In the reflectivity configuration, tests show that the lowest temperature MODELING, METHODOLOGY obtained with the synchrotron probe incident on the sample is 99 mK, and AND INSTRUMENTATION the corresponding hold times are about 120 minutes. For transmission SYNCHROTRON SOLEIL HIGHLIGHTS 2020 measurements (see figure) where the two optical apertures are needed, the lowest temperature reached is 144 mK and the hold time is reduced to 97 minutes. AILES BEAMLINE For such THz domain measurements, the detection is achieved with a Associated publication bolometer held at 1.6 K combined with a 50 µm Mylar allowing for a noise- to-signal ratio lesser than 1 % over the spectral range 10 – 50 cm, and-1 A new Setup for probing condensed reaching 0.1% between 15 cm and 45 cm at 0.5 cm resolution. In the far-1 -1 -1 matter in the Far IR to THz ranges at infrared range, the heat input from the photon beam is higher and the lowest sub-Kelvin temperatures on the AILES beamline at SOLEIL. temperature reached is better than 250 mK. B. Langerome, T. Souske, K. Rader, The ensemble dedicated to the THz and IR spectroscopies at sub-Kelvin M. Verseils, L. Tongtong, S. de Brion, temperatures, is now available on the AILES beamline of synchrotron L. Manceron, J.-B. Brubach & P. Roy. SOLEIL. This instrument is suited to investigate quantum effects Infrared Physcics and Technology, occurring in condensed matter. Thanks to the synchrotron radiation, 107: art.n° 103223 (2020). measurements can be performed in transmission and in reflectivity with excellent reproducibility at temperatures lower than 250 mK. References FIGURE 1 [1] W.J. Padilla et al. , Rev. Sci. Inst., 75, 4710 (2004). [2] N. Maleeva et al., Nature Comm. 9, 3889 (2018). [3] Row et al. Rev. Sci. Inst., 87, 033105 (2016). [4] P. Roy et al., Infrared Physics & Technology, 49, 139 (2006). Corresponding authors Pascale Roy & Jean-Blaise Brubach Synchrotron SOLEIL L’Orme des Merisiers BP 48 – 91192 GIF-SUR-YVETTE Cedex France Pascale.roy@synchrotron-soleil.fr jean-blaise.brubach@ synchrotron-soleil.fr Captions FIGURE 1: Transmission (a) and reflectivity (b) optical configurations of the setup. After exiting the interferometer (grey compartment on the left), the beam is redirected using various motor at the entrance of the cryocooler (pink compartment). In the latter, the focused beam is incident on the cooled sample. The transmitted beam (or reflected FIGURE 2 beam), is redirected toward the detector. The change between transmission and reflectivity is possible with a right-angle, dividing mirror and two flip mirrors. Camera, lamp and additional beam splitter are used for the alignment of the beam on the entrance of the cryocooler chamber. FIGURE 2: Evolution of the Temperature of the cooled sample in the reflectivity/transmission configurations (Time zero corresponds to the end of the magnetic cycle). For these measurements, the aperture diameter was 2 mm, the sample diameter was 1mm, and the spectral range of incident photons was10 - 100 cm. The lower curve (black)1 was measured without photon beam (all optical ports blocked), the middle curve (red) was measured in reflectivity configuration (with one optical port open). The Upper curve (green) was measured in transmission configuration with two optical ports open. 81