William H. Dumbaugh

Nonlinear optical susceptibilities of high‐index glasses

We report results of degenerate four‐wave mixing measurements of nonresonant nonlinearities in a variety of high‐index lead and bismuth containing oxide glasses and the chalcogenide As2S3. The third‐order nonlinear susceptibilities of the oxide glasses are found to scale with the heavy metal content. A lead‐bismuth‐gallate glass was identified with a nonresonant χ3 equal to 42±7×10−14 esu, which is approximately three times larger than that of any glass previously reported.

Recent advances in heavy-metal oxide glass research

Our laboratory recently has announced the formation of glasses based on the oxides of lead bismuth and gallium. These glasses are unusual in that they contain none of the traditional glass-forming caflons (eg. silicon boron germanium or phosphorous) yet exhibit a remarkable stability. In addition to this stability these compositions exhibit some rather unique properties such as the ability to transmit well into the infrared region (to about 8 microns) and a high nonresonant optical nonlinearity 3 (of 42 xlO 14 esu). To take advantage of this latter property for optical switching applications it is desirable to prepare the glass as an optical waveguide. Silica additions were made to a heavy metal oxide base glass in an effort to derive compositions suitable for core and cladding. The present paper describes the effects of these additions. 1.

Preliminary ultraviolet transmission data for beryllium fluoride glasses

Abstract Ultraviolet and infrared transmittance curves are given for several BeF2-type glasses. The BeF2 content of the glasses varied from 100% to less than 50 mol %. Intrinsic limitations on the transmittance of these glasses as well as impurity absorptions from the glass making process are discussed.

Infrared Transmitting Germanate Glasses

The infrared cut-off of glasses is primarily determined by the frequency of vibration of the cation-anion bonds. In order to extend infrared transmittance to longer wavelengths cations and anions of larger sizes and lower field strengths should be used; however, physical and chemical properties become poorer. For silicate glasses, this cut-off is about 5 pm. If germanium is used as the glass network former instead of silicon, the cut-oft moves out to about 6 μm. Of all types of glasses, the germanates provide the optimum combination of transmission, physical, and chemical properties. While the size of glass form-ing areas for germanates is smaller than that for silicates, properties can be varied some-what to fit a particular application. Lxpansion coefficients (25°-300°C) can vary from about 50 x 10-11°C to over 100 x 1011°C with mechanical hardness, Youngs modulus, and chemical durability generally decreasing with increasing expansion. While the cut-off is due to the germanium-oxygen bond vibration, the shape of the transmission curve approaching zero transmission from about 4.5 pm to 6 pm can be significantly affected by the quantity and type and modifying oxides. An optimum glass with respect to infrared transmission, low thermal expansion, meltability, formability, and cost was selected and designated Code 9/54. Originally, this glass was melted in crucibles and pressed into domes of rather poor quality. However, more zecently a process has been devised to melt Code 9754 glass in an optical tank and then press into various shapes with standard first grade optical quality (i.e., glass contains no visible striae), a total bubble cross section of 5-0.10 mm2 per 100 cm3, and no cracks or checks. The glass has a thermal expansion (25°C-300°C) of 63.6 x 10-7PC, a Youngs modulus of 8.58 x 103 kg/mm2, and a refractive index (ND) of 1.660. The minimum uncoated transmission of a 1.35 mm thick sample is 73% at 5 μm and 35% from 4.2 μm down through the visible.

Silica-rich glasses in the TiO2Al2O3SiO2 system

Abstract Ternary glasses in the TiO2Al2O3SiO2 system have received only very limited attention, although both Al2O3SiO2 and TiO2SiO2 glasses have been extensively studied and exhibit interesting properties. In this paper, the ternary glass-forming region and physical properties are described. Unusual volume contraction was found for some compositions which allowed strengthening by surface compression.

Infrared-Transmitting Oxide Glasses

Most current research on infrared glasses has concentrated on non-oxide systems which transmit to beyond 7 μm. There are still applications in the 2 to 6 μm range which can best he filled by oxide glasses which generally have better physical and chemical properties than the oxide-free materials. Of all glass systems, silicates have the largest compositional area which provides very stable glasses with good physical and chemical properties. Unfortunately, the IR absorption edge extends only to between 4 and 9 μm. This absorption edge can be optimized by minimizing silica content by dilution with oxides whose cation-oxygen bond vibrates with lower frequency. Transmission can be extended even farther by replacing Si+4 as the network former with other network forming cations with weaker bonding, such as Ge+4, Sb+3, or Te+4. Properties and stability to crystallization of these glasses, as a rule, become poorer as IR transmission improves. By far, the best transmission of any oxide glass belongs to a relatively new class of glasses based on networks formed by bismuth and/or lead oxides. They transmit out to R to q pm, have expansion coefficients (29°-200°C) from 83x10-7/°C to 112x10-7/°C, and refractive indices as high as 2.2 at 4 μm. They have sufficient stability to be cast into 8cm x Rcm x 1.9cm slabs.

Strong composite glasses

Abstract Glass strength can be enhanced by several methods including thermal tempering and ion exchange which put the surface in compression. Overlaying a higher expansion core with a lower expansion surface cladding to achieve a compressive surface is also known. A new modification of the overlay technique involves pairs of glasses which are melted separately and delivered to a single compound orifice that overlays one glass on the other as they leave the orifice. This is in contrast to most of the previous overlay methods in that the surfaces of the two glasses which form the interface are fluid and flaw-free. Physical property and composition constraints are presented for glasses which achieve a modulus of rupture as high as 42 kg/mm2. Stress relationships and profiles are also shown.

Oxide Glasses With Superior Infrared Transmission

The glass-forming areas of two new systems based on the oxides of lead, gallium, and bismuth and cadmium, gallium, and bismuth have been mapped out. These glasses can be melted at 1000°C for 20 minutes and cast into homogeneous pieces at least as large as 30 mm X 30 mm X 15 mm. Their expansion coefficients (25°C-200°C) range from 83 X 10-7/°C to 112 X 10-7/°C, and they are relatively soft with Knoop hardness (100g) in the 225 region. The refractive index (ND) is in the vicinity of 2.4. The lower absorption edge is about 470 nm (yellow color) but they transmit out to 81m in 2 mm thickness. This is the best infrared transmission for any oxide glass which is sufficiently stable to devitrificationon cooling from the melt to enable sizeable pieces to be formed.

Materials and Processes For Silicon TFT's On Aluminosilicate Glass: An Alternative Soi Technology

As-deposited polycrystalline silicon and argon ion laser recrystallized silicon thin film transistors (TFTs) have been fabricated on Corning Code 1729 glass substrates. This novel aluminosilicate glass has an expansion coefficient matched to that of silicon and a chemical durability comparable to that of fused silica. N-channel enhancement mode transistors were made using conventional IC device fabrication procedures (including thermal oxidation to form the gate insulator) modified to have a maximum processing temperature of 800 C. The- polycrystalline silicon TFTs exhibit leakage currents of less than 2x10 -11 A/ μm; of channel width and good stability and reproducibility. Transistors made in the recrystallized silicon show field effect electron mobilities as high as 270 cm 2 /V s, approximately 15 times the mobility of comparable devices made in as-deposited polycrystalline silicon. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do the comparable polycrystalline silicon devices. Major advantages of this TFT technology include the use of a novel, potentially low cost glass substrate and the simultaneous processing of both polycrystalline and recrystallized silicon devices on the same substrate material. This approach represents a new avenue for the incorporation of active devices into a variety of applications including integrated active matrix displays.