  Gravitational microlensing events are powerful tools for the study of stellar
populations. In particular, they can be used to discover and study a variety of
binary systems. A large number of binary lenses have already been found through
microlensing surveys and a few of these systems show strong evidence of orbital
motion on the timescale of the lensing event. We expect that more binary lenses
of this kind will be detected in the future. For binaries whose orbital period
is comparable to the event duration, the orbital motion can cause the lensing
signal to deviate drastically from that of a static binary lens. The most
striking property of such light curves is the presence of quasi- periodic
features, which are produced as the source traverses the same regions in the
rotating lens plane. These repeating features contain information about the
orbital period of the lens. If this period can be extracted, then much can be
learned about the lensing system even without performing time-consuming,
detailed light curve modeling. However, the relative transverse motion between
the source and the lens significantly complicates the problem of period
extraction. To resolve this difficulty, we present a modification of the
standard Lomb-Scargle periodogram analysis. We test our method for four
representative binary lens systems and demonstrate its efficiency in correctly
extracting binary orbital periods.
