Trivalent Neodymium-Doped Double Molybdate/Tungstate Composite Laser Crystals

Abstract

The use of inhomogeneous broadening in composite disordered crystals has been widely recognized as a successful approach to enhancing the spectral bandwidth of rare-earth ions in optical spectra. In this study, composite disordered laser crystals of rare-earth alkali metal double molybdate/tungstate, doped with 2 atom % Nd 3+ and represented by the general formula Nd:NaGd-(Mo x W 1−x O 4 ) 2 (x = 0.5, 0.7 and 0.9), were grown using the Czochralski method. The crystal structure of the disordered laser crystals was determined to be of the tetragonal phase with a space group of I4 1 /a, as confirmed through X-ray diffraction (XRD) and Rietveld refinement analyses. The spectroscopic properties of the disordered laser crystal, encompassing absorption, emission, and fluorescence decay characteristics were investigated. The (MoO 4 ) 1.0 (WO 4 ) 1.0 composite crystal exhibited an exceptionally broad absorption bandwidth, with a full width at half-maximum (FWHM) of 21 at 808 nm, approximately 10 times wider than that of the well-known Nd:YAG crystal. Moreover, the composite crystal demonstrated the generation of a continuous-wave 1.06 μm laser, which was further frequency-doubled to produce a 532 nm laser. Additionally, the passively Q-switched laser behavior of the composite crystal at 1.06 μm was explored, utilizing tungsten disulfide as a saturable absorber. In summary, the double molybdate/tungstate composite disordered crystal exhibits advantageous characteristics, such as a low melting point (approximately 1200 °C), stable physical−chemical properties, and remarkable spectroscopic properties. These features highlight the potential applications of these composite crystals in all solid-state lasers. Highquality Nd-doped double molybdate/tungstate composite disordered laser crystals were grown by the Czochralski method. By implementing a composite engineering strategy, an exceptionally inhomogeneous spectral broadening with an fwhm of up to 21 at 808 nm was achieved.