We show that in a nonlinear microscopy system the effects of chromatic and spherical aberrations are revealed by a difference in the focal positions corresponding to the shortest pulse duration and the minimum lateral resolution. By interpreting experimental results from a high-numerical-aperture two-photon microscope using a previously reported spatio-temporal model, we conclude that the two-photon autocorrelation of the pulses at the focal plane can be used to minimize both the chromatic and spherical aberrations of the system. Based on these results, a possible optimization strategy is proposed whereby the objective lens is first adjusted for minimum autocorrelation duration, and then the wavefront before the objective is modified to maximize the autocorrelation intensity.
Rutkauskas, M., Reid, D. T., Garduño-Mejía, J., & Garduño-Mejía, J. (2017). Time-domain measurements reveal spatial aberrations in a sub-surface two-photon microscope. Applied Optics, 56(17), 5047-5053. https://doi.org/10.1364/AO.56.005047