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The special symmetry properties of second-harmonic generation at the surface of a GaAs crystal are used in a technique which measures the shape of the fast pulses from a mode-locked Nd-glass laser. The pulses studied were found to have a full width at half power of between 4 and 6 picoseconds. The technique is capable of measuring pulse widths at least as short as 4 × 10−13 sec.
John A. Armstrong (Sun,) studied this question.