  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.
