Measuring ultra-short pulse widths before and after the objective with a home built autocorrelator

In multiphoton microscopy, measurements and compression of the laser pulse width at the setup plays an important role in optimizing the fluorescence output with minimal laser power applications. For example, in deep two and three-photon intravital microscopy it is very crucial to have shortest laser pulses for efficient fluorescence excitation with lowest possible laser power at the sample. There are several published experimental methods and techniques for measuring the group delay dispersion and pulse width. Yet, there are practical limitations for their implementation and beam optimization at intravital setups in individual labs or microscope facility. Here, we present a method to construct a portable optical collinear autocorrelator, to probe the beam directly after the objective and at desired place in the beam path to measure the pulse width, and to optimize the pulse width with a pulse compressor. Finally, we demonstrate that the method increases fluorescence excitation efficiency in three-photon microscopy.