In absorption spectroscopy, the absorption of a sample manifests as a change of the radiation source intensity. This imposes two main limitations on detection sensitivity: Firstly, the smallest detectable signal is lower-bound by excess source noise. Secondly, resolving small changes of a comparatively large signal requires high-dynamic-range detection. Previous work in the field of dual-beam Fourier transform infrared spectroscopy  successfully suppressed excess source noise by measuring the combined interferogram and anti-interferogram. However, the resulting strong constant background still required high-dynamic-range detection and digitization.
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