Ytterbium‐doped apatite‐structure crystals: A new class of laser materials

A new class of Yb‐lasers is summarized in this article. The apatite family of crystals, based on the hexagonal structure of the mineral fluorapatite, has been found to impose favorable spectroscopic and laser properties on the Yb³⁺ activator ion. Crystals of Yb‐doped Ca₅(PO₄)₃F, Sr₅(PO₄)₃F, Ca_xSr_5−x(PO₄)₃F, and Sr₅(VO₄)₃F have been grown and investigated. Several useful laser crystals have been identified which offer a variety of fundamental laser parameters for designing diode‐pumped systems. In general, this class of materials is characterized by high emission cross sections (3.6–13.1×10⁻²⁰ cm²), useful emission lifetimes (0.59–1.26 ms), a strong pump band (σ_abs=2.0–10.0×10⁻²⁰ cm²), and pump and extraction wavelengths near 900 and 1045 nm, respectively. Efficient lasing has been demonstrated for several of the members of this class of materials, and high optical quality crystals have been grown by the Czochralski method. A summary of the laser parameters and a discussion of the Yb:apatite class of lasers is presented.