Tarek Mohamed

Development of an electro-optical device for storage of high power laser pulses

Abstract We have constructed and tested a storage ring for high power ps to ns laser pulses. The aim of the optical laser ring is to increase the efficiency of using a high power laser pulse in different applications and particularly in laser-induced recombination at CRYRING. Efforts to increase the efficiency of using high power laser pulses by using different kind of optical cavities are going on in different laboratories around the world. In our case we use a very fast electro-optical switch to inject the laser pulse into an optical ring, where the used Pockels cell is driven by a fast high voltage pulser with a rise time

Spectroscopic study of Mg-like Ni by means of dielectronic recombination of stored ions

Dielectronic recombination resonances of Ni17+ that form doubly excited states in Mg-like Ni were studied in the energy range up to 6.5 eV. We observed 3sel → 3pnl, 3dnl (Δn = 0) resonances and a single 3sel → 4s4p (Δn = 1) resonance in this energy region. A relativistic many-body perturbation theory calculation was performed to predict the positions and strengths of the resonances in this region. A comparison of the experimental data with the calculation yields an overall good agreement as regards the resonance positions and strengths. The discrepancies are predominantly theoretical underestimations of the rate coefficient. The 3s1/2–3p1/2 and the 3s1/2–3p3/2 energy splittings have been determined from the experiment.

Determination of the Ni XVIII plasma recombination rate coefficient.

The electron-ion recombination and electron-impact ionization of several astrophysically abundant C, N, O, and Ni ions have been investigated using the synchrotron storage ring CRYRING. The recombination rate coefficients predominanty used in the analyses of emission line spectra and for ionization balance calculations are determined from isoelectronic fits and extrapolations of theoretical and limited experimental results available from the literature. The rate coefficients reported by various authors differ by an order of magnitude for various ion species. For low temperature plasmas(<104 K), the available information on resonant recombination rate coefficients is even more limitied and, unfortunately, most available data has been determined from LS coupling calculations, which can have adverse effects on recombination rates due to the mistreatment of autoionizing states. For ions of C, N, and O, the production of metastable states complicates the experimental rate coefficient determinations. Some attempts have been made in this work to utilize both recombination and electron-impact ionization in estimating the metastable ion beam fractions present. Other metastable fractions have been determined by comparing the experimental recombination spectra to intermediate coupling calculations. Some of the absolute recombination rate coefficients reported in this work are given for the first time while many others vastly improve the spectral resolution of previous experiments, allowing for a more detailed study of the low energy resonances which contribute to the resonant recombination rate coefficient at low plasma electron temperatures. This increased resolution has also lead to the observation of trielectronic recombination resonances which greatly influence low temperature recombinaion rates in some ions.

A linear optical trap with active medium for experiments with high power laser pulses

A linear optical trap for circulating high power laser pulses and tuning these pulses to high repetition frequency of several tens of MHz has been developed. A ns excimer pumped dye laser pulse has been injected with help of a Wollaston prism and a synchronized Pockels cell into an optical trap formed by two highly reflecting mirrors in a linear configuration. The test was done at λ = 580 nm, but the optical trap can be used without limitations in a broad band of optical wavelengths (400-700 nm). Power considerations give an increase of the efficiency of the optical trap of about 7 times compared to single passage of the laser pulse through the experimental section. The time structure of the trapped laser pulses can be controlled by changing the distance between the two high reflecting mirrors. The efficiency of the optical trap strongly depends upon optical losses. To compensate the optical losses, an amplifying cell was introduced, and the efficiency was about 60 times higher than that by single passage of the laser pulse through the experimental section.

A seeded dye laser cavity for intracavity experiments

A seeded dye laser cavity, synchronously pumped by the 2nd harmonic of the Nd:YAG laser has been designed and experimentally tested. The used seed signal was the well defined narrow linewidth output laser signal (▵λ = 0.013 nm) from the excimer-dye laser system. Energy considerations showed that the intracavity laser energy, that can be used for an experimental section inside the cavity, can reach an efficiency of 20% of the pumping energy. The wavelength and linewidth are fully controlled by the wavelength and linewidth of the seeding laser.

Broadband optical trap for increasing the duty factor of high power pulsed laser systems

An optical trap for storage of high power laser pulses and tuning of these pulses to a high repetition frequency of several tens of MHz has been developed at our laboratory. A ns excimer pumped dye laser pulse has been injected with help of a Wollaston prism and a synchronized Pockels cell into an optical trap formed by two high reflecting mirrors in a linear configuration. The efficiency of the optical trap strongly depends upon optical losses. Power consideration gives an increasing of the efficiency of the optical trap of about 7 times compared to a single passage of the laser pulse through the experimental section. A controlled time structure of the trapped laser pulses is shown. To compensate optical losses an amplifying cell was introduced, that increased the efficiency by a factor of 25, where back and forward train of laser pulses is taken into account.

High resolution studies of electron-ion recombination

The formation of atoms by recombination of free electrons with ions is a fundamental process and plays a central role in astro-physical and fusion plasmas. It can be seen as time-inverse photo-ionization, auto-ionization, or electron-impact ionization. Here, we show how these processes can be measured with cooler-storage rings, such as CRYRING at MSL, with very high accuracy. The status of theoretical modeling is briefly reviewed and anomalies are uncovered. We discuss some examples of recombination for ions where strong dielectronic recombination resonances occur. With cooler-storage rings, these resonances can today be measured with meV accuracy, and from the spectra of the dielectronic resonances, very accurate values for energy splittings and resonance strengths are derived. These allow crucial tests of relativistic, correlation, and QED effects in these systems.

High Resolution Recombination Measurements of Stored Ions

The accuracy obtained in electron‐ion recombination experiments at storage rings has reached a level which allows strenuous tests of theoretical models and the ability to derive accurate, and useful, information for applications such as plasma modeling and diagnostics. Here we present two such recombination experiments performed at the heavy ion storage ring CRYRING. First, we investigated the possibility to derive a temperature dependent plasma rate coefficient for Na‐like Ni, which has been observed in emission lines from active solar regions and laboratory plasmas. Second, we determined the 2s1/2‐2p1/2 energy splitting in Li‐like Kr. Such a highly charged ion exhibits large QED contributions (∼1.5 eV) which are difficult to represent in theoretically calculations. The experimental value for the splitting was determined to within 8 meV while the theoretically determined value is only accurate to within 19 meV.