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Abstract: We present a high harmonic generation source driven by a nonlinearly compressed fiber laser system resulting in a record high photon flux of 1011 photons/s in single harmonics from 50- 70 eV. This unique property of the HHG source is underlined by static T-MOKE experiments with permalloy samples.
Keywords: Ultrafast nonlinear optics, Multiharmonic generation, Lasers, fiber
Published in RUNG: 08.08.2018; Views: 5259; Downloads: 0
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Abstract: The Cherenkov Telescope Array (CTA) will be the next-generation gamma-ray observatory, investigating gamma-ray and cosmic ray astrophysics at energies from 20 GeV to more than 300 TeV. The observatory, consisting of large arrays of imaging atmospheric Cherenkov telescopes in both the southern and northern hemispheres, will provide full-sky coverage and will achieve a sensitivity improved by up to an order of magnitude compared to existing instruments such as H.E.S.S., MAGIC and VERITAS. CTA is expected to discover hundreds of new TeV gammaray sources, allowing it to significantly advance our understanding of the origin of cosmic rays, to probe much larger distances in the universe, and to search for WIMP dark matter with unprecedented sensitivity in TeV mass range. The development of CTA is being carried out by a worldwide consortium of scientists from 32 countries. Consortium scientists have developed the core scientific programme of CTA and institutes of the Consortium are expected to provide the bulk of the CTA components. The construction of CTA is overseen by the CTA Observatory that will in the future manage observatory operations, the guest observer programme, and data dissemination. This talk will review the scientific motivation for CTA, focusing on the key science projects that form the core programme of research. The talk will outline the design of CTA, including the science drivers, overall concept, performance optimization, and array layouts. The current status of CTA, including sites, prototype telescope progress, and steps forward will also be described.
Keywords: CTA, next-generation gamma-ray observatory, gamma rays
Published in RUNG: 16.02.2018; Views: 5752; Downloads: 145
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Abstract: Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800 nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400 nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800 nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to <150 meV while preserving excellent time resolution of about 30 fs.
Keywords: angle-resolved photoemission spectroscopy, ARPES, high harmonic generation, ultrafast surface science
Published in RUNG: 20.04.2017; Views: 6750; Downloads: 0
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Abstract: Capturing the dynamic electronic band structure of a correlated material presents a powerful capability for uncovering the complex couplings between the electronic and structural degrees of freedom. When combined with ultrafast laser excitation, new phases of matter can result, since far-from-equilibrium excited states are instantaneously populated. Here, we elucidate a general relation between ultrafast non-equilibrium electron dynamics and the size of the characteristic energy gap in a correlated electron material. We show that carrier multiplication via impact ionization can be one of the most important processes in a gapped material, and that the speed of carrier multiplication critically depends on the size of the energy gap. In the case of the charge-density wave material 1T-TiSe 2 , our data indicate that carrier multiplication and gap dynamics mutually amplify each other, which explains—on a microscopic level—the extremely fast response of this material to ultrafast optical excitation. Self-amplified photo-induced gap quenching in a correlated electron material. Available from: https://www.researchgate.net/publication/308804379_Self-amplified_photo-induced_gap_quenching_in_a_correlated_electron_material [accessed Apr 20, 2017].
Keywords: high harmonic generation, charge-density wave material, 1T-TiSe2, non-equilibrium electron dynamics, ultrafast surface science
Published in RUNG: 20.04.2017; Views: 7159; Downloads: 0
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