GGG Crystals Research Articles

CW lasing in Yb3+ : GGG crystals pumped at 0.925 μm

Single-mode cw lasing was obtained for the first time in Yb3+ : GGG crystals at room temperature at 1.030 and 1.037 μm upon pumping Yb3+ ions by a 0.925-μm neodymium-doped fibre laser. Lasing was observed at the transitions between the lower Stark sublevel of the 2F5/2 level and the upper Stark sublevels of the 2F7/2 ground state of Yb3+ ions. The study of lasing characteristic showed that lasing occurs according to the four-level scheme. The lasing threshold with respect to the absorbed power was 85 mW and the slope lasing efficiency was 20%. Upon 1.7-W pumping, the output power of 310 mW was achieved with the output resonator mirror with the transmission coefficient of 1%. The effective cross section of the lasing transition was 0.9×10-20 cm2.

Spectral properties and charge transfer luminescence of Yb 3+:Gd 3Ga 5O 12 (Yb:GGG) crystal

The Yb (10%):GGG and Yb (30%): GGG crystals have been grown by the Czochralski method. The chemical compositions are: Yb 1.07Gd 1.74Ga 5.19O 12 and Yb 0.33Gd 2.47Ga 5.2O 12. The absorption and emission spectra of Yb:GGG crystal at room temperature have been measured. The spectroscopic parameters of Yb:GGG and Yb:YAG have been compared. Optical absorption spectra of Yb:GGG show 4f–4f transitions related to Gd 3+ ion around 300 nm, and also an onset of charge transfer (CT) transitions from oxygen ligands to Gd 3+ or Yb 3+ cations below 240 nm.The CT absorption of Yb 3+ is largely overlapped by that of Gd 3+ ions.

Thermal lensing in diode-pumped ytterbium Lasers-Part I: theoretical analysis and wavefront measurements

A theoretical and experimental study of thermal lensing in Yb-doped crystals is presented. In this first part, we focus on theoretical considerations and we describe an original technique suitable for thermal lensing measurements in end-pumped materials. We first derive an expression of the temperature distribution with account of absorption saturation and pump beam divergence inside the crystal, and we address a more general discussion on the particularities of quasi-three-level lasers, as far as thermal effects and fracture issues are concerned. The thermal lens was then measured using a simple technique based on a Shack-Hartmann wavefront analyzer, under lasing and nonlasing conditions. We demonstrate that the technique allows precise wavefront measurements even on small spots. Thermal lensing measurements are finally presented in Yb-doped YAG, GGG, YCOB, GdCOB, KGW, and YSO crystals.

Transient color centers in GGG crystals

Electron pulse induced absorption and their decay kinetics have been investigated in samples of GGG crystals with different starting absorption spectra. It is shown that for all samples there appears a wide transient absorption (TA) band with two maxima in the region 14,000-17,000 v cm m 1 and 22,000-26,000 v cm m 1 . TA decay kinetics measurements in 14,000 v cm m 1 and 22,000 v cm m 1 are two-exponential (with half-time order several tens and several hundreds ns). Analyzing the obtained results, we can suppose that low and high energy TA bands are connected with the F + (or O m ) and F transient color centers (TCC) respectively.

Spectroscopic data on 2‐μm laser systems

Some of our recent spectral and energy transfer results on Tm3+-based 2-?m solid state laser systems are presented. Based on experimental data, with an improved algorithm and parameterized crystal field calculations, complete energy level diagrams for Tm3+ in YAG and GGG are obtained. The sets of crystal field parameters could be used to estimate a series of important spectral data for laser emission. A discussion of the spectral characteristics and the nature of Tm3+ multisite structure is also presented. The static spectral modifications in Cr3+ codoped with Tm3+ YAG or GGG crystals, due to mutual crystal field perturbations of the two dopants, are connected with Cr3+-Tm3+ pairs. The high-resolution data offer direct evidence that the Cr31-Tm3+ energy transfer is governed for near neighbor Cr3+(a)-Tm3+(c) pairs by a shortrange, most probably superexchange, interaction. The contribution of multipolar interactions should be considered only for more distant pairs, while at large distances, dipole-dipole interaction is dominant. The data suggest that the sensitization with Cr3+ determines not only an efficient way of transfer of excitation from the pumping sources to active ions but could produce changes of the spectal and temporal behavior of the latter.

Efficient lasing near 1.4 μm in a (Cr, Ce, Nd):Gd3Ga5O12 crystal

The lasing and spectroscopic properties of (Cr Nd):Gd3Ga5O12 [(Cr, Nd):GGG] and Nd:YAG crystals in the wavelength region 1.3–1.45 μm are compared. The cross sections for stimulated transitions of Nd3+ ions in this spectral region are found. Lasing at a wavelength of 1.4237 μm has been achieved in the (Cr, Ce, Nd):GGG crystal for the first time. An energy of 2.3 J in the light pulse has been achieved at an absolute efficiency of 1.2% during flash pumping of a free-running laser based on a (Cr, Ce, Nd):GGG crystal at this wavelength. An average laser output power of 21.6 W has been achieved at a pulse repetition frequency of 13 Hz. The advantages of (Cr, Nd):GGG crystals over Nd:YAG crystals for oscillation in the 1.4-μm region are discussed.

Compensation of capillarity in Gd 3Ga 5O 12 growth

Based on a known theory, a linear digital filter has been developed in order to estimate the crystal radius from the measured weight error signal during Czochralski growth of GGG crystals. We investigated the effect of the filtering on weight error data measured duting GGG growth. The dynamic responses of radius error and measured weight error have been characterized by using estimates of the transfer functions relating heating power to crucible weight and crystal radius error. The results show that the dynamic response of the uncompensated signal of a balance weighing the crucible during growth is much faster than the response of the crystal radius. In the frequency regime of our test signals, the uncompensated weight variations can be considered as a noisy version of the radius error, rather than a real weight variation of the unsolidified charge.

Influence of multisites in the energy transfer of chromium and neodymium doubly doped GGG crystals

By using a high resolution fluorescence technique, a systematic study of the different crystal field sites appearing in Gd 3Ga 5O 12: Nd 3+, Cr 3+ has been performed. Five Nd 3+ sites (denoted as α, β, γ, δ and ε) have been detected and only one of them (ε) appears as a consequence of the presence of Cr 3+ ions. Decay time measurements show that Cr 3+ → Nd 3+ energy transfer takes place in the five Nd sites but more efficiently in the new ε site.

Growth and investigation of Nd 3+ and Ce 3+ doped gadolinium gallium garnets

(Nd,Ce):GGG crystals were grown by Czochralski technique. The imperfection of the as-grown crystals such as constitutional supercooling, dislocation was observed and also eliminated during the growing processes. Color center after ultra-violet irradiation of such crystals has been studied. Ce in this crystal plays a role not only as a sensitizing ion but also as an anti-ultraviolet irradiation element. From the measurement of absorption and fluorescence spectra it can be seen that there exists energy transfer between Ce and Nd. The laser output efficiency of the crystals is higher than that of Nd:GGG with the same size and the same quality. This means that (Nd,Ce):GGG might be a promising laser material.

BIREFRINGENCE IMAGES OF END-ON SCREW DISLOCATIONS IN GGG CRYSTALS CONTAINING ALONG-RANGE PLANE STRAIN FIELD

摘要 基于弹性各向同性和弹光各向异性的考虑, 获得了长程应变场中沿位错线观察的螺型位错双折射像的解析表达式以及其计算机模拟像, 成功地解释了G G G 晶体中实验观察到的螺型位错像所具有的两瓣一黑一白的衬度特征. Abstract The expression for intensity distribution and computer simulated images of screw dislocations with Burgers vector l/2 (111) viewed end-on in gernet crystals subjected to a long-range strain have been obtained by considering only the anisotropy of the photo-elastic property of the material. The computer-simulated images of end-on screw dislocations show two fold symmetry with a pair of dark and bright petals which result from the effect of a longe-range plane strain field superimposed on screw dislocation. The computer-simulated images are in good agreement with the experimental images in GGG crystals. 作者及机构信息 葛传珍；张京；冯端 1. 南京大学物理系 Authors and contacts Ge Chuan-zhen; Zhang jing; Feng Duan 参考文献 施引文献

Sensitizing of Nd^3+ luminescence by Cr^3+ in gallium garnets

The kinetics and energetics of chromium-sensitized neodymium luminescence of several codoped gallium garnets (YAG, YSGG, GGG, and GSGG) have been measured and interpreted in terms of microscopic physical-energy-transfer mechanisms. Sensitized luminescence in YAG and in YSGG is well described by the static energy-transfer process; a migration-accelerated energy transfer process is determined to be operative in GGG and GSGG crystals.

Three-dimensional representation of growth defects in GGG crystals

Three-dimensional representation of growth defects in GGG crystals

Fluid flow effects on the growth of GGG and doped GGG crystals

Fluid flow effects on the growth of GGG and doped GGG crystals

The growth of two inch diameter GGG crystals

The economical, technical and scientific aspects of the growth of two-inch diameter GGG crystals are discussed.

Growth of 3’’ diameter Gd3Ga5O12 crystals

As the bubble technology has progressed from the research stage into pilot plant operation, the need for larger diameter substrates has developed. Today, typical 3 in. diameter crystals of GGG weigh between 9000 and 10 000 grams and are grown from charges of 12 000 grams or more. The growth of 3 in. diameter GGG crystals with low defect densities 1(?/cm2) presents several problems which are not encountered during the growth of small diameter crystals. The first problem encountered is one of proper scaling of the growth furnace and growth parameters. The second problem is that of melt composition to insure a uniform lattice parameter throughout the entire crystal. A third area which can present problems is the size and mass of the charge required for 3 in. diameter crystals. Each of the parameters and their relationship to crystal imperfections is discussed.

Inversion of the direction of the solid-liquid interface on the Czochralski growth of GGG crystals

In the process of the crystal growth of Gd 3Ga 5O 12 by the Czochralski method, the shape of the solid-liquid interface drastically changes from convex to concave toward the melt at a certain crystal diameter under a constant seed rotation rate condition. It is due to the remelting of the old crystal and is related to the balance between a natural convection and a forced one caused by crystal rotation. The relationship between the conditions of the inversion and the growth parameters have been examined by growing the crystals under various conditions. The inversion diameter which gives the inversion of the interface was expressed as (Re η/ϱ) 1 2 ω s -1 2 by introducing the Reynolds number Re.