Hiromichi Takebe

Preparation and properties of GeGaS glasses for laser hosts

Abstract The preparation and purification of GeGaS glasses were studied. A purified glass doped with 1000 ppm Pr 3+ exhibits a quantum efficiency of 50% in the 1 G 4 → 3 H 5 transition at 1.3 μm based on fluorescence lifetime measurement and Judd-Ofelt analysis. The effects of Ga and S contents on glass transition and crystallization temperatures, density, refractive index and spontaneous emission probabilities from the 4 F 3 2 level of Nd 3+ were examined. Compositional dependences of properties are discussed in terms of bond types.

Effect of modifier ions on fluorescence and absorption of Eu3+ in alkali and alkaline earth silicate glasses

Fluorescence and absorption spectra of Eu3+ in silicate glasses have been measured. The fluorescence intensity ratio of 5D0 → 7F2 to 5D0 → 7F1 transitions of Eu3+ increases with increasing ionic radius in the order of Li < Na < K for binary alkali silicate glasses and with decreasing ionic radius in the order of Ba < Sr < Ca for binary alkaline earth silicate glasses. It was found for the first time that the intensity ratio exhibited a maximum with the addition of alkaline earth oxides in alkali alkaline earth silicate glasses. The variation of intensity ratio and the Judd-Ofelt parameter, Ω2, with composition depended on the structural change in the vicinity of Eu3+ ions and EuO covalency.

Compositional dependence of the valency state of Cr ions in oxide glasses

Absorption spectra of Cr ions in multi-component oxide glasses melted in Ar were measured. The integrated extinction coefficient is used as a parameter to analyze the redox reaction of Cr3+ and Cr6+ in glass samples. The relative content of Cr6+ increased and that of Cr3+ decreased with increasing basicity in silicate and borate glasses; this result is consistent with previous studies. On the contrary, only Cr3+ exist in phosphate glasses. Cr4+ ions were found only in aluminate, gallate and alumino-silicate glasses with modifier contents ≥ 60 mol%. The relationship between point defects and Cr4+ formation is examined on the basis of electron spin resonance measurements. We concluded that the superoxide ion radical (O2−) and the peroxy bonding (-O-O-) oxidize Cr3+ to Cr4+ in aluminate, gallate, and alumino-silicate glasses.

Glass fiber poling and applications

Recent developments in the application of poled optical fibers to second harmonic generation and electrooptic light modulation are reviewed.

Effect of poling conditions on second-harmonic generation in fused silica.

A systematic study of the effects of poling time and applied voltage on second-harmonic (SH) generation in thermally poled silica glass reveals that the SH signal is proportional to the square of the applied voltage and that the speed of the poling process increases with the applied voltage. Prior treatment of the samples is found to affect the poling process, and the optimum poling conditions are observed to depend on the poling atmosphere. The mechanism of thermal poling is discussed in the light of these new results.

Compositional variation in the structure of Ge–S glasses

Abstract X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence (XRF) and Raman spectroscopies have been used to characterize the structure of Ge–S binary glasses in the compositional range 57–90 at.% S, together with evaluating the valences of Ge and S. XPS reveals that Ge4+ and Ge2+ states are formed and especially, Ge2+ exists in the range 57–62 at.% S. The roles of Ge4+- and Ge2+-relating species in glass structure are discussed. The combined results of XRF and Raman spectroscopies suggest that S–S bonds are present in all the S-rich glasses of >67 at.% S, short S chains are formed up to 76.5 at.% S and then S8 rings are formed at the S-richer side. The compositional dependence of the molar volume calculated from the measured densities of glasses is qualitatively related to the structural units of the Ge–S glasses.

Refractive index and material dispersions of multi-component oxide glasses

Abstract Refractive index dispersion curves in the wavelength region of 0.40 to 5.03 μm are presented for multi-component oxide glass systems: borate, silicate, aluminate, germanate, tellurite, antimonate and heavy metal gallate. The material dispersion was determined using the refractive index data. Reflection spectra in the ultraviolet and infrared regions were measured to investigate the effects of electronic transitions and lattice vibrations on the material dispersion. Thallium tellurite, thallium antimonate and lead gallate glasses exhibit zero material dispersion wavelengths (ZMDWs) over 2.4 μm. The factors affecting the ZMDW are discussed.

Correlation between radiative transition probabilities of rare-earth ions and composition in oxide glasses

The compositional dependences of spontaneous emission probabilities of rare-earth ions such as Nd3+ and Er3+ were studied for silicate, phosphate and borate glasses using the Judd-Ofelt theory. The effect of the covalency of the rare-earth ion sites on the emission probabilities was estimated from the variations of the profiles of the absorption spectra in terms of the nephelauxetic effect. The spontaneous emission probabilities which depended on the intensity parameters, Ω4 and Ω6, were strongly affected by the ionic packing ratio of the glass host.

Spectroscopic properties of Nd3+ and Pr3+ in gallate glasses with low phonon energies

Absorption and fluorescence spectra of Nd3 +were measured in potassium tantalum gallate, lead bismuth gallate (PBG), fluorozirconate (ZBLAN), and Ge-Ga-S glasses. A Judd -Ofelt analysis was performed to determine the spontaneous emission probability and stimulated emission cross section of the4 F3/2 ?4 I11/2 transition of Nd3 +. Raman spectra were studied to clarify the maximum phonon energies of the glasses. The fluorescence of the1 G4?3 H5 transition of Pr3 + in a dehydrated PBG glass was observed for the first time to our knowledge. The PBG glass has a higher quantum efficiency than that of ZBLAN glass based on the Judd -Ofelt analysis.

Refractive index dispersion of gallium lanthanum sulfide and oxysulfide glasses

Refractive indexes were measured for Ga2S3-La2S3 and Ga2S3-La2O3 glasses in the range of 0.48 and 1.71µm using the minimum deviation method. Data is analyzed by the Wemple equation based on the single oscillator model. These glasses have relatively large average bandgaps Eo, and electronic oscillator strengths Ed, in comparison with other chalcogenide glasses. Possible origins of these features are discussed. Introduction: Gallium lanthanum sulfide (GLS) glass is one of leading candidates for 1.3 µm optical fibre amplifiers [1], infrared lasers [2,3], acousto-optic modulators [4], and optical switching devices [5]. It possesses high quantum efficiencies of the forced electric dipole transitions, resulting from high radiative rate and low non-radiative multiphonon decay rate. These desirable properties follow from its high refractive indexes over 2.4 [6] and a low maximum phonon energy of ~ 425/cm [1]. GLS glass is of particular interest for practical devices because of its relatively low toxicity, thermal stability and ability to draw into fibre, as well as its superior optical properties. The high refractive index with a wide optically transparent range of 0.5 and 10µm [4] also results in high third-order optical nonlinearity due to the electronic origin for ultra-fast optical switching [5]. The purpose of this study is to measure accurate refractive indexes of GLS-based glasses in the UV and near-infrared region, which are useful data to characterize optical materials, and to discuss their dispersion characteristics in comparison with other chalcogenide, oxide and fluoride glasses for optic applications