  Microlenses with typical stellar masses (a few ${\rm M}_{\odot}$) have
traditionally been disregarded as potential sources of gravitational lensing
effects at LIGO/Virgo frequencies, since the time delays are often much smaller
than the inverse of the frequencies probed by LIGO/Virgo, resulting in
negligible interference effects at LIGO/Virgo frequencies. While this is true
for isolated microlenses in this mass regime, we show how, under certain
circumstances and for realistic scenarios, a population of microlenses (for
instance stars and remnants from a galaxy halo or from the intracluster medium)
embedded in a macromodel potential (galaxy or cluster) can conspire together to
produce time delays of order one millisecond which would produce significant
interference distortions in the observed strains. At sufficiently large
magnification factors (of several hundred), microlensing effects should be
common in gravitationally lensed gravitational waves. We explore the regime
where the predicted signal falls in the frequency range probed by LIGO/Virgo.
We find that stellar mass microlenses, permeating the lens plane, and near
critical curves, can introduce interference distortions in strongly lensed
gravitational waves. For those lensed events with negative parity, (or saddle
points, never studied before in the context of gravitational waves), and that
take place near caustics of macromodels, they are more likely to produce
measurable interference effects at LIGO/Virgo frequencies. This is the first
study that explores the effect of a realistic population of microlenses, plus a
macromodel, on strongly lensed gravitational waves.
