Room temperature multiwavelength erbium-doped fiber ring laser using a highly nonlinear photonic crystal fiber

A multiwavelength laser source is demonstrated with a high power erbium-doped fiber amplifier as the gain medium. A highly nonlinear photonic crystal fiber (PCF) is inserted in the ring cavity to provide nonlinear gain by four-wave mixing. A Sagnac loop is incorporated in the ring cavity serving as a comb-like multichannel filter. The comparison between fiber ring laser without PCF and with PCF shows that the highly nonlinear PCF can generate a larger number of excited wavelengths and help stabilize the output power.     

Study of FeOx/Au inverse model catalysts by in situ sum frequency generation vibrational spectroscopy

In this work a complex experimental setup is described which was developed by connecting an ultra-high vacuum multi-technique surface analysis system and a sum frequency generation vibrational spectrometer. This arrangement provides a unique environment to study interfaces under in situ conditions by a combination of complementary techniques. Preliminary results of CO adsorption experiments on gold and iron oxide thin layers grown on gold are presented as application examples of the experimental setup.     

Analysis of t-butylphenol acetylene condensed resin with methyl-methine linkages in vulcanized rubber by pyrolysis-gas chromatography/mass spectrometry

Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd.     

Influence of pump beam size on laser diode end-pumped solid state lasers

Based on space-dependent rate equation, the lowest threshold input power for diode end-pumped solid state lasers is obtained for pump spot size w_p → 0. However, when the pump beam waist is decreased, the far-field half-angle increases due to the same beam quality, which will influence the match between the pump volume and mode volume. Most importantly, when the pump beam waist is decreased, the temperature and temperature gradient in the laser rod would be very high due to the resulting heat, which would cause material distortion, variation of refractive index, instability of laser resonator etc. We analyze the temperature distributions with different pump beam sizes and conclude that the condition w_p ≈ w₀ (the radius of the laser beam at the laser rod) is often taken as a rough guide to the optimum case.     

Grammian solutions and pfaffianization of a non-isospectral and variable-coefficient Kadomtsev-Petviashvili equation

In this paper, we first present the Grammian determinant solutions to the non-isospectral and variable-coefficient Kadomtsev-Petviashvili (vcKP) equation. Then, by using the pfaffianization procedure of Hirota and Ohta, a new non-isospectral and variable-coefficient integrable coupled system is generated. Moreover, Gramm-type pfaffian solutions of the pfaffianized system are proposed.     

On Cyclic Caps in Projective Spaces

Let H be a subgroup of a cyclic Singer group of PG (n,q). In this paper we study the following problem: When is a point orbit of H a cap? A necessary and sufficient condition for this is derived and used to give a short proof of some results by Ebert [6] and to show that small orbits are typically caps.     

Symmetry classes of tensors associated with certain groups

We discuss the existence of an orthogonal basis consisting of decomposable vectors for some symmetry classes of tensors associated with certain subgroups of the full symmetric group The dimensions of these symmetry classes of tensors are also given