Laser transitions under resonant optical pumping of donor centres in Si:P

Terahertz stimulated emission of phosphorus donors in silicon optically excited by radiation from the free-electron laser FELIX has been studied. It is found that a spectral line of the Si:P laser emission depends on pump frequency. Stimulated emission arises on the 2p₀→1s(E) intra-centre transition (21.2 meV) under resonant pumping of the 2p₀ state and on the 2p₀→1s(T₂) transition (22.3 meV) under pumping of the 2p_± or higher odd-parity donor states. The line shift is attributed to the Auger redistribution of the 1s(E)- and 1s(T₂)-state populations. Received: 7 November 2002 / Revised version: 7 April 2003 / Published online: 14 May 2003 RID="*" ID="*"Corresponding author. Fax: +49-30/6705-55-07, E-mail: sergeij.pavlov@dlr.de RID="**" ID="**"On leave from: The Institute for Physics of Microstructures, Nizhny Novgorod, Russia     

High-efficiency clean EUV plasma source at 10–30 nm, driven by a long-pulse-width excimer laser

A long-pulse-width high-output energy (120 ns FWHM, 7 J) XeCl laser has been focused on thin tape targets (Cu and Ta) to generate more than 100-ns-long (FWHM) EUV pulses in the 10–30 nm spectral region, suitable for projection microlithography. The conversion efficiency was more than 20% over a 2π solid angle. We observed debris emission using a gated CCD camera, and measured the debris speed for different irradiation conditions. We found irradiation conditions such that the measured velocities were low enough that simple mechanical devices combined with krypton at low-pressure could efficiently stop both ionic debris and cluster debris. Our results show that a suitable combination of driving-laser characteristics, target material and thickness, environment gas and mechanical choppers can make clean and increase the power of EUV solid-target laser-plasma sources. Received: 21 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +39-06/9400-5334, E-mail: bollanti@frascati.enea.it     

Uniform Continuity of a Family of Weakly Regular Set Functions on Topological Spaces

Conditions for the uniform continuity of a family of weakly regular set functions defined on an algebra h62303g326480175/xxlarge931.gif" alt="Sgr" align="BASELINE" BORDER="0"> h62303g326480175/xxlarge8835.gif" alt="sup" align="MIDDLE" BORDER="0"> h62303g326480175/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"> of subsets of a h62303g326480175/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">-topological space (T,h62303g326480175/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">) and taking values in an arbitrary topological space are found.     

On Fučik Spectra and Periodic Solutions

In this paper, we continue extending the theory of boundary-value problems to ordinary differential equations and inclusions with discontinuous right-hand side. To this end, we construct a new version of the method of shifts along trajectories. We compare the results obtained by the new approach and those obtained by the method of Fuh8358848658g1436/xxlarge269.gif" alt="ccaron" align="BASELINE" BORDER="0">ik spectra.     

Orders on Braid Groups

It is shown that the braid group h3407950v656m373/10469_2004_Article_469355_TeX2GIFIE1.gif" alt=" $$B\left( n \right)\left( {n \geqslant 3} \right)$$ " align="middle" border="0"> defies lattice ordering.     

Novel Synthesis of 2β,3β,20β-Triacetoxy-5 -pregnan-6-one

Pregnenolone (2) is used in a novel synthesis of 2h743522r1ul24128/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">,3h743522r1ul24128/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">,20h743522r1ul24128/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-triacetoxy-6-ketosteroid (6), a key intermediate in the preparation of 20-hydroxyecdysone (1)     

Are the Elements Elementary? Nineteenth-Century Chemical and Spectroscopical Answers

We analyze the role and influence of a tradition of research linked to the concept of h0vaat31dee30v5t/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0">primary matterh0vaat31dee30v5t/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> in nineteenth-century studies on the nature of the elements.The suggestion of William Prout (1785-1850) in 1816 that the atomic weights of pure chemical elements are whole numbers and multiples of the atomic weight of hydrogen, taken as unity, was met with serious confutations,which in turn prompted several attempts to save Prouth0vaat31dee30v5t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s hypothesis.We discuss these attempts in detail and the objections raised against them, for instance by Dmitry Ivanovich Mendeleev (1834-1907). We pay particular attention to the use of spectroscopy as a method for proving the existence of elementary forms of matter inside atoms. Leaders in this field of research were two English scientists, the astrophysicist Norman Lockyer (1836-1920) and the chemist William Crookes (1832- 1919). Both of their approaches involved the idea of primary matter. However, while Crookesh0vaat31dee30v5t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s approach proved to be incorrect, Lockyerh0vaat31dee30v5t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s ideas survived for several years and supported the discovery of the electron by J.J.Thomson (1856-1940).     

Nature of the Peierls- to Mott-insulator transition in 1D

In order to clarify the physics of the crossover from a Peierls band insulator to a correlated Mott-Hubbard insulator, we analyze ground-state and spectral properties of the one-dimensional half-filled Holstein-Hubbard model using quasi-exact numerical techniques. In the adiabatic limit the transition is connected to the band to Mott insulator transition of the ionic Hubbard model. Depending on the strengths of the electron-phonon coupling and the Hubbard interaction the transition is either first order or evolves continuously across a narrow intermediate phase with finite spin, charge, and optical excitation gaps. Received 7 July 2002 / Received in final form 21 October 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: holger.fehske@physik.uni-greifswald.de