  In this paper we show that information on both the differential and common
mode free-mass response to a gravitational wave can provide important
information on discriminating the direction of the gravitational wave source
and between different theories of gravitation. The conventional Michelson
interferometer scheme only measures the differential free-mass response. By
changing the orientation of the beam splitter, it is possible to configure the
detector so it is sensitive to the common-mode of the free-mass motion. The
proposed interferometer is an adaptation of the Fox-Smith interferometer. A
major limitation to the new scheme is its enhanced sensitivity to laser
frequency fluctuations over the conventional, and we propose a method of
canceling these fluctuations. The configuration could be used in parallel to
the conventional differential detection scheme with a significant sensitivity
and bandwidth.
