A new setup for probing condensed matter in the Far IR to THz ranges at sub-Kelvin temperatures on the AILES beamline at SOLEIL

•A spectroscopic setup dedicated to the study of materials at sub-K temperature.•Far-IR and Terahertz spectroscopy with reproducibility better than 0.5%.•Reflectivity and transmission measurements down to 95 mK and 144 mK, respectively.•Cooling based on an adiabatic demagnetization refrigerator. A new spectroscopic setup dedicated to the optical study of materials in the sub-Kelvin temperature range, available on the AILES beamline of synchrotron SOLEIL is described. This ensemble, based on an adiabatic demagnetization refrigerator, has been designed for spectroscopy in the far-infrared and terahertz domains. The combination of the cryogenic set-up with synchrotron radiation allows for reflectivity and transmission measurements down to 95 mK and 144 mK, respectively, with reproducibility better than 0.5%.