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Because existing calorimeters are not adequate to measure Q -switched laser pulses accurately, we have designed a calorimeter in which the beam passes through two glass disks, one of green plate (absorbing from 0·6-1·6 μm), the other of clear plate. A laser pulse creates a temperature difference which is sensed by thermocouples. 70% of the incident energy passes through the device and is available for experiment. Thermal drift is low enough to obtain 1% accuracy at 10 mJ input energy. For energies up to 0·1 J, any pulse length from 1 s to 0·1 ps can be used. Energies up to 50 J can be used provided the power density at the glass does not exceed 40 MW cm −2 . The device is dependent on a conventional calorimeter for calibration (limiting the absolute accuracy to 2%), and the sensitivity is wavelength dependent, thus limiting its use to wavelengths where a free running laser is available; ways of overcoming this disadvantage are discussed.
J. G. Edwards (1970) studied this question.