Identification, preparation, and characterization of several polymorphs and solvates of terazosin hydrochloride.

The phenomenon of polymorphism is prevalent in pharmaceuticals, yet it is unusual to identify more than three or four forms for any particular drug. Terazosin hydrochloride has been found to exist at room temperature in four solvent-free forms that can be isolated directly, one solvent-free form that can be prepared by desolvation of a methanolate, a methanol solvate, and a dihydrate. This study presents characterization and methods for preparation of each of these forms. Data are also presented demonstrating the relative stability of these forms.

Attenuation measurement in glasses for optical communications: an immersion method.

In fiber waveguides for optical communication losses of a few dB/km have been realized. To measure the attenuation in bulk glass rods, which are often used as starting material for fiber production, an accuracy of at least 1 dB/km is desirable. With the method reported, the losses were determined from transmission measurements on 3-cm long samples. To eliminate surface losses the samples were immersed in a liquid of about the same refractive index. For two types of synthetic vitreous silica-Suprasil 1 and Suprasil Wl-the attenuation was measured between 400 nm and 750 nm. These loss-spectra show that for Suprasil 1, with the exception of the region of OH absorption, the limit of the intrinsic losses of pure silica is reached, while Suprasil Wl shows considerably higher attenuation in the whole region. The measuring accuracy achieved so far was estimated to be about +/-1 dB/km.

Attenuation measurement in low-loss optical glass by polarized radiation.

For the production of fiber waveguides suitable for optical communications cables, glasses with extremelylow attenuation are required. A new method is described for measuring the optical attenuation of bulk glasses in the wavelength range of 0.4-1.1 microm. Using a quartz halogen source with highly stabilized radiation power, a linearly polarized, monochromatic, collimated beam was produced, passing the sample at the Brewster angle. Transmission loss, residual reflection, and surface scattering were measured by low-noise photodiodes and integrating digital voltmeters. A stability of 10(-5) and a resolution of 10(-5) or better were achieved. Results for two different kinds of commercial glasses, fused quartz (Ultrasil) and synthetic vitreous silica (Suprasil W1), are reported and discussed.

Reactively evaporated films of scandia and yttria.

Sc(2)O(3) and Y(2)O(3) films were prepared by evaporation from resistance heated boats in a residual gas atmosphere of oxygen. Films of much lower absorptance were obtained than from coatings produced in high vacuum. The short wavelength limit of high transparency was between 300 nm and 400 nm, while the long wavelength absorption edge was reached at about 11 microm. Refractive indices of 1.8-2.0 were measured for both oxides. The influence of annealing on the optical- properties of the films was investigated. The films were amorphous and proved to be mechanically very stable and water resistant. Electron micrographs showed smooth and uniform surfaces. By antireflection coatings of yttria the transmittance of silicon was increased from 52% to 99.4% at the maximum. Possible advantages by the application of Sc(2)O(3) and Y(2)O(3) instead of SiO for antireflection coatings on GaAs laser surfaces are discussed.

Reactive evaporation in ionized gases.

By conventional reactive evaporation techniques, films with a certain deviation from stochiometric composition and, therefore, increased absorptance and dielectric losses were obtained. By ionization of the residual gas a considerable increase of reactivity has been achieved. The construction of a discharge tube with a region of high current density for ionization is described. The tube was arranged inside a bell jar. The ionized gas emerged from a nozzle in the wall of the tube directly into the high vacuum region. Production parameters for SiO(2), SiO(x)N(y), and TiO(2) films were evaluated. On unheated substrates SiO(2) films, which are practically free of absorptance down to 190 nm, and TiO(2) films with refractive indices up to 2.3, were obtained.

Properties of Evaporated SiO(2), SiO(x)N(y), and TiO(2), Films.

Films of SiO(2), SiO(x)N(y), and TiO(2), were prepared by reactive evaporation in ionized gases. Refractive index, absorptance, ir transmittance, stability, structure, and stress of these films were investigated. The SiO(2) films had the same refractive index as bulk quartz glass and an absorption coefficient of less than 40 cm(-1) at 190 nm. The internal stress in the SiO(2) films was considerably lower than that for silicon oxide films prepared by conventional reactive evaporation. SiO(x)N(y), films formed extremely smooth surfaces when heated in air after evaporation. On unheated substrates TiO(2) films with refractive indices up to 2.3 and an absorption coefficient of less than 40 cm(-1) at 633 nm were obtained. All films were x-ray amorphous and proved to be mechanically stable and water resistant.

Production and properties of vacuum evaporated films of thorium fluoride.

Experiments for the production of vacuum evaporated films of thorium oxyfluoride showed that these films cannot be produced by direct evaporation of thorium oxyfluoride, because this material decomposes at approximately 1000 degrees C into ThF(4) and ThO(2). ThF(4) evaporates at approximately 900 degrees C and yields very stable films. The production of ThF(4) films is described and the dispersion of the refractive index, the dielectric constant, and the useful range of high transparency are reported. Precautions for the handling of ThF(4), because of its radioactivity, are given.

The influence of various parameters on the refractive index of evaporated dielectric films.

The influence of residual gas pressure and of deposition rate on the refractive index of Na(3)AlF(6) and ThF(4) films was investigated. Transition from high to medium deposition rates causes a distinct decrease of the refractive index, but a further reduction of the deposition rate gives practically no additional change. Increasing the residual gas pressure from 2 or 4 x 10 (-6) to 2 x 10 (-5) torr has no influence on the refractive Index although at 2 x 10 (-4) torr a lower value was measured. The refractive indices of Na(3)AlF(6), ThF(4), and ZnSe coatings deposited on Ag and Al films were found to be essentially the same as those obtained on dielectric multilayers.