Experimental characterization of nonlinear harmonic generation in planar and helical undulators

We present an experimental characterization of the process of coherent harmonic generation in single-pass free electron lasers. The harmonic radiation is obtained by seeding the electron beam stored in the Elettra storage ring with a Ti:sapphire laser. Different methods for generating harmonics are compared between them, and a detailed characterization of the emitted light is performed for different polarizations. Our results also contribute to the debate about the possible presence of a coherent on-axis signal in helical undulators. In this respect, we provide an experimental confirmation of recent theoretical studies that predict no coherent on-axis signal.     

Infrared Applications at ANKA

ANKA is a relatively new synchrotron radiation facility at the Forschungszentrum Karlsruhe, a large government research center in the southwest of Germany. The acronym stands for Angstrom Source Karlsruhe. The electron storage ring is 110.4 m in circumference and stores a 2.5 GeV electron beam at a typical current of 200 mA. The facility has been open for users since March 2003.     

High density plasmas for recombination X-ray lasers

The scaling of recombination XUV lasers to shorter wavelengths requires laser plasmas produced at initial electron densities close to solid. With pump laser pulses longer than a few tens of picoseconds the hydrodynamic motion of the plasma during the interaction makes this difficult to achieve. In contrast, when picosecond laser pulses are used the laser energy is absorbed close to solid density since the plasma expansion is insignificant during the laser pulse. This results in hot near solid density plasmas which are needed for hydrogenic recombination X-ray lasers operating in the water window. Experimental observations have shown that a fully ionized aluminium plasma with a temperature of about 400 eV and a density well above 10²³ cm^–3 is produced when an aluminium target is irradiated with a single 3.5 ps high power KrF laser pulse.     

The theory of coherent optimized-nanostructure taking laser into account the electron-electron interaction

An analytic theory of generation of a coherent laser (laser possessing a coherent electronic subsystem) operating on an optimized nanostructure is developed taking into account the electron-electron interaction. This interaction must be included since it may lead to a violation of stringent resonance conditions of coherent lasing of unipolar lasers in view of the fact that the population in such lasers increases with the pumping current. Using the Hartree-Fock approximation, analytic solutions of the Schrödinger equation were obtained for a strong electromagnetic field with open boundary conditions. The expressions derived for polarization current and electron concentration make it possible to determine the power and frequency of generation as well as amplification profile and other characteristics. It is shown that optimal lasing is realized even when electron-electron interactions are taken into account. In this optimal mode with tuning, no population inversion is required (the populations of working levels are identical). The lasing efficiency is equal to unity; the resonance-tunneling coherent pumping is effective since reflection is zero, and the amplification profile is not broadening by the field. Multimode generation stability, good spectral characteristics, and high limiting powers can be expected.     

ESRF: A Quest for Excellence in Service to Users

The ESRF, the European Synchrotron, is the world's most intense X-ray source and a center of excellence for fundamental and innovation-driven research in condensed and living matter science. Located in Grenoble, France, the ESRF owes its success to the international cooperation of 21 partner nations, of which 13 are Members and 8 are Scientific Associates. It took its first electron beam and users in 1992 and has been in full operation for scientific users from Europe and all over the world since 1994.     

Technical Report: UV and VUV Radiometry Programs at the Synchrotron Ultraviolet Radiation Facility (SURF III)

The fourth international workshop on Adaptive and Active X-ray &; XUV Optics (ACTOP11) was held on April 4–5, 2011, at Diamond Light Source in Oxfordshire, UK. This workshop follows on from earlier, successful active optic events at SOLEIL (2006), Elettra (2008), and Osaka (2009).     

Meeting Report: Ten Years of Atomic and Molecular Science at Elettra

On the 31^st of May and the 1^st of June, 2007, a workshop to celebrate 10 years of atomic and molecular science was held at Elettra. The occasion marked the 10^th anniversary since the first beamtime was officially allocated to a user at the Gas Phase beamline, namely George King of Manchester University. As a satisfied user, King was not only present, but had beamtime during the workshop.     

Research activities at the PALS research infrastructure

The Prague Asterix Laser System (PALS) Research Infrastructure (RI) in Prague, one of only four kJ-class laser facilities in EU, has been offering its beam time to European researchers for already 14 years, since 2004 in the framework of the LASERLAB-Europe consortium. Till June 2014, the PALS RI has provided 4313 experimental days for a total of 41 projects with 303 international users from 42 different research institutions. Its principal experimental facility is a terawatt sub-ns iodine laser (1315?nm) with an optional plasma-based zinc XUV laser (21.2?nm), and an auxiliary Ti:Sapphire fs laser (1?J, 70?fs) exploited for femtosecond plasma probing and experiments with synchronised femtosecond and sub-nanosecond laser pulses at mean laser intensities of up to 30?PW/cm². The lasers are equipped with several target facilities and rich sets of instruments for both active and passive plasma diagnostics. The PALS main research areas include development and applications of secondary laser sources of high-energy ions and both coherent and non-coherent high-intensity XUV radiation, laboratory astrophysical and inertial fusion-relevant studies. In this paper, the main results having been achieved at PALS in the framework of LASERLAB-EUROPE international access activities during the last four years are highlighted.     

The Mössbauer effect data center: A report

The Mössbauer Effect Data Center is unique in its operation and the kind of information services that it provides. It is probably the only user-supported information center in the basic sciences. This has been primarily possible due to the broad support and encouragement the center receives from the international Mössbauer community. This report also discusses the demographics of the Mössbauer community: identifying such items as the most active areas of research in Mössbauer Spectroscopy, where is this research being done and who is doing it. Also, examined is where Mössbauer research investigations are being published. BITNET and other forms of electronic mail are being widely used in the scientific community. This is also the case in the Mössbauer community. Directories and list-servers are being established.     

First FEL Winter School in Taiwan

The free electron laser (FEL) is widely regarded as the core technology of the fourth-generation light source in the international scientific community, as the development of such technology is making remarkable progress in recent years. FEL offers scientists the means to probe the nano-scale and outer-space world beyond the fullest extent of the existing scientific boundary. Compared to the cost of building a large-scale advanced research facility, the investments of the most ambitious FEL facilities, such as the Linac Coherent Light Source (LCLS) in the U.S. and SPring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan, are much more expensive. However, there is great interest in the development of smaller and more affordable FELs.     

703-to 731-nm FI laser excited by a transverse inductive discharge

It is proposed to use a pulsed transverse inductive discharge for exciting gas lasers operating on electron transitions in atoms and molecules. An electron transition laser on fluorine (FI) atoms pumped by a transverse inductive discharge is developed. Lasing at three wavelengths (703.75, 712.79, and 731.1 nm) is obtained by exciting He-F₂ (NF₃) gas mixtures in a pressure range from 20 to 350 Torr. The results of experimental investigation of the spectral, temporal, and energy characteristics of the inductive FI laser are presented.     

GaAs1-xPx中混晶无序与Fe深中心的性质

对不同组分的掺FeⅢ-Ⅴ族混晶GaAs1-xPx,测量了Fe深受主中心空穴热发射的非指数恒温暗电容瞬态及DLTS谱。用混晶无序使Fe深能级展宽的模型理论拟合实验结果,得到Fe能级Gauss型展宽的半宽和中心能级的热发射率,并确定出基态空穴跃迁的中心能级的焓变与组分的关系:先是减少,而后增大,与由光电容方法得到的Gibbs自由能变量与组分x的关系明显不同。 进一步讨论表明,上述两种测量方法得到的Fe中心的激活能不同,可能反映Fe中心的键合状态和混晶无序诱导的品格弛豫的影响。     

The transportable cesium fountain clock NIM5: its construction and performance

The second laser cooling cesium fountain clock NIM5 at the National Institute of Metrology (NIM) China adopts the (1,1,1) direct optical molasses ( OM) configuration. NIM5 has been running with a stability of 3×10⁻¹⁵/d and an operation ratio of 99% since 2007. Preliminary evaluations of NIM5 in 2008 showed a typical combined uncertainty of 3×10⁻¹⁵. The NIM5 clock is operating in parallel with NIM’s first fountain clock NIM4. NIM4 and NIM5 are used to steer the frequency of the calculated NIM atomic time TA-c(NIM) and the first set of results are promising. We are now at the stage of comparing the frequency of NIM5 with UTC to support the independent frequency shift evaluations of NIM5 and contribute to the international atomic time in the near future.      

Compact high power subnanosecond nitrogen and “open air” lasers at 760 torr

A simple N₂ laser is described operating at a pressure of 760 torr. The device in pure nitrogen yields a peak power of about 2 × 400 kW and it also works with open air as laser gas. Pulse lengths of ≈ 0.3 ns are measured.     

Production and investigations of negative osmium ions for fundamental applications: REOSTRAP

High quality measurements in respect to accuracy, resolving power and sensitivity using negative osmium ions confined in ion traps will contribute to answer questions in modern fundamental physics. A proposed system to carry out these measurements would require a laser desorption ion source, and an ion-trap system. Following the recent laser spectroscopy investigations at the Max-Planck Institute for Nuclear Physics in Heidelberg, the goals of the proposed system should focuss on the laser cooling of negative osmium ions since such a system could be used to cool antiprotons to very low temperatures via collisions (sympathetic cooling) for efficient antihydrogen formation in its ground state. Furthermore, together with rhenium ions, the confinement of osmium ions in a Penning trap is important to determine the mass difference ¹⁸⁷Re-¹⁸⁷Os, and therefore the Q-value in the decay of ¹⁸⁷Re (T _1/2?=?4×10¹⁰ years) with unprecedented accuracy. This Q-value is an important constraint for the determination of the mass of the electron antineutrino as aimed by the international MARE collaboration. In this paper several mechanisms are considered for the preparation of the negative ions in order to apply laser cooling.     

Production of ion and electron streams by pulsed-laser ablation of Ta and Cu

A Nd:YAG laser with 10⁹ W/cm ² pulse intensity, operating at 532 nm wavelength, is used to ablate Ta and Cu targets placed in vacuum. The ablation process generates a plasma in front of the target surface, which expands along the normal to target surface. The ion and electron emissions from the plasma were measured by Faraday cups placed at different angles with respect to the normal to target surface. In the range of laser intensities from 10⁷ to 10⁹ W/cm², the fast electron yield is lower than the ion yield and it increases at higher laser intensities. The ablation threshold, the emission yield, the ion and electron average energies and the plasma ion and electron temperatures were measured for ion and fast electron streams.     

Luminescence of silicon Dioxide — silica glass, α-quartz and stishovite

This paper compares the luminescence of different modifications of silicon dioxide — silica glass, α-quartz crystal and dense octahedron structured stishovite crystal. Under x-ray irradiation of pure silica glass and pure α-quartz crystal, only the luminescence of self-trapped exciton (STE) is detected, excitable only in the range of intrinsic absorption. No STE luminescence was detected in stishovite since, even though its luminescence is excitable below the optical gap, it could not be ascribed to a self-trapped exciton. Under ArF laser excitation of pure α-quartz crystal, luminescence of a self-trapped exciton was detected under two-photon excitation. In silica glass and stishovite mono crystal, we spectrally detected mutually similar luminescences under single-photon excitation of ArF laser. In silica glass, the luminescence of an oxygen deficient center is presented by the so-called twofold coordinated silicon center (L.N. Skuja et al., Solid State Commun. 50, 1069 (1984)). This center is modified with an unknown surrounding or localized states of silica glass (A.N. Trukhin et al., J. Non-Cryst. Solids 248, 40 (1999)). In stishovite, that same luminescence was ascribed to some defect existing after crystal growth. For α-quartz crystal, similar to silica and stishovite, luminescence could be obtained only by irradiation with a lattice damaging source such as a dense electron beam at a temperature below 80 K, as well as by neutron or -irradiation at 290 K.     

Lasing of diode-pumped c-cut Tm, Ho:YAlO3

We report on a diode-pumped Tm, Ho:YAlO₃ (c-cut) laser operating at 274 K. The maximum output power reaches 163 mW at an absorbed pump power of 2.3 W. A conversion efficiency from the absorbed pump power to laser output of 7.1% is demonstrated in Tm, Ho:YAlO₃, corresponding to a slope efficiency of 11.1%. The output center wavelength of Tm, Ho:YAlO₃ is 2102 nm with about a 2-nm FWHM. As far as we know, our work represents the first investigation of the laser performance of c-cut Tm, Ho:YAlO₃ at 274 K.     

The USA and International Mössbauer Community

In the four decades since Rudolph L. Mössbauer's two papers launched the research community, almost 50,000 Mössbauer publications have appeared in the scientific literature. Most of the early pioneers have departed in recent years for various reasons. The Mössbauer society's international collaborations, the breadth of research topics in the field, and what has been and is being investigated are analyzed. The Mössbauer Effect Data Center's central role in the community over the years is discussed.     

New FIR Laser Lines from CHD2OH Methanol

We have investigated CHD₂OH methanol as source of far-infrared (FIR) laser radiation using the optical pumping technique. Our new waveguide pulsed CO₂ laser, with peak powers as high as some kW, has allowed us to observe 12 new lines. Each of them is characterized in wavelength, relative polarization, intensity, optimum operating pressure and pump offset from the center of the exciting CO₂ line.