Torsion Pendulum Photometer

An instrument is described for making fundamental measurements of high energies of pulsed laser beams. The principle of operation is the transfer of beam-photon momentum to angular momentum of a double-reflecting ballistic torsional pendulum. The operating pressure is below 5×10−5 mm Hg. The sensitivity is 2.55±0.04 cm/J, and damping of initial oscillations before making a measurement is not required. In addition to providing the capability of simultaneous energy measurement and use of a laser beam, the measurements made with this instrument appear to be more accurate than with a commercial calorimeter used for comparison.