Search

The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^2{\mathrm{S}}_{1/2}{-}^2{\mathrm{P}}_{{1}/2}$$\end{document}2S1/2-2P1/2 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^2{\mathrm{S}}_{1/2}{-}^2{\mathrm{P}}_{{3}/2}$$\end{document}2S1/2-2P3/2 transitions in Li-like carbon ions stored and cooled at a velocity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta \approx 0.47$$\end{document}β≈0.47 in the experimental storage ring (ESR) at the GSI Helmholtz Centre in Darmstadt have been investigated in a laser spectroscopy experiment. Resonance wavelengths were obtained using a new continuous-wave UV laser system and a novel extreme UV (XUV) detection system to detect forward emitted fluorescence photons. The results obtained for the two transitions are compared to existing experimental and theoretical data. A discrepancy found in an earlier laser spectroscopy measurement at the ESR with results from plasma spectroscopy and interferometry has been resolved and agreement between experiment and theory is confirmed.

Scientific reports 11(1), 9370 (2021). doi:10.1038/s41598-021-88926-w, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

This repository contains the experimental raw data, the analyzed data and corresponding scripts as well as figures for the "Proton beam quality enhancement by spectral phase control of a PW-class laser system" publication. https://doi.org/10.1038/s41598-021-86547-x

Scientific reports 11(1), 17660 (2021). doi:10.1038/s41598-021-97511-0, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

We show how optical free-electron lasers and enhanced incoherent Thomson scattering radiation sources can be realized with Traveling-Wave Thomson-Scattering (TWTS) today. Emphasis is put on the realization of optical free-electron lasers (OFELs) with existing state-of-the-art technology for laser systems and electron accelerators. The conceptual design of optical setups for the preparation of laser pulses suitable for TWTS OFELs and enhanced Thomson sources is presented. We further provide expressions to estimate the acceptable alignment tolerances of optical components for TWTS OFEL operation. Examples of TWTS OFELs radiating at 100 nm, 13.5 nm and 1.5 Å as well as an incoherent source at 40 pm highlight the feasibility of the concept and detail the procedure to determine the optical components parameters of a TWTS setup.

Laser ion accelerators utilize high-power laser pulses in tight-focusing geometries to provide pulsed, high-intensity ion beams. Efficient capturing, transport and application of these beams is an ongoing effort which depends on precise knowledge of the accelerated ion distribution's properties and how to control these. For example, it is known that the propagation direction of the accelerated ions can be controlled by tilting the driving laser pulse-front. Since laser pulse-front tilts can be present accidentally, for example by a small misalignment of the compressor gratings in a chirped-pulse amplification system, knowledge of the scaling of the pulse-front tilt at a target position is desired. The talk gives relations for pulse-front orientation dependent on setup parameters and identifies regimes were pulse-front tilt has a sizable impact.

The development of high-intensity short-pulse lasers in the Petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets for the generation of high energy ion beams. The optimization of the acceleration process demands comprehensive diagnostic of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly sensible in the case of cryogenic hydrogen jet targets [1]. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronized probe laser system for off-harmonic probing at the DRACO laser operated at the Helmholtz-Zentrum Dresden–Rossendorf showed promising performance [2]. Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating is used as a hybrid stretcher and compressor unit [3]. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ. By deploying the probe laser pulses in laser-proton acceleration experiments with renewable cryogenic hydrogen jet targets, the plasma self-emission could be significantly suppressed while studying the temporal evolution of the expanding plasma jet. Hence, for varied drive laser contrast parameters, by the use of a plasma mirror, the on target contrast was measured and correlated to the temporal drive laser profile. References [1] L. Obst, et al. Efficient laser-driven proton acceleration from cylindrical and planar cryogenic hydrogen jets. Sci. Rep., 7:10248, 2017. [2] T. Ziegler, et al. Optical probing of high intensity laser interaction with micron-sized cryogenic hydrogen jets. Plasma Phys. Control. Fusion, 2018. doi:10.1088/1361-6587/ aabf4f. [3] L. Loeser, et al. A compact and robust millijoule CPA laser system based on Yb:CaF₂ delivering 160fs pulses. under review.

Traveling-Wave Thomson-Scattering (TWTS) is a novel Thomson scattering geometry which allows for orders of magnitude higher photon yields than classic head-on Thomson sources. TWTS thereby remains compact and provides narrowband and ultra-short ultraviolet to γ-ray radiation pulses just as classic Thomson sources. Even the realization of optical free-electron lasers is possible with the TWTS geometry since it provides both optical undulators with thousands of periods needed to microbunch the electron beam and a reduction of electron beam quality requirements compared to classic Thomson scattering to a level technically feasible today. TWTS employs a side-scattering geometry depicted in fig. 1. Laser and electron propagation direction of motion enclose the interaction angle ϕ. Tilting the laser pulse front with respect to the wave front by half the interaction angle ensures continuous overlap of electrons and laser pulse over the whole laser pulse width while the laser pulse crosses the electron beam trajectory. In this way the interaction length becomes controllable by the laser pulse width and independent of the laser pulse duration. Utilizing wide, petawatt class laser pulses for TWTS allows to realize thousands of optical undulator periods. The variability of TWTS with respect to the interaction angle can be used to control the radiation wavelength even for electron sources with fixed energy. For a fixed target wavelength on the other hand, the free choice of interaction angle enables control over electron beam quality requirements. Small interaction angle scenarios (ϕ∼10°) typically yield the best trade-off between requirements on electron beam quality, laser power and laser intensity stability. In the talk we will show that TWTS OFELs emitting extreme ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems. We detail an experimental setup to generate the tilted TWTS laser pulses which aims at compactness and provides focusing of these high-power pulses and compensation of dispersion accompanying pulse-front tilts. The method presented for dispersion compensation is especially relevant when building high yield X- and γ-ray sources in large interaction angle setups of TWTS.

We report on the energetic and beam quality performance of the second to the last main amplifier section HEPA I of the PEnELOPE laser project. A polarization coupled double-12-pass scheme to verify the full amplification capacity of the last two amplifiers HEPA~I and II was used. The small signal gain for a narrow band cw laser was 900 and 527 for a broadband nanosecond pulse, demonstrating 12.6 J of output pulse energy. Those pulses, being spectrally wide enough to support equivalent 150 fs long ultrashort pulses, are shown with an excellent spatial beam quality. A first active correction of the wavefront using a deformable mirror resulted in a Strehl ratio of 76 % in the single-12-pass configuration for HEPA I.

Generating and controlling ultrashort, pulse-front tilted laser pulses is essential for Traveling-Wave Electron Acceleration (TWEAC), Traveling-Wave Thomson Scattering (TWTS) and Traveling-Wave Optical FELs (TWTS-OFELs). All these applications require controlling angular and group-delay dispersion, while keeping experimental setups as compact as possible. However, the varying requirements with respect to laser power, extent of focal region, incident angles and laser mode quality lead to differing strategies in designing experimental setups. In this overview poster we provide answers to the question: What experimental efforts in terms of laser system and optics are necessary in current labs for first proof-of-principle realizations of the different applications of "Traveling-Wave" laser pulses -- ranging from low-bandwidth and yield-enhanced Thomson sources (TWTS), laser-based electron accelerators beyond the LWFA depletion and dephasing limits (TWEAC) and ultimately an optical free-electron laser (TWTS-OFEL)?

The Traveling-Wave Thomson-Scattering geometry is introduced and the possibility to realize optical free-electron lasers with it explained. An example setup for a TWTS OFEL providing 1 Angström radiation is shown and its application to the probing of the ion dynamics in a laser driven cryogenic hydrogen slab presented.

The development of high-intensity short-pulse lasers in the petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets to generate proton beams with multiple 10 MeV energy per nucleon. The optimization of the acceleration process calls for a comprehensive exploration of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly well suited in the case of cryogenic hydrogen jet targets [1]. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronizable probe laser system for off-harmonic probing at the DRACO laser at the Helmholtz-Zentrum Dresden – Rossendorf showed promising performance [2]. Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator (Light Conversion) operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating (Optigrate Corp) is used as a hybrid stretcher and compressor unit. The subsequent diode pumped regenerative Yb:CaF2 laser amplifier includes a spectral shaping element and chirped mirrors for GDD compensation. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ and thus extends the recent developments [3] into the sub 200 fs region. Additionally, we present recent experimental results deploying the upgraded probe laser system and its harmonics in an experiment dedicated to laser-proton acceleration from a renewable cryogenic hydrogen jet at the DRACO laser.

Generating and controlling ultrashort, pulse-front tilted laser pulses is essential for Traveling-Wave Electron Acceleration (TWEAC), Traveling-Wave Thomson Scattering (TWTS) and Traveling-Wave Optical FELs (TWTS-OFELs). All these applications require controlling angular and group-delay dispersion, while keeping experimental setups as compact as possible. However, the varying requirements with respect to laser power, extent of focal region, incident angles and laser mode quality lead to differing strategies in designing experimental setups. This overview poster provides answers to the question: What experimental efforts in terms of laser system and optics are necessary in current labs for first proof-of-principle realizations of the different applications of "Traveling-Wave" laser pulses -- ranging from low-bandwidth and yield-enhanced Thomson sources (TWTS), laser-based electron accelerators beyond the LWFA depletion and dephasing limits (TWEAC) and ultimately an optical free-electron laser (TWTS-OFEL)?

The presentation will give an overview of the recent experiments for laser driven proton acceleration with high contrast at the high power laser system Draco at HZDR. We present results of an experimental campaign employing a pure condensed hydrogen jet as a renewable and debris free target. Different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane around the wire-like target, reaching cut-off energies of up to 20 MeV and exceeding 109 protons per MeV per steradian. Evaluation of two different target geometries (cylindrical with a diameter of 2µm, 5µm or 10µm and planar with 2x20 µm²) demonstrating more optimized acceleration conditions from the planar hydrogen jet. We report on modulations of laser accelerated protons by strong filamentary electromagnetic fields. Such modulations are related to the appearance of electron Weibel instability in the preplasma at the rear side of the target and impose important constraints on the preplasma level for high-quality proton acceleration [1]. Furthermore we present the usage of optical probing to study the laser plasma interaction providing plasma density measurements at the time of the interaction and to precisely determine the jet position. Recorded probe images taken up to 100 ps after the laser pulse arrived at the target, indicating plasma density modulations from pinching effects along the jet axis.

Developments in the field of laser plasma accelerators have been pushed by applications like radiation therapy in the past years. The acceleration of particle to higher energies is one of the key questions for such applications. Probing methods offer the capability for investigating the laser target interaction and thus allow for studying the acceleration process. In this talk results obtained by optical probing in recent experiments for laser driven proton acceleration with high contrast at the high power laser Draco at HZDR are presented. Draco delivers pulses of 30 fs and 5 J at 800 nm, focused to a 3 µm spot by a F/2.5 off-axis parabolic mirror. We present results of an experimental campaign using a cryogenic hydrogen jet as a renewable debris free target. The hydrogen jet’s nominal electron density is approximately 30 times the critical density for 800 nm and its shape and size can be varied. For instance cylindrical geometries with diameters of 2µm, 5µm or 10µm were used. The laser plasma interaction could be monitored on-shot with two temporally synchronized optical probe beams perpendicular and longitudinal to the Draco laser axis. Recorded probe images taken up to 100 ps after the laser pulse arrived at the target indicate plasma density modulations from pinching effects along the jet axis. A possible driver for those density modulations is a strong surface current which has been studied with 2D-PIC simulations. Such density modulations may modify the shape of the electron sheath and thereby alter the beam profile of the laser accelerated protons.

We present a pure condensed hydrogen jet as a renewable and debris-free target for high power laser experiments. The jet's nominal electron density is approximately 30 times the critical density and its diameter can be varied to be 2µm, 5µm or 10µm and thus allowing to study the regime of relativistic transparency. Different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane around the wire-like target. Radiochromic film stacks in forward direction display signatures of filament-like structures, stemming from a Weibel-like instability generated at the rear side of the target in the underdense plasma region.

Applications like radiation therapy of cancer have pushed the development of laser plasma accelerators and defined levels of control and necessary particle beam stability in laser plasma experiments. The poster will give an overview of a recent experiment for laser driven particle acceleration with high contrast at the high power laser Draco at HZDR, delivering pulses of 30fs and 5J. We present results of an experimental campaign employing a cryogenic hydrogen jet as a renewable target. The jet's nominal plasma density is approximately 30 times the critical density and its diameter can be varied to be 2µm, 5µm or 10µm and thus allowing to study the regime of relativistic transparency. In addition a planar aperture was commissioned, providing a different geometry of the hydrogen jet. Different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane around the wire-like target. Radiochromic film stacks in laser forward direction display filament-like structures, stemming from a Weibel-like instability generated at the rear side of the target. Furthermore the micro-jet target could be monitored on-shot with a temporally synchronized optical probe beam perpendicular and almost parallel to the pump laser axis. Recorded probe images taken on a timescale of several 10’s of picoseconds indicating plasma density modulations from pinching effects along the jet axis.

Traveling-Wave Thomson-Scattering (TWTS) can realize ultra-compact, inherently synchronized and highly brilliant light sources from the ultraviolet to the hard X-ray range. In TWTS ultrashort laser pulses and relativistic electron bunches are utilized in a side-scattering geometry where laser pulse and electron bunch direction of motion enclose an interaction angle. Thereby the laser electric field provides the undulator field in which electrons oscillate and emit radiation during interaction. By employing tilted laser pulses TWTS ensures continuous overlap of laser and electrons while these traverse the laser cross-sectional area. Tilting the laser pulse-front compensates the spatial separation of electrons and laser at begin and end of the interaction originating from their different propagation directions. Combining laser pulse-front tilt and side-scattering in TWTS enables interaction over hundreds to thousands of optical undulator periods, enough to allow for optical free-electron laser (OFEL) operation since microbunching of the electron bunch and thus coherent radiation amplification can be achieved. After shortly introducing the TWTS scattering geometry, the design of optical setups to generate the tilted TWTS laser pulses is presented in the talk. This setup strategy provides dispersion compensation, required due to angular dispersion of the laser pulse, and is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups. Determining parameters of the setup is illustrated in an example of an ultraviolet TWTS OFEL and an outlook is given on the design of hard X-ray TWTS sources.