  Ultracold neutrons (UCNs) are a useful tool for fundamental physics
experiments. They can be used to probe the lifetime of free neutrons, search
for new CP violating processes and exotic interactions beyond the Standard
Model, perform Ramsey spectroscopy, and carry out neutron-optical interference
experiments. All of these experiments require high neutron count rates for good
statistics. For optimal exploitation of experimental beam time, these
experiments need to be prepared and, at times, even simulated in advance. To
this end, it is crucial to know the velocity-dependent UCN flux at each beam
position. Knowing the absolute neutron flux also allows for an absolute
calibration of previously gathered data. Using the same time-of-fight
experimental setup, we have measured the differential neutron flux of three out
of the four UCN beam ports at the PF2 instrument at Institut Laue--Langevin,
Grenoble. These beam ports are commonly used for UCN flux experiments and
proof-of-principle tests.
