Method for Pulsewidth Measurement of Ultrashort Light Pulses Generated by Phase-Locked Lasers using Nonlinear Optics

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Abstract
A nonlinear optics experimental arrangement is proposed for the measurement of the pulsewidth of ultrashort light pulses. The experiment consists of a Michelson‐like arrangement in which each light pulse is split into two pulses which are delayed and polarized orthogonally to one another. The two pulses are propagated as ordinary and extraordinary rays through a nonlinear crystal whose orientation is chosen so that the second harmonic is only generated by the interaction arising from the superposition of these two pulses. The pulsewidth is obtained from the dependence of the intensity of the second harmonic upon the relative delay of the pulses. This method suggests itself for coincidence measurements of pulse delays including those due to optical path variations. The experimental arrangement is given and an analysis for light pulses from an ideal phase locked laser is carried out. The resolution time of the coincidence method as limited by phase matching considerations is calculated. For the example of a phase‐locked Nd laser and a 1‐mm‐thick KDP crystal the numerical value of the resolution time is about 1 psec.