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1. Ultra-intense few-cycle light fields

Light pulses with few-optical-cycle duration and precisely controlled fields reaching strengths of a few TV/m correspond to the state-of-the art of femtosecond laser technology. They allow the acceleration of free electrons almost to the speed of light in vacuum within a fraction of an optical cycle and the steering of these relativistic electrons with the tailored electric and magnetic fields. This way, they enable the investigation of laser-plasma interaction from a novel perspective and the generation of few-femtosecond to attosecond electron and XUV / X-ray sources.

We synthesize these waveforms from two separate spectral regions to approach an octave spanning spectrum corresponding to sub-two optical-cycle pulse duration combined with pulse energies and intensities boosting the interaction to the relativistic realm (>10 W/cm ). Our light source is based on the optical parametric synthesizer principle and its main properties are:

Light Wave Synthesizer 100 (LWS100)

580 – 1020 nm spectrum
≤4.5 fs FWHM pulse duration
450-500 mJ energy
100 TW peak power
10 Hz repetition rate
1.2 µm FWHM focus size
≈10 W/cm intensity (corresponding to a ≈20)

We have another laser providing quasi-single cycle pulse duration with lower sub-mJ energy:

Femtopower Compact Pro

550 – 1000 nm spectrum
<4 fs FWHM pulse duration (corresponding to 1.5 optical cycles)
400 µJ energy
>0.1 TW peak power
1 kHz repetition rate

Further reading :

D. E. Rivas, A. Borot, D. E. Cardenas, G. Marcus, X. Gu, D. Herrmann, J. Xu, J. Tan, D. Kormin, G. Ma, W. Dallari, G. D. Tsakiris, I. B. Földes, S.-w. Chou, M. Weidman, B. Bergues, T. Wittmann, H. Schröder, P. Tzallas, D. Charalambidis, O. Raszkazovskaya, V. Pervak, F. Krausz, and L. Veisz, "Next Generation Driver of Attosecond and Laser-plasma Physics", Scientific Reports, Vol. 7, 5224 (2017).

D. Herrmann, C. Homann, R. Tautz, M. Scharrer, P. St. J. Russell, F. Krausz, L. Veisz, and E. Riedle, "Approaching the full octave: noncollinear optical parametric chirped pulse amplification with two-color pumping", Opt. Express, Vol. 18, 18752-18762 (2010).

D. Herrmann, L. Veisz, R. Tautz, F. Tavella, K. Schmid, V. Pervak, and F. Krausz, "Generation of sub-three-cycle, 16 TW light pulses by using noncollinear optical parametric chirped-pulse amplification", Opt. Lett., Vol. 34, No. 16, 2459-2461 (2009).

J. M. Mikhailova, A. Buck, A. Borot, K. Schmid, C. M. S. Sears, G. D. Tsakiris, F. Krausz, and L. Veisz, "Ultrahigh-contrast few-cycle pulses for multipetawatt-class laser technology", Opt. Lett., Vol. 36, 3145-3147 (2011).

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2. Intense and isolated attosecond pulses for nonlinear

spectroscopy

The appearance and tremendous development of attosecond physics during the last slightly more than a decade lead to the next generation temporal metrology. A novel source is established of the shortest pulses ever created based on high-harmonic generation in gas media. Furthermore, various applications have been demonstrated to explore time-resolved electron dynamics (mainly) of the valence electrons. Nowadays, one of the main limitations of this technology to investigate even core electron dynamics is the low energy (photon number) of the generated XUV pulses.

We utilize our Light Wave Synthesizer 20 to generate about two orders-of-magnitude more intense isolated attosecond pulses in the 100 eV regime in neon gas than conventional kHz systems are capable of. To this end we developed a folded 40-m long vacuum beamline that allows loose focusing of the laser pulses into a gas source, where the harmonics are generated. The characterization of these intense XUV pulses and their first application for nonlinear attosecond physics has also been performed. The two-photon absorption around 93 eV and 115 eV photon energy has been observed in the inner orbital shells of xenon. This achievement opens the door for observing the ultrafast motion of electrons deep inside atoms.

Further reading :

D. E. Rivas, B. Major, M. Weidman, W. Helml, G. Marcus, R. Kienberger, D. Charalambidis, P. Tzallas, E. Balogh, K. Kovács, V. Tosa, B. Bergues, K. Varjú, and L. Veisz; Propagation-enhanced generation of intense high-harmonic continua in the 100-eV spectral region, Optica, Vol. 5, 1283 (2018).

B. Bergues, D. E. Rivas, M. Weidman, A. A. Muschet, W. Helml, A. Guggenmos, V. Pervak, U. Kleineberg, G. Marcus, R. Kienberger, D. Charalambidis, P. Tzallas, H. Schröder, F. Krausz, and L. Veisz; Tabletop nonlinear optics in the 100-eV spectral region, Optica, Vol.5, 237 (2018).

https://doi.org/10.1364/OPTICA.5.000237

3. Relativistic attosecond physics

Light-matter interaction beyond a certain intensity level (~10 W/cm ) naturally leads to the ionization of the material and the generation of ions and free electrons. These electrons quiver / oscillate in the field of the laser. Further increasing the light intensity at another certain limit (beyond ~10 W/cm at 800 nm laser wavelength) the free electrons are accelerated within portion of an optical cycle almost to the speed of light in vacuum and oscillate relativistically. The effect of the magnetic component of the laser field on these relativistic electrons compared to the electric component becomes significant. Our ultra-intense sub-two-cycle light source (LWS-20) generates intensities even much beyond this threshold. Its controlled fields steer relativistic electron motion in collective (electron plasma waves) as well as individual (vacuum laser acceleration) manner with attosecond precision. This way a new generation of ultra-brilliant electron and X-ray sources is realized with attosecond temporal duration in tailored experiments for possible industrial, medical and scientific applications.

3A. Intense attosecond light source

Generation of high-order harmonics from the relativistic interaction of few-cycle laser light with solid density plasmas is a promising, but challenging source of isolated attosecond pulses with unprecedented energies in the tens of µJ range and beyond as well as very high photon energy in the keV range. We are investigating this interaction regime with LWS-20 as driver laser to develop the first relativistic source of isolated attosecond pulses.

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Further reading :

Y. Nomura, R. Hörlein, P. Tzallas, B. Dromey, S. Rykovanov, Zs. Major, J. Osterhoff, S. Karsch, L. Veisz, M. Zepf, D. Charalambidis, F. Krausz, and G. D. Tsakiris, "Attosecond phase locking of harmonics emitted from laser-produced plasmas", Nature Phys., Vol. 5, 124-128 (2009).

P. Heissler, R. Hörlein, J. M. Mikhailova, L. Waldecker, P. Tzallas, A. Buck, K. Schmid, C. M. S. Sears, F. Krausz, L. Veisz, M. Zepf, and G. D. Tsakiris, "Few-cycle driven relativistically oscillating plasma mirrors: a source of intense isolated attosecond pulses", Phys. Rev. Lett., Vol. 108, 235003 (2012).

Dmitrii Kormin, Antonin Borot, Guangjin Ma, William Dallari, Boris Bergues, Márk Aladi, István B. Földes, and Laszlo Veisz, "Spectral interferometry with waveform-dependent relativistic high-order harmonics from plasma surfaces", Nature Communications, Vol. 9, 4992 (2018).

https://doi.org/10.1038/s41467-018-07421-5

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3B. Sub-two-cycle-driven relativistic electron source

Relativistic laser-plasma interactions provide uniquely short electron bunches in the few-MeV to few-GeV energy regime. We intend to advance laser-based electron acceleration towards 1-fs to attosecond durations with few MeV to few tens of MeV energy, characterize the electron pulses and apply them for diffraction/microscopy with few-femtosecond resolution and to generate attosecond X-ray sources.

Further reading :

K. Schmid, L. Veisz, F. Tavella, S. Benavides, R. Tautz, D. Herrmann, A. Buck, B. Hidding, A. Marcinkevicius, U. Schramm, M. Geissler, J. Meyer-ter-Vehn, D. Habs, and F. Krausz "Few-Cycle Laser-Driven Electron Acceleration", Phys. Rev. Lett., Vol. 102, 124801 (2009).

A. Buck, M. Nicolai, K. Schmid, C. M. S. Sears, A. Sävert, J. M. Mikhailova, F. Krausz, M. C. Kaluza, and L. Veisz, "Real-time observation of laser-driven electron acceleration", Nature Phys., Vol. 7, 543-548 (2011).

A. Buck, J.Wenz, J. Xu, K. Khrennikov, K. Schmid, M. Heigoldt, J. M. Mikhailova, M. Geissler, B. Shen, F. Krausz, S. Karsch, and L. Veisz, "Shock-front injector for high-quality laser-plasma acceleration", Phys. Rev. Lett., Vol. 110, 185006 (2013).

D. E. Cardenas, T. M. Ostermayr, L. Di Lucchio, L. Hofmann, M. F. Kling, P. Gibbon, J. Schreiber, and L. Veisz; Sub-cycle dynamics in relativistic nanoplasma acceleration, Scientific Reports 9:7321 (2019).