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The optical spectroscopic properties of RE3+ (Nd, 1 at. % or Yb, 1 to 10 at. %)-doped calcium-lithium-niobium-gallium garnet (CLNGG) single crystals and ceramics in the 10 K-300 K range are analyzed. In these compositionally disordered materials, RE3+ substitute Ca2+ in dodecahedral sites and the charge compensation is accomplished by adjusting the proportion of Li+, Nb5+, and Ga3+ to the doping concentration. The crystals and ceramics show similar optical spectra, with broad and structured (especially at low temperatures) bands whose shape depends on temperature and doping concentration. At 10 K, the Nd3+ 4I9/2 → 4F3/2, 5/2 and Yb3+ 2F7/2 → 2F5/2 absorption bands, which show prospect for diode laser pumping, can be decomposed in several lines that can be attributed to centers with large differences in the crystal field. The positions of these components are the same, but the relative intensity depends on the doping concentration and two main centers dominate the spectra. Non-selective excitation evidences broad emission bands, of prospect for short-pulse laser emission, whereas the selective excitation reveals the particular emission spectra of the various centers. The modeling reveals that the nonequivalent centers correspond to RE3+ ions with different cationic combinations in the nearest octahedral and tetrahedral coordination spheres, and the most abundant two centers have 4Nb and, respectively, 3Nb1Li in the nearest octahedral sphere. At 300 K, the spectral resolution is lost. It is then inferred that the observed optical bands are envelopes of the spectra of various structural centers, whose resolution is determined by the relative contribution of the temperature-dependent homogeneous broadening and the effects of crystal field disordering (multicenter structure, inhomogeneous broadening). The relevance of spectroscopic properties for selection of pumping conditions and of laser design that would enable utilization of the broad optical bands for efficient laser emission and reduced heat generation is discussed. [ABSTRACT FROM AUTHOR]

The spectroscopic characteristics of Dy3+ in YAG (Y3Al5O12) transparent ceramics prepared by solid state synthesis were investigated, with special attention to the visible (yellow, blue) emissions that could be pumped directly by the new developed blue-violet or near UV laser diodes. The absorption and emission spectra, recorded at different temperatures from 10 to 300 K, were analyzed and relevant new parameters, improved energy level scheme, temperature effects, intensity parameters based on Judd-Ofelt theory and radiative transition rates, branching ratios, etc., were estimated and the data are compared with previous reports on garnet single crystals. The potential of the Dy3+: YAG transparent ceramics for yellow or blue laser emission is discussed. [ABSTRACT FROM AUTHOR]

The characteristics of Nd→Yb energy transfer in (Nd, Yb):Y3Al5O12 (YAG) transparent ceramics, obtained from steady state and dynamic spectral studies on different single doped and codoped samples, prepared by solid state synthesis, are presented. The Yb3+ emission in codoped (Nd, Yb):YAG samples under cw excitation of the donors (Nd3+) revealed efficient energy transfer to Yb3+ (at low temperatures too), due to the overlap of the Nd3+ 4F3/2→4I9/2 emission and Yb3+ 2F7/2→2F5/2 absorption. From the global decays of the Nd3+ 4F3/2 level in single and codoped samples, the transfer efficiencies were estimated; they increase with Yb3+ content reaching ∼93% for 1 at. % Nd, 5 at. % Yb:YAG sample. The mechanisms and parameters of the Nd→Yb energy transfer were inferred from the Nd3+ decays in the codoped samples, after the separation of the self-quenching inside the donors (Nd3+) from the transfer to acceptors (Yb3+). It was proved that the Nd→Yb energy is resonant and dominated by dipole-dipole interactions. Due to the large transfer efficiencies, (Nd, Yb):YAG ceramic could be a promising material for Yb3+ emission under pumping in strong Nd3+ absorption lines. [ABSTRACT FROM AUTHOR]

Systematic high resolution spectral investigations of trivalent holmium doped in Sc2O3 polycrystalline transparent ceramic were performed. The spectral characteristics (Stark energy levels, absorption, and emission cross sections) as well as the Judd–Ofelt (JO) intensity parameters Ωt(t=2,4,6) for the f-f transitions of the C2-symmetry center of Ho3+ in Sc2O3 transparent ceramics were determined. The JO intensity parameters are used to estimate the emission probabilities, radiative lifetimes, and branching ratios of the different Ho3+ transitions. The emission gain cross section for the 5I7→5I8 and 5I6→5I8 transitions of special interest for laser application were determined. [ABSTRACT FROM AUTHOR]

An analysis of the high resolution optical spectra (10 and 300 K) of the self-stimulated Raman scattering active Nd:SrWO4 crystal was performed. Crystals doped only with low concentrations of Nd or codoped with Na+ or Nb5+ grown in N2 or air atmosphere were investigated. The single Nd-doped crystals show five main centers, whereas codoping with Na+ in the ratio Na/Nd=3/1 (in melt) simplifies considerably the spectra. Codoping with Nb5+ does not lead to a dominant center and introduces a new one. Growth in air revealed the role of the oxygen in the charge compensation and multicenter structure of the spectra. The spectral characteristics of the nonequivalent centers (levels, intensities, and polarization) function on concentration of Nd3+ and of codoping ions and growth conditions were analyzed. The polarization data show that only one center has ideal local symmetry S4. Based on the crystal structure, previous results, and the new spectral data, an attempt to connect various spectral nonequivalent centers to the charge compensators (Sr2+ vacancies, interstitial oxygen, Na+, and Nb5+) is made and structural models for various centers are proposed. The implications of these findings on the laser emission characteristics and on the selection of the pumping transitions are also discussed. [ABSTRACT FROM AUTHOR]

Spectroscopic investigation of Er3+ doped Sc2O3 transparent ceramics was performed in order to assess its potential as a laser material for different emission wavelengths. The Judd–Ofelt intensity parameters for the f-f transitions of the C2-symmetry center of Er3+ in Sc2O3 transparent ceramics, inferred from the room temperature absolute intensities of the absorption bands in the 370–1600 nm range, are Ω2=3.57×10-20 cm2, Ω4=1.61×10-20 cm2, and Ω6=0.79×10-20 cm2. These parameters are comparable to those reported for Er3+ in other sesquioxide single crystals. The Judd–Ofelt intensity parameters are used to determine the emission probabilities, radiative lifetimes, and branching ratios of the different Er3+ transitions. The emission cross sections of the potential laser transitions at ∼1.5 μm were determined using the reciprocity method, and the potential laser gain versus wavelength for the 4I13/2→4I15/2 was analyzed. [ABSTRACT FROM AUTHOR]

Nd3+-activated strontium lanthanum aluminate Sr1-xNdyLax-yMgxAl12-xO19 (ASL:Nd) crystals give efficient 4F3/2→4I9/2 laser emission at 900 nm, whose properties depend on the x and y composition parameters. Based on high-resolution spectroscopy and emission decay, this paper demonstrates that the composition dependence of the laser emission is caused by the presence of two structural centers, C1 and C2, whose relative proportion in crystals is determined by composition parameter x. From the spectral data and crystal structure it is inferred that C2 center that prevails at low x, corresponds to a Nd3+ in a Sr2+ (2d) site of D3h local symmetry with no nearby Ln3+ (La3+ or Nd3+) ions. The C1 center lines, prevailing at large x parameter, which are broader and shift with composition, are composite lines of various structural centers of Nd3+ in a Sr2+ site with different occupancy of nearest-neighbor sites by Ln3+. The influence of the spectral and emission dynamics features of these centers on the laser properties is discussed and criteria for the selection of optimal composition is inferred. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Analyzes the nonexponential behavior of the kinetics of the initial laser level for three-micron generation in an erbium&sup3+;:YAlO[sub3] crystal under intense pump in the [sup4]S[sub3/2] level. Models used to explain the absence of self-saturation for three-micron room-temperature laser emission; Factor that contributes to the energy transfer to accidental impurities; Type of impurities.

Presents information on a study which analyzed the absorption and emissions spectra of thulium ions in gadolinium gallium garnet to identify the Stark levels involved in pumped and laser emission processes of the system. Description of thulium ions; Methodology of the study; Results and discussion.

Presents a study that analyzed the effects of energy transfer on the quantum efficiency of neodymium-doped yttrium-aluminum garnet (YAG) crystals. Information on methods to determine the quantum efficiency of the crystals; Analysis of the non-exponential decay of luminescence for neodymium ion in YAG; Evaluation of the energy processes affecting the luminescence decay.

It is shown that owing to the improvement of the laser emission parameters at the fundamental frequency and to the reduction of the heat generated by nonradiative processes, the direct pumping into the emitting level of Nd:YVO4 enhances considerably the power emitted at the second harmonic in an intracavity frequency-doubling device. In the case of a laser with an a-cut 0.27 at. % Nd:YVO4 crystal frequency-doubled with a GdCa4O(BO3)3 (GdCOB) crystal cut for Type I frequency doubling in the plane XY, an enhancement of the emitted power at 532 nm by about 100% was obtained for ∼1100-mW incident Ti:sapphire laser pump at 880 nm compared with the traditional pumping at 809 nm. It is inferred that besides the improvement of the efficiency, this modality of pumping would enable the scaling of these devices to higher power. [ABSTRACT FROM AUTHOR]

Highly transparent Sc2O3 ceramics with uniform doping up to 0.5 at. % Nd and with (Nd, Yb) codoping are reported. The spectroscopic and emission decay properties of Nd:Sc2O3 ceramics are similar to those of single crystals. Highly efficient Nd-to-Yb energy transfer is observed in the codoped ceramics. It is inferred that these materials have potential for construction of Nd or Nd-sensitised-Yb lasers. [ABSTRACT FROM AUTHOR]

Neodymium-doped strontium lanthanum aluminate crystals Sr1-xLax-yNdyMgxAl12-xO19 contain two structural Nd centers with slightly different spectroscopic properties, whose proportion is determined by the composition parameter x. By choosing a composition with x=0.4, which grants the dominance of one of these centers (the center C1), whose properties are suitable for quasi-three-level Nd laser scheme, efficient 901 nm continuous-wave laser emission (slope efficiency ∼0.74) was obtained under 792 nm Ti:sapphire laser pumping. Preliminary experiments evidence the possibility of obtaining 450.5 nm radiation by frequency doubling. Owing to the large absorption linewidth (∼4 nm) this crystal shows good prospect for diode laser pumping. [ABSTRACT FROM AUTHOR]

The possibility of basic enhancement of the overall optical-to-optical efficiency of intracavity frequency-doubling devices for the 1 μm continuous-wave (cw) Nd lasers by direct pumping into the emitting level and by using concentrated laser materials is discussed. This possibility is demonstrated for 1.0 and 2.4 at. % Nd:Y[sub 3]Al[sub 5]O[sub 12] (Nd:YAG) crystals pumped by a Ti:sapphire laser at 885 nm. A slope efficiency of 0.79 in absorbed pump power was obtained for the 1064 nm emission of a 1.0 at. % Nd:YAG crystal. The effect of enhancement of intracavity emission on the second-harmonic emission is manifested in a drastic reduction of emission threshold and in an increased dependence on the absorbed power. The use of concentrated Nd:YAG crystal enables a better use of the pump power and improves the overall optical efficiency of the intracavity frequency-doubling devices. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

One-micron continuous-wave (cw) laser emission with 0.80 slope efficiency (0.79 optical-to-optical efficiency) under Ti: sapphire and 0.75 slope efficiency relative to absorbed power under diode-laser pumping at 880 nm into the emitting level is demonstrated in a 1-mm-thick, 1.0-at. % Nd:YVO[sub 4] crystal. These values are superior to those obtained with 809-nm pumping into the level [sup 4]F[sub 5/2], and can be explained consistently by the effect of the quantum defect between the pump and laser radiation, the superposition of pump and laser mode volumes, the pump-level efficiency and the residual optical losses. In the analysis of the 809-nm pumping data a pump-level efficiency equal to the unity was employed, as determined with a method based on the pump-saturation effects on absorption. [ABSTRACT FROM AUTHOR]

The 885-nm Ti:Sapphire pumping into the emitting level [SUP4]F[SUB3/2] of Nd:YAG produces a highly efficient (0.68 slope efficiency in absorbed power) 946-nm laser emission; a strong reduction of heat generation could be also obtained. [ABSTRACT FROM AUTHOR]

The possibilities of improvement of laser emission characteristics and reduction of heat generation by direct pumping at 887 nm into the emitting level [sup 4]F[sub 3/2] of Nd[sup 3+] in the self-frequency-doubling crystal Nd-GdCOB [GdCa[sub 4]O(BO[sub 3])[sub 3]] are discussed. Enhanced laser emission performances at fundamental 1060 nm, and especially at the self-frequency-doubled 530 nm wavelengths as compared to the traditional 811 nm pumping into the [sup 4]F[sub 5/2] level, are demonstrated. [ABSTRACT FROM AUTHOR]

Highly efficient 1064 nm continuous-wave laser emission under 885 nm diode pumping in concentrated Nd: Yttrium aluminum garnet (YAG) crystals (up to 3.5 at. % Nd) and ceramics (up to 3.8 at. % Nd) is reported. A highly doped (2.4 at. %) Nd:YAG laser, passively Q switched by a Cr[sup 4+]:YAG saturable absorber, is demonstrated. [ABSTRACT FROM AUTHOR]

Examines the effect of nearest-neighbor pairs on the energy transfer in Nd:YAG laser system. Analysis on the laser luminescence model through two models; Description of the anomalous decay system by the energy transfer theory; Reduction of the luminescence relative quantum efficiency.

The possibility of using the thermally activated optical absorption bands for a resonant pump in the emitting level of highly doped Nd laser materials is discussed. This potential is demonstrated by the continuous wave 1064 nm laser emission under 885 nm pump in concentrated (up to 6.8 at. %) Nd:YAG ceramics. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]