Hidekazu Hashima

TEMPERATURE DEPENDENCE OF NEGATIVE NONLINEAR ABSORPTION EFFECT IN AN ERBIUM-DOPED BORATE GLASS

The dependence of negative nonlinear absorption effect on sample temperature was investigated in erbium-doped borate glass, using an 810.0 nm laser diode. Reversed-phase waveforms were observed in the transmitted waveform in the temperature range of -200 to 750°C. The glass transition temperature was measured to be 708°C by differential thermal analysis. It is suggested that the effect can be obtained even when the glass is in the form of a supercooled liquid, because it is formed by optical transitions of the erbium ion inner shell.

Effect of Additives on Absorption Edge Energy in Bismuth Phosphate Glass

The effect of third-additive oxides on absorption edge energy was studied in binary bismuth phosphate glass. The edge energy was shifted toward lower energies by the substitution of third-additive oxides for P2O5. The substitutions of glass-network-forming (NWF) oxides and glass-network-modifying (NWM) oxides resulted in distinct linear relationships between the edge energy and Duffys ideal basicity. The energy shift against the calculated basicity was larger for the substitution of NWF oxides than for that of NWM oxides. Moreover, the substitution of intermediate oxides gave a similar tendency to the substitution of NWF oxides rather than to that of NWM oxides for both relationships. It was deduced that electron donation is more sensitive to the substitution of NWF oxides than to that of NWM oxides. On the other hand, a 238 cm-1 Raman band, which is attributed to the Bi–O vibration mode, shifted toward higher wave numbers by the substitution of all of the oxides. The 238 cm-1 band showed a linear relationship with the ideal basicity similar to the relationship between the edge energy and the basicity. Sensitivity against electron donation was consistent with both the Bi–O bond strength and the absorption edge energy.

Local precipitation of upconversion nanocrystals in rare-earth-doped oxyfluoride glasses by laser irradiation

Rare earth-doped oxyfluoride glass of the 50SiO2 -50PbF2 -5ErF3 composition in molar ratio was developed. When the oxyfluoride glass is heat-treated at the first cystallization temperature, the glass gives the glass-ceramic in which rare earth-containing fluorite-type nanocrystals of about 20 nm in diameter uniformly precipitate in the glass matrices. The glass-ceramic is trasnparent to the naked eye like no heat-treated oxyfluoride glass. The glass-ceramic exhibits highly efficient upconversion luminescence under 800 and/or 980 nm laser light excitation. On the other hand, the oxyfluoride glass can be locally changed to glass-ceramic in the forms of dot, line, plane, letter, etc. by thermal energies generated from light absorption of various lasers. In the case of CO2 laser irradiation the formation of such glass-ceramic occurs near the surface of glass. In the case of 800 or 980 nm irradiation by Ti:sapphire laser or laser diodes, on the other hand, the formation of such glass-ceramic occurs near the surface and/or inside of glass. The glass-ceramic parts can be easily read by upconversion luminescence under laser excitation. Therefore, the presently developed rare earth-doped oxyfluoride glass can be utilized as optical devices of the writing and reading memory, which can be utilized as specific devices for security information.

Upconversion of glass ceramics and its application

Oxyfluoride glasses of the compositions of 50SiO2•50PbF2•(5 - x)GdF3•xErF3 and 50SiO2•50PbF2•(5 - y)GdF3•0.1NdF3•yYbF3•0.1(Tb, Ho, Er or Tm)F3 in molar ratio (x =0.3 - 5 and y = 0 - 5) were developed. The oxyfluoride glasses were heat-treated at their first crystallization temperatures. Consequently, the crystals of -PbF2:(trivalent rare-earth ions) solid solutions uniformly precipitated in the scales of 15 20 nm in diameter in silicate glass matrices. These glass-ceramics were transparent to the naked eye. The glass-ceramics gave highly efficient upconversion luminescence based on the Tb3+, Ho3+, Er3+ or Tm3+ ion under 800 and/or 980 nm light excitation. These oxyfluoride glasses can be locally changed to glass-ceramics in the forms of dots, lines, letters, planes, etc. by irradiation of various lasers. The forms written by laser irradiation can be easily read from upconversion luminescence generated by the 800 and/or 980 nm laser illumination. Thus, the present oxyfluoride glasses can be applied to an optical memory device for specific information. Plates, fibers, thin films and coating-films in which the glass-powders are embedded in inorganic and/or organic polymers are considered as the shapes of oxyfluoride glasses that can be utilized as the device.

All-Optical Inverter Operating with a 1.5 µm Laser in Erbium-Doped Phosphate Glass

The dependence of an all-optical inverter derived from the negative nonlinear absorption effect on both the modulation degree and frequency was investigated in erbium-doped phosphate glass using a 1.5 µm laser diode. With a decreasing degree of incident modulation, a reversed-phase waveform was obtained in the transmitted laser at modulation degrees less than 86%. The reversed-phase transmitted waveforms were observed at modulation frequencies from 10 Hz to 250 MHz and at wavelengths from 1530.0 to 1545.0 nm. The wavelength dependence of the negative nonlinear absorption effect agreed with the transmitted spectra for the erbium-doped phosphate glass. The negative nonlinear absorption effect for 1.5 µm can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.

LOW-Tg BISMUTH PHOSPHATE GLASSES FOR GLASS-IMPRINTING AND FABRICATION OF 2D SUB-WAVELENGTH STRUCTURE

We have developed zinc-bismuth-phosphate glasses, which have deformation temperatures under 450°C and refractive indices higher than 1.7, in order to produce an antireflection structure on the surface by a glass-imprinting process. Two-dimensionally arrayed conical cavities of sub-wavelength size were fabricated on a SiC mold by electron lithography and dry etching techniques. The sub-wavelength periodic structure was transferred onto the glass surface by a glass-imprinting process using the mold. The sub-wavelength structure suppressed the reflectance by approximately 90%. A weak maximum was observed in the reflection spectra around 400–500 nm, which decreased in intensity and shifted toward shorter wavelengths with decreasing pitch.

Negative nonlinear absorption effect in glasses containing a large amount of erbium oxide

Compositions which vitrify by means of a conventional glass melting method, containing a large amount of erbium ion were investigated in aluminosilicate, phosphate, borate, borosilicate, telluride and fluoride systems. As a result of melting test, we obtain some glasses which contain higher than 20 mol% erbium. In transparent materials containing erbium an anomalous optical absorption phenomena have been reported by Maeda et al. With increasing in an incident laser light intensity, the transmitted one through the transparency such as the glass decreases, that is called negative nonlinear absorption (NNA) effect. With a particular modulation degree of an incident laser light, the transmitted waveform were reversed in phase to an incident one. The NNA effect in these glasses was observed over a wide band of the wavelength, while in erbium doped yttrium aluminum garnet and erbium doped lutetium aluminum garnet crystals were observed at a narrow band. The discrepancy of the NNA effect between the glasses and the crystals might be explained in the term of absorption spectrum associated with erbium. Namely, the absorption spectra of erbium doped yttrium aluminum garnet crystal have a narrow absorption band of 788 nm, while that of the glasses have broad absorption band of about 800 nm.

All-optical inverter operating over a temperature range of -200oC to 750oC in erbium-doped borate glass

An all-optical inverter, which operates over a temperature range of -200 to 750 degree(s)C, was demonstrated in erbium- doped borate glass. The dependence of negative nonlinear absorption effect on sample temperature and modulation degree was investigated, using an 810.0 nm laser diode. Reversed-phase waveforms were observed in the transmitted waveform in the temperature range. The glass transition temperature was measured to be 708 degree(s)C by differential thermal analysis. With a decreasing modulation degree, the reversed-phase waveform was obtained. The effect has a characteristic which is almost independent of the sample temperature because it is formed by optical transitions of the inner shell of the erbium ion.

All-Optical Inverter Operating up to 850?C in an Erbium-Doped Phosphate Glass

The dependence of an all-optical inverter on both sample temperature and modulation frequency was investigated in an erbium-doped phosphate glass using a 809.5 nm laser diode. The reversed-phase waveforms were observed in the transmitted waveform in a temperature range of -220 to 875°C. The glass transition temperature was measured to be 697°C by differential thermal analysis and the glass was in the form of supercooled liquid between 700 and 930°C. An all-optical inverter which had a negative input-output characteristic was demonstrated in a temperature range of -200 to 850°C.

Preparation of PbTiO3 thin films by ion-beam sputtering

Abstract Lead titanate thin films were deposited on Pt substrates. When a sintered oxide target of stoichiometric composition was used, the content of lead in the film was less than that of the target. This suggests that the content of lead at the surface of the target decreases in the course of sputtering. In order to increase the lead on the target surface, metallic lead was evaporated onto the target during ion-beam sputtering. The effect of Pb evaporation and oxygen partial pressure on the crystal structure of the films was studied. Peiovskite films were obtained with controlled evaporation of metallic lead.