Emission Kinetics of Yb3+ Upper Laser Level in Optical Ceramics of Different Thicknesses Based on Y2O3

Oxysulfide optical ceramics doped by Nd 3+ for one micron lasing

: Preliminary investigation into the development of techniques to create fluoride ceramics has shown that the main principles and approaches suitable for the development of oxide ceramics could not be applied for fluorides. The hot pressing formation technique from initial single crystals was optimized to enable obtainment of stable high optical ceramics from simple fluorides and their solid solutions doped with different RE3+ ions. The spectroscopic properties of Yb3+ ions in fluoride ceramics of different compositions were investigated and the advantages of fluoride hosts to include a long upper laser level lifetime as well as a low minimal pumping intensity were demonstrated. The possibility of manipulating the spectroscopic and laser properties through the usage of different fluoride hosts was demonstrated and different tuning ranges for Yb3+ ions were realized. Fluoride CaF2:Yb3+ ceramics were prepared by hot pressing single crystals and by the standard technique from powder and laser oscillations were obtained. Neodymium doped laser ceramics were obtained and the spectroscopic properties of different optical centers were determined. It was shown that selective excitation of non-quenched tetragonal optical centers resulted in a shorter oscillation wavelength with higher slope efficiency. It was also demonstrated that by using solid solutions of SrF2-LaF3, problems of low quantum yield arising from Nd-Nd paired optical centers were diminished enabling high oscillation efficiencies regardless of the laser diode pump wavelength.

Optical ceramics activated by neodymium or ytterbium and based on Y2O3 with inclusions of CeO2 , ZrO2 , and HfO2 containing optical inhomogeneities in the form of an orange peel are investigated. It is indicated that in the ceramics with such inclusions not only the crystallite size and porosity, but also the transmission near the edge of the fundamental absorption band decrease, and the theoretically predicted transparency is not achieved (even in the infrared range). It is reported that in the ceramics containing Hf 4+ and Zr4+ , Hf 3+ and Zr3+ , additionally depopulating the 4 F 3/2 upper laser level of the Nd3+ ion activator, are also present. The dependences of the Nd:Y2O3 crystal lattice parameter on the Hf 4+ or Nd3+ content in it, constructed based on the results of x-ray diffraction analysis, are linear, that is, no peculiarities are observed for solid solutions of these compounds. Energy dispersion analysis with a resolution of about 1 μm also indicates the uniformity of the distribution of the chemical elements throughout the sample. At the same time, estimates based on the Rayleigh light scattering in the ceramics indicate that one of the additional phases must have sizes smaller than λ/20 = 20 nm. By the method of high-resolution transmission electron microscopy, particles with composition modulated on the nanolevel are detected in the 90(Nd0.01Y0.99)2O3 + 10HfO2 nanopowder from which the ceramics are synthesized given that the lattice period remains unchanged.

In this paper, Er:Y2O3 optical ceramics were fabricated and details of the synthesis were presented. The spectral–luminescent properties of Er3+:Y2O3 optical ceramics were investigated. The absorption and emission cross-section spectra were determined. The luminescence kinetics at near 1.6 µm was single exponential and the lifetime of erbium 4I13/2 energy level was determined. In the frame of the conventional Judd–Ofelt theory, the emission properties of the energy levels of erbium 4I13/2 and 4I11/2 involved in laser operation at near 1.6 µm were calculated. The gain coefficient curves for typical values of the relative population of the upper laser level 4I13/2 were presented. The composition and structure were studied using the SEM, XRD, FTIR spectroscopy, and X-ray computer tomography techniques.