This optical spectrometer measures absorption coefficients in ferromagnetic and antiferromagnetic materials, indicating high sensitivity at cryogenic temperatures.
We present the design of a continuous-wave, highly sensitive optical spectrometer for millimeter-wave frequencies between 50 and 1000 GHz, with optimal performance at cryogenic temperatures. The spectrometer uses photomixing of near-infrared light to generate radiation over a wide frequency range, and the optical power absorbed by the sample is determined directly by measuring the sample temperature. This enables a dynamic range of up to 106 for the absorption coefficient below liquid-helium temperatures, making it suitable for measurements on highly reflective samples. The instrument can also be used in combination with high magnetic fields. In order to validate its performance, we measure the ferromagnetic resonance in the Mott insulator YTiO3, the electron spin resonance in a standard free-radical reference compound, and the antiferromagnetic resonance in a van der Waals magnetic material.
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Rogić et al. (2025) studied this question.
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