Measurement of the temperature dependence of the refractive index of CdZnTe

We have been developing a CdZnTe immersion grating for a compact high-dispersion mid-infrared spectrometer (wavelength range 10 to 18 μm, spectral resolution R=λ/Δλ>25,000, and operating temperature T<20 K). Using an immersion grating, the spectrometer size can be reduced to 1/n (n: refractive index) compared with 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∼10 K) in the mid-infrared wavelength range. As the first result, we report the temperature dependence of n of CdZnTe at the wavelength of 10.68 μm. 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, and 298 K. We find that n of CdZnTe at λ=10.68 μm is 2.6371±0.0022 at 12.57±0.14 K, and the average temperature dependence of n between 12.57±0.14 K and 70.57±0.23 K is Δn/ΔT=(5.8±0.3)×10−5 K−1.