Soft X-ray laser spectroscopy on trapped highly charged ions at FLASH

Institut für Experimentalphysik, University of Hamburg, Hamburg, Hamburg, Germany
Physical Review Letters (Impact Factor: 7.51). 06/2007; 98(18):183001. DOI: 10.1103/PhysRevLett.98.183001
Source: PubMed


In a proof-of-principle experiment, we demonstrate high-resolution resonant laser excitation in the soft x-ray region at 48.6 eV of the 2 (2)S(1/2) to 2 (2)P(1/2) transition of Li-like Fe23+ ions trapped in an electron beam ion trap by using ultrabrilliant light from Free Electron Laser in Hamburg (FLASH). High precision spectroscopic studies of highly charged ions at this and upcoming x-ray lasers with an expected accuracy gain up to a factor of a thousand, become possible with our technique, thus potentially yielding fundamental insights, e.g., into basic aspects of QED.

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    • "The experiments, which benefit from high integrated flux are, e.g., spectroscopy of highly charged ions and cold molecular ions, produced with low concentration in the ion traps [1] [2]; spectroscopy of low Z elements [3], and studies of low populated mass selected clusters [6]. High integrated photon flux is greatly appreciated by the photon-induced materials processing applications. "
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    ABSTRACT: Keywords: free electron laser, linear accelerator, vacuum ultraviolet (VUV) source. The fabulous properties of the coherent radiation generated with the free electron lasers (FEL) gained broader perspective on the experimental capabilities in physics, chemistry, biology and medicine. They raise from the nanometer-ranged wavelength, femtosecond-ranged pulse duration and brightness in the range of 10 29 photons/(s·mrad 2 ·mm 2 ·0.1% bandwidth) accompanied by up to megahertz repetition frequency. Such a light source extends experimental capabilities in spectroscopy, photon counting, imagining, photo-induced material processing and warm dense plasma creation. We propose to settle a high average power VUV FEL facility POLFEL at the Andrzej Soltan Institute for Nuclear Studies in Świerk. POLFEL is planned as a node of the EuroFEL network of complementary facilities, recommended by ESFRI. The great weight of the synchrotron radiation studies in modern science and technology makes us recognize the next, fourth generation light source facility as an instrument which will effectively improve the impact of research being run in Poland. Presented concept benefits from the long and wide experience of Polish scientists and engineers involved in the FEL activities world wide. Here we present an the overview of the general layout of the planned facility, paying a special attention to its novel solutions. The ground breaking feature of POLFEL is a continuous wave (cw) or near-cw operation. It will be achieved with a linear superconducting (sc) accelerator fed with a low emittance sc-electron injector furnished with the thin film sc lead photocathode. There are three outstanding characteristics of the VUV radiation emitted by FEL, which are often named as its fundamental advantages: femtosecond pulse duration, huge peak brilliance and high average intensity. As the first two of them are adequately accounted in the existing facilities or those being in the advanced phase of construction: FLASH, FERMI and LCLS, we turn our efforts towards the last of mentioned parameters – the average power. The principal goal, which dictates that approach, is to enable experiments requiring maximization of the time integrated number of interacting photons. They are experiments dealing with diluted samples and/or processes occurring with a low probability [1-3]. For those experiments, the significant improvement of experimental capabilities can be achieved when the recent progress in reduction of detectors readout time [4] goes together with the higher repetition rate of the light source. POLFEL will operate basing on the SASE (Self-Amplified Spontaneous Emission) principle [5] and will generate the light as displayed in Table 1.
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    ABSTRACT: We report wavelength measurements of H-like and He-like ions obtained with a novel x-ray spectrometer at the Heidelberg Electron Beam Ion Trap. The experimental uncertainty for the Lyman-alpha1 wavelength in Cl16+ is reduced by a factor of 3 and, as expected, excellent agreement with theory is maintained. For the resonance line in He-like Ar16+, an uncertainty of only deltalambda/lambda=2x10(-6) was achieved. This is the most precise x-ray wavelength reported for highly charged ions to date, and allows to test recent predictions on QED two-electron and two-photon radiative corrections for He-like ions. The results also point to the advantages of establishing absolute x-ray wavelength standards using Lyman-alpha transitions (in the present case Ar17+ Lyman-alpha1) to supersede the current ones.
    Physical Review Letters 10/2007; 99(11):113001. DOI:10.1103/PHYSREVLETT.99.113001 · 7.51 Impact Factor
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    ABSTRACT: In vast regions of the universe highly charged ions (HCI [1, 2]) are the predominant form of visible matter. Their importance extends to high-temperature terrestrial plasmas, such as those used in fusion research. Yet, accurate prediction of their electronic structure remains a challenge for theory due to the strong electromagnetic field in which the remaining bound electrons dwell. Experimental accuracy has now reached the performance limits of conventional photon spectroscopy in the soft and hard x-ray regions. In this work [3], we report on the resonant laser excitation of the 2(2)S(1/2) - 2(2)P(1/2) transition of the Li-like Fe(23+) ion at 48.6 eV, an energy range hitherto unattainable with powerful lasers. The HCI stored in an electron beam ion trap (EBIT [4]) were resonantly excited by ultra-brilliant radiation generated at the Free electron LASer in Hamburg (FLASH [5]). While yielding a relative statistical error of only 2.2.10(-5), and extending laser spectroscopy on HCI from the near ultraviolet [6] to the soft X-ray region, this novel experiment demonstrates immediate potential to push the current limits of precision by orders of magnitude. Such experiments allow to verify predictions of quantum electrodynamics (QED) in a strong field environment where perturbation theory [7, 8] fails. Future EBIT experiments at upcoming x-ray free electron lasers (X-FEL) like the Stanford Linear Coherent Light Source (LCLS) or the European X-FEL will pave the way for laser spectroscopy into the hard x-ray region.
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