Jose J. Fernandez

New data on the physical properties of Y3Al5O12-based nanocrystalline laser ceramics

Microhardness and fracture toughness of highly transparent Y3Al5O12-and Y3Al5O12: Nd3+-based nanocrystalline ceramics are measured for the first time. For the Y3Al5O12: Nd3+ laser ceramics, the use of a longitudinal scheme with a diode-laser pumping at a wavelength of 1.3186 mm (4F3/2 → 4I13/2 channel) enabled one to attain an output power of continuous-wave lasing of ∼3.7 W with 35% efficiency.

Spectroscopic properties of Pr3+ ions in fluorophosphate glass

The visible luminescence of Pr 3+ -doped fluorophosphate glasses of composition (in mol%) 60NaPO 3 -15BaF 2 -(25 - x)GdF 3-x PrF 3 (x=0.1, 0.2, 0.5, 1, 2, 5, and 10) has been investigated as a function of concentration at different temperatures by using steady-state and time-resolved laser spectroscopy. The fluorescence of the 1 D 2 level shows a strong concentration quenching for Pr 3+ concentrations higher than x = 0.1 mol% even at 4.2 K. The non-exponential character of the decays of the 1 D 2 level when increasing concentration, together with the behaviour of the effective decay rates as a function of Pr 3+ concentration, indicate the presence of a dipole-dipole quenching process in the framework of a limited diffusion regime.

Time resolved spectroscopy of laser output of Nd3+ doped calcium, niobium, gallium garnet

Abstract Stimulated emission experiments in the 4 F 3 2 → 4 I 11 2 transition of Nd3+ in Ca3(GaNb)3O12 show that two laser lines are emitted simultaneously and both independently. These experiments show the behaviour of the laser emission from two distinguishable subsets of Nd3+ sites. This behaviour has been modeled using a four-level spectral rate-equation laser model, assuming the existence of two kinds of Nd3+ populations with different emission spectra and a homogeneous line broadening at each site. The model explains the measured laser spectrum as well as the time delay between the emission of both laser lines.

Luminescence study of chromium (III) in Zirconium Barium Fluoride glass (ZBLA)

The optical properties of trivalent chromium ions in ZBLA glass have been studied for different concentrations of Cr 3+ . Optical absorption, luminescence and lifetimes were investigated in a wide temperature range. Analysis of lifetime data, emission and time resolved spectra have yielded the following results. There are two kinds of metal sites characterized by two gaussian emissions and two lifetimes, the higher energy gaussian being associated with the long emission lifetime. The two sites have the same thermal quenching mechanism independent of concentration

Nd3+ optical multisites in the Ca3(Nb,Ga)2Ga3O12 laser garnet crystal

Abstract Laser excited site-selective luminescence of Nd 3+ ion in the Ca 3 (Nb,Ga) 2 Ga 3 O 12 garnet crystal has been investigated for the 4 F 3 2 → 4 I 11 2 and 4 F 3 2 → 4 I 9 2 transitions. Six main non-equivalent crystal field sites were detected in the garnet. The crystal splitting scheme of the 4 F 3 2 and 4 I 9 2 manifolds was obtained for each Nd 3+ site. Energy transfer between Nd 3+ sites was observed by using time resolved spectroscopy.

Nd3+ and Eu3+ active sites in Bi12SiO20 and Bi12SiO20: V5+ crystals

Abstract Site-selective laser spectroscopy of Nd 3+ and Eu 3+ in pure and vanadium codoped Bi 12 SiO 20 (BSO) single crystals has been carried out in order to investigate the possible crystal-field sites for rare earth ions. Three different sites for Nd 3+ and five different sites for Eu 3+ , which depend on vanadium concentration, were found and optically isolated. A discussion on the nature of the Nd 3+ and Eu 3+ active sites as well as the thermal quenching of their luminescence is also given.

Pulsed laser deposition of rare-earth-doped glasses: a step toward lightwave circuits

Pulsed Laser Deposition (PLD) is used to produce Er-doped lead-niobium germanate (PbO–Nb2O5–GeO2) and fluorotellurite (TeO2–ZnO–ZnF2) thin film glasses. Films having high refractive index, low absorption and large transmission are obtained in a narrow processing window that depends on the actual PLD configuration (O2 pressure ∼a few Pa, Laser energy density ∼2-3 J cm-2 for the results presented in this work). However, Er-doped thin film glasses synthetized at room temperature using these experimental parameters show poor photoluminescence (PL) performance due to non-radiative decay channels, such as a large OH- concentration. Thermal annealing allows improving PL intensity and lifetime (τPL), the latter becoming close to that of the parent Er-doped bulk glass. In addition, the use of alternate PLD from host glass and rare-earth targets allows the synthesis of nanostructured thin film glasses with a controlled rare-earth concentration and in-depth distribution, as it is illustrated for Er-doped PbO–Nb2O5–GeO2 film glasses. In this case, PL intensity at 1.53 μm increases with the spacing between Er-doped layers to reach a maximum for a separation between Er-doped layers ≥ 5 nm, while τPL is close to the bulk value independently of the spacing. Finally, the comparison of these results with those obtained for films grown by standard PLD from Er-doped glass targets suggests that nanostructuration allows reducing rare-earth clustering and concentration quenching effects.

Luminescence of Er3+ Ions in Nanocrystalline Glass-Ceramics

This work analyzes the influence of the nanocrystals on the luminescence properties of Er3+ions in transparent oxyfluoride tellurite glass-ceramics obtained by heat treatment of the precursor Er-doped glass. The comparison between the fluorescence properties of Er-doped glass and glass-ceramic suggests that a fraction of Er3+ ions are forming nanocrystals while the rest remain in a glass environment. The presence of ErF3 nanocrystals has a strong effect in the upconverted red emission from4F9/2 level. The time evolution of the upconverted red emission shows that energy transfer upconversion processes are responsible for the increase of this emission in the glass-ceramic sample.

Room-temperature picosecond high-order stimulated Raman scattering in laser garnet crystal hosts Gd{sub 3}Ga{sub 5}O{sub 12}, Gd{sub 3}Sc{sub 2}Ga{sub 3}O{sub 12}, and Ca{sub 3}(Nb,Ga){sub 2}Ga{sub 3}O{sub 12}

High-order Stokes and anti-Stokes generation in the visible and near-infrared in cubic laser crystal hosts Gd3Ga5O12, Gd3Sc2Ga3O12, and Ca3(Nb,Ga)2Ga3O12 was observed for the first time. All scattering-laser components were identified and attributed to the SRS-active vibration modes of these garnet crystals.High-order Stokes and anti-Stokes generation in the visible and near-infrared in cubic laser crystal hosts Gd{sub 3}Ga{sub 5}O{sub 12}, Gd{sub 3}Sc{sub 2}Ga{sub 3}O{sub 12}, and Ca{sub 3}(Nb,Ga){sub 2}Ga{sub 3}O{sub 12} was observed for the first time. All scattering-laser components were identified and attributed to the SRS-active vibration modes of these garnet crystals. (letters to the editor)