Philipp H. Klein

Vacuum ultraviolet laser emission from Nd+3:LaF3

Laser emission at 172 nm has been produced by pumping a Nd:LaF3 crystal with incoherent Kr*2 radiation at 146 nm. The 5‐ns pulse contained approximately 20–30 μJ of energy. Fluorescence measurements indicate potential for tuning from 170–175 nm, which should be observable with OH−‐free crystals.

Chemically-formed buffer layers for growth of cubic silicon carbide on silicon single crystals

Abstract Buffer layers of cubic silicon carbide were formed by reaction of (100) Si substrates with propane in hydrogen at 1380–1400°C. Reaction times ranged from 5 to 600 s. Reproducibility was improved by wet etching of substrates. Even for buffer-layer thicknesses of less than 10 nm, their reflectance spectra were identical to that of SiC. Crystal layers of cubic SiC were deposited on buffers by reaction of silane and propane in hydrogen at 1400°C for 15 min. Reflectance spectra of these crystal layers suggest that short buffer-layer-formation times favor crystal layer perfection.

Additive and electrolytic coloration of NaF

It is shown that well‐characterized F and M centers can be introduced into NaF crystals by both additive and electrolytic coloring techniques. This success is attributed primarily to a substantial elimination of hydroxyl‐ion contamination.

Thin film growth of YBa2Cu3O7 by spray pyrolysis

Thin films of YBa2Cu3O7 have been grown by spray pyrolysis of aqueous nitrate solutions. Substrate temperatures ranging from 250 to 850°C were investigated for the deposition reaction. Multiphase material was obtained at low substrate temperatures, whereas single phase material resulted at substrate temperatures above 750°C. Annealing the films in 1 atm of flowing oxygen at 875–975°C resulted in single phase material with the familiar orthorhombic “1–2–3” crystal structure regardless of deposition temperatures. Superconducting transition temperatures up to 74 K and transition widths as narrow as 3 K were obtained for annealing temperatures in the range of 945–975°C. Materials were characterized by X-ray diffractometry, scanning electron microscopy, and resistive superconducting transition measurements.

Techniques For Measuring Absorption Coefficients In Crystalline Materials

Absorption coefficients smaller than 0.001 cm-1 can, with more or less difficulty, be measured by several techniques. With diligence, all methods can be refined to permit measurement of absorption coefficients as small as 0.00001 cm-1. Spectral data are most readily obtained by transmission (spectrophotometric) methods, using multiple internal reflection to increase effective sample length. Emissivity measurements, requiring extreme care in the elimination of detector noise and stray light, nevertheless afford the most accessible spectral data in the 0.0001 to 0.00001 cm-1 range. Single-wavelength informa-tion is most readily obtained with modifications of laser calorimetry. Thermo-couple detection of energy absorbed from a laser beam is convenient, but involves dc amplification techniques and is susceptible to stray-light problems. Photoacoustic detection, using ac methods, tends to diminish errors of these types, but at some expense in experimental complexity. Laser calorimetry has been used for measurements of absorption coefficients as small as 0.000003 cm-1. Both transmission and calorimetric data, taken as functions of intensity, have been used for measurement of nonlinear absorption coefficients.

Potassium bromide for infrared laser windows: Crystal growth, chemical polishing, and optical absorption☆

Potassium bromide single crystals have been prepared with 10.6-..mu..m bulk absorption coefficients smaller than the intrinsic value for potassium chloride. Of several halogen-producing vapors studied, that of carbon tetrachloride is most effective in decreasing infrared absorption. Water-grinding, followed by polishing with HBr solutions, produces nonabsorbing and etch-pit-free surfaces on planes remote from (100). Hydroxyl lines are absent from infrared absorption spectra of all crystals. Vacuum-ultraviolet absorption at 215 nm shows presence of between 0.01 and 4.0 OH/sup -/ ions per million anions. Incomplete removal of metaborate (BO/sub 2//sup -/) by iodine monobromide or by hexabromobenzene is evident in infrared absorption spectra.

Removal of cations from zirconium to permit its use in low loss fluoride optical fibers

For attainment of near-intrinsic losses in the 2 to 4 µm range, concentrations of cations such as iron, cobalt, nickel, and copper must lie in the 0.2 to 10 ppb range (1 ppb = 1 mol/109 mol of glass). Commercial grades of zirconium salts tend to form colloids and to contain hundreds or thousands of times more than the tolerable concentrations. We have found filtration to be partially effective for colloid removal. Working with relatively concentrated (2 molar, about 17% by weight) solutions of Zr salts, we have introduced about 7000 ppb each of Fe, Co, Ni, and Cu. We have determined that all of these metals can readily be removed by laboratory-scale ion-exchange methods to meet the cation-purity standards for near-intrinsic absorption.

Removal Of Fe, Co, Ni, And Cu From Zr For 0.01-Db/Km Fluoride Optical Fibers

For attainment of 0.01-dB/km absorption losses in the 2-4 micrometer range, iron, cobalt, nickel, and copper concentrations in fluoride fibers must lie in the 0.2-10 range. (1 PPB = 1 mol/109 mol glass.) Commercial grades of zirconium salts tend to form colloids and to contain hundreds or thousands of times more than the tolerable concentrations. We have found filtration to be partially effective for colloid removal. Working with rela-tively concentrated (2 molar, about 17% by weight) solutions of Zr salts, we have introduced about 7000 PPB each of Fe, Co, Ni, and Cu. We have determined that all of these metals can readily be removed, by laboratory-scale ion-exchange methods, to meet the absorption stan-dards for 0.01-dB/km absorption.

Chemical Analysis of Trace Impurities

Ideally, analytical methods for materials used in halide glasses must detect and differentiate impurity levels down to the parts-per-billion or parts-per-trillion level. These sensitivities are required for transition-metal and rare-earth ions, as well as for ammonium, hydroxide, and some other nonmetallic ions. Dissolved oxygen, carbon dioxide, and even argon are also of concern, as is dispersed elemental carbon.

Measuring Absorption Coefficients In Crystalline Materials

Absorption coefficients smaller than 0.001 cm 1 can, with more or less difficulty, be measured by several techniques. All methods can be refined to permit measurement of absorption coefficients as small as 0.00001 cm -1. Spectral data are most readily obtained by transmission (spectrophotometric) methods, using multiple internal reflection to increase effective sample length. Emissivity measurements, requiring extreme care in the elimination of detector noise and stray light, nevertheless afford the most accessible spectral data in the 0.0001-0.00001- 1cm-range. Single-wavelength information is most readily obtained with modifications of laser calorimetry. Thermocouple detection of energy absorbed from a laser beam is convenient, but involves dc amplification techniques and is susceptible to stray-light problems. Photoacoustic detection, using ac methods, tends to diminish errors of these types, but at some expense in experimental complexity. Laser calorimetry has been used for measurements of absorption coefficients as small as 0.000005 cm-1. Both transmission and calorimetric data, taken as functions of intensity, have been used for measurement of nonlinear absorption coefficients.