Application of Laser-Induced Breakdown Spectroscopy for Measuring Chromium Concentration in Chromium-Doped Zinc Selenide (Cr:ZnSe) Laser Materials

Chromium-doped zinc selenide (Cr:ZnSe) crystals are the gain media of choice for mid-infrared lasers operating over a 1.9-3.4 µm spectral range. In this study, we used laser-induced breakdown spectroscopy (LIBS) of Cr:ZnSe polycrystalline materials to improve the sensitivity of detecting chromium concentration in the laser-active materials. The fundamental harmonic of a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was used as an excitation source. After calibration of the LIBS signal, we calculated that chromium's limit of detection (LOD) was 30 parts per million (ppm). Normalization of the Cr(I) intensity peak at 357.9 nm by the square root of the Zn(I) peak at 636.2 nm reduced the LOD to 20 ppm and increased the coefficient of determination to R² ≈ 0.98. These results demonstrate the potential of LIBS for microscale mapping of dopant distributions in laser crystals and for on-site monitoring of material quality during fabrication.