The spectral and temporal light emission properties of liquid argon have been studied in the context of its use in large liquid rare-gas detectors for detecting Dark Matter particles in astronomy. A table-top setup has been developed. Continuous and pulsed low energy electron beam excitation is used to stimulate light emission. A spectral range from 110 to 1000 nm in wavelength is covered by the detection system with a time resolution on the order of 1 ns.

Intense, focused heavy ion beams from SIS can deposit a high power and high energy in the target material. The primary excitation and subsequent relaxationand thermalization processes can be studies when gases are used as the target material. Light emission from the whole beam excited volume can be observed at least at wavelengths where the target material is optically thin. This aspect can be used to study the beam profile by optical methods.

J. Ling1, S. Udrea1, N. Shilkin2, S. El Moussati1, A. Fedenev3, A. Fertman4, D.H.H. Hoffmann1, A. Hug1,3, A. Kantsyrev4, A. Khudomyasov4, M. Kulish2, N. Markov4, V. Mintsev2, D. Nikolaev2, V. Ternovoi2, V. Turtikov4, A. Ulrich5, D. Varentsov3, D. Yuriev2, and Y. Zhao6 1TUD, Darmstadt, Germany; 2IPCP, Chernogolovka, Russia; 3GSI, Darmstadt, Germany; 4ITEP, Moscow, Russia; 5TUM, Garching, Germany;6IMP, Lanzhou, China

It is well known that beams of energetic particles traversing gas targets may be observed in the visible spectral range due to the glow which is induced by the interaction of the projectiles with the gas atoms or molecules. However, it is by far not obvious that the spatial shape of the glow intensity represents the beam profile in a quantitative way. Therefore we are trying to find conditions where this is the case by performing spectroscopic studies of the light emitted from particle beam excited gas targets. Figure 1: Ar spectrum: 300mbar, grating 150grv/mm (The instrumental response function is applied) One concept which we follow is to use rare gases as the target material since they are chemically stable when they are irradiated. Another possible target gas is nitrogen. Emission spectra for various gas densities and beam intensities are observed. The goal is to find emission features (spectral lines or molecular bands) which are in an ideal case only emitted due to direct excitation by the projectiles and for which the emission time is short compared with the hydrodynamic expansion time of the target gas. If in addition to these conditions the light output is linear or at least quantitatively related to the flux of the projectiles it should be possible to accurately measure the beam profiles of the particle beam. In earlier studies at the Munich Tandem accelerator we had found that argon ion lines (ArII) are only weakly excited by the secondary electrons and should fulfill most of the conditions stated above. Experiments with optical filters for the corresponding wavelength range have already been performed and an influence of the selected wavelength range on the registered beam profiles has been demonstrated [1]. The underlying spectroscopy, however, is not yet fully developed. Spectroscopic experiments have therefore been performed at the HHT target station of the SIS18 in 2009. An overview spectrum emitted from argon excited by a pulsed 350AMeV 238 U beam with 800ns pulse length and 2 · 10 9 projectiles per pulse is shown in Fig.1. The spectrum is unfortunately still dominated by impurity lines of nitrogen and OH* (see e.g. [2, 3]). The 4p − 4s ArI lines appear strongly in the red and near infrared. Some of the ArII lines which we had aimed at for measuring beam profiles do appear but they are very weak. It was also found that they ride on …

J. Ling1, S. Udrea1, N. Shilkin2, S. El Moussati 1, A. Fedenev 3, A. Fertman4, D.H.H. Hoffmann1, A. Hug1,3, A. Kantsyrev4, A. Khudomyasov 4, M. Kulish2, N. Markov4, V. Mintsev2, D. Nikolaev2, V. Ternovoi2, V. Turtikov4, A. Ulrich5, D. Varentsov3, D. Yuriev2, and Y. Zhao6 1TUD, Darmstadt, Germany; 2IPCP, Chernogolovka, Russia; 3GSI, Darmstadt, Germany; 4ITEP, Moscow, Russia; 5TUM, Garching, Germany;6IMP, Lanzhou, China

V. Ternovoi1, S. El Moussati 2, A. Fedenev 3, A. Fertman4, A.A. Golubev4, D.H.H. Hoffmann2, A. Hug2,3, B. Ionita2, A. Kantsyrev4, A. Khudomyasov 4, M. Kulish1, J. Ling2, N. Markov4, V. Mintsev1, D. Nikolaev1, A. Pyalling1, N. Shilkin1, V. Turtikov4, S. Udrea2, A. Ulrich5, D. Varentsov3, K. Weyrich3, D. Yuriev1, and Y. Zhao6 1IPCP, Chernogolovka, Russia; 2TUD, Darmstadt, Germany; 3GSI, Darmstadt, Germany; 4ITEP, Moscow, Russia; 5TUM, Munich, Germany;6IMP, Lanzhou, China

Processes on surface of liquid metals under the action of XeCl-laser with pulsed energy of 50 mJ are studied. Relaxation time of the surface of melted Gallium and Wood and Gallium-Indium alloys is determined. Minimal relaxation time (about 4 ms) was found to be for Ga and Ga-In alloy. Qualitative description of the processes based on the assumption of capillary waves formation oil the melted metal surface was suggested. Suggestion on the selection of liquid metal with minimal surface relaxation time was made based oil the suggestion.

A simple table-top windowless system for extreme ultraviolet (XUV) spectroscopy which avoids differential pumping for both the radiation source and the detector is presented. The radiation source uses excimer emission from rare gases excited with low energy (13 keV) electron beam. Broadband emission in the entire wavelength range from 60 to 140 nm is demonstrated using He, Ne and a Ne-Ar gas mixture. It was observed that the so-called third continuum is absent in Ne when low energy electron-beam excitation is used in contrast to earlier results using high energy ion beam excitation. An application of the set-up for a LiF transmission measurement close to the cut-off wavelength (105 nm) is demonstrated. It is shown how the radiation source could be applied in a simple and efficient technique of material treatment with XUV/VUV radiation.

The interaction of Xe- (λ~1.73 µm) and XeCl- (0.308 μm) lasers radiation with surfaces of metal and TiN-ceramic coatings on glass and steel substrates has been studied. Correlation between parameters of surface erosion (area of crater and amount of evaporated material versus laser focus position and number of pulses) was investigated. Monitoring of laser induced erosion on smooth polished surfaces was performed using optical microscopy. The correlation has been revealed between characteristic zones of thin coatings damaged by irradiation and energy distribution over laser beam cross section allowing evaluation of defects and adhesion of coatings.

An atmospheric-pressure CO2 laser with an electron-beam-initiated discharge produced in a working mixture is developed. The laser output energy of 18 mJ from a ~6-cm3 active volume is achieved. The laser operation with a pulse repetition rate of up to 5 Hz is demonstrated. The specific energy deposit of ~0.1 J cm-3 is obtained in the CO2:N2:He = 1:1:4 gas mixture at the atmospheric pressure during a pulsed nonself-sustained discharge with ionisation amplification.

An electron-beam-pumped laser on Xe atomic transitions is experimentally investigated at various pump durations and powers within wide ranges of pressures and working mixtures including additions of molecular gases. It is shown that the maximum specific lasing powers are achieved at high specific pump powers (above 200 kW cm-3 atm-1) and durations of the beam current pulse of tens of nanoseconds in high-pressure Ar — Xe mixtures with molecular gas additions (N2 and CO2). A specific output radiation power of ~ 4 kW cm-3 is obtained. For a pump pulse durations from hundreds of nanoseconds to 1 μs, the highest lasing energies are reached without molecular additions at a comparatively low beam-current density (the specific pump power is ~ 10 kW cm-3 atm-1). However, in setups with specific pump powers above 40 kW cm-3 atm-1 and a working-mixture pressure limited by the strength of the laser chamber, molecular additions result in an increase in the radiation energy and efficiency. In wide-aperture facilities with high pump powers, molecular additions improve the distribution of the radiation power density over the laser-beam cross section.

Time correlated optical emission spectra of argon, krypton and xenon in the wavelength range from 110 to 450nm, and 0 to 6000 ns time interval, recorded at the Munich Tandem accelerator using heavy ion beam excitation with 2ns beam pulses, were measured in order to clarify the origin of the so called third rare gas excimer continua. Experiments were performed at xenon and krypton pressures between 50 and 250mbar, and argon pressures between 230 and 1500mbar. All spectra clearly show different distinct peaks, emerging at different time delays after excitation. These spectral maxima are interpreted as arising from excimer emissions by separate radiating species, formed by gas kinetic processes. While the spectral shape of the components. forming the third continuum radiation in the heavy rare gases krypton and xenon turned out to be of complicate structure. in the case of argon all wavelength spectra could be reproduced by fitting a limited number of Gaussian functions with fixed center wavelengths and fixed widths to the data. Hereby, six distinct maxima, appearing at four different times after the excitation pulse, could be identified.Besides the 2(nd) continuum at about 128nm and the "Left Turning Point Region" (LTP) at 155nm, emission maxima were found at 177nm, 188nm, 199nm, 212nm, 225nm, and 245nm. A reaction pathway, leading to the various emission structures is suggested, essentially combining the pathways proposed earlier by other authors.

High quality, time correlated optical emission spectra of argon in the wavelength range from 110 to 300 nm, and 0 to 128 ns time interval, recorded at the Munich Tandem accelerator, using heavy ion beam excitation with 2 ns beam pulses were measured in order to clarify the origin of the so called third rare gas excimer continuum. Experiments were performed at argon pressures between 230 and 1500 mbar. The spectra clearly show several distinct peaks, emerging at different time delays after excitation. These spectral maxima are interpreted, as arising from excimer emissions by separate radiating species, formed by gas kinetic processes. All wavelength spectra obtained could be reproduced by fitting a limited number of Gaussian functions with fixed center-wavelengths and widths to the data. Six distinct maxima, appearing at four different times after the excitation pulse, could be identified. Besides the 128 nm peak of the 2nd continuum and the `left turning point' region around 155 nm, emission maxima were found at 177 nm, 188 nm, 199 nm, 212 nm, 225 nm, and 245 nm. A novel interpretation of the reaction pathways, leading to the various emission bands within the third continuum is proposed, essentially by combining the pathways proposed earlier by other authors. In this approach, the emission at 188 nm, occurring at early times and low pressures, is assigned to the decay of doubly charged dimers Rg22+. The emission at 199 nm, with a build-up time longer than 10 ns at 500 mbar, could then be attributed to the Rg32+ molecule. A transition to Rg2+* states will then occur by potential curves level crossing. The emission bands at 177 nm, 212 nm, and 225 nm are attributed to this Rg2+* molecule. The 245 nm continuum, appearing only at late times and high pressures, can then be attributed to the optical decay of Rg3+* clusters.