Research and development on optical fiber technology, made in the last decade, has rapidly improved the transmission characteristics, and has succeeded in reducing the attenuation loss to the ultimate limit in silica based optical fibers. Such loss reduction not only acceralates the practical use of the optical fibers for optical transmission media, but also gives detailed data on optical absorption and scattering phenomena. This paper describes the loss mechanism in optical fibers including the intrinsic and the extrinsic ones, and another intention of this paper is to describe howto minimize the extrinsic losses by the actual fiber fabrication processes. The emphasis is put on the reduction of OH-ions and waveguide imperfections by the Modified Chemical Vapor Deposition (MCVD) and the Vapor-phase Axial Deposition (VAD) method.
In the He-Zn hollow cathode laser discharge under laser operating conditions, the He pressure and anode wall temperature (zinc atom density) dependences on metastable densities of He23S1 and Zn4p3Po2 and Zn+4s2S1/2 ion density and also the discharge current dependence on metastable density of He23S1 have been measured by an optical absorption technique. The apparent peaks of metastable densities of He and Zn and Zn+4s2S1/2 ion density have been observed at a He pressure of about 14 torr, and 15 torr, respectively.The population densities of long-lived excited states of He23S1, Zn4p3Po2 and Zn+4s2S1/2 in each of the peaks are 1.2×1011, 3.2×109 and 8.5×1010cm-3, respectively. By using the experimental results of these population densities, the dominant excitation processes for Zn II 4s22D3/2, 5/2 and 4f2Foo5/2, 7/2 upper laser levels arediscussed qualitatively.
DAPS measurements were made with a commercial cylindrical-mirror-analyzer (CMA) and low-energy-electron diffraction (LEED) optics used in Auger electron spectroscopy (AES) systems. The in-situ measurements of DAPS and AES were also performed on metal surfaces of Kovar alloy, Ti, Cr, Fe, Ba, La and U. From the result of the direct comparison between DAPS and SXAPS (soft x-ray appearance potential spectroscopy) spectra on Cr metal surface, it can be shown thatDAPS is free from the details of the deexcitation mechanism following the excitation, but SXAPS depends on them. The DAPS spectrum of U metal can be clearly obtained in the lower energy region (_??_100 eV) without diffraction effect, and the double peak at the O3 level is observed with the separation of 4.5 eV. DAPS method is a more surface-sensitive technique and complementary to AES.
A drift tube was constructed for absolute measurements of ionic transport coefficients and reaction rate coefficients of clustering in the pressure range 1.0_??_10Torr at room temperature. In order to eliminate unknown effects at a differential pumping section, the drift tube has no mass spectrometer. Some design guides to drift tube methods are presented and a simple relation between electric fielddistortion and dimensions of guard rings is derived. Details of the apparatus andsome results are reported. The systematic error and the random error of the apparatus are estimated to be ±1.0% and ±0.5%, respectively, at the measurement of mobility.
The growth mechanisms of long-chain molecular crystals studied by surface characteriza-tion have been briefly summarized. The characteristic growth mechanisms of lateral and basal planes of long-chain compound were analysed by the measurements of growth kinetics from solution phase. The generation mechanisms of giant screw dislocations responsible for the spiral growth of the basal plane were summarized and the recent studies for the mechanism, in which the giant screw dislocations can be introduced as a result of interactive actions of laterally-moving growth steps, have been described. The surface characterization for vacuum-deposited thin films, i. e., long-chain molecular films and metal films has been alsodescribed with respect to the properties of the surfaces of long-chain compounds.
Immiscibilities found in III-V compound semiconductor alloys are reviewed. The existence of the miscibility gap is closely related to the excess free energy of mixing. It has been shown that regular solution approximation with DLP interaction parameter can explain well the position and the range of miscibility gap in the phase diagram. The miscibility is suggested to be affected by lattice matching with substrate as well as the supersaturation with which the alloy was grown.
This review describes the principles of hollow cathode lasers. A brief history of advances in the field is presented, together with a discussion of topics of current interest. In particular, the factors determining the electron energy distribution in the cathode-fall region, stabilization of hollow cathode discharge athigh current, and the wide range of wavelengths available from a single laser are discussed.