Measuring spectral transmission and refractive index of AgCl1−xBrx (0 ⩽ x ⩽ 1) and Ag1−xTlxBr1−xIx (0 ⩽ x ⩽ 0.05) at the wavelength of 10.6 μm

• Refractive index was measured by FTIR for AgCl1−xBrx, Ag1−xTlxBr1−xIx (0 ⩽ x ⩽ 1, x ⩽ 0.05).
• It proved to rise from AgCl to AgBr and to TlI, growing faster in the second case.
• MIR and UV–NIR spectra showed transmission broadening due to AgBr or TlI introduction.
• Left edge and refractive index became linear for greater AgBr or TlI contents.
• We used two errors to introduce the scattering of the refractive index.

We measured the complex refractive index at the wavelength of 10.6 μm with the help of Fourier transform infrared spectroscopy for polycrystalline plates of the following compositions AgCl1−xBrx (0 ⩽ x ⩽ 1) and Ag1−xTlxBr1−xIx, where x varied from 0 to 0.05. In order to do it we chose a segment of the spectrum, which was recorded with a high resolution (0.5 cm−1) using the HgCdTe detector and which had a set of 10 identical peaks. It is shown that the real part of the refractive index rises along with increasing the substituting component fraction in the solid solution from 1.99 to 2.17 for AgCl1−xBrx and from 2.17 to 2.24 within the range of TlI mole fraction up to 0.05 for Ag1−xTlxBr1−xIx. We considered errors introduced by the spectrometer resolution and the accuracy rating of the micrometer, which was used to measure sample thickness. It is seen in the spectra, recorded for the second system with a lower resolution and using a deuterated and l-alanine doped triglycine sulfate detector, that increasing the thallium monoiodide fraction results in widening the transmission range towards bigger wavelengths. We also plan to use the obtained refractive index values for simulating mid-infrared optical fibers, the polycrystalline structure of which is close to the structure of the plates under investigation.