A technique is introduced that determines power distribution in fibers from the measured near-field pattern, assuming that: (1) the optical power distributes uniformly among degenerated modes with the same propagation constant, (2) enough modes are excited to ensure the validity of calculation by geometrical optics, and (3) the phase of each propagation mode has no correlation. Experiments verifed that the fibers have the function of flattening power distribution among modes with the same propagation constant. This fact shows that assumption (1) does not severely limit the applicability of the technique. Wave optical calculation is done to determine the numbers of modes that must be excited to satisfy assumption (2). As an example of application of the technique, differential mode attenuation of graded-index fibers is determined from longitudinal variation of the measured near-field pattern.

The electronic structure, ionization potentials, and photoabsorption spectra of monosilane molecules SiH4, SiF4, and SiCl4 were calculated using the discrete variational (DV) Xα method. Valence molecular orbitals (MOs) of SiH4 consist (from the lowest) of two occupied bonding MOs between Si and H, a1 and t2. Inner valence MOs of SiF4 and SiCl4 consist of the bonding MOs between Si and halogen, a1 and t2, and outer valence MOs consist of bonding MOs a1 and t2, and the MOs e, t2, and t1 localized on halogen. The lowest unoccupied MOs of SiH4 include two antibonding states t2 and a1, and two localized states, e and t2. The lowest unoccupied MOs of SiF4 and SiCl4 are antibonding states a1 and t2 between Si and halogen. Calculated ionization potentials agree well with measured photoelectron spectra. Calculation of the photoabsorption spectrum for Si 2p core excitation for SiH4, SiF4, and SiCl4 shows that peak positions and intensities agree well with measured photoabsorption spectra in both gas and solid phases. The absorption bands of SiH4, measured near the edge and at about 125 eV, consist of transitions from core to antibonding states consistent with experiments. The four main absorption bands of SiF4 and SiCl4 measured between 105 and 140 eV are assigned to transitions from the core Si 2p level to antibonding MOs a1, t2, e, and t2. Calculated photoabsorption spectrum for valence excitation of SiH4 agrees well with measurements. The first and second absorption bands measured at about 138 and 128 nm correspond to the transition from bonding to antibonding states between Si and H. This is consistent with the facts that monosilane is photolyzed in Xe 147 nm ultraviolet light in a vacuum and that fluorescence has not been observed from 130 to 150 nm, because these are interpreted in terms of photodissociation by transition from bonding to antibonding states. Photoabsorption spectra for valence excitation of SiF4 and SiCl4 are also calculated. We found that the first absorption band consists of two transitions from localized states on halogen to antibonding states between Si and halogen (t2→a1 and t1→t2 ).

A method is described which makes full use of the data gathered in measuring the elastic constants and internal friction of small samples undergoing free decay. A Fourier transform approach is employed which first determines accurately the period and starting phase of the free decay and checks the purity of the signal. This information is then used along with the original data to determine the internal friction of the sample.

A new molecular beam epitaxy (MBE) system coupled with a 100 kV maskless ion implanter via an ultrahigh vacuum (UHV) sample transfer module was constructed. This system can grow epitaxial layers with ion beam pattern-implantation without exposing a sample surface to the outer atmosphere. Buried Be implanted layers in MBE grown GaAs were fabricated using this apparatus. Because of the contamination-free UHV growth process, the photoluminescent intensity depth profile of the grown crystal showed no degradation at the interface where the MBE growth was interrupted for the ion implantation process.

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