Simple technique to reveal a slow nonlinear mechanism in a z-scanlike n_2 measurement

We report a simple technique to determine whether the nonlinear mechanism that dominates the results of a z-scan n2 measurement is slower than the duration of the exciting pulse. In this technique, the temporal waveform of the beam transmitted through an aperture is observed, instead of total energy per pulse as in a normal z-scan measurement. Using a doubled Nd:YAG laser, we observed a slow response in index change in the absorptive material methyl nitroaniline, whereas CS2 showed fast response compared with the laser pulse width of 65 ns.

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