S. N. Ushakov

Calcium niobium gallium and calcium lithium niobium gallium garnets doped with rare earth ions––effective laser media

Abstract The results of spectroscopy and laser action of disordered calcium niobium gallium (CNGG) and calcium lithium niobium gallium (CLNGG) garnets doped with Nd3+, Eu3+, Er3+, Ho3+ and Tm3+ were displayed. The structure and some optical and physical properties of CNGG and CLNGG-crystals were studied. Activator centers construction and the mechanism of inhomogeneous broadening and splitting of spectral lines of rare earth ions (TR3+) in CNGG and CLNGG-crystals were analyzed. Possibilities of laser media based on CNGG and CLNGG with TR3+-ions for pulse free running, Q-switch, CW and ultrashort pulse operation regimes were considered.

Raman spectra and phase transformations of the MLn(WO4)2 (M = Na, K; Ln = La, Gd, Y, Yb) tungstates

The 300-K crystal structure, phase transformations, and melting of the MLn(WO4)2 (M = Na, K; Ln = La, Gd, Y, Yb) tungstates and the structure of their melts were studied by Raman spectroscopy.

Spectroscopic investigations of NaGd(WO4)2 and NaLa(MoO4)2 single crystals doped by Yb3+ ions

New potential ytterbium-doped laser crystals-disordered scheelite-like double sodium-gadolinium tungstate NaGd(WO4)2 and sodium-lanthanum molybdate NaLa(MoO4)2, had been grown by Czochralski technique. Polarized absorption and fluorescence spectra as well as fluorescence decay kinetics had been measured for these crystals, doped with Yb3+ ions. Gain cross-section for different population inversion of 2F5/2 level had been calculated.

Spectroscopic and lasing properties of calcium niobium gallium garnet activated with Cr3+ and Nd3+

An investigation was made of the luminescence and lasing spectra of a calcium niobium gallium garnet crystal activated with Cr3+ and Nd3+ ions. An effective nonradiative energy transfer from the chromium to the neodymium ions was discovered. The probability of an elementary Cr→Nd interaction event was determined. A detailed study was made of the Stark structure of the ground (4I9/2) and metastable (4F3/2) levels of Nd3+. Selective laser excitation was used to identify four main optical Nd3+ centers for which the splitting schemes of the 4I9/2 and 4F3/2 levels were constructed. Lasing was observed at 300 K as a result of the 4F3/2→4I11/2 transition in crystals activated with Cr3+ and Nd3+.

Intensities of hypersensitive transitions in garnet crystals doped with Er3+ ions

We examine the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er3+ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of garnets with different contents of Al3+ and Sc3+ ions (Gd2.4Er0.5Sc1.8Al3.3O12, Gd2.4Er0.5Sc1.9Al3.2O12, Gd2.4Er0.5Sc2.0Al3.1O12) is performed, as a result of which the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca3(NbGa)5O12 crystals doped with Er3+ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity parameter Ω2 of Er3+ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the symmetry of the local environment of Er3+ ions in these crystals is C1, C2, or C2ν. We reveal that, as the concentration of Er3+ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition 4I15/2 → 2H11/2 of Er3+ ions and their intensity parameter Ω2 tend to decrease, which can be related to an increase in the relative fraction of Er3+ ions with higher symmetry of the local environment.

Yb3+ ion in calcium niobium gallium garnet crystals: Nearest neighbor environment and optical spectra

We have studied inhomogeneously broadened optical spectra of the Yb3+ ion in calcium niobium gallium garnet crystals using selective laser excitation, time-resolved luminescence spectroscopy, and 2F5/2 luminescence decay measurements under excitation in different portions of the absorption spectrum. We have identified spectral features due to individual optical centers differing in excitation and luminescence wavelengths and excited-state lifetime. Tentative structures of the optical centers responsible for the inhomogeneous broadening of the spectra are described.

Phase Transformations and Melt Structure of Calcium Metasilicate

The β → α phase transition, melting, crystallization, and vitrification of calcium metasilicate were studied by high-temperature Raman scattering spectroscopy. The results demonstrate that, in the course of melting, the [Si3O9] metasilicate rings, which form the structural basis of the α phase, transform mainly into [SiO3]∞ anions. The structural similarity or dissimilarity of the CaO · SiO2 melt to crystalline phases is shown to have a crucial effect on its crystallization/vitrification behavior.

Synthesis and spectroscopy of sodium-gadolinium tungstate NaGd(WO4)2 crystals activated by Tm3+ ions

Single crystals of disordered double sodium-gadolinium tungstate NaGd(WO4)2 doped with Tm ions were grown by the Czochralski method. The polarized absorption and emission spectra of these crystals with different activator concentrations and the decay kinetics of the 3H4 and 3F4 excited states of Tm3+ ions at 300 K were investigated. The absorption and emission cross sections of the expected laser transition 3F4 ↔ 3H6 in the Tm3+ ion were determined and the amplification spectra of the active laser medium NaGd(WO4)2:Tm at different levels of inverse population of the upper laser level 3F4 of the Tm3+ ion were constructed. The prospects for using these crystals as active media in 2-μm solid-state lasers are discussed.

Spectroscopy of Disordered Laser Crystals

The nonuniform broadening of optical spectra is analyzed for two types of rare-earth-activated disordered laser crystals: substituted garnets and yttria-stabilized zirconia (ZrO2–Y2O3). By decomposing nonuniformly broadened, composite R3+ absorption and luminescence bands, several principal centers (K and L for Eu3+ andA, B, C, and D for Nd3+) are identified and correlated with particular configurations of the near-neighbor environment of the activator ions (optical centers). It is shown that the formation of activator associates has a weaker effect on the optical spectra than the nearest neighbor coordination of the activator.

Growth and Spectroscopic Study of Yb3+-Activated YVO4 Crystals

The absorption and luminescence spectra of Yb3+ and the luminescence decay kinetics for the Yb3+2F5/2 level in YVO4:Yb3+ crystals are studied. The luminescence cross section for the Yb3+2F5/2 → 2F7/2transition in YVO4:Yb3+ is determined by the Füchtbauer–Ladenburg method, and the radiative lifetime of Yb3+ is evaluated.