparatus for measuring the power of radiation that includes float means (16) and force balancing means (48, 50, 60, 80). The float means includes a target (46) for the radiation and is constructed such that the net gravitational force, including buoyancy force, if any, acting on the float means tends to accelerate the float means in a first direction. The force balancing means includes drive means (80) for providing a drive signal and means (50) responsive to the drive signal for exerting a balancing force on the float means in a second direction opposite the first direction, such that the magnitude of the balancing force corresponds to a characteristic of the drive signal. The drive means is adapted to vary such characteristic of the drive signal, to thereby vary the balancing force, such that when the drive signal is controlled so as to cause the float means to be suspended at a predetermined height, the characteristic of the drive signal provides a measure of the force exerted on a target as a result of the radiation striking the target, and therefore of the power of the radiation. The float means preferably comprises a magnetic material (48) and the force balancing means comprises an electromagnet (50). The apparatus may directly measures the force of acoustical or electromagnetic radiation on the target, or may measure the change in buoyancy of the target caused by electromagnetic radiation heating and changing the density of the target.

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