Parallel beam interferometric detectors of gravitational waves

We discuss interferometric detection of gravitational waves using multiple bounce parallel beam systems. We consider as an example the simplest design that allows us to remove the laser frequency fluctuations, and yet gives a remaining nonzero gravitational wave signal, viz., an antiparallel pair of folded beams. The resultant sensitivity, however, is about B times smaller than the sensitivity of a two-arm Michelson interferometer optimally operating with B reflections. We have calculated other, less symmet- rical, designs with similar results. Parallel beam interferometric detectors could possibly be preferred for engineering reasons, site availability, and simplicity of response.