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fuelastic back-scattering of stray light is a long-standing and fundamental problem in high sensitivity interferometric measurements and a potential limitation for advanced gravitational wave detectors. The emerging parasitic interferences cannot be distinguished from a scientific signal via conventional single readout. In this work, we propose the subtraction of inelastic back-scatter signals by employing dual homodyne detection on the output light, and demon strate it for a table-top Michelson interferometer. The additional readout contains solely parasitic signals and is used to model the scatter source. Subtraction of the scatter sig nal reduces the noise spectral density and thus improves the measurement sensitivity. Our scheme is qualitatively different from the previously demonstrated vetoing of scatter signals and opens a new path for improving the sensitivity of future gravitational-wave detectors and other back-scatter limited devices. Scattered light is a long-standing problem in gravitational-wave (GW) detectors. These detectors reach relative strain sensitivities in the order of 10-22 / v'HZ 1, employing kilometer scale Michelson interferometers that operate with high-power laser light. Stray light is produced for example by anti-reflection coatings of transmissive optics or micro-roughness of mirror sur faces. Inelastic backscattering from vibrating surfaces in the surrounding causes a frequency shift of the light and recombination with the interferometer mode produces a spurious signal at the interferometer output. Especially frequency up-conversion of light that is back-scattered from sources with large motional amplitudes leads to broadband disturbances that can spoil the sensitivity of a detector over a large frequency range. Observations of these, so called 'scatter shoulders', were described for example for Virgo's second science run 2. For third generation de tectors, which aim for the extension towards lower frequencies (< 10 Hz), significantly improved mitigation schemes against back-scattered light will be required 3. In this work we demonstrate a new readout scheme that enables the subtraction of stray light induced disturbance signals in the post-processing of the measurement data. We employ dual