Calcium Niobium Gallium Research Articles

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

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.

The nature of nonequivalent Nd3+ centers in CNGG and CLNGG

Abstract Results on the spectroscopic investigations and modeling of Nd3+ nonequivalent center structure in calcium niobium gallium garnet (CNGG) and calcium lithium niobium gallium garnet (CLNGG) are presented. The low temperature absorption, emission under selective excitation and lifetimes on a large variety of samples with Nd3+ varying between 0.1 and 5 at.% are analyzed. At least five different types of centers have been separated. Based on spectral data along with previous reports on the composition of the crystals a model of Nd3+ five-center structure in CNGG and CLNGG disordered crystals is proposed. The relative intensities for all the centers can be explained consistently by the structural possibilities of occupation of the first cationic octahedral sphere around the Nd3+ site. Starting from an unique average composition of this sphere our modeling suggests a correlated placement of the cations in the first octahedral sphere around Nd3+: the larger charge of Nd3+ as compared to the substituted Ca2+ leads to a local depletion of Nb5+ ions, accompanied by a corresponding enhancement of the lower-charge cations ( Ga 3+ , Li + ) or vacancies as compared with the undoped crystals.

Optical Properties of Er3+ Ions in Calcium Niobium Gallium Garnet (CNGG) Crystals

Single crystals of Er3+-doped calcium niobium gallium garnet (CNGG) were grown using the Czochralski technique, and the single crystal fibers with diameter of 0.81 mm were grown by the micro pulling-down method. The absorption and luminescence spectra by Er3+ ions in these materials have been investigated together with the luminescence decay. The same results are obtained between the crystals and fibers. Broad absorption lines are obtained which are suggested to be due to the Er3+ ions with various site symmetries. By the excitation with 266 nm radiation, the luminescence bands are observed at 490, 535, 545, 554, 656 and 669 nm. The 545 nm luminescence due to the 4S3/2 → 4I15/2 transition is found to have two decay components: the fast decay component of 15.1 μs and the slow component of 30.5 μs. A delay time of 3.7 μs was found between the excitation pulse and the 656 and 669 nm luminescence bands due to the 4F9/2 → 4I15/2 transition while no delay was found for the other luminescence bands.

Growth by the μ-pulling-down method and spectroscopic investigation of Nd 3+-doped calcium niobium gallium garnet

The growth of CNGG : Nd 3+ fibres (Ca 3Nb 1.6875Ga 3.1875O 12) by the μ-pulling-down method is described. Their room temperature spectroscopy is given. The branching ratios of the fluorescences at 0.9, 1.06, 1.3, 1.9 μm are, respectively, 0.389, 0.485, 0.123, 0.003. Liquid helium temperature investigations show that several nonequivalent Nd 3+ sites exist in the garnet lattice.

Vibrational spectra of a Ca-Nb-Ga garnet (CNGG) single crystal studied by Raman and infrared reflectivity spectroscopy

Calcium niobium gallium garnet (CNGG), a new non-linear optical material, is studied by Raman and infrared reflectivity spectroscopy at low and at room temperature for various scattering configurations. No structural phase transition is observed in the temperature range of the experiments. The phonons are classified within their symmetry species in the space group assumption; their dynamical parameters such as wavenumber, damping and oscillator strength are obtained on the basis of the infrared reflectivity spectra analysis. The comparison of the infrared and Raman activity of the phonon modes is in favour of the aforementioned space group; however, Pockels electrooptic coefficient room temperature measurements did not allow us to confirm this space group.

Continuous lasing at a 2 μm wavelengthin calcium niobium gallium garnet crystals at room temperature

Continuous lasing resulting in the emission of radiation of the 2.02 μm wavelengthwas achieved in Tm3+-activated calcium niobium gallium garnet crystals at room temperature. Lasing was observed when the Tm3+ ions were excited by Nd:YAG laser radiation with λ = 1.06 μm. The output radiation power was 0.02 W. Mechanisms of nonlinear absorption of the pump radiation were investigated.

Distribution Coefficient of Rare-Earth Active Ions in Calcium Niobium Gallium Garnet

Distribution coefficients of Nd3+, Tm3+ and Er3+ in calcium niobium gallium garnet (CNGG) single crystals have been investigated. The values of the equilibrium distribution coefficient, k0, of Nd3+, Tm3+ and Er3+ in CNGG single crystals have been determined to be 0.55, 1.09 and 1.14, respectively. It is shown that the distribution coefficients of Nd3+ in CNGG single crystals are larger than those in other garnet crystals such as Y3Al5O12 and Gd3Ga5O12. The variation of the k0 values is discussed in relation to the ionic radii of each of the cations.

Steady-state and time-resolved laser spectroscopy of Cr3+ and Nd3+ singly and doubly doped calcium niobium gallium garnet.

The optical properties of ${\mathrm{C}}^{3+}$,${\mathrm{Nd}}^{3+}$, and ${\mathrm{Cr}}^{3}$:${\mathrm{Nd}}^{3+}$ ions in ${\mathrm{Ca}}_{3}$(GaNb${)}_{2}$${\mathrm{Ga}}_{3}$${\mathrm{O}}_{12}$ (CNGG) garnet have been investigated in the 4.2--550 K temperature range by using steady-state and time-resolved laser spectroscopy. The luminescence of trivalent chromium in a singly doped crystal shows a strong thermal quenching above room temperature, which can be analyzed on the basis of the quantum-mechanical single-configurational-coordinate model by using the Struck-Fonger method. Low-temperature absorption, excitation, and time-resolved luminescence spectra of the ${\mathrm{Nd}}^{3+}$ ion in a singly doped crystal show inhomogeneous broadening associated with the existence of different sites for ${\mathrm{Nd}}^{3+}$ ions. ${\mathrm{Cr}}^{3+}$-to-${\mathrm{Nd}}^{3+}$ radiative and nonradiative energy transfer has been demonstrated from the time-resolved emission spectra and the decrease of the ${\mathrm{Cr}}^{3+}$ fluorescence lifetime. The nonradiative ${\mathrm{Cr}}^{3+}$\ensuremath{\rightarrow}${\mathrm{Nd}}^{3+}$ energy transfer is consistent with a dipole-dipole transfer process.

Growth and characterization of calcium niobium gallium garnet (CNGG) single crystals for laser applications

We have successfully grown new laser crystals with a disordered type structure, calcium niobium gallium garnet (CNGG), by the Czochralski technique. Undoped, Nd and, Tm and Ho doped CNGG single crystals about 25 mm in diameter and 70 mm in length were grown using Pt and Ir crucibles. The doped CNGG single crystals were found to have broad absorption spectra which are attractive for laser diode pumped lasers. The growth conditions, crystal quality and spectroscopic properties of the CNGG for laser applications are reported.

Spectroscopic and lasing properties of calcium niobium gallium garnet activated with Tm3+and Cr3+ions

An investigation was made of spectroscopic and lasing properties of a calcium niobium gallium garnet crystal (CNGG) activated with Tm and Cr. A study was made of the kinetics of decay of the luminescence emitted by the Cr3+ ions. Efficient nonradiative transfer of energy from the Cr3+ to the Tm3+ ions was observed at room temperature. Stimulated radiation was generated in CNGG:Tm:Cr crystals (due to the 3F4→3H6 transition) under conditions of free running: the wavelength of this radiation was 2.02 μm at room temperature.

Lasing of a calcium niobium gallium garnet crystal activated with chromium and erbium (λ = 2.71 μm)

An investigation was made of the luminescence spectra and lasing parameters of a calcium niobium gallium garnet crystal activated with chromium and erbium. The lifetimes of the upper 4I11/2 and lower 4I13/2 active levels of the Er3+ ions were determined. The lasing parameters of the crystal (λlas = 2.71 μm) were determined under free-running conditions at room temperature.

Efficient active media based on Nd3+-activated calcium niobium gallium garnets

A spectroscopic investigation was made of Nd3+-activated crystals of calcium niobium gallium (CNGG) and calcium lithium niobium gallium (CLNGG) garnets. The energy parameters of active elements made of these crystals were determined for the first time. The absolute efficiency of a CNGG:Nd3+ crystal was 3.5%, higher than the efficiency (2.7%) of a YAG:Nd3+ crystal of high optical quality. The average output power obtained at a pulse repetition frequency of 50 Hz for a CLNGG crystal was 40 W and the efficiency was 2.7% for an active element 6 mm in diameter and 80 mm long. A comparison of the lasing characteristics of CNGG:Nd3+ and CLNGG:Nd3+ crystals revealed a considerable superiority of the latter in respect of several parameters: the damage threshold (which was twice as high), the divergence, and the influence of a thermal lens at high pump powers. Room-temperature lasing of CNGG:Nd3+ and CLNGG:Nd3+ crystals was observed as a result of the 4F3/2 ← 4I11/2 transition at three wavelengths: 1059.3, 1061.5, and 1066 nm.

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+.