In situ pulse dispersion estimation via third-harmonic generation interferometric autocorrelation for multiphoton microscopy

Third-harmonic generation interferometric autocorrelation with D-LUTE estimates baseline GDD and TOD at the objective focal plane, showing pulse durations 1.4–1.7× transform-limited at 1300 and 1600 nm.

• Why it matters: Three-photon microscopy depends on excitation pulse quality, but GDD/TOD are rarely measured at the imaging location, risking reduced peak intensity and degraded imaging performance.
• What they did: The authors add a compact THG interferometric autocorrelator module to two microscope systems, fit baseline GDD/TOD using D-LUTE with a joint two-measurement procedure validated on synthetic data.
• The result: At 1300 and 1600 nm, pulse durations are longer than transform limit at every condition, driven predominantly by TOD that varies ~2.7-fold between systems, and in mouse brain shows no measurable broadening up to nearly a millimeter depth.