Referierte Publikationen

2012

S. Zherebtsov, F. Süssmann, C. Peltz, J. Plenge, K. J. Betsch, I. Znakovskaya, A. S. Alnaser, N. G. Johnson, M. Kübel, A. Horn, V. Mondes, C. Graf, S. A. Trushin, A. Azzeer, M. J. J. Vrakking, G.G. Paulus, F. Krausz, E. Rühl, T. Fennel, and M. F. Kling
Carrier-envelope phase-tagged imaging of the controlled electron acceleration from SiO2 nanospheres in intense few-cycle laser fields
New J. Phys., 14 :075010 (July 2012)
Abstract:
Waveform-controlled light fields offer the possibility of manipulating ultrafast electronic processes on sub-cycle timescales. The optical lightwave control of the collective electron motion in nanostructured materials is key to the design of electronic devices operating at up to petahertz frequencies. We have studied the directional control of the electron emission from 95 nm diameter SiO_2 nanoparticles in few-cycle laser fields with a well-defined waveform. Projections of the three-dimensional (3D) electron momentum distributions were obtained via single-shot velocity-map imaging (VMI), where phase tagging allowed retrieving the laser waveform for each laser shot. The application of this technique allowed us to efficiently suppress background contributions in the data and to obtain very accurate information on the amplitude and phase of the waveform-dependent electron emission. The experimental data that are obtained for 4 fs pulses centered at 720 nm at different intensities in the range (1 - 4) × 10^13 W cm^(−2) are compared to quasi-classical mean-field Monte-Carlo simulations. The model calculations identify electron backscattering from the nanoparticle surface in highly dynamical localized fields as the main process responsible for the energetic electron emission from the nanoparticles. The local field sensitivity of the electron emission observed in our studies can serve as a foundation for future research on propagation effects for larger particles and field-induced material changes at higher intensities.
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I. Hofmann, J. Meyer-ter-Vehn, X. Yan, and H. Al-Omari
Chromatic energy filter and characterization of laser-accelerated proton beams for particle therapy
Nucl. Instr. Meth. Phys. Res. A, 681 :44 (July 2012)
Abstract:
The application of laser accelerated protons or ions for particle therapy has to cope with relatively large energy and angular spreads as well as possibly significant random fluctuations. We suggest a method for combined focusing and energy selection, which is an effective alternative to the commonly considered dispersive energy selection by magnetic dipoles. Our method is based on the chromatic effect of a magnetic solenoid (or any other energy dependent focusing device) in combination with an aperture to select a certain energy width defined by the aperture radius. It is applied to an initial 6D phase space distribution of protons following the simulation output from a Radiation Pressure Acceleration model. Analytical formula for the selection aperture and chromatic emittance are confirmed by simulation results using the TRACEWIN code. The energy selection is supported by properly placed scattering targets to remove the imprint of the chromatic effect on the beam and to enable well-controlled and shot-to-shot reproducible energy and transverse density profiles.
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J. Seres, E. Seres, and C. Spielmann
Classical model of strong-field parametric amplification of soft x rays
Phys. Rev. A, 86 :013822 (July 2012)
Abstract:
We present a detailed theoretical description of laser driven x-ray parametric amplification, which has been experimentally demonstrated by Seres et al. [Nature Phys. 6 455 (2010)] together with a supporting basic model. The process is based on the parametric interaction of an x-ray photon with a laser accelerated electron in a Coulomb field. With the extended model we are able to estimate the gain cross section also for a finite energy distribution of the interacting electrons as well as to consider dephasing between the electrons and the x-ray field. The improved model is capable of describing the recent experimental findings much more accurately.
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T. Schlegel, and V. Tikhonchuk
Classical radiation effects on relativistic electrons in ultraintense laser fields with circular polarization
New J. Phys., 14 :073034 (July 2012)
Abstract:
The propagation of a relativistic electron with initial energy ≥ 100 MeV in a number of simple one-dimensional laser field configurations with circular polarization is studied by solving the relativistic equation of motion in the Landau–Lifschitz approach to account for the radiation friction force. The radiation back-reaction on the electron dynamics becomes visible at dimensionless field amplitudes a ≥ 10 at these high particle energies. Analytical expressions are derived for the energy and the longitudinal momentum of the electron, the frequency shift of the light scattered by the electron and the particle trajectories. These findings are compared with the numerical solutions of the basic equations. A strong radiation damping effect results in reduced light scattering, forming at the same time a broad quasi-continuous spectrum. In addition, the electron dynamics in the strong field of a quasistationary laser piston is investigated. Analytical solutions for the electron trajectories in this complex field pattern are obtained and compared with the numerical solutions. The radiation friction force may stop a relativistic electron after propagation over several laser wavelengths at high laser field strengths, which supports the formation of a stable piston.
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M. Möller, Y. Cheng, S. Khan, B. Zhao, K. Zhao, M. Chini, G.G. Paulus, and Z. Chang
Dependence of high-order-harmonic-generation yield on driving-laser ellipticity
Phys. Rev. A, 86 :011401 (July 2012)
Abstract:
High-order-harmonic-generation yield is remarkably sensitive to driving laser ellipticity, which is interesting from a fundamental point of view as well as for applications. The most well-known example is the generation of isolated attosecond pulses via polarization gating. We develop an intuitive semiclassical model that makes use of the recently measured initial transverse momentum of tunneling ionization. The model is able to predict the dependence of the high-order-harmonic yield on driving laser ellipticity and is in good agreement with experimental results and predictions from a numerically solved time-dependent Schrödinger equation.
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H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann
Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers
Opt. Express, 20 :15710 (July 2012)
Abstract:
The temporal behavior of mode instabilities in active large mode area fibers is experimentally investigated in detail. Thus, apart from the onset threshold of mode instabilities, the output beam is characterized using both high-speed camera measurements with 20,000 frames per second and photodiode traces. Based on these measurements, an empiric definition of the power threshold of mode instabilities is introduced. Additionally, it is shown that the temporal dynamics show a transition zone between the stable and the unstable regimes where well-defined periodic temporal fluctuations on ms-timescale can be observed. Finally, it is experimentally shown that the larger the mode-field area, the slower the mode-instability fluctuation is. The observations support the thermal origin of mode instabilities.
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B. Döbrich, and A. Eichhorn
Can we see quantum gravity? Photons in the asymptotic-safety scenario
J. High Energ. Phys., 156 :1 (June 2012)
Abstract:
In the search for a quantum theory of gravity it is crucial to find experimental access to quantum gravitational effects. Since these are expected to be very small at observationally accessible scales it is advantageous to consider processes with no tree-level contribution in the standard model, such as photon-photon scattering. We examine the implications of asymptotically safe quantum gravity in a setting with extra dimensions for this case, and point out that various near-future photon-collider setups, employing either electron or muon colliders, or even a purely laser-based setup, could provide a first observational window into the quantum gravity regime.
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J. Bierbach, C. Rödel, M. Yeung, B. Dromey, T. Hahn, A. Pour, S. Fuchs, A. E. Paz, S. Herzer, S. Kuschel, O. Jäckel, M.C. Kaluza, G. Pretzler, M. Zepf, and G.G. Paulus
Generation of 10 µW relativistic surface high-harmonic radiation at a repetition rate of 10 Hz
New J. Phys., 14 :065005 (June 2012)
Abstract:
Experimental results on relativistic surface HHG at a repetition rate of 10 Hz are presented. Average powers in the 10 μW range are generated in the spectral range of 51 to 26 nm (24 - 48 eV). The surface harmonic radiation is produced by focusing the second-harmonic of a high-power laser onto a rotating glass surface to moderately relativistic intensities of 3 × 10^19 W cm^−2. The harmonic emission exhibits a divergence of 26 mrad. Together with absolute photon numbers recorded by a calibrated spectrometer, this allows for the determination of the extreme ultraviolet (XUV) yield. The pulse energies of individual harmonics are reaching up to the μJ level, equivalent to an efficiency of 10^−5. The capability of producing stable and intense high-harmonic radiation from relativistic surface plasmas may facilitate experiments on nonlinear ionization or the seeding of free-electron lasers.
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C. Jauregui, T. Eidam, H.-J. Otto, F. Stutzki, F. Jansen, J. Limpert, and A. Tünnermann
Physical origin of mode instabilities in high-power fiber laser systems
Opt. Express, 20 :12912 (June 2012)
Abstract:
Mode instabilities, i.e. the rapid fluctuations of the output beam of an optical fiber that occur after a certain output power threshold is reached, have quickly become one of the most limiting effects for the further power scaling of fiber laser systems. Even though much work has been done over the last year, the exact origin of the temporal dynamics of this phenomenon is not fully understood yet. In this paper we show that the origin of mode instabilities can be explained by taking into account the interplay between the temporal evolution of the three-dimensional temperature profile inside of the active fiber and the related waveguide changes that it produces via the thermo-optical effect. In particular it is proposed that non-adiabatic waveguide changes play an important role in allowing energy transfer from the fundamental mode into the higher order mode. As it is discussed in the paper, this description of mode instabilities can explain many of the experimental observations reported to date.
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R. Märtin, G. Weber, R. Barday, Y. Fritzsche, U. Spillmann, W. Chen, R. D. DuBois, J. Enders, M. Hegewald, S. Hess, A. Surzhykov, D. B. Thorn, S. Trotsenko, M. Wagner, D. F. A. Winters, V. A. Yerokhin, and T. Stöhlker
Polarization Transfer of Bremsstrahlung Arising from Spin-Polarized Electrons
Phys. Rev. Lett., 108 :26480 (June 2012)
Abstract:
We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. By means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. For the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy.
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M. Baumgartl, C. Lecaplain, A. Hideur, J. Limpert, and A. Tünnermann
66 W average power from a microjoule-class sub-100 fs fiber oscillator
Opt. Lett., 37 :1640 (May 2012)
Abstract:
Performance scaling of passively mode-locked ultrashort-pulse fiber oscillators in terms of average power, peak power, and pulse energy is demonstrated. A very-large-mode-area fiber laser in an all-positive group-velocity-dispersion ring cavity configuration with intracavity spectral filter, mode-locked by nonlinear polarization evolution, emits 66 W of average power at 76 MHz repetition rate, corresponding to 0.9 μJ pulse energy. The pulses are dechirped to 91 fs outside the cavity with an average power of 60 W remaining after the compressor. The generated pulse peak power is as high as 7 MW.
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B. Bergues, M. Kübel, N. Johnson, B. Fischer, N. Camus, K. Betsch, O. Herrwerth, A. Senftleben, A. Sayler, T. Rathje, T. Pfeifer, I. Ben-Itzhak, R. Jones, G. Paulus, F. Krausz, R. Moshammer, J. Ullrich, and M. Kling
Attosecond tracing of correlated electron-emission in non-sequential double ionization
Nat. Commun., 3 :813 (May 2012)
Abstract:
Despite their broad implications for phenomena such as molecular bonding or chemical reactions, our knowledge of multi-electron dynamics is limited and their theoretical modelling remains a most difficult task. From the experimental side, it is highly desirable to study the dynamical evolution and interaction of the electrons over the relevant timescales, which extend into the attosecond regime. Here we use near-single-cycle laser pulses with well-defined electric field evolution to confine the double ionization of argon atoms to a single laser cycle. The measured two-electron momentum spectra, which substantially differ from spectra recorded in all previous experiments using longer pulses, allow us to trace the correlated emission of the two electrons on sub-femtosecond timescales. The experimental results, which are discussed in terms of a semiclassical model, provide strong constraints for the development of theories and lead us to revise common assumptions about the mechanism that governs double ionization.
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G. Weber, H. Bräuning, S. Fritzsche, A. Gumberidze, R. Märtin, R. Reuschl, M. Schwemlein, U. Spillmann, A. Surzhykov, D. F. A. Winters, and T. Stöhlker
Compton polarimeters for the study of hard X-rays arising from energetic collisions of electrons and ions with matter
AIP Conf. Proc., 1438 :73 (May 2012)
Abstract:
Novel position-sensitive x-ray detectors are presented that, when applied as Compton polarimeters, enable precise and efficient linear polarization studies of hard x-rays up to several 100 keV. We give an analytical formula which yields a rough estimate of the polarimeter efficiencies of such detector systems. Moreover, we briefly summarize a recent linear polarization measurement of the Lyman-α1 radiation in a H-like high-Z system, namely U91+.
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T. Gottschall, M. Baumgartl, A. Sagnier, J. Rothhardt, C. Jauregui, J. Limpert, and A. Tünnermann
Fiber-based source for multiplex-CARS microscopy based on degenerate four-wave mixing
Opt. Express, 20 :12004 (May 2012)
Abstract:
We present a fiber-based laser source for multiplex coherent anti-Stokes Raman scattering (CARS) microscopy. This source is very compact and potentially alignment-free. The corresponding pump and Stokes pulses for the CARS process are generated by degenerate four-wave mixing (FWM) in photonic-crystal fibers. In addition, an ytterbium-doped fiber laser emitting spectrally narrow 100 ps pulses at 1035 nm wavelength serves as pump for the FWM frequency conversion. The FWM process delivers narrow-band pulses at 648 nm and drives a continuum-like spectrum ranging from 700 to 820 nm. With the presented source vibrational resonances with energies between 1200 cm^(−1) and 3200 cm^(−1) can be accessed with a resolution of 10 cm^(−1). Additionally, the temporal characteristics of the FWM output have been investigated by a cross-correlation setup, revealing the suitability of the emitted pulses for CARS microscopy. This work marks a significant step towards a simple and powerful all-fiber, maintenance-free multiplex-CARS source for real-world applications outside a laboratory environment.
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A. Przystawik, A. Kickermann, A. Al-Shemmary, S. Düsterer, A. M. Ellis, K. von Haeften, M. Harmand, S. Ramakrishna, H. Redlin, L. Schroedter, M. Schulz, T. Seideman, N. Stojanovic, J. Szekely, F. Tavella, S. Toleikis, and T. Laarmann
Generation of the simplest rotational wave packet in a diatomic molecule: Tracing a two-level superposition in the time domain
Phys. Rev. A, 85 :052503 (May 2012)
Abstract:
We introduce a time-domain approach to explore rotational dynamics caused by intramolecular coupling or the interaction with dissipative media. It pushes the time resolution toward the ultimate limit determined by the rotational period. Femtosecond pulses create a coherent superposition of two rotational states of carbon monoxide. The wave-packet motion is observed by subsequent Coulomb explosion, which results in a time-dependent asymmetry of spatial fragmentation patterns. The asymmetry oscillation prevails for at least 1 ns, covering more than 300 periods with no decoherence. Long time scans will allow weak perturbations of the order of ΔE/E = 10^(−4) to be discerned. Our conclusions are confirmed by a fully quantum-mechanical model.
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J. Rothhardt, A. M. Heidt, S. Hädrich, S. Demmler, J. Limpert, and A. Tünnermann
High stability soliton frequency-shifting mechanisms for laser synchronization applications
J. Opt. Soc. Am. B, 29 :1257 (May 2012)
Abstract:
We analyze frequency-shifting mechanisms in photonic crystal fibers (PCFs). In contrast to the generally used approach of launching pulses in the negative group velocity dispersion (GVD) region of PCFs, we suggest employing a fiber with a higher zero dispersion wavelength that is pumped in the positive GVD region. Results of a numerical optimization reveal that the amplitude stability of the frequency-shifted pulses can be improved by more than 1 order of magnitude and the timing jitter arising from input fluctuations by 2 orders of magnitude by a proper choice of the fiber dispersion. The presented approach and optimization will improve the performance of timing- and amplitude-sensitive applications, such as nonlinear microscopy and spectroscopy or optical synchronization for optical parametric chirped pulse amplification significantly.
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M. Baumgartl, B. Ortac, J. Limpert, and A. Tünnermann
Impact of dispersion on pulse dynamics in chirped-pulse fiber lasers
Appl. Phys. B, 107 :263 (May 2012)
Abstract:
We report on a systematic study of an environmentally stable mode-locked Yb-doped fiber laser operating in the chirped-pulse regime. The linear cavity chirped-pulse fiber laser is constructed with a saturable absorber mirror as nonlinear mode-locking mechanism and a nonlinearity-free transmission-grating-based stretcher/compressor for dispersion management. Mode-locked operation and pulse dynamics from strong normal to strong anomalous total cavity dispersion in the range of +2.5 to -1.6 ps^2 is experimentally studied. Strongly positively chirped pulses from 4.3 ps (0.01 ps^2) to 39 ps (2.5 ps^2) are obtained at normal net-cavity dispersion. In the anomalous dispersion regime, the laser generates average soliton feature negatively chirped pulses with autocorrelation pulse durations from 0.8 ps (−0.07 ps^2) to 3.9 ps (-1.6 ps^2). The lowered peak power due to the pulse stretching allows one to increase the double pulse threshold. Based on the numerical simulation, different regimes of mode locking are obtained by varying the intra-cavity dispersion, and the characteristics of average soliton, stretched-pulse, wave-breaking-free and chirped-pulse regimes are discussed.
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Ph. A. Korneev, S. V. Popruzhenko, S. P. Goreslavski, T.-M. Yan, D. Bauer, W. Becker, M. Kübel, M. F. Kling, C. Rödel, M. Wünsche, and G.G. Paulus
Interference Carpets in Above-Threshold Ionization: From the Coulomb-Free to the Coulomb-Dominated Regime
Phys. Rev. Lett., 108 :223601 (May 2012)
Abstract:
The velocity map recorded in above-threshold ionization of xenon at 800 nm exhibits a distinct carpetlike pattern of maxima and minima for emission in the direction approximately perpendicular to the laser polarization. The pattern is well reproduced by a numerical solution of the time-dependent Schrödinger equation. In terms of the simple-man model and the strong-field approximation, it is explained by the constructive and destructive interference of the contribution of the long and the short orbit. Strictly perpendicular emission is caused by ionization at the two peaks of the laser field per cycle, which results in a 2ℏω separation of the above-threshold ionization rings.
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G. Weber, R. Märtin, A. Surzhykov, M. Yasuda, V. A. Yerokhin, and T. Stöhlker
PEBSI – A Monte Carlo simulator for bremsstrahlung arising from electrons colliding with thin solid-state targets
Nucl. Instr. Meth. Phys. Res. B, 279 :155 (May 2012)
Abstract:
We present a Monte Carlo code dedicated to the simulation of bremsstrahlung arising in collisions of polarized electrons with thin target foils. The program consists of an electron transport algorithm taking into account elastic electron-nucleus scattering and inelastic collisions with target electrons as well as a treatment of polarized-electron bremsstrahlung emission. Good agreement is found between the predictions of the electron transport code and data stemming from other simulation programs and experiments. In addition, we present first results from the bremsstrahlung simulation which indicate a significant decrease in the degree of linear polarization of bremsstrahlung even for the thinnest gold targets considered.
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M. Grieser, Yu. A. Litvinov, R. Raabe, K. Blaum, Y. Blumenfeld, P. A. Butler, F. Wenander, P. J. Woods, M. Aliotta, A. Andreyev, A. Artemyev, D. Atanasov, T. Aumann, D. Balabanski, A. Barzakh, L. Batist, A.-P. Bernardes, D. Bernhardt, J. Billowes, S. Bishop, M. Borge, I. Borzov, F. Bosch, A. J. Boston, C. Brandau, W. Catford, R. Catherall, J. Cederkall, D. Cullen, T. Davinson, I. Dillmann, C. Dimopoulou, G. Dracoulis, Ch. E. Düllmann, P. Egelhof, A. Estrade, D. Fischer, K. Flanagan, L. Fraile, M. A. Fraser, S. J. Freeman, H. Geissel, J. Gerl, P. Greenlees, R. E. Grisenti, D. Habs, R. von Hahn, S. Hagmann, M. Hausmann, J. J. He, M. Heil, M. Huyse, D. Jenkins, A. Jokinen, B. Jonson, D. T. Joss, Y. Kadi, N. Kalantar-Nayestanaki, B. P. Kay, O. Kiselev, H.-J. Kluge, M. Kowalska, C. Kozhuharov, S. Kreim, T. Kröll, J. Kurcewicz, M. Labiche, R. C. Lemmon, M. Lestinsky, G. Lotay, X. W. Ma, M. Marta, J. Meng, D. Mücher, I. Mukha, A. Müller, A. Murphy, G. Neyens, T. Nilsson, C. Nociforo, W. Nörtershäuser, R. D. Page, M. Pasini, N. Petridis, N. Pietralla, M. Pfützner, Z. Podolyak, P. Regan, M. W. Reed, R. Reifarth, P. Reiter, R. Repnow, K. Riisager, B. Rubio, M. S. Sanjari, D. W. Savin, C. Scheidenberger, S. Schippers, D. Schneider, R. Schuch, D. Schwalm, L. Schweikhard, D. Shubina, E. Siesling, H. Simon, J. Simpson, J. Smith, K. Sonnabend, M. Steck, T. Stora, T. Stöhlker, B. Sun, A. Surzhykov, F. Suzaki, O. Tarasov, S. Trotsenko, X. L. Tu, P. Van Duppen, C. Volpe, D. Voulot, P. M. Walker, E. Wildner, N. Winckler, D. F. A. Winters, A. Wolf, H. S. Xu, A. Yakushev, T. Yamaguchi, Y. J. Yuan, Y. H. Zhang, and K. Zuber
Storage ring at HIE-ISOLDE Technical design report
Eur. Phys. J. ST, 207 :1 (May 2012)
Abstract:
We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.
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J. Habib, O. Guilbaud, B. Zielbauer, D. Zimmer, M. Pittman, S. Kazamias, C. Montet, T. Kühl, and D. Ros
Low energy prepulse for 10 Hz operation of a soft-x-ray laser
Opt. Express, 20 :10128 (April 2012)
Abstract:
The influence on Nickel-like Molybdenum soft-x-ray laser performance and stability of a low energy laser prepulse arriving prior to the main laser pumping pulses is experimentally investigated. A promising regime for 10 Hz operation has been observed. A four times increase in soft-x-ray laser operation time with a same target surface is demonstrated. This soft-x-ray laser operation mode corresponds to an optimum delay between the prepulse and the main pulses and to a prepulse energy greater than 20 mJ. We also show that this regime is not associated with a weaker degradation of the target or any reduced ablation rate. Therefore the role of preplasma density gradient in this effect is discussed.
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J. Rothhardt, S. Demmler, S. Hädrich, J. Limpert, and A. Tünnermann
Octave-spanning OPCPA system delivering CEP-stable few-cycle pulses and 22 W of average power at 1 MHz repetition rate
Opt. Express, 20 :10870 (April 2012)
Abstract:
We report on an OPCPA system delivering CEP-stable pulses with a pulse duration of only 1.7 optical cycles at 880 nm wavelength. This pulse duration is achieved by the generation, optical parametric amplification and compression of a full optical octave of bandwidth. The system is pumped by a high average power Yb-fiber laser system, which allows for operation of the OPCPA at up to 1 MHz repetition rate and 22 W of average output power. Further scaling towards single-cycle pulses, higher energy and output power is discussed.
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T. Rathje, N. Johnson, M. Möller, F. Süssmann, D. Adolph, M. Kübel, R. Kienberger, M. F. Kling, G.G. Paulus, and A. M. Sayler
Review of attosecond resolved measurement and control via carrier-envelope phase tagging with above-threshold ionization
J. Phys. B, 45 :074003 (April 2012)
Abstract:
A precise, real-time, single-shot carrier–envelope phase (CEP) tagging technique for few-cycle pulses was developed and combined with cold-target recoil-ion momentum spectroscopy and velocity-map imaging to investigate and control CEP-dependent processes with attosecond resolution. The stability and precision of these new techniques have allowed for the study of intense, few-cycle, laser-matter dynamics with unprecedented detail. Moreover, the same stereo above-threshold ionization (ATI) measurement was expanded to multi-cycle pulses and allows for CEP locking and pulse-length determination. Here we review these techniques and their first applications to waveform characterization and control, non-sequential double ionization of argon, ATI of xenon and electron emission from SiO_2 nanospheres.
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J. Limpert, F. Stutzki, F. Jansen, H.-J. Otto, T. Eidam, C. Jauregui, and A. Tünnermann
Yb-doped large-pitch fibres: effective single-mode operation based on higher-order mode delocalisation
Light Sci. Appl., 1 :e8 (April 2012)
Abstract:
Rare earth-doped fibres are a diode-pumped, solid-state laser architecture that is highly scalable in average power. The performance of pulsed fibre laser systems is restricted due to nonlinear effects. Hence, fibre designs that allow for very large mode areas at high average powers with diffraction-limited beam quality are of enormous interest. Ytterbium-doped, rod-type, large-pitch fibres (LPF) enable extreme fibre dimensions, i.e., effective single-mode fibres with mode sizes exceeding 100 times the wavelength of the guided radiation, by exploiting the novel concept of delocalisation of higher-order transverse modes. The non-resonant nature of the operating principle makes LPF suitable for high power extraction. This design allows for an unparalleled level of performance in pulsed fibre lasers.
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F. Stutzki, F. Jansen, A. Liem, C. Jauregui, J. Limpert, and A. Tünnermann
26 mJ, 130 W Q-switched fiber-laser system with near-diffraction-limited beam quality
Opt. Lett., 37 :1073 (March 2012)
Abstract:
We demonstrate a Q-switched fiber laser system emitting sub-60 ns pulses with 26 mJ pulse energy and near-diffraction-limited beam quality (M^2 < 1.3). In combination with a repetition rate of 5 kHz, a corresponding average output power of 130 W is achieved. This record performance is enabled by a large-pitch fiber with a core diameter of 135 µm. This fiber allows for effective single-mode operation with mode field diameters larger than 90 µm even at average output powers exceeding 100 W.
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