Norbert Champion

Experimental study of radiative shocks at PALS facility

We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.

Energy levels of 4f3 in the Nd3+ free ion from emission spectra

The emission spectrum of neodymium produced by vacuum spark sources was observed in the vacuum ultraviolet on two normal-incidence spectrographs. In an initial result, more than 550 lines have been identified as transitions from 85 4f 2 5d levels to 37 levels of the 4f 3 ground configuration in the free ion Nd 3+ . The levels 4f 34 F3/2 and 4 I11/2, responsible for the wellknown 1064 nm laser line, have respective positions of 11 698.57 ±0. 1c m −1 and 1897.07 ±0. 1c m −1 above the ground level 4 I9/2. The newly found levels of 4f 3 constitute the first isolated 4f N configuration (N > 2) and therefore enable checks of effective parameters that represent far configuration interaction. Slater parameters F k (4f, 4f) derived from Nd 3+ :LaCl3 are 3% to 5% smaller

Ionization photophysics and spectroscopy of cyanoacetylene

Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11-15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC3N involves new aspects and new assignments of the vibrational components to excitation of the A(2)Σ(+) and B(2)Π states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B(2)Π state of HC3N(+). A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C(2)Σ(+) state of HC3N(+) at ≈17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6-15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C-H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised.

Ionization photophysics and Rydberg spectroscopy of diacetylene

Photoionization of diacetylene was studied using synchrotron radiation over the range 8–24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron–photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IEad = (10.17 ± 0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE = (16.15 ± 0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions , C3H+, and C2H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11–13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n = 4–11), R2(ndσg, n = 4–7) and R3(ndδg, n = 4–6) converging to the A2Πu state of the cation, and to a new series R′1(nsσg, n = 3) converging to the state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed.

Analysis of the free ion spectrum of Er3+(Er IV)

The vacuum spark spectrum of erbium is observed in the wavelength region 705–2460 A where transitions between the low-lying configurations , , and take place. Predictions of energy levels and electric dipole transition probabilities by means of the Cowan codes served for a complete revised analysis of the spectrum. The identification of 591 spectral lines as transitions mostly between low levels of these four configurations led to the determination of 120 energy levels. Radial parameters obtained in least-squares fits of both parities are compared with ab initio Hartree–Fock integrals including relativistic corrections. The mean error of the fits are respectively 41 cm−1 for 38 known levels of the odd parity configurations + and 49 cm−1 for 82 known levels of the even configurations + .

Observation of core-excited configuration in four-time ionized neodymium Nd4+ (Nd V)

Laboratory observation of the Nd V spectrum has been extended to shorter wavelength region down to 370 A. The analysis, based on 304 spectral lines led to the determination of 104 energy levels of the core-excited configuration 5p54f25d. The configuration interaction effects were studied by parametric calculations (Slater–Racah) of the odd-parity configurations where energy parameter values were least-squares fitted against the observed levels, starting with their Hartree-Fock values. The results confirmed the reduction of transition probabilities for the 5p64f2-5p64f5d transitions predicted in the previous Nd V study.

Characterization of Zn X-Ray Laser at PALS Centre, Its Applications in Dense Plasma Probing and Astrophysics

This report presents the results from experiments at PALS Centre using a Zn X-ray laser with the pulse length of 0.15 ns and the wavelength of 21.2 nm, working in single or double pass regime with the output energy of 0.4 mJ or 4 mJ per pulse, respectively. The current X-ray laser was experimentally examined to obtain its temporal coherence and spectral width using a path-difference interferometer. The double pass regime shows that QSS plasma based source-amplifier is promising for “short” fs soft X-ray pulses. The X-ray laser is commonly used for user’s experiments. Its advantages can be shown in applications such as probing of dense plasmas (up to 2.5×1024 cm−3) or single shot experiments (4×1014 photons/pulse). The simple technique based on Talbot effect was used to obtain the gradients of electron densities of line plasmas produced under conditions corresponding to XRL’s amplifiers operating in TCE and QSS regime. To investigate radiative shock wave in laboratory is challenging in aspects of the optimization of experimental parameters. Due to the high electron density (1022 cm−3) produced in the gas medium propagated by the shock wave, the velocity of the shock wave, and the absorption losses on optical elements, it is necessary to use the energetic single shot probe.

Critical Components for XUV Probing of Laser Driven Shocks

Radiative shocks can be produced in gases using high-energy lasers. As the electron density may be higher than the critical density for visible light, radiography with soft x-ray radiation becomes very promising technique to probe these shocks. Feasibility of this method has been proven employing zinc soft x-ray laser at 21.2 nm as backlighter. The experiment has shown high requirements on quality of the imaging optics and windows of the gas filled cell.

VUV Dissociative Photoionization of Quinoline in the 7–26 eV Photon Energy Range

Abstract The dissociative photoionization of quinoline was studied by photoionization mass spectrometry and ion yield measurements over a synchrotron photon excitation energy range 7–26 eV. The ionic and neutral products were identified with the aid of thermochemical calculations that, in some cases, led to deeper understanding of photodissociation pathways and the determination of upper limits of heats of formation of ionic and neutral dissociation products. A detailed comparison between the 20 eV photon excitation and 70 eV electron impact mass spectra, coupled with estimation of thermochemical appearance energies, leads to assignment of the dissociative ionization cation and neutral products for each detected ion. Reaction schemes for formation of these products are proposed in a number of cases. Ion intensities in the photon and electron impact mass spectra were used to consider extending a rule of charge retention in simple bond cleavage to more complex cases of dissociative ionization.

Analysis of the VUV emission spectrum of the Er3+ ion (Er IV)

This paper reports a summary of results obtained on the spectrum of the Er3+ ion (Er IV). The analysis of high resolution VUV emission spectrum led to the identification of about 590 spectral lines in the wavelength region of (851A– 2277A) and the determination of 120 energy levels belonging to the 4f11, 4f105d, 4f106s and 4f106p configurations, above the ground level 4f11 4I15/2. Parametric studies of the configurations including configuration interactions provided level compositions in intermediate coupling scheme.