Physics studies with brilliant narrow-width γ-beams at the new ELI-NP Facility

The Extreme Light Infrastructure Nuclear Physics (ELI-NP) Facility in Magurele is a European research centre for ultrahigh intensity lasers, laser–matter interaction, nuclear science and material science using laser-driven radiation beams. It is the first project within the European Strategic Forum for Research Infrastructure (ESFRI) agenda financed by the European Regional Development Fund. The nuclear physics research programme of the facility is focussed on studies with brilliant narrow-width γ-beams and experiments in extreme laser fields.     

Physics opportunities with polarized e − and e + beams at TESLA

Beam polarization at e⁺-e^– linear colliders will be a powerful tool for high precision analyses. Often it is assumed that the full information from polarization effects is provided by polarization of the electron beam and no further information can be obtained by the simultaneous polarization of the positrons. In this paper we point out the advantages of polarizing both beams, and summarize the polarization-related results of the Higgs, Electroweak, QCD, SUSY and Alternative Theories working groups of the ECFA/DESY workshop for a planned linear collider operating in the energy range s = 500-800 GeV.     

Generating 10–40 MeV high quality monoenergetic electron beams using a 5 TW 60 fs laser at Tsinghua University

A unique facility for laser plasma physics and advanced accelerator research has recently been built at Tsinghua University. This system is based on a Tsinghua Thomson scattering X-ray source(TTX),which combines an ultrafast TW laser with a synchronized 45 Me V high brightness linac. In our recent laser wakefield acceleration experiments,we have obtained 10–40 Me V high quality monoenergetic electron beams by running the laser at 5 TW peak power. Under certain conditions a very low relative energy spread of a few percent can be achieved. Absolute charge calibration for three different scintillating screens has also been performed using the linac system.     

Distributed Bragg reflector laser(1.8 μm) with 10 nm wavelength tuning range

We report a 1.8 μm two-section distributed Bragg reflector laser using butt-jointed In Ga As P bulk material as the waveguide core layer. The threshold current is 17 m A and the output power is 8 m W on average. The threshold current, output power, and emitting wavelength dependences on temperature are measured. The obtained wavelength tuning range is 10 nm. This device has potential applications in simultaneous multiple-gas detection.     

Physics program of open charm and heavy c(c-) states at the BES-Ⅲ experiment

We present the physics program of the open charm and heavy c(c-)states above the D(D-)production energy threshold,which will be studied with the BES-Ⅲ detector at the BEPC-Ⅱ collider in the coming years.Based on some full Monte Carlo simulations with the BES-Ⅲ detector,we predict the accuracy levels on measuring some physical quantities related to D0,D+and D+s decays as well as some non-charmed decays of the heavy c(c-)states.     

Gas-discharge XeF* (B→X) laser with high specific output energy

The discharge characteristics of the XeF* (BX) laser are investigated. The NF₃ and Xe partial pressure of the laser gas mixture and the total gas pressure have been varied. A highest specific output energy of 4.7 J/l with an efficiency of 0.5% was obtained from a X-ray preionized Ne/Xe/NF₃ gas mixture at 6 bar with single-pulse excitation through a multichannel spark gap.     

Optical free induction decay (OFID) 10 μm co2 laser systems

This paper describes new unproved and reliable optical free induction decay (OFID) picosecond-pulse CO₂-10 μm laser systems, differing mainly in the pump laser and in the peak power of the generated pulses. In this context a single-mode TEA-CO₂-10 μm laser preionized by a novel surfacecorona discharge was developed. Our improved plasma shutters operate as optical switches at variable gas pressures. They are triggered either by a laser-produced surface plasma or by an electrical high voltage discharge. With respect to the first trigger scheme we found new target materials for the surface plasma generation, i.e. metallized graphites. In the second scheme the electrical discharge is initiated by the TEA-laser pulse via a new laser-triggered spark gap. Single-mode TEA-CO₂-10 μm laser, plasma shutter plus a spectral filter form the OFID laser system, which generates the picosecond pulses. An electronic control completes the system as reliable working tool. Each of the OFID laser systems developed is capable to produce 10 μm pulses with a duration of 30–300 ps.Numerical calculations are performed to estimate the influence of various parameters on pulse shape and duration. Since a direct measurement of the time variation of the short pulses by fast IR detectors is not possible, we measure the picosecond pulses by means of an optical autocorrelation method with optical second harmonic generation. For the first time this is performed with polycrystalline material, e.g. GaAs or ZnSe, instead of a single crystal, e.g. GaAs or Te.     

Nuclear quadrupole interactions at 187W(β-) 187Re in ZrW2O8

In ZrW₂O₈, a material with negative thermal expansion, two nuclear quadrupole interactions at ¹⁸⁷W(β^-) ¹⁸⁷Re with equal populations were determined by time differential perturbed angular correlation to be (at 295 K): ν_{\mathrm{Q} 1} = 336(1) MHz, η₁ = 0 and ν_Q2 = 1391(2) MHz, η₂ = 0.053(4). The nuclear quadrupole interactions are assigned to two crystallographically distinct tungsten sites. These results are the bases for further TDPAC studies of the negative thermal expansion on a microscopic scale. This revised version was published online in August 2006 with corrections to the Cover Date.     

Extreme gravity tests with gravitational waves from compact binary coalescences: (I) inspiral–merger

The observation of the inspiral and merger of compact binaries by the LIGO/Virgo collaboration ushered in a new era in the study of strong-field gravity. We review current and future tests of strong gravity and of the Kerr paradigm with gravitational-wave interferometers, both within a theory-agnostic framework (the parametrized post-Einsteinian formalism) and in the context of specific modified theories of gravity (scalar–tensor, Einstein–dilaton–Gauss–Bonnet, dynamical Chern–Simons, Lorentz-violating, and extra dimensional theories). In this contribution we focus on (i) the information carried by the inspiral radiation, and (ii) recent progress in numerical simulations of compact binary mergers in modified gravity.     

Experimental studies of (n, α) reaction cross-sections performed at the Institute for Physics and Power Engineering

Studies of (n, α) reaction cross-sections on a number of isotopes over a wide range of neutron energies were performed systematically at the Institute for Physics and Power Engineering (IPPE) A new spectrometer that includes an ionization chamber and a pulse shape digitizer were used. The experimental technique and the results of measurements of the reaction cross-sections ¹⁶O(n, α)¹³C, ¹⁴N(n, α)¹¹B, ²⁰Ne(n, α)¹⁷O, ³⁶Ar(n, α)³³S, ⁴⁰Ar(n, α)³⁷S, ¹⁰B(n, α)⁷Li, and ⁵⁰Cr(n, α)⁷Li, are described.     

5.1-ps passively mode-locked Nd:Gd_(0.42)Y_(0.58)VO_4 laser with a LT-GaAs absorber

We propose a diode end-pumped passively mode-locked Nd:Gd_(0.42)Y_(0.55)VO_4 (Nd:GdYVO_4) laser at 1064 nm using a GaAs absorber grown at low temperature as the output coupler.Stable continuous-wave (CW) mode locking with a 5.1-ps pulse duration at a repetition rate of 113 MHz is obtained.The maximum average output power is 2.29 W at the incident pump power of 12 W with the slope efficiency of about 24.8%.     

Diode-pumped Tm:KY(WO4)2 laser passively Q-switched with PbS-doped glass

Glass doped with PbS quantum dots is presented as a saturable absorber (SA) for a passive Q-switching of a diode-pumped 1.9 μm Tm:KYW laser. Output pulses with energy of 44 μJ at a repetition rate of 2.5 kHz with an average output power of 110 mW were obtained. The Q-switching conversion efficiency was 33%. The absorption saturation intensity of the glass doped with PbS quantum dots with a mean radius of 5.2 nm at a wavelength of 2 μm was measured to be 1.5 MW/cm².     

AES analysis of nitridation of Si(100) by 2–10 keV N+2 ion beams

Ion beam nitridation of Si(100) as a function of N⁺₂ ion energy in the range of 2–10 keV has been investigated by in-situ Auger electron spectroscopy (AES) analysis and Ar⁺ depth profiling. The AES measurements show that the nitride films formed by 4–10 keV N⁺₂ ion bombardment are relatively uniform and have a composition of near stoichiometric silicon nitride (Si₃N₄), but that formed by 2 keV N⁺₂ ion bombardment is N-rich on the film surface. Formation of the surface N-rich film by 2 keV N⁺₂ ion bombardment can be attributed to radiation-enhanced diffusion of interstitial N atoms and a lower self-sputtering yield. AES depth profile measurements indicate that the thicknesses of nitride films appear to increase with ion energy in the range from 2 to 10 keV and the rate of increase of film thickness is most rapid in the 4–10 keV range. The nitridation reaction process which differs from that of low-energy (< 1 keV) N⁺₂ ion bombardment is explained in terms of ion implantation, physical sputtering, chemical reaction and radiation-enhanced diffusion of interstitial N atoms.     

Optimization of hybrid laser – TIG welding of 316LN steel using response surface methodology (RSM)

In the present study, the hybrid laser – TIG welding parameters for welding of 316LN austenitic stainless steel have been investigated by combining a pulsed laser beam with a TIG welding heat source at the weld pool. Laser power, pulse frequency, pulse duration, TIG current were presumed as the welding process parameters whereas weld bead width, weld cross-sectional area and depth of penetration (DOP) were considered as the process responses. Central composite design was used to complete the design matrix and welding experiments were conducted based on the design matrix. Weld bead measurements were then carried out to generate the dataset. Multiple regression models correlating the process parameters with the responses have been developed. The accuracy of the models were found to be good. Then, the desirability approach optimization technique was employed for determining the optimum process parameters to obtain the desired weld bead profile. Validation experiments were then carried out from the determined optimum process parameters. There was good agreement between the predicted and measured values.     

Graphene-based passively Q-switched Nd:KLu(WO4)2 eye-safe laser operating at 1,425 nm

With graphene as saturable absorber, an Nd:KLu(WO₄)₂ eye-safe laser operating at 1,425 nm is demonstrated. To the best of our knowledge, this is the first demonstration that an Nd:KLu(WO₄)₂ laser operates at the eye-safe 1.4-μm region. A maximum total average output power of 170 mW is obtained under the pump power of 9.6 W, corresponding to an optical–optical efficiency of 1.77 %. The minimum pulse width and the highest pulse repetition rate are 153 ns and 97 kHz, respectively. Also the characteristics of the graphene used as saturable absorber for a 1.4-μm laser were studied for the first time.