A shell-wise calculation method and a quantal harmonic-oscillator model have been used to calculate the electronic stopping cross sections for heavy ions colliding with atoms or penetrating matter. The electronic energy loss is given in an impact parameter formalism. In order to generalize the theoretical models, which pertain to the cese of point charge interacting with matter, to the case for heavy ions, an effective stopping charge hased on the modified BK theory is used by way of simple scaling in the calculations. The comparisons between the calculated results and the experimental data demonstrate a favourable evidence to justify the theoretical models.

The q-coherent states are indeed minimum uncertainty states for corresponding q-deformed operators, The time evolution of q-coherent states are given by introducing the q-boson Hamiltoninn analogous to the one for normal bosons. It is shown that initially prepared q-coherent states are no longer the eigenstates of q-annihilation operator during time evolution and eventually become squeezing states. The squeezing properties are studied numerically.

We have studied the squeezing of the two-mode radiation fields in a nonlinear optical fiber with gain, The coupling nonlinear Schr?dinger equations corresponding to the circularly polarized radiation fields with gain are derived by means of the method of path integrals. The minimized power spectra of the quantum noise of these fields are obtained with a first-order perturbation approximation in the frequency domain. Detailed numerical analyses of the results are performed and presented graphically, taking zero-dispersion, normal and anomalous dispersion into account.

The cavity configurations designing and the experimental results of a 200MHz CW actively mode-locked Nd:YAG laser are reported. Arid 26W CW output and 16W CW mode-locked output power were obtained at a single lamp pumped power of 3.5kW, with pulse duration 100 ps.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

The creation of defects in GaP bombarded with MeV ^{4}He ions has been studied under ultra-high-vacuum condition by Rutherford backscattering/channeling (RBS/C) method, and the absolute damage cross section σ_{d} for GaP has been determined under bombardment of 1.0 MeV ^{4}He ions, with the measured value 8.0xl0^{-18} cm^{2}. Our experimental results suggest that the defect generation rate is strongly related to the surface condition. When the GaP covered with a thin amorphous layer, a significant ion beam annealing effect will be observed. The present results show that for GaP the damage is produced mainly by nuclear collision.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

SHI ZHI-XIANG, JI HE-LIN, ZHANG YI-TONG, JIN XIN, XU XIAO-NONG, DING SHI-YING, YAO XI-XIAN, WANG CHANG-AN, WANG RUI-LAN, LI HONG-CHENG, ZHANG HUI, SUN ZHI-JIAN, YANG SEN-ZU

Chin. Phys. B 1994, 3 (2): 0124; doi: 10.1088/1004-423X/3/2/006
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Magnetic hysteresis loops have been measured for YBa_{2}Cu_{3}O_{6+x}, GdBa_{2}Cu_{3}O_{6+x} and Tl_{2}Ba_{2}Ca_{2}Cu_{3}O_{10-y} films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density J_{cm} has been derived approximately. The field and temperature dependence of J_{cm} for all samples can be written as: J_{cm}= J_{c0}(T)×f(B,T), Where f(B,T) = 1 - Aln(B/B_{0}(T)), which is similar to the transport critical density strongly affected by flux creep: J_{ct} = J_{c0}(B,t)(1 - (k_{B}T/U_{0})ln(BΩd/E_{c})). The extraordinary similarity suggests that J_{cm} is determined not only by flux pinning but also by flux creep. In the first formula, f(B,T) may be correlated with the effect of flux creep on J_{cm}, and J_{c0}(T) is determined by flux pinning. J_{c0}(T) is independent of magnetic field and is proportional to (T_{c} - T). Similar results have also been found for other samples. It may be the common characteristic of high-T_{c} superconductors. Magnetic relaxation of YBa_{2}Cu_{3}O_{6+x} and GdBa_{2}Cu_{3}O_{6+x} films has been measured at LN_{2} temperature. Using the equation of Hagen et al., effective activation energy U_{0} has been deduced, which is about 0.3eV, one order bigger than the value obtained by A = k_{B}T/U_{0}. U_{0} is almost independent of the field in the field range selected.

More than 300% anisotropic persistent spectral holes were written in and read out in some materials such as THP/PMMA and TMP/PMMA with high signal-to-noise ratio by CW linearly polarized light. The effect of probe angle and modulation field on the hole depth and hole shape were also interpreted by using polarisation spectra hole burning theroy.

In this paper we report some new experimental results concerning the elastic properties of periodic and quasiperiodic superlattices studied by means of Brillouin spectroscopy. The observation of both bulk and surface acoustic phonons as well as the fitting using effective medium approximation on the phonon spectrum enables us to extract accurately some rele-vant effective elastic constants in both structures. We have verified that the elastic anomaly which occurs in the periodic structures is also present in quasiperiodic ones. These results imply that the interaction mechanism of Fermi electrons with reduced Brillouin zone bound-ary is not responsible for the observed elastic anomalies, The comparative study of these superlattices proves that the elastic anomaly is relevant directly to interfacial effects.

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