Measurement of the Temperature Dependence of the Refractive Index of CdZnTe

Abstract

We have been developing a CdZnTe immersion grating for a compact high-dispersion mid-infrared spectrometer (wavelength range 10--18 $\mu$m, spectral resolution $R=\lambda /\Delta \lambda >25,000$, operating temperature $T<20$ K). Using an immersion grating, the spectrometer size can be reduced to $1/n$ ($n$: refractive index) compared to conventional diffraction gratings. CdZnTe is promising as a material for immersion gratings for the wavelength range. However, the refractive index $n$ of CdZnTe has not been measured at $T<20$ K. We have been developing a system to precisely measure $n$ at cryogenic temperatures ($T\sim 10$ K) in the mid-infrared wavelength range. As the first result, this paper reports the temperature dependence of $n$ of CdZnTe at the wavelength of 10.68 $\mu$m. This system employs the minimum deviation method. The refractive index $n$ of CdZnTe is measured at temperatures of \( T = 12.57, 22.47, 50.59, 70.57, \text{ and } 298 \, \text{K} \). We find that $n$ of CdZnTe at $\lambda =$ 10.68 $\mu$m is $2.6371\pm 0.0022$ at $12.57\pm 0.14$ K, and the average temperature dependence of $n$ between 12.57 $\pm$ 0.14 K and 70.57 $\pm$ 0.23 K is $\Delta n/\Delta T=(5.8\pm 0.3)\times 10^{-5}$ K${}^{-1}$.