Chromium Diffusion Doping of Commercial ZnSe and CdTe Windows for Mid-infrared Solid-state Laser Applications
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Chromium diffusion doping of commercial ZnSe and CdTe windows for mid-infrared solid-state laser applications U. Hömmerich*,+, I. K. Jones*, EiEi Nyein*, and S.B. Trivedi** *Hampton University, Department of Physics, Hampton, VA 23668 **Brimrose Corporation of America, 19 Loveton Circle, Baltimore, MD 21152 + e-mail: [email protected] ABSTRACT We report on the preparation and optical spectroscopy of diffusion doped Cr: ZnSe and Cr: CdTe windows for applications in mid-infrared (MIR) solid-state lasers. Cr doping was achieved in both materials through a thermal diffusion process controlled by temperature (750°-850 °C) and time (~0.25-6 days). Commercial CrSe powder (99.5% purity) was used as the dopant source. All samples exhibited the characteristic spectroscopic features of tetrahedrally coordinated Cr2+ ions with absorption bands centered between 1700-1900 nm and MIR emission bands extending from 2000-3200 nm. Various samples of Cr: ZnSe and Cr: CdTe were prepared with Cr2+ peak absorption coefficients from ~0.1 cm-1 to ~29 cm-1. The calculated Cr2+ concentration ranged from ~1x1017cm-3 to 3x1019cm-3 using absorption-cross sections of 1.1x10-18 cm2 for Cr: ZnSe and 2.2x10-18 cm2 for Cr: CdTe. The room temperature decay times for Cr: ZnSe and Cr: CdTe were measured to be between 5-6 µs and 3-4 µs, respectively. Quenching of the Cr emission was observed for Cr concentrations above ~1x1019 cm-3 for Cr: ZnSe and ~0.5x1019 cm-3 for Cr: CdTe. The absorption and MIR emission properties of diffusion doped Cr: ZnSe and Cr: CdTe windows as a function of Cr concentration will be discussed. INTRODUCTION
The infrared optical properties of transition metal (Cr2+, Co2+, and Fe2+) doped II-VI semiconductors have attracted significant attention for potential application in tunable midinfrared lasers [1-10]. Room temperature laser activity in the 2-3.4 µm range has been demonstrated from several Cr2+ doped II-VI semiconductors including Cr: ZnS [1,2], Cr: ZnSe [1-3], Cr: Cd0.85Mn0.15Te [4], Cr: Cd0.55 Mn0.45Te [5], Cr: CdTe [6], and Cr: CdSe [7]. The optical center in these materials has been ascribed to Cr2+ ions occupying tetrahedral cation (Zn, Cd) lattice sites. Despite the promising results reported for Cr2+ laser crystals, the full potential of this new class of MIR gain media has not yet been explored. Ongoing research efforts on Cr2+ laser crystals are focused on: i) optimizing the material preparation in terms of Cr doping and passive losses, ii) overcoming the poor thermal properties of II-VI hosts through new laser designs, and iii) tuning the optical properties of Cr2+ ions through compositional engineering [6,9]. Cr doping of II-VI materials has been achieved through either in-situ doping during growth or through a thermal diffusion process [1-10]. In this paper, we present recent results on the incorporation of Cr2+ ions in commercial polycrystalline windows of ZnSe and CdTe through a thermal diffusion process. Cr doped ZnSe and CdTe samples with different Cr2+ concentrations were prepared by varying
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