Fig. 1. The transmitted spectra of PbTe film at 80, 140, 200, 260, and 300 K.

Fig. 2. The relationship between the refractive index and wavelength at 80–300 K, during the range of 7–12 μm.

Fig. 3. The relationship between An and T.

Fig. 4. The relationships between (a) Bn and (b) Cn and T.

Fig. 5. The contrast of the designed spectra by the formula and the measured spectra at (a) 80 and (b) 300 K.