Tadaoki Yamashita

Preparation and characteristics of Li2B4O7 : Cu phosphor

Abstract Li 2 B 4 O 7 : Cu crystal phosphor prepared by a sintering method was found to have the most promising characteristics for use as TLD, i.e., a TL emission band at 368 nm and a moisture resistant property.

TeOx thin films for an optical disc memory

Tellurium suboxide thin films TeOx were found to change in refractive index and extinction coefficient on thermal or optical heating, with accompanying changes in the reflectivity and transmission. The preparation method and thermal or optical properties of the TeOx thin films were investigated to obtain a stable and highly sensitive optical disc memory. A two‐source evaporation method using Te and TeO2 provided uniform and any desired composition. The properties of the film depended on the x value; increasing x to as large as x=1.2, which represents a Te‐poor composition, produced an excellent humidity and heat stability, and decreasing x to 0.8 made the film more sensitive to a laser diode, but susceptible to humidity. The TeO1.1 thin film was found to sufficiently satisfy all requirements for practical disc applications. A reflective optical disc was prepared using the TeO1.1 thin film deposited on a polymethylmethacrylate substrate with grooves for optical tracking. This disc is capable of recording v...

Thermal changes of optical properties observed in some suboxide thin films

Suboxide thin films of SbOx, TeOx, MoOx, and GeOx (x is smaller than the stoichiometric value for each component) were found to have the property of showing a critical change in their absorption coefficients and refractive indices at elevated temperatures. The thin‐film samples were prepared by evaporating a mixture of the stoichiometric oxide powder and a deoxidization metal powder such as tungsten. The critical temperatures of these thin films are 150, 120, 150, and 280 °C, respectively. The absorption coefficients before and after the heat treatment are 2.5×104 (before) and 6.1×104 (after), 8×104 and 1.0×105, 5.6×103 and 1.1×104, and 4.9×104 and 1.8×105 cm−1, respectively. Their refractive indices are 1.8 (before) and 1.9 (after), 3.1 and 3.5, 1.8 and 2.1, and 2.5 and 2.8, respectively. As determined by x‐ray diffraction analysis, these thin films are composed of very small metal grains and stoichiometric oxide grains. The thermal changes accompanied by the optical constant changes are mainly due to st...

New Optical Erasable Medium Using Tellurium Suboxide Thin Film

A suboxide thin film of TeOx ( x is smaller than the stoich.Lometric value ) containing a small amount of additives of such metals and semimetals as Sn and Ge has been found to have the property of showing a reversible change in its optical constants when the film was exposed in turn to two diode laser spots with different sizes, and this property can be utilized for an erasable disc. For recording, a TeOx thin film deposited on a PMMA substrate is irradiated by a diffraction limited laser spot, 0.8 pm in dia., modulated in response to an input electrical signal. This causes a micro-sized area of the film to be suddenly heated and rapidly quenched, resulting in a decrease in optical reflectivity. This recorded bit can be erased at real time by the irradiation of a diffused laser spot to an elliptical shape, 1 x 10 pm, by which the bit recovers its optical properties. An optical head having the two laser beams, one for recording/playback and one for erasing, has been developed. Real time erasing and recording at the same time has been achieved for a video signal. In excess of a million record/erase cycles have been demonstrated with no significant degradation in playback signal quality or erasability. Carrier-to-noise ratio, C/N, was more than 55 dB at 5 MHz, 30 kHz bandwidth.

Sub-Oxide Thin Films For An Optical Recording Disk

Thin films of SbOx, GeOx, TeOx, MoOx, InOx and PbOx ( x is smaller than the stoichiometric value for each component ) were found to have a feasibility to be applied to an optical recording disc. Upon heating, these thin films are critically changed in their optical constants at 150°, 280°, 120°, 150°, 120° and 100°C, respectively. The contrast ratios before to after heat treatment of the GeOx, TeOx and MoOx films of 1000 - 2000 Å thick are very high, they are 50, 20 and 15, respectively. Among them, the TeOx (x ≈1.1) film was excellent in both the sensitivity and the contrast ratio, and an optical recording disc was prepared by depositing the TeOx on a PMMA disc, substrate. Video-signals can be recorded and played back using a laser diode (λ =8300 Å, N.A.= 0.5) at the laser power of 6 - 8 mW incident. The carrier to noise ratio at 5 MHz was in excess of 55 dB.

Light pulses emitted at microfractures formed by friction between two solid materials

Short-duration light pulses have been observed to be emitted at the moment of microfracture (pit size of 10-20 µm) when two solids are rubbed against each other. When a fused silica sample is scratched by a diamond grain, the observed light pulses have a rise time of less than 10 ns and pulse width of 10-20 ns. A continuous spectrum at 500-800 nm is observed, suggesting 3000° C material part. At 300-400 nm, intense line spectra are observed, which suggests the existence of gaseous *O2 molecules desorbed from SiO2. When the solid fractures, the fractured part heats up to a very high temperature almost instantaneously, and cools down within 10-20 ns.

Calcium Sulfate Activated by Lead and Manganese for Thermoluminescence Dosimetry

CaSO4: Pb, Mn has been found to be free from the serious disadvantage of rapid fading possessed by CaSO4: Mn, the most sensitive thermoluminescence phosphor available so far. A study has been made on the effect of lead and manganese content on CaSO4, and it is concluded that lead in CaSO4 produces new traps for radiation energy, resulting in improvement of the properties of the phosphors for dosimetry. The optimum content of such activator additives was found to be 0.2 mol/0 of lead and 3 mol/0 of manganese. The improved phosphor thus obtained produces glow peaks at 160° and 190°C, and the energy yield of the thermoluminescence is about which is twice that of CaSO4: Mn. The more significant properties of this phosphor from the viewpoint of application to radiation dosimetry include: (1) Linear responce from 50μR to 104R (2) Minimum detectable dose of 50μR±25% by experimental reader (3) Fading rate of 5% in a week

Laser Nanometer Probe Utilizing Beam Diffraction Pattern Change as a Function of Displacements from the Focal Point.

A laser diode (λ = 780 nm) probe, from which an half-circular beam irradiates in-focus to an objective surface and the diffraction pattern formed on the suface near the focal point is detected by a two-part-divided photo-diode throughout the same optical path, is proposed. The principle of the measurement is discussed by the diffraction pattern change analysis. The response characteristics of the probe prepared are measured; the obtained dynamic ranges are ±1 μm-2 nm for f=3.6 mm, and ±100-0.2 μm forf =23 mm lens. When the output signal, the difference currents of the two parts of the detector, is normarized by the summation of them, it becomes a simple function of displacements inspite of the condition of the material surface; the displacement response curves for a mirror sample, a low reflectivity glass sample and a steel sample having a mean roughness of 1.3 μm, are quite similar.

Investigation of the TSEE of Various Oxides and Sulfates

The TSEE of various oxides and sulfates were investigated in order to obtain a highly sensitive material for radiation dosimetry. As a result, BeO heated above 165°C in O2 or air, and Na- or Li-doped BeO heated above 140°C were found to have the best sensitivities to radiation. The materials which showed sensitivities nearly as high as BeO were MgO, Al2O3, WO3, PbO, CaSO4, SrSO4 and BaSO4.

Lithium Borate Activated with Copper and Silver for TLD

Lithium borate (Li2B4O7) is known as one of the most promising thermoluminescence materials because of its low dependence on photon energy. A new phosphor, Li2B4O7 activated with copper and silver (0.02_??_Cu, 0.02_??_Ag), has been developed and found to have the following thermoluminescence characteristics.(1) Its thermoluminescence emission bands lie in the near ultraviolet region; a dominant peak appears at 368 mμ (by Cu) and another smaller one at 268 mμ.(2) The main thermoluminescence glow peak appears at 185°C (by Ag), and another smaller one at 110°C.(3) The thermoluminescence output detected by a widely used photomultiplier (1P21) is about 3 times larger than that of Li2B4O7: Mn, and the expoure response is linear in an exposure range from 10 mR to 300R.(4) Fading is less than 9% in 2 months.