The recent advance of the analysis of atomic structures at crystal surfaces by means of low-energy electron diffraction (LEED) is reviewed. A short list of the basic physical factors determining the LEED intensities is followed by a description of the basic ideas of the theoretical methods used at present for calculating intensities. A few examples of the comparison between theoretical and experimental results are shown, at first for clean metal surfaces and then those with simple adsorbed layers. Along with that a few interesting physical problems are discussed. The so-called averaging methods for obtaining kinematical intensities are shortly reviewed. It is concluded that the theory can reproduce experimental results more or less satisfactorily in these simple cases, so that we can expect a further development into more complicated, but more practically significant cases.
Recent studies on the adsorption of common gases on various single crystal planes of tungsten are reviewed. First, being of great importance, preparation and characterization of well-defined solid surfaces briefly was discussed. One of the promising experiment for under-standing of the fundamental process of adsorption would be the use of the single crystal sur-faces of tungsten which easily get clean. The measurement of the surface potential of some common gases on such planes extensively has been carried out with good accuracy by the author. So far, there are some arguments on whether the adsorbate would be atomic or mo-lecular, when diatomic molecules are adsorbed on tungsten. In particuar, hydrogen or nitrogen on W(100), and β-CO/W, being quite interesting but still unsettled, were discussed with the results of the surface potential measurement, flash desorption, LEED observation and new in-formations from FES and UPS in available.
The idea of using discharged Xe gas as variable refractive index medium at 1.1526 μm of Ne laser was conceived on the expectation of the effect near the anomalous dispersion of Xe. Its refractive index was measured by means of Jamin interferometer. As the result of measurement, it was shown that discharged Xe gas (weakly ionized) of nearly 30 Torr brings about a change in refractive index of about -10-5 (Δn). Such magnitude of Δn will be able to vary Ne laser's frequency at 1.15μm over more than 500 MHz if the cell containing discharged Xe gas of appropriate length is put into the laser cavity. It was made-clear that the cause of Δn is mainly due to the effect near the anomalous dispersions of the transitions 3d5-3p6 (1.1494μm, Δn>0), 3d6-2p4 (1.1617μm, Δn>0) by measuring Xe spectra, mixing Kr gas with Xe gas, and irradiating specified Xe spectra.
An optical heterodyne detection-system, consisting of two closely successive ultrasonic wa-ves and an optical mask with a reference signal, has been studied for the purpose of real-time correlational signal processing. The first order in the double diffraction spectrum of laser light by the ultrasonic waves can provide a signal light wave as well as a reference one for photo-mixing. The signal and reference waves arise from the first and second ultrasonic waves, re-spectively. For a system without the mask two time-varying signals, applied to the ultrasonic waves, can be processed in a form of real-time convolution obtainable from the envelope of a beat signal. When the mask is set in the system and only a time-varying signal is fed to one of the ultrasonic waves, the mask and time signals can be processed in a form of real-time correlation.
Phase demodulation of an optical beat signal is demonstrated analytically and experimen-tally. In an ordinary room for experiments a pair of different successive ultrasonic waves can generate a stable beat signal operating at the difference in frequency between the two ultrasonic waves. A conventional phase demodulation technique can be available for recover-ing the phase of the generated beat signal. This system puts forth its potential in real-time processing for time-dependent optical phases. As an example, the phase fluctuation of the beat signal, caused by thermally turbulent atmosphere, is processed statistically with satisfactory accuracy.