Adalbert Ding

Improvement of passive Q-switching performance reached with a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4.

Passive Q-switching performance was found to be greatly improved by use of a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4 compared with that achieved with Nd:YVO4 and Nd:GdVO4. At an absorbed pump power of 12 W, an average output power of 2.78 W was obtained at a pulse repetition frequency of 15.4 kHz with an optical conversion efficiency of 23.2%, and the slope efficiency was determined to be 45.5%. The resulting pulse energy, peak power, and pulse width were 181 microJ, 26.6 kW, and 6.8 ns, respectively.

Efficient passive Q-switching operation of a diode-pumped Nd:GdVO 4 laser with a Cr 4+ :YAG saturable absorber

A diode-pumped highly efficient Cr4+:YAG passively Q-switched Nd:GdVO4 laser formed by a plano–concave resonator has been demonstrated. At the highest attainable absorbed pump power of 11.4 W, 4.05 W of average output power, which was two thirds of the maximum corresponding cw output, was achieved with an optical conversion efficiency of 35.5%, and the slope efficiency was determined to be 46.8%, reaching 85% of the magnitude of its cw counterpart. The resulting shortest pulse duration, single-pulse energy, and peak power were found to be 13 ns, 90 μJ, and 7 kW, respectively, with a pulse repetition frequency (PRF) of 45 kHz. Two particularly modified resonator configurations were employed; the largest pulse energy and the highest peak power reached were, respectively, 154 μJ and 11.2 kW at 8.5 W of absorbed pump power. An analytical relation between the PRF and the absorbed pump power is given for a passively Q-switched laser, showing good consistency with experiment with a Nd:GdVO4 laser. The dependence of the operational parameters on the pump power and on the output coupling was also investigated experimentally. Issues involving the criterion for passive Q switching are discussed in some detail for Cr4+:YAG passively Q-switched neodymium-doped vanadate lasers.

Pulse energy enhancement in passive Q-switching operation with a class of Nd:GdxY1−xVO4 crystals

Passive Q-switching operation with a class of Nd:GdxY1−xVO4 crystals has been demonstrated. Compared to Nd:YVO4 and Nd:GdVO4, the pulse energy produced with Nd:Gd0.64Y0.36VO4 under certain conditions was found to be enhanced by factors of 6.0 and 2.5, while the peak power enhanced by factors of 14.7 and 3.6, respectively. At the incident pump power of 9.6 W, 1.3 W of average output power was obtained, with the pulse energy, peak power, and pulse repetition frequency being 166 μJ, 24.5 kW, and 7.7 kHz, respectively.

Laser-assisted production of multi-walled carbon nanotubes from acetylene

Abstract A production method of carbon nanotubes using the catalytic decomposition of acetylene has been developed. Metal clusters are formed by laser vaporisation of solid nickel in situ in a hot reaction tube containing a mixture of acetylene and argon. The laser generated clusters act as catalysts for the growth of nanotubes. With this method multi-walled tubes were obtained with inner diameters of 3–10 nm and outer diameters of 10–100 nm. Transmission electron microscopy shows that the tubes are highly graphitic. The results obtained are explained by a growth model.

THERMODYNAMICS OF THE SOLAR CORONA AND EVOLUTION OF THE SOLAR MAGNETIC FIELD AS INFERRED FROM THE TOTAL SOLAR ECLIPSE OBSERVATIONS OF 2010 JULY 11

We report on the first multi-wavelength coronal observations, taken simultaneously in white light, Hα 656.3 nm, Feix 435.9 nm, Fex 637.4 nm, Fexi 789.2 nm, Fexiii 1074.7 nm, Fexiv 530.3 nm, and Nixv 670.2 nm, during the total solar eclipse of 2010 July 11 from the atoll of Tatakoto in French Polynesia. The data enabled temperature differentiations as low as 0.2 × 10 6 K. The first-ever images of the corona in Feix and Nixv showed that there was very little plasma below 5 × 10 5 K and above 2.5 × 10 6 K. The suite of multi-wavelength observations also showed that open field lines have an electron temperature near 1×10 6 K, while the hottest, 2×10 6 K, plasma resides in intricate loops forming the bulges of streamers, also known as cavities, as discovered in our previous eclipse observations. The eclipse images also revealed unusual coronal structures, in the form of ripples and streaks, produced by the passage of coronal mass ejections and eruptive prominences prior to totality, which could be identified with distinct temperatures for the first time. These trails were most prominent at 10 6 K. Simultaneous Fex 17.4 nm observations from Proba2/SWAP provided the first opportunity to compare Fex emission at 637.4 nm with its extreme-ultraviolet (EUV) counterpart. This comparison demonstrated the unique diagnostic capabilities of the coronal forbidden lines for exploring the evolution of the coronal magnetic field and the thermodynamics of the coronal plasma, in comparison with their EUV counterparts in the distance range of 1–3 R� . These diagnostics are currently missing from present space-borne and ground-based observatories.

Mapping the Distribution of Electron Temperature and Fe Charge States in the Corona with Total Solar Eclipse Observations

The inference of electron temperature from the ratio of the intensities of emission lines in the solar corona is valid only when the plasma is collisional. Once collisionless, thermodynamic ionization equilibrium no longer holds, and the inference of an electron temperature and its gradient from such measurements is no longer valid. At the heliocentric distance where the transition from a collision-dominated to a collisionless plasma occurs, the charge states of different elements are established, or frozen-in. These are the charge states which are subsequently measured in interplanetary space. We show in this study how the 2006 March 29 and 2008 August 1 eclipse observations of a number of Fe emission lines yield an empirical value for a distance, which we call Rt , where the emission changes from being collisionally to radiatively dominated. Rt ranges from 1.1 to 2.0 R ☉, depending on the charge state and the underlying coronal density structures. Beyond that distance, the intensity of the emission reflects the distribution of the corresponding Fe ion charge states. These observations thus yield the two-dimensional distribution of electron temperature and charge state measurements in the corona for the first time. The presence of the Fe X 637.4 nm and Fe XI 789.2 nm emission in open magnetic field regions below Rt , such as in coronal holes and the boundaries of streamers, and the absence of Fe XIII 1074.7 nm and Fe XIV 530.3 nm emission there indicate that the sources of the solar wind lie in regions where the electron temperature is less than 1.2 × 106 K. Beyond Rt , the extent of the Fe X [Fe9+] and Fe XI emission [Fe10+], in comparison with Fe XIII [Fe12+] and Fe XIV [Fe13+], matches the dominance of the Fe10+ charge states measured by the Solar Wind Ion Composition Spectrometer, SWICS, on Ulysses, at –43° latitude at 4 AU, in March-April 2006, and Fe9+ and Fe10+ charge states measured by SWICS on the Advanced Composition Explorer, ACE, in the ecliptic plane at 1 AU, at the time of both eclipses. The remarkable correspondence between these two measurements establishes the first direct link between the distribution of charge states in the corona and in interplanetary space.

Photoionization dynamics of C60 studied with synchrotron radiation

Solitary C60 has been ionized applying synchrotron radiation. The photoionization dynamics of C60 resulting from single photon ionization in the energy range of 15–120 eV are reported. A comparison is made with other recent reports focusing the ionization and fragmentation behaviour of C60 as a result of certain energy transfer processes to the cluster. The actual ionization mechanism, the temperature dependence on the ion yield cureve and the fragmentation behaviour of ionic C60 are discussed.

Ionisation and fragmentation dynamics of highly fluorinated fullerenes C60F46,48 and C70F54,56 after excitation with synchrotron radiation

Highly fluorinated fullerenes of the composition C60Fx with x = 46, 48 and C70Fx with x = 54, 56 have been ionised by single photon absorption. The resulting ions have been detected by means of time-of-flight mass spectrometry. For all species under investigation, the careful analysis of the photo-ion yield curves at threshold revealed identical ionisation energies of 12.0 eV with an uncertainty of ±0.1 eV for the C60-based molecules and ±0.2 eV for the C70-based ones.

Electron energy loss spectroscopy of free C60 and C70

Electron energy loss spectroscopy has been performed with samples of pure C60 and C70 using primary electron energies between 10 and 1100 eV. The experimental data could be explained in terms of optically forbidden and allowed transitions, and by collective excitations (plasmons), which could be distinguished by their dependence on the energy of the primary electron.

IMAGING COMET ISON C/2012 S1 IN THE INNER CORONA AT PERIHELION

Much anticipation and speculation were building around comet ISON, or C/2012 S1, discovered on 2012 September 21 by the International Scientific Optical Network telescope in Russia, and bound for the Sun on 2013 November 28, with a closest heliocentric approach distance of 2.7 R ?. Here we present the first white light image of the comets trail through the inner corona. The image was taken with a wide field Lyot-type coronagraph from the Mees Observatory on Haleakala at 19:12 UT, past its perihelion passage at 18:45 UT. The perfect match between the comets trail captured in the inner corona and the trail that had persisted across the field of view of 2-6 R ? of the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph Experiment/C2 coronagraph at 19:12 UT demonstrates that the comet survived its perihelion passage.