Tetsuro Izumitani

Optical properties, fluorescence mechanisms and energy transfer in Tm3+, Ho3+ and Tm3+ -Ho3+ doped near-infrared laser glasses, sensitized by Yb3+

Abstract The optical properties of the rare elements Tm3+, Ho3+ and Yb3+ were systematically investigated in various glasses. The Tm3+ doped aluminozircofluoride glass shows higher quantum efficiency, longer lifetime and stronger fluorescence intensity than Tm3+ doped YSGG crystal and other Tm3+ doped glasses for the 3 H 4 → 3 H 6 transition. Similar quantum efficiency, longer lifetime and stronger fluorescence intensity were also found in Ho3+ doped aluminozircofluoride glass for the 5 I 7 → 5 I 8 transition. The higher quantum efficiencies of Tm3+ and Ho3+ in aluminozircofluoride glass are due to the longer lifetime and the lower phonon energy. The fluorescence mechanisms and energy transfer in the Yb3+ -Tm3+ system, Yb3+ -Ho3+ system and Yb3+ - Tm3+ -Ho3+ system were studied. The very strong fluorescence intensities in the Yb3+ -Tm3+ system for Tm3+ and the Yb3+ -Tm3+ -Ho3+ system for Ho3+ which are 1.68 times that of Tm3+ doped YSGG crystal and 2.25 times that of Tm3+Ho3+ codoped YSGG crystal are attributed to the efficient Yb3+ → Tm3+, Yb3+ → Ho3+ and Tm3+ → Ho3+ energy transfer processes. The fluorescence processes are described by cross relaxations of 2 F 5 2 → 3 H 5 → 3 H 4 → 3 H 6 → 2 F 7 2 and 2 F 5 2 → 3 H 5 (or 2 F 5 2 → 5 I 6 → 3 H 5 ) → 3 H 4 → 5 I 7 → 5 I 8 → 3 H 6 → 2 F 7 2 .

Room-temperature persistent spectral hole burning in Sm 2+ -doped fluoride glasses

Persistent spectral hole burning is observed in Sm(2+)-doped glasses at room temperature. The holes are burned in the (7)F(0) ? (5)D(0), (5)D(1) lines of the Sm(2+) ions in three kinds of fluoride glass. The dependence of the burning efficiency on the sample and on the burning intensity is measured. The intensity dependence is approximately linear, and no antihole is observed around the burned hole. The hole-burning mechanism is discussed. The temperature dependence of the homogeneous width is also measured.

Gradient-index rod lens made by a double ion-exchange process.

Gradient-index rod lenses with a parabolic-index profile have been fabricated by a double Na-Ag ion-exchange process, and their optical characteristics have been evaluated. The numerical aperture and minimum focused spot diameter of the 2-mm diam rod lens were 0.58 and 2.5 microm for lambda = 0.63 microm, respectively. Because of the high diffusing rate for Ag ions, this technique offers the possibility of making large-sized (larger than 10 mm-diam) rod lenses for photographic uses.

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.

Blue, green and 0.8 μm Tm3+, Ho3+ doped upconversion laser glasses, sensitized by Yb3+

To obtain efficient upconversion laser glass, the optical properties of Tm3+ and Ho3+ were investigated in various glasses. Fluoride glass was selected as base glass for upconversion. The efficient upconversion fluorescences corresponding to the 1G4→3H6 and 3H4→3H6 transitions of Tm3+ and the 5S2→5I8 transition of Ho3+ were observed in Yb3+-Tm3+ and Yb3+-Ho3+ doped aluminozircofluoride glasses excited at 980 nm. The very stronge blue and green emission light can be observed visually. The upconversion processes observed were two-photon processes for 3F4→3H6, 5S2→5I8 transitions and three-photon processes for the 1G4→3H6 transition and can be described by a rate equation model. The energy transfer and energy back-transfer were analyzed in Yb3+-Tm3+ and Yb3+-Ho3+ systems. The relationship between emission intensity, pumping intensity and dopant concentrations is described using a rate equation model and shows good agreement with experiments. The dynamics of excited state (Yb3+2F52) is also analyzed with the diffusion-limited model based on Yokota-Tanimoto theory.

Luminescence of Sm2+ -doped fluoride glasses

Abstract We have investigated the optical properties of Sm 2+ -doped fluoride glasses having three different compositions. The absorption and emission spectra reveal that the immediate fluorine environment surrounding the Sm 2+ ion is nearly identical for the three glass compositions, and is probably characterized by a high coordination number. The emission yield, on the other hand, is sensitively dependent on the composition of the glasses. It is theorized that the interaction of the host conduction band with the 4f 5 5d and 5 D 0 states is largely responsible for opening up a nonradiative decay pathway from the 5 D 0 emitting level, to the 7 F ground state levels. As a consequence, the glasses based on heavy metal ions give smaller emission yields than those primarily based on smaller cations.

One-directional gradient-index slab lens

A gradient-index slab lens (2.5–3.4 mm thick) with parabolic-index profiles along the direction of thickness has been fabricated by a molecular stuffing process, and its refractive-index profiles have been evaluated.

Reflection spectra of various kinds of oxide glasses and fluoride glasses in the vacuum ultraviolet region

Abstract Reflection spectra of silicate, borate, phosphate, fluorophosphate and fluoride glasses are studied in the spectral region of 2–13 eV in order to understand their dispersion behaviors in the visible region from the point of view of atomic structures. The absorption bands due to bridging oxygen ions or fluorine ions are found at 11.6 eV and 10.4–9.5 eV in silicate glasses, at 10.2 and 8.8 eV in borate glasses, at 9.5 eV in phosphate glasses, at 11.2 eV in fluorophosphate glasses and at 11 eV in fluorozirconate glasses. In silicate glasses, the bands due to nonbridging oxygen ions are found in the region 8.8-4.9 eV. They shift to lower energies with increasing ionic radius, in the order of Ca 2+ , Sr 2+ and Ba 2+ , for the glasses containing low valency cations, while they shift to higher energies with increasing ionic radius, in the order of Ti 4+ , Zr 4+ and Th 4+ or in the order of Nb 5+ and Ta 5+ , for the glasses containing high valency cations. In glasses containing large amounts of PbO, strong bands due to PB 2+ ions appear in the lower energy regions of 6.3–5.6 eV and 5.2–4.7 eV.

Gradient-index slab lens with high numerical aperture.

A near-parabolic profiled 1-D lens with high N.A. (=0.70) has been fabricated by an indiffusion ion exchange and cementing technique. Maximum longitudinal aberration is lower than 0.2 mm all over the lens thickness. The focused beamwidth is ~5 μm.

Fundamental absorption of glasses in the vacuum ultraviolet region

Abstract Reflection spectra of silicate, borate, phosphate, fluophosphate and fluoride glasses were measured in the spectral region 2–13 eV in order to correlate dispersion to the absorption wavelength of glass. The bands due to bridging ions and nonbridging ions were found in the range 11.6−8.8 eV and 8.8−4.9 eV respectively. It was confirmed that the bands due to nonbridging ions shift to lower energy for low valent cations and shift to higher energy for high valent cations with increasing ionic radius.