Multiwatt, tunable, diode-pumped CW Yb:GdCOB laser

We demonstrate that Yb-doped Ca₄GdO(BO₃)₃ (GdCOB) crystals are suitable for the development of high-power diode-pumped lasers emitting at around 1.04 μm. A 15%-doped Yb:GdCOB crystal was longitudinally pumped with a cw fiber-coupled diode emitting 10 W at 976 nm. While 5.2 W of diode power was absorbed, we obtained 3.2 W of 1043-μm laser light, with a beam quality factor M² equal to 3, and 2.5 W in a diffraction-limited beam. Furthermore, the laser is continuously tunable between 1018 and 1086 nm. Thermal effects have been investigated with a Shack–Hartmann wavefront analyser: although thermal lensing is not negligible, it does not affect the performance of the laser with the resonator design we used. Received: 1 August 2000 / Revised version: 18 September 2000 / Published online: 21 February 2001     

Kilohertz extreme-ultraviolet light source based on femtosecond high-order harmonic generation from noble gases

A compact, versatile table-top kilohertz source of coherent extreme-ultraviolet (XUV) radiation in the wavelength region 18–100 nm, based on high-order harmonic generation from noble gases induced by a 40-femtosecond Ti:sapphire laser system, is presented. The XUV beamline delivers at its output 10⁸ photons/s at a wavelength of 23 nm. The monochromatized XUV radiation is directly focused onto a 10^-2-mm² spot by a toroidal grating, allowing one to reach intensities higher than 10⁶ W/cm². Optimization results are presented for a new XUV-generating geometry, utilizing a ‘semi-infinite’ quasi-static gas cell and strong focusing. In those conditions, we observe an anomalous inversion between the cutoffs of argon and krypton, with the krypton spectrum extending to much higher orders than expected in an adiabatic limit. Received: 9 July 2001 / Revised version: 1 August 2001 / Published online: 7 November 2001     

Polarization induced 2D hole gas in GaN/AlGaN heterostructures

The generation of high density 2D hole gases is crucial for further progress in the electronic and optoelectronic nitride devices. In this paper, we present systematic theoretical studies of Mg-doped GaN/AlGaN gated heterostructures and superlattices. Our calculations are based on a self-consistent solution of the multiband k.p Schrödinger and Poisson equation and reveal that the hole 2D sheet density is mainly determined by the polarization induced interface charges. For an aluminium concentration of 30%, the induced hole density in the heterostructure can reach values up to 1.5×10¹³ cm⁻². In the GaN/AlGaN superlattices, the hole sheet density increases with the superlattice period and saturates for a period of 40 nm at a value of 1.5×10¹³ cm⁻².     

Functional Polymers. XXII. Ultraviolet Absorbers with 2(2-Hydroxyphenyl)2H-benzotriazole and 2-Hydroxybenzophenone (or Acetophenone) Chromophors in the Same Molecule

Benzotriazolization of 2,4-dihydroxyacetophenone and 2,4-dihydroxybenzophenone has given dibenzotriazolized products: 3,5- [di (2H-benzotriazole-2-yl)]2,4-dihydroxyacetophenone, and 3,5-[di (2H-benzotriazole-2-yl)] 2,4-dihydroxybenzophenone. These compounds are expected to be effective and useful UV absorbers as they both have the 2 (2-hydroxyphenyl)2H-benzotriazole unit and the 2-hydroxybenzophenone (or acetophenone) unit in the molecule. The compounds were characterized by their spectral behavior and particularly by careful study of their UV spectrum.     

Counting statistics of collective photon transmissions

We theoretically study cooperative effects in the steady-state transmission of photons through a medium of N radiators. Using methods from quantum transport, we find a cross-over in scaling from N to N² in the current and to even higher powers of N in the higher cumulants of the photon counting statistics as a function of the tunable source occupation. The effect should be observable for atoms confined within a nano-cell with a pumped optical cavity as photon source.     

Stress‐enhanced dislocation density reduction in multicrystalline silicon

Stress is generally perceived to be detrimental for multicrystalline silicon (mc‐Si), leading to dislocation multiplication during crystal growth and processing. Herein, we evaluate the role of stress as a driving force for dislocation density reduction in mc‐Si. At high temperatures, close to the melting point (>0.8T_m), we observe that the application of stress as well as the relief of residual stress, can modify the density of pre‐existing dislocations in as‐grown mc‐Si under certain conditions, leading to a net local reduction of dislocation density. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

常微分方程课程中案例教学的探索、实践与思考

介绍了作者在常微分方程教学中对案例教学所做的一些探索、实践与思考.