Gallium Garnet Crystal Research Articles

Thermally-induced depolarization in the optical elements of the transition configuration

Dependence of thermally-induced depolarization on the diameter of the laser beam and the ratio of the length of the optical element to its diameter is investigated experimentally and numerically. The conditions under which the thermal depolarization depends on the diameter of the beam for end-face and side cooling are determined. Numerical modeling is supported by experimental results obtained on terbium–gallium garnet crystal and magneto optical glass MOG-04 samples. It is shown that the depolarization is reduced (1 − ν)2 times during the transition from long rod to short. It is shown that for a short rod with side cooling, depolarization also depends on the diameter of the beam, as it decreases by 20% when the beam diameter is increased. With the end-face cooling, depolarization will be reduced by more than 10 times if the diameter of the beam is increased from the minimum to the maximum possible.

Czochralski growth of Sr2Tb8(SiO4)6O2 crystals for visible–near IR magneto-optical applications

Sr2Tb8(SiO4)6O2 crystals have been grown and investigated for the first time for magneto-optical applications. The X-ray powder diffraction confirms that the compound crystallizes in the hexagonal system, with a common oxyapatite structure. The as-grown crystal exhibits low thermal expansion anisotropy (αa/αc≈1.1), and the hardness is about 5.0Moh. The temperature dependence of the magnetic susceptibility indicated that the Sr2Tb8(SiO4)6O2 crystal exhibits paramagnetic behavior over the experimental temperature-range 2–300K. The present investigations demonstrate that Sr2Tb8(SiO4)6O2 crystals show a higher visible transparency and a larger Faraday rotation than terbium gallium garnet (TGG) crystals. Sr2Tb8(SiO4)6O2 is therefore a very promising material in particular for new magneto-optical applications in the visible–near IR wavelength region.

Thermal, spectroscopic and laser properties of Nd3+ in gadolinium scandium gallium garnet crystal produced by optical floating zone method

A neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG) single crystal with dimensions of Φ 5×20mm2 has been grown by means of optical floating zone (OFZ). X-ray powder diffraction (XRPD) result shows that the as-grown Nd:GSGG crystal possesses a cubic structure with space group Ia3d and a cell parameter of a=1.2561nm. Effective elemental segregation coefficients of the Nd:GSGG as-grown crystal were calculated by using X-ray fluorescence (XRF). The thermal properties of the Nd:GSGG crystal were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficient, and the thermal conductivity of this crystal was calculated. The absorption and luminescence spectra of Nd:GSGG were measured at room temperature (RT). By using the Judd–Ofelt (J–O) theory, the theoretical radiative lifetime was calculated and compared with the experimental result. Continuous wave (CW) laser performance was achieved with the Nd:GSGG at the wavelength of 1062nm when it was pumped by a laser diode (LD). A maximum output power of 0.792W at 1062nm was obtained with a slope efficiency of 11.89% under a pump power of 7.36W, and an optical–optical conversion efficiency of 11.72%.

Low-temperature time-domain terahertz spectroscopy of terbium gallium garnet crystals

We report an experimental observation of high frequency magnetic excitations in terbium gallium garnet crystals using terahertz time-domain spectroscopy. We show that precessional modes of terbium magnetic sublattices can be excited by a magnetic field of a terahertz broadband pulse. We study and discuss the dependence of the observed resonances upon the temperature and the strength and orientation of the bias magnetic field. The behavior of the observed magnetic modes is in agreement with the theory of paramagnetic resonance in the multisublattice system. We also show that the illumination of the crystal with intense optical pulses destroys the magnetic ordering. Our results demonstrate that the time-domain terahertz spectroscopy can be a powerful tool by which to study high frequency properties of dielectric magnetic materials, with perceived extensions to studies in femtomagnetism and magnonics.

Evidence of multicenter structure of cerium ions in gadolinium gallium garnet crystals studied by infrared absorption spectroscopy

Low temperature, infrared absorption spectra of gadolinium gallium garnet crystals doped with Ce are presented. In the region of intraconfigurational 4$f$-4$f$ transitions the spectra exhibit existence of at least two different, major Ce${}^{3+}$ related centers in the GGG crystals and also some other centers at lower concentration. The spectrum of 4$f$-4$f$ intrashell transitions of Ce${}^{3+}$ ions extends up to about 3700 cm${}^{\ensuremath{-}1}$ due to the large splitting of the ${}^{2}$${F}_{7/2}$ excited state. In the visible region the absorption spectrum shows influence of symmetry-related selection rules. The absorption coefficient changes in the region of 4${f}^{1}$-5${d}^{1}$ transitions due to thermal population of the second level, belonging to the ${}^{2}$${F}_{5/2}$ ground state. This suggests that the symmetry of the site occupied by Ce${}^{3+}$ ions, which substitute Gd${}^{3+}$, is higher than ${D}_{2}$ expected for garnet hosts.

Ultrafast inverse Faraday effect in a paramagnetic terbium gallium garnet crystal

Conventional wisdom dictates that magneto-optical and optomagnetic phenomena are reciprocal and of equal strength. We test this assumption in a pump-probe experimental study of the ultrafast inverse Faraday effect in a terbium gallium garnet crystal. The thorough quantitative analysis of the observed polarization response unambiguously demonstrates a remarkable discrepancy of several orders of magnitude between the strengths of the direct and the inverse effects. This finding further questions the validity of standard magnetic models relying on the use of the static Verdet constant on subpicosecond time scales.

Compensation of Thermally Induced Distortions in a GGG-Based Cryogenic Faraday Isolator

We describe a cryogenic Faraday isolator with a gadolinium gallium garnet (GGG) crystal used for the first time as a magneto-optic element. Simultaneous compensation of thermally induced depolarization and thermal lensing using FK51 glass is demonstrated theoretically and experimentally. The temperature dependence of the ratio of thermo-optical constants P/Q is measured in the temperature range of 300-80 K for the GGG crystal and FK51 glass. The possibility of using this device at laser powers of ~20 kW is shown.

THz near-field Faraday imaging in hybrid metamaterials

We report on direct measurements of the magnetic near-field of metamaterial split ring resonators at terahertz frequencies using a magnetic field sensitive material. Specifically, planar split ring resonators are fabricated on a single magneto-optically active terbium gallium garnet crystal. Normally incident terahertz radiation couples to the resonator inducing a magnetic dipole oscillating perpendicular to the crystal surface. Faraday rotation of the polarisation of a near-infrared probe beam directly measures the magnetic near-field with 100 femtosecond temporal resolution and (λ/200) spatial resolution. Numerical simulations suggest that the magnetic field can be enhanced in the plane of the resonator by as much as a factor of 200 compared to the incident field strength. Our results provide a route towards hybrid devices for dynamic magneto-active control of light such as isolators, and highlight the utility of split ring resonators as compact probes of magnetic phenomena in condensed matter.

Optical pressure and temperature sensor based on the luminescence properties of Nd^3+ ion in a gadolinium scandium gallium garnet crystal

Hypersensitivity to pressure and temperature is observed in the near-infrared emission lines of the Nd(3+) ion in a Cr(3+),Nd(3+):Gd(3)Sc(2)Ga(3)O(12) crystal, associated to the R(1,2)((4)F(3/2))→Z(5)((4)I(9/2)) and R(1,2)((4)F(3/2))→Z(1)((4)I(9/2)) transitions. The former emissions show large linear pressure coefficients of -11.3 cm(-1)/GPa and -8.8 cm(-1)/GPa, while the latter show high thermal sensitivity in the low temperature range. Thus this garnet crystal can be considered a potential optical pressure and/or temperature sensor in high pressure and temperature experiments up to 12 GPa and below room temperature, used in diamond anvil cells and excited with different UV and visible commercial laser due to the multiple Cr(3+) and Nd(3+) absorption bands.

Pressure-induced luminescence of cerium-doped gadolinium gallium garnet crystal

Studies of the spectroscopic properties of Ce${}^{3+}$ dopant in bulk Gd${}_{3}$Ga${}_{5}$O${}_{12}$:Ce crystal under pressure are presented. In spite of strong intershell $4f\ensuremath{\rightarrow}5d$ absorption bands at ambient pressure, the cerium luminescence in Gd${}_{3}$Ga${}_{5}$O${}_{12}$ is entirely quenched even at low temperature. It has been shown that applying pressure allows for recovery of the $5d\ensuremath{\rightarrow}4f$ radiative transitions. Further increase of pressure improves the emission efficiency. This effect is analyzed in terms of two possible phenomena: (i) by pressure-induced electronic crossover of the excited 5$d$ energy level of the Ce${}^{3+}$ with the conduction band bottom of the host crystal, and (ii) by decrease of electron-lattice coupling with increasing pressure, resulting in reduction of the Stokes shift and nonradiative transitions between the low vibrational levels of the 5$d$ state and high vibrational levels of the ground 4$f$ state. The results of high-pressure absorption and luminescence measurements point out that the ambient-pressure luminescence quenching is caused by the donor-like charge transfer processes due to the resonant location of the Ce${}^{3+}$ 5$d$ electronic levels with respect to the host conduction band. In such a situation, the ionization of Ce${}^{3+}$ to Ce${}^{4+}$ occurs, accompanied by large lattice relaxation, which enables the nonradiative recombination to the Ce 4$f$ state. The pressure-induced approach of the conduction-band bottom of the host crystal by the excited 5$d$ energy level of the Ce${}^{3+}$ results in mixing between conduction band states and the 5$d$ state, and the broadband luminescence from this mixed state is observed at pressures from 30 up to about 60 kbar. Then, for pressures exceeding 60 kbar, this luminescence is replaced by the classic ${\mathrm{Ce}}^{3+}\phantom{\rule{0.16em}{0ex}}5d\ensuremath{\rightarrow}4f$ transitions. Using a simple anticrossing model and configuration coordinate model in the appropriate pressure range, quantitative description of the system has been carried out, and the pressure-induced decrease of electron-lattice coupling has been shown.

The effect of crucible bottom deformation on the quality of Nd:GGG crystals grown by Czochralski method

AbstractIn this paper, we report the growth of neodymium doped Gadolinium Gallium Garnet (Nd: GGG) crystal using Czochralski (CZ) method, and study the effects of crucible bottom deformation and thermal insulator thickness on the growth process and crystal quality. Garnet structure and <111> crystallography orientation of the crystal were confirmed by the X‐Ray diffraction (XRD) analysis. Macroscopic defects, residual stresses, quality, and homogeneity of the crystals were investigated by means of parallel plane polariscope and laser fizeau interferometer respectively and the results compared together. Experimental observations show that the crucible bottom deformation from flat to convex, and decreasing the thickness of zirconia insulator under the crucible result in the formation of lateral cores and increasing the crystal inhomogeneity and tensions, leading to the decrease of the crystal quality. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on Continuous Monitoring Glucose Concentration with Terbium Gallium Garnet Crystal

In a continuing effort to develop a noninvasive means of monitoring glucose levels using many methods. In this paper a laser, closed-loop, system was designed and a model was developed to extract the glucose concentration information by Faraday rotation with Terbium Gallium Garnet Crystal(TGG Tb3Ga5O12). The system was tested using various concentrations of glucose. The results show that for a static, non-moving sample, glucose can be predicted. For the physiologic range (0-16mmol/l) for either laser wavelength (523nm or 632.8nm), the Correlation coefficient value (R2) are 09977and 0.9995 respectively. The measurement results of 24 hours show the system with good stability, which error is less than 0.05%.

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.

Interaction of Er3+ ions in Er-doped calcium — niobium — gallium garnet crystals

The processes of nonradiative energy transfer in calcium — niobium — gallium garnet (CNGG) crystals doped with Er3+ ions are studied. It is found that the energy of erbium ions in the Er:CNGG crystal with the erbium atomic concentrations CEr=6% and 11% is transferred via the nonradiative co-operative processes 4I11/2→ 4I15/2, 4I11/2→ 4F7/2, 4I11/2→ 4I15/2, 4I13/2→ 4F9/2; and 4I13/2→ 4I15/2, 4I13/2→ 4I9/2, whose efficiency increases with increasing intensity of exciting radiation. It is shown that the cross-relaxation processes 4S3/2→4I9/2, 4I15/2→4I13/2, whose intensity depends on the concentration of Er3+ ions, are characteristic for Er:CNGG crystals with the Er atomic concentration above 1%.

Spectroscopy of gadolinium gallium garnet crystals doped withY b3 + revisited

The optical spectroscopy measurements of gadolinium gallium garnet (GGG) crystals dopedwith Yb show evidence of the presence of non-equivalent optical centers with very similarradiative decay rates. The energy level schemes of those centers have been determined onthe basis of optical absorption, luminescence and Raman experiments. Crystal field fittingresulted in two sets of slightly different crystal field parameters for two non-equivalent Ybcenters. Both sets of parameters describe perfectly the experimentally detectedY b3 + energy levels. Correlation between systematic trends in the experimental energy levelschemes and crystal field parameters is discussed.

Efficient triwavelength laser with a Nd:YGG garnet crystal

We demonstrate a laser-diode pumped efficient triwavelength laser at about 1.06microm with a Nd-doped yttrium gallium garnet crystal for the first time, to our knowledge. Continuous wave output power of 7.15W was achieved under an absorbed pump power of 14.1W, corresponding to the slope efficiency of 52.7%. With Cr:YAG as the saturable absorber, passive Q-switching performance was obtained. The shortest pulse width, largest pulse energy, and highest peak power were obtained at 3.1ns, 153.8microJ, and 46.6kW, respectively. The laser spectrum was found to be a triwavelength, with respective wavelengths of 1062.1, 1060.3, and 1058.9nm, and three laser transitions were assigned.

Optical waveguides in Nd:GGG crystals produced by H^+ or C^3+ ion implantation

The optical waveguides in neodymium-doped gadolinium gallium garnet crystal are fabricated, to our knowledge for the first time, by either H(+) or C(3+) ion implantation. The reconstructed refractive index profiles of the planar waveguides have shown, in both cases, the typical "enhanced well" + "barrier" distributions. The two-dimensional modal profiles of the channel waveguides, obtained by using an end-face coupling arrangement, are in good agreement with the simulated modal distributions. After moderate thermal annealing at 200 degrees C, the propagation loss of the H- and C-ion-implanted channel waveguides are reduced down to approximately 1.5 and approximately 1.6 dB/cm, respectively, which exhibits acceptable guiding qualities for applications on potential integrated laser generation.

Composition and dissociation processes analysis in crystal growth of Nd:GGG by the Czochralski method

The composition and dissociation reactions during the growth of gadolinium gallium garnet (GGG) crystal, doped with neodymium grown by the Czochralski (Cz) technique have been studied. The properties of structural Nd:GGG were investigated by the X-ray diffraction (XRD). The X-ray analyses confirm the thermodynamic calculations results. Our thermodynamic calculations show that there is a critical temperature about 2068±5 K° at standard condition. When the growth temperature is higher than this temperature, the metallic iridium could be observed on the crystal–melt interface.

Property Studies of Optical Waveguide Formed by keV He-Ion Implanted into a Nd:CNGG Crystal

A planar optical waveguide was formed in a neodymium-doped calcium niobium gallium garnet (Nd:CNGG) crystal by using 500-keV He-ion implantation with a dose of 2 × 10 ions/cm at room temperature. The dark modes were observed by using a prism coupling method, and the refractive index profile was reconstructed using a reflectivity calculation method (RCM). The SRIM2006 code (stopping and range of ions in matters, code 2006) was used to simulate the damage profile in the ion-implanted sample. The photoluminescence spectra of the samples showed fairly good potential for used as a laser waveguide.

Equation of state for gadolinium gallium garnet crystals: Experimental and computational study

Experimentally and theoretically determined elastic properties of gadolinium gallium garnet, Gd3Ga5O12, under high-pressure are reported. The x-ray diffraction part of the study was performed using a diamond-anvil cell at pressures up to 25 GPa, at conditions ascertaining hydrostatic compression up to about 10 GPa. The experimental bulk modulus, K0=169(15) GPa, and its first derivative, K0′=3.6(2.9), were derived from the diffraction data collected in pressure range limited to 10.2 GPa, assuming the Birch–Murnaghan equation of state. Ab initio calculations yielded K0=161(8) GPa and K0′=5.4(0.6) being in excellent agreement with the experiment.