Publications

arXiv (2021)

Strong-field photoemission from nanostructures and the associated temporally modulated currents play a key role in the development of ultrafast vacuum optoelectronics. Optical light fields could push their operation bandwidth into the petahertz domain. A critical aspect for their functionality in the context of applications is the role of charge interactions, including space charge effects. Here, we investigated the photoemission and photocurrents from nanometric tungsten needle tips exposed to carrier-envelope phase-controlled few-cycle laser fields. We report a characteristic step-wise increase in the intensity-rescaled cutoff energies of emitted electrons beyond a certain intensity value. By comparison with simulations, we identify this feature as the onset of charge-interaction dominated photoemission dynamics. Our results are anticipated to be relevant also for the strong-field photoemission from other nanostructures, including photoemission from plasmonic nano-bowtie antennas used in carrier-envelope phase-detection and for PHz-scale devices.

Optica (2020)

We demonstrate a novel method to measure the temporal electric field evolution of ultrashort laser pulses. Our technique is based on the detection of transient currents in air plasma. These directional currents result from subcycle ionization of air with a short pump pulse and the steering of the released electrons with the pulse to be sampled. We assess the validity of our approach by comparing it with different state-of-the-art laser-pulse characterization techniques. Notably, our method works in ambient air and facilitates a direct measurement of the field waveform, which can be viewed in real time on an oscilloscope in a similar way as a radio frequency signal.

arXiv (2020)

Multiphoton excitation of a solid by a few-cycle, intense laser pulse forms a very non-equilibrium distribution of charge carriers, where occupation probabilities do not necessarily decrease with energy. We show that, under certain conditions, significant population inversion can emerge between pairs of valence- or conduction-band states, where transitions between the Bloch states are dipole-allowed. This population inversion leads to stimulated emission in a laser-excited solid at frequencies where the unperturbed solid is transparent. We establish the optimal conditions for observing the strong-field-induced optical gain.

Optica (2020)

The ability to measure and control the carrier–envelope phase (CEP) of few-cycle laser pulses is of paramount importance for both frequency metrology and attosecond science. Here, we present a phase meter relying on CEP-dependent photocurrents induced by circularly polarized few-cycle pulses focused between electrodes in ambient air. The new device facilitates compact, single-shot CEP measurements under ambient conditions and promises CEP tagging at repetition rates orders of magnitude higher than most conventional CEP detection schemes, as well as straightforward implementation at longer wavelengths.

Conference on Lasers and Electro-Optics (2020)

We demonstrate an attosecond one-photon photoconductive switch by injecting conduction band carriers in dielectrics using vacuum-ultraviolet light pulses. Femtosecond pulse- driven currents reveal intra- and inter-band conduction band carrier dynamics.

Nature Communications (2020)

The sub-cycle interaction of light and matter is one of the key frontiers of inquiry made accessible by attosecond science. Here, we show that when light excites a pair of charge carriers inside of a solid, the transition probability is strongly localized to instants slightly after the extrema of the electric field. The extreme temporal localization is utilized in a simple electronic circuit to record the waveforms of infrared to ultraviolet light fields. This form of petahertz-bandwidth field metrology gives access to both the modulated transition probability and its temporal offset from the laser field, providing sub-fs temporal precision in reconstructing the sub-cycle electronic response of a solid state structure.

Nonlinear Optics (NLO) (2019)

We demonstrate that non-linear excitation in solids can be used for the charge control with attosecond precision and for the sampling of optical waveforms in ambient conditions, covering spectral range from ultra-violet to far-infrared.

Advances in Ultrafast Condensed Phase Physics (2018)

We present a new technique to measure electric fields over a 1 PHz bandwidth spanning the infrared to ultraviolet with sub-femtosecond temporal resolution via the sub-cycle control of injected charge carriers in dielectric media. The fidelity of the reconstructed electric fields are benchmarked against attosecond streaking and electro-optic sampling and provide detailed information about the temporal evolution of the charge carrier density in materials exposed to strong laser fields. The resulting optoelectronic technique allows for many methods of attosecond physics to be applied to a compact, table-top measurement, without necessitating the generation of attosecond XUV pulses.

Physical Review A (2018)

High-order-harmonic generation by a highly nonlinear interaction of infrared laser fields with matter allows for the generation of attosecond pulses in the XUV spectral regime. This process, well established for atoms, has been recently extended to the condensed phase. Remarkably well-pronounced harmonics up to order ∼30 have been observed for dielectrics. We establish a route toward an ab initio multiscale simulation of solid-state high-order-harmonic generation. We find that mesoscopic effects of the extended system, in particular the realistic sampling of the entire Brillouin zone, the pulse propagation in the dense medium, and the inhomogeneous illumination of the crystal, have a strong effect on the harmonic spectra. Our results provide an explanation for the formation of clean harmonics and have implications for a wide range of nonlinear optical processes in dense media.

Ruhr-Universität Bochum (2016)

In this work we experimentally investigated strong IR and THz electric field light-matter interaction with semiconductor and dielectric solids. During the strong-field IR experiments we observed a generation of a new spectrum for crystalline and polycrystalline diamond samples. In case of the strong THz experiments, 3 types of non-linear phenomenon were observed: THz-inducedchange of a refractive index, generation of a new spectrum and anomalous THzinduced absorption. It was found that the observed non-linear effects strongly depend on the sample and its orientation. We also investigated a relevance of ponderomotive energy concept for strong THz field interactions, and concluded that the magnitude of the electric field is probably more relevant quantity for description of the new spectra generation in case of the strong-field interactions.