Accurate, high-resolution dispersive Fourier-transform spectroscopy with undetected photons

We present dispersive Fourier-transform spectroscopy with undetected photons using a nonlinear interferometer based on spontaneous parametric down-conversion. The interferometer transfers mid-infrared information of sample interaction to the near-infrared, which allows using low-noise silicon-based detectors, enabling accurate measurements with extremely low light exposure. We demonstrate a dispersion measurement of gaseous methane with an accuracy greater than 1 part in 10 6 , which is limited by random phase noise. The Fourier-transform approach allows high resolution, rotational-line resolving spectroscopy of both, the absorptive and dispersive properties of a sample in a simple and robust measurement concept.