Experimental setup inside the cryogen-free dilution refrigerator (IMAGE)
Caption
The cuprous oxide crystal (red cube) was placed on a sample stage at the center of the dilution refrigerator. Researchers attached windows to the shields of the refrigerator that allowed optical access to the sample stage in four directions. The windows in two directions allowed transmission of the excitation light (orange solid line) and luminescence from paraexcitons (yellow solid line) in the visible region. The windows in the other two directions allowed transmission of the probe light (blue solid line) for induced absorption imaging. To reduce incoming heat, researchers carefully designed the windows by minimizing the numerical aperture and using a specific window material. This specialized design for the windows and the high cooling power of the cryogen-free dilution refrigerator facilitated the realization of a 64 millikelvin minimum base temperature.
Credit
Yusuke Morita, Kosuke Yoshioka and Makoto Kuwata-Gonokami, The University of Tokyo
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