Laser-Induced Breakdown Spectroscopy of Cr:ZnSe Gain Media

Chromium-doped Zinc Selenide (Cr:ZnSe) crystals are the gain media of choice for middle infrared lasers operating over a 2-3.4 µm spectral range. We report on laser-induced breakdown spectroscopy (LIBS) study of Cr:ZnSe polycrystals prepared with different regimes of Cr diffusion for measuring the variation of Cr distribution and crystals stoichiometry. LIBS is a rapid, real-time analytical technique that analyzes the spectral emission from laser-induced plasmas enabling fast chemical analysis without sample preparation. The optical emission of Zinc-Selenium-Chromium (Zn-Se-Cr) plasma produced by LIBS is studied here. An experimental setup was designed using a Q-switched Nd:YAG laser operating at 1064 nm (up to 100 mJ per pulse at 20 Hz rep rate) and an Echelle spectrometer with an ICCD detector. The electron number density is measured using the Stark broadening method using the neural Zn I (481.05nm) line. In contrast, the electron temperature is estimated employing the Boltzmann plot method of several Zn emission lines. For applications where a sub-ppb limit of detection (LOD) is required, a combination of LIBS with laser-excited atomic fluorescence spectroscopy (LEAFS) enables superior sensitivity (sub-ppt). We will also discuss the integration of the LIBS system with LEAFS.