Robert J. Ginther

Optical Waveguides Formed by Thermal Migration of Ions in Glass

We present our results on optical waveguides formed by thermal diffusion of ions in glass. It was found that the peak of the ion-exchanged region can be shifted into the substrate interior by limiting the diffusion process. We also found that low loss films (<0.1 dB/cm) can be fabricated using this process and that the modal losses in these films do not agree with those losses predicted by existing theories. Also, the ion-exchange process has proved to be a simple means for fabricating tapered-edge couplers.

Defect centers in a pure‐silica‐core borosilicate‐clad optical fiber: ESR studies

An electron‐spin‐resonance (ESR) study has been carried out on γ‐ray‐induced color centers in a pure‐SiO2‐core B2O3⋅3SiO2‐clad prototype optical fiber and in bulk glasses of the core and cladding compositions. Defects in the core material included the familiar silicon E′ center and other centers tentatively attributed to oxygen‐associated structures. Approximately 102 times more centers per unit mass and unit γ‐ray dose were created in the cladding material than in the core glass; these comprised just three defect types: the boron‐oxygen hole center (BOHC), the silicon E′ center, and a boron analog of the latter, the boron E′ center. These same defects were also observed in the irradiated prototype fiber in concentrations comparable to those attained in the bulk glass of the cladding composition. The unexpectedly high radiation sensitivity of the fiber, therefore, would appear to be due to the efficient production of (intrinsic) boron‐related defects in the cladding. Considerable insight has been gained i...

The sensitized luminescence of manganese-activated calcite

Synthetic manganese‐activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000–3500A, while they are luminescent under cathode‐ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural calcites is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave‐length ultraviolet‐excited luminescence of all natural calcites to the action of an auxiliary impurity. The essential identity of the cathode‐ray excited luminescence spectra of CaCO3:Mn, CaCO3: (...

New Cerium Activated Scintillating Glasses

The synthesis of cerium activated scintillating glasses is being continued, and two new types have been developed. One of these, a magnesium aluminum borate, is similar to the alkali borate glasses reported previously and was made in an effort to provide a scintillating glass with the highest possible boron content in which a reasonable pulse height could be retained. Its pulse height with gamma excitation is 5.0 per cent of a Nal(Tl) crystal. The second glass developed is a lithium magnesium aluminum silicate. This glass has a pulse height 14.0 per cent of the Nal(Tl) crystal and is the most efficient material prepared in this program. Preliminary studies indicate that energy transfer between the base glass and the activator does occur, and that the efficiency of glass scintillators is not limited by the absence of energy transfer. mission.

New Thermoluminescent Dosimeter

A simple dosimeter design is described in which a thermoluminescent phosphor is mounted on an electrically heatable support in an evacuated or gas‐filled envelope. With CaF2:Mn as the phosphor, the device detects gamma‐ray doses in the milliroentgen range and is linear in response up to at least 2×105 r. Dose readings can be made in less than a minute with simple instrumentation requiring no darkroom facilities. The dosimeter may be reused many times. The response is independent of dose rate at least over the range 10 mr/min to 7000 r/min. With suitable tin shields the response is independent of energy over the range 40 kev to 1.25 Mev. The advantages of this device for monitoring of personnel in health physics operations are pointed out.

Some Optical Properties of Lead-Activated Sodium Chloride Phosphors

Absorption and luminescence phenomena in NaCl:Pb phosphors have been found to be rather complex. Melt-grown NaCl:Pb has an asymmetrical, 2730A-peaked absorption band. The variation of emission spectrum with wave-length of excitation within this band shows that it consists of two poorly resolved absorption bands, one peaking at 2730A and the other at 2900A. At low Pb concentrations, irradiation into the first of these causes a near-ultraviolet emission peaking at 3200A; irradiation into the second causes a visible emission peaking at about 4500A. At high Pb concentrations, irradiation into the first band gives a second near-ultraviolet emission band peaking at 3850A in addition to the one peaking at 3200A. Precipitated NaCl:Pb shows all the above phenomena, and in addition, has an excitation band peaking at 2600A, producing simultaneously a 3300A-peaked emission and a visible emission. The NaCl:Pb phosphors are unstable, deteriorating after a few days at room temperature and more rapidly at 130°. X-irradiation of these phosphors destroys the above absorption and emissions, and gives a print-out effect due apparently to the formation of colloidal Pb. The x-rayed material can be excited by near ultraviolet to give a red emission, peaking at about 6100A. Some suggestions concerning the interpretation of the above phenomena are given.

Ultraviolet Phosphors and Fluorescent Sun Tan Lamps

An investigation was undertaken of phosphors capable of converting primary ultraviolet radiation (Hg line, 2537 angstroms) to radiation in the erythemal or sun tan ultraviolet region (2900–3200 angstroms). Several types of alkaline earth silicates and phosphates activated with lead or thallium were found to be practical. Among these was a calcium phosphate activated with thallium and containing about 1.3 moles of calcium per mole of phosphate. This phosphor not only showed a good initial erythemal emission, but when used in an experimental fluorescent lamp maintained a high percentage of this emission for the several hundred hours tested. The lamp was constructed of special glass and coated with the above phosphor, but otherwise was similar to commercial fluorescent lamps. In addition, the investigation showed some similar types of phosphors to be efficient in the neighboring “black-light” ultraviolet region (approximately 3400–3800 angstroms), and to give more emission in that region than the cerium-activated phosphors commonly used at present. Some discussion of sun tan lamp and fixture design is also included.

Anomalous fading of CaF2:Mn thermoluminescent dosimeters☆

Abstract A surprising effect encountered in the application of the thermoluminescence of CaF 2 :Mn to dosimetry is the initially high fading rate. This fading is much more rapid than would be expected considering the high-temperature, apparently uncomplicated glow curve of CaF 2 :Mn. This effect is present when rapid heating rates (∼20°C/min) are used to obtain the glow curve, but when slow heating rates (∼20°C/min) are employed no fading is observed. It was determined that the glow curve is a composite of several closely spaced components of varying stability. With rapid heating rates all the glow curve components are shifted upward in temperature, causing preferential thermal quenching of the stabler (higher temperature) components. The composite glow curve is thus distorted and the unstable components, being attenuated to a lesser degree, give a greater contribution to the thermoluminescence output.

Laser‐Stimulated Thermoluminescence in Glass

Thermoluminescence has been investigated as a tool for the detection of damage precursors in laser glass samples exposed to 1.06‐μ laser radiation. Exposure which did not produce visible damage gave very small thermoluminescence yields. Damaged glasses produced stronger thermoluminescence, but in even those the effect is not large enough to provide a convenient materials test. A quenching action due to neodymium was noted. The emitting centers are believed to be impurities in the glass.