A reliable cw Lyman-α laser source for future cooling of antihydrogen

We demonstrate a reliable continuous-wave (cw) laser source at the 1 S–2 P transition in (anti)hydrogen at 121.56 nm (Lyman-α) based on four-wave sum-frequency mixing in mercury. A two-photon resonance in the four-wave mixing scheme is essential for a powerful cw Lyman-α source and is well investigated.     

Towards sympathetic cooling of trapped ions with laser-cooled Mg + ions for mass spectrometry and laser spectroscopy

Sympathetic cooling by laser cooled Mg ions has been proposed as a method for fast cooling of highly charged ions to a very low temperature. The paper describes the construction of the solid state laser system at 279.63 nm required for laser cooling of the Mg ions. The laser system is composed of a fiber laser at 1,118.54 nm and two successive second harmonic generation (SHG) ring cavities for frequency quadrupling. In the first SHG cavity, non-critical phase matching of a lithium triborate (LBO) crystal is used for doubling from 1,118.54 to 559.27 nm. The second SHG cavity uses critical phase matching of a β-barium borate (BBO) crystal for doubling from 559.27 to 279.63 nm. With the aid of Boyd–Kleinmann theory, optimum experimental parameters are calculated and used for an efficient SHG. Besides this, the paper intends to be a shortcut for practical applications of the Boyd–Kleinmann theory for SHG.     

Development and application of a pipeline sonar system

Based on the principle of active sonar detection,a pipeline sonar sys-tem has been developed for detecting the water accumulated in undergroundgas-pipelines,and the effectiveness of this system verified through field-testing.The working process,experimental results and some considerations in the deter-mination of sonar parameters are described in this paper.     

Design and performance of a video-based laser beam automatic alignment system

A laser alignment system is applied to a high power laser facility for inertial confinement fusion. A design of the automated, close-loop laser beam alignment system is described. Its function is to sense beam alignment errors in a laser beam transport system and automatically steer mirrors preceding the sensor location as required to maintain beam alignment. The laser beam is sampled by a sensor package, which uses video cameras to sense pointing and centering errors. The camera outputs are fed to a personal computer, which includes video digitizers and uses image storage and software to sense the centroid of the image. Signals are sent through the computer to a stepper motor controller, which drives stepper motors on mirror mounts preceding the beam sampling location to return the beam alignment to the prescribed condition. Its optical principles and key techniques are given. The pointing and centering sensitivities of the beam alignment sensor package are analyzed. The system has been verified on the     

Cavity induced shift and narrowing of the positronium Lyman-α transition

We report experiments in which the line shape of the Lyman-alpha (1S-2P) transition was measured for positronium (Ps) atoms both inside and outside a porous silica target. The energy interval ΔE for confined atoms was observed to be larger than that of free Ps by 1.26±0.06 meV. A configuration interaction calculation yields results that are consistent with our ～5 nm sample, and suggests that ΔE decreases dramatically for larger cavity diameters. The linewidth of the transition, (0.066±0.004) nm (FWHM), is about half of what one would expect for free Ps at room temperature due to the Dicke line narrowing effect of confinement. Such measurements can be used to determine void sizes in porous films and Ps dynamics therein, and elimination of the Doppler spread of atoms in a porous film could be useful for the efficient excitation of a Ps gas.     

Measurements of hyperfine structure and shift for atomic uranium by laser induced-fluorescence spectroscopy

The paper reports that the isotope shift between natural uranium isotope 235and 238 and the hyperfine sturcture width width of U~(235) were measured by means of laser-in-duced fluorescence spectroscopy.The A and B hyperfine structure splitting constants of U~(235)were also given for 14643 cm~(-1),15720 cm~(-1)and 15631 cm~(-1) levels.     

Development of system and technology for m?ssbauer spectroscopic microscope

We have been developing a “M?ssbauer Spectroscopic Microscope (MSM)” which consists of a focusing lens for 14.4?keV γ-rays and a high precision X–Y stage. The measuring system both for electrons and γ-rays combined with a new M?ssbauer driver, i.e., “a moving coil actuator with a liner encoder” enables us to measure the mapping images simultaneously corresponding to different spectral components. The system has a controlling system based on a LabVIEW program and a LIST mode data acquisition system (NIKI-GLASS/A3100). To investigate a correlation between the microstructure of a sample and ⁵⁷Fe atoms, a scanning electron microscope (APCO/Mini-EOC) is also installed to this system.     

Development of a new P–T controlling system for neutron-scattering experiments

We developed a new device involving an individual P–T controlling system for neutron-scattering experiments available at 0–10 GPa and at 77–473 K. Thanks to the thermal insulators made of zirconia and glass-fiber-reinforced plastic under the anvils, temperature only around anvils can be controllable with fast heating/cooling rate of<20 K/min, and it also allows us to use normal hydraulic oil even at low temperatures, which has much less risk of leaking compared with helium gas. The feasibility test for this system for neutron diffraction experiments for ice VIII shows that the full decompression is established without any technical difficulty, which used to be not straightforward by the previous systems.     

Measurement of nuclear moments and radii by collinear laser spectroscopy and by β-NMR spectroscopy

Experiments using laser spectroscopy and nuclear magnetic resonance techniques have been performed at ISOLDE on the unstable isotopes of several light elements. The results include nuclear ground state spins, magnetic dipole and electric quadrupole moments, and the behaviour of mean square nuclear charge radii within isotopic strings. These give important information about the nuclear structure at shell closures and close to the drip lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Implementation of a preamplifier-amplifier system for radiation detectors used in Mössbauer spectroscopy

We report the assembly and testing of a preamplification and amplification system for pulses produced by gaseous radiation detectors commonly used in Mössbauer spectroscopy. The system is composed by a pair of commercial integrated circuits A203 and A206, which operate as charge sensitive preamplifier-shaping amplifier and linear amplifier-low level discriminator, respectively. The integrated circuits were interconnected in the unipolar output mode and placed inside a metallic shielding, which prevents noise amplification for a suitable signal-noise ratio. The system was tested by irradiating a proportional counter LND-45431 with characteristic X rays of 6.3 keV and gamma rays of 14.4 keV emitted by a Mössbauer radioactive source of ⁵⁷Co (Rh). Unipolar pulses with Gaussian profile were obtained at the output of the linear amplifier, whose amplitudes were close to 0.4 V for 6.3 keV X rays and 1.4 V for 14.4 keV gamma rays. Pulse height spectra showed that the system allows a satisfactory identification of the X-rays and gamma rays emitted by the ⁵⁷Co source, giving the possibility to make a good selection of the 14.4 keV peak for having a suitable signal-noise ratio in the Mössbauer spectra. Absorption percentages of 14 % were found by taking the Mössbauer spectra of a natural iron absorber. The assembly and tests of the system are presented through this paper.     

Development of the 10 TW ‘ATTILA’ Nd laser system

A high power laser system called ‘ATTILA’ (Almost-Table Top Terawatt Intense Laser) (10 TW) is under development at the University of Milano, Bicocca. Once fully functional ATTILA will produce 10 J, 1 picosecond pulses, reaching the power of 10 TW. The system is based on the chirped pulsed amplification technique and uses Nd:glass single-pass amplification.

The amplifier chain can be injected with two different oscillators: a Nd:YLF oscillator by Quantronix, stretched by an optical fiber, and a Nd:glass femtosecond oscillator by TimeBandwidth (Zurich), stretched by diffraction gratings, both delivering nanojoules pulses. A regenerative amplifier increasing the energy up to 1 mJ follows these.

Recently, we have implemented an automatic control system for the stabilization of mode-locking in the Quantronix oscillator. This is based on the active control of cavity length and on accurate stabilization of mode-locker temperature. A PC using LabView software drives the system. We are now beginning the installation of an adaptive optics system with a deformable mirror in order to optimize the optical quality and focusability of the beam.

Our final goal is to obtain an intensity of 10¹⁸ W/cm² on target. This will allow the production of relativistic electrons and energetic protons, and the study of relativistic plasma physics and of matter in extreme conditions.     

Study on cooling process of cryogenic system for superconducting magnets of BEPCⅡ

In the upgrade project of the Beijing Electron Positron Collider (BEPCⅡ), three superconducting magnets are employed to realize the goal of two orders of magnitude higher luminosity. A cryogenic system with a total capacity of 0.5~kW at 4.5~K was built at the Institute of High Energy Physics (IHEP) to support the operations of these superconducting devices. For preparing the commissioning of the system, the refrigeration process was simulated and analyzed numerically. The numerical model was based on the latest engineering progress and focused on the normal operation mode. The pressure and temperature profiles of the cryogenic system are achieved with the simulation. The influence of the helium mass flow rates to cool superconducting magnets on the thermodynamic parameters of their normal operation is also studied and discussed in this paper.     

Diagnostic system for two dimension intensity distribution of laser beam

The diagnostic system for two dimension(2-D)intensity distribution of laserbeam is a measuring instrument for many parameters of laser beam.2-D intensity distributionplot of laser beam is obtained by the two dimension scanning mirror which is controlled by amicrocomputer to scan the laser beam on a detector.Many parameters of laser beam such asthe isointensity distribution plot,the beam diameter,the beam waist diameter,the laser pow-er,the diverge angle and the beam brightness,are given by means of the microcomputer pro-cessing the data measured.Theoretical analysis of beam parameter transform is given.     

Controlled calibration method for laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy(LIBS)is a potential technique for rapid analysis of samples present in solids,gases and liquids.In the last two decades it was an object of extensive studies.Controlled calibration method used to analysis the LIBS spectra is investigated.Compared with the inner calibration and calibration-free(CF)methods,this new method overcomes"matrix effect",and demonstrates a better ability to cope with the spectra.It is used to analyze natural soil,and errors of the concentration are decreased about 5%.The result shows that the new method is feasible and accurate.     

Properties of halo nuclei measured by laser and β NMR spectroscopy

The application of laser spectroscopy methods for a detailed investigation of nuclear moments and charge radii of halo nuclei has been restricted to only a few cases. Three such experiments are discussed, showing the potential of these methods for research on the nuclear halo structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Coherent laser spectroscopy of ¯pHe+

The facilities of the coherent laser pulse spectroscopy of the ¯pHe⁺ transitions are considered taking the magnetic structure of the energy levels into account. The possibility for the observation of the dynamics of intramolecular motions is also analyzed.     

Infrared emission spectroscopy of a new Σ-Σ system of TiCl

The spectra of TiCl have been reinvestigated in the 4200-8500 cm⁻¹ region using the 1-m Fourier transform spectrometer associated with the National Solar Observatory at Kitt Peak. The molecules were excited in a microwave discharge lamp operated with 3.0 Torr of He and a trace of TiCl₄ vapor, and the spectra were recorded at a resolution of 0.01 cm⁻¹. Three new bands with origins near 6938.9, 6900.2, and 6861.7 cm⁻¹ have been assigned as the 0-0, 1-1, and 2-2 bands of a new - transition. This assignment is supported by our recent ab initio calculations on TiCl and ZrCl [J. Chem. Phys. 114 (2001) 3977]. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted for the states.