Search Results
Transition from ballistic to drift motion in high-field transport in GaAs
2013, Bowlan, P., Kuehn, W., Reimann, K., Woerner, M., Elsaesser, T., Hey, R., Flytzanis, C.
With strong THz pulses, we measure ultrafast transport of electrons, holes, and an electron-hole plasma in GaAs. The transition from ballistic to drift-like transport is strongly influenced by electron-hole scattering.
Mikrooptische Dünnschicht-Komponenten zur Effizienzverbesserung der Kollimation von Diodenlaser-Arrays (MDK)
2002, Nerreter, S., Seewald, G., Fischer, A., Neumann, U., Tischer, M., Grunwald, R.
[no abstract available]
Generation of terahertz radiation from ionizing two-color laser pulses in Ar filled metallic hollow waveguides
2010, Babuškin, Ihar, Skupin, Stefan, Herrmann, Joachim
The generation of THz radiation from ionizing two-color femtosecond pulses propagating in metallic hollow waveguides filled with Ar is numerically studied. We observe a strong reshaping of the low-frequency part of the spectrum. Namely, after several millimeters of propagation the spectrum is extended from hundreds of GHz up to 150 THz. For longer propagation distances, nearly single-cycle near-infrared pulses with wavelengths around 4.5 μm are obtained by appropriate spectral filtering, with an efficiency of up to 0.25 %.
Adjustable pulse compression scheme for generation of few-cycle pulses in the mid-infrared
2014, Demircan, Ayhan, Amiranashvili, Shalva, Brée, Carsten, Morgner, Uwe, Steinmeyer, Günter
An novel adjustable adiabatic soliton compression scheme is presented, enabling a coherent pulse source with pedestal-free few-cycle pulses in the infrared or mid-infrared regime. This scheme relies on interaction of a dispersive wave and a soliton copropagating at nearly identical group velocities in a fiber with enhanced infrared transmission. The compression is achieved directly in one stage, without necessity of an external compensation scheme. Numerical simulations are employed to demonstrate this scheme for silica and fluoride fibers, indicating ultimate limitations as well as the possibility of compression down to the single-cycle regime. Such output pulses appear ideally suited as seed sources for parametric amplification schemes in the mid-infrared.
Schlussbericht vom 10.08.2004 zum Thema: Verbundprojekt: Aufbau und Test eines Messstandes zur Untersuchung gespeicherter Nanopartikel mit Synchrotronstrahlung : bmb+f-Förderschwerpunkt Kondensierte Materie, Großgeräte der physikalischen Grundlagenforschung
2004, Widdra, Wolf
[no abstract available]
Tailoring THz radiation by controlling tunnel photoionization events in gases
2011, Babushkin, Ihar, Skupin, Stefan, Husakou, Anton, Köhler, Christian, Cabrera-Granado, Eduardo, Bergé, Luc, Herrmann, Joachimj
Applications ranging from nonlinear terahertz spectroscopy to remote sensing require broadband and intense THz radiation which can be generated by focusing two-color laser pulses into a gas. In this setup, THz radiation originates from the buildup of the electron density in sharp steps of attosecond duration due to tunnel ionization, and subsequent acceleration of free electrons in the laser field. We show that the spectral shape of the THz pulses generated by this mechanism is determined by superposition of contributions from individual ionization events. This provides a straightforward analogy with linear diffraction theory, where the ionization events play the role of slits in a grating. This analogy offers simple explanations for recent experimental observations and opens new avenues for THz pulse shaping based on temporal control of the ionization events. We illustrate this novel technique by tailoring the spectral width and position of the resulting radiation using multi-color pump pulses.
Symmetry breaking and strong persistent plasma currents via resonant destabilization of atoms
2017, Brée, Carsten, Hofmann, Michael, Babushkin, Ihar, Demircan, Ayhan, Morgner, Uwe, Kosareva, Olga G., Savelev, Andrei B., Husakou, Anton, Ivanov, Misha
The ionization rate of an atom in a strong optical field can be resonantly enhanced by the presence of long-living atomic levels (so called Freeman resonances). This process is most prominent in the multiphoton ionization regime meaning that ionization event takes many optical cycles. Nevertheless, here we show that these resonances can lead to fast subcycle-scale plasma buildup at the resonant values of the intensity in the pump pulse. The fast buildup can break the cycletocycle symmetry of the ionization process, resulting in generation of persistent macroscopic plasma currents which remain after the end of the pulse. This, in turn, gives rise to a broadband radiation of unusual spectral structure forming a comb from terahertz (THz) to visible. This radiation contains fingerprints of the attosecond electronic dynamics in Rydberg states during ionization.
An ultrashort X-ray emission from gas clusters irradiated by ultrashort laser pulses : final report for the project FST-D-ISR-10 ; [Forscherverbund: German Israeli Cooperation in Ultrafast Laser Technologies (GILCULT)]
2004, MBI
[no abstract available]
Directionality of THz emission from photoinduced gas plasmas
2011, Köhler, Christian, Cabrera-Granado, Eduardo, Babushkin, Ihar, Bergé, Luc, Herrmann, Joachim, Skupin, Stefan
Forward and backward THz emission by ionizing two-color laser pulses in gas is investigated by means of a simple semi-analytical model based on Jefimenko's equation and rigorous Maxwell simulations in one and two dimensions. We find the emission in backward direction having a much smaller spectral bandwidth than in forward direction and explain this by interference effects. Forward THz radiation is generated predominantly at the ionization front and is thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model.
Ultrafast spatio-temporal dynamics of terahertz generation by ionizing two-color femtosecond pulses in gases
2010, Babushkin, Ihar, Kuehn, Wihelm, Köhler, Christian, Skupin, Stefan, Bergé, Luc, Reimann, Klaus, Woerner, Michael, Herrmann, Joachim, Elsaesser, Thomas
We present a combined theoretical and experimental study of spatio-temporal propagation effects in terahertz (THz) generation in gases using two-color ionizing laser pulses. The observed strong broadening of the THz spectra with increasing gas pressure reveals the prominent role of spatio-temporal reshaping and of a plasma-induced blue-shift of the pump pulses in the generation process. Results obtained from (3+1)-dimensional simulations are in good agreement with experimental findings and clarify the mechanisms responsible for THz emission.
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