arXiv subjects

Tobias Kroh

Publications and source records attributed to Tobias Kroh.

3 recordsLinked to original sources

arXiv2021

Ultrafast electron diffractometer with Terahertz-driven pulse compression

Terahertz (THz)-based electron manipulation has recently been shown to hold tremendous promise as a technology for manipulating and driving the next-generation of compact ultrafast electron sources. Here, we demonstrate an ultrafast electron diffractometer with THz-driven pulse compression. The electron bunches from a conventional DC gun are compressed by a factor of 10 and reach a duration of ~180 fs (FWHM) with 10,000 electrons/pulse at a 1 kHz repetition rate. The resulting ultrafast electron source is used in a proof-of-principle experiment to probe the photoinduced dynamics of single-crystal silicon. The THz-compressed electron beams produce high-quality diffraction patterns and enable observation of the ultrafast structural dynamics with improved time resolution. These results validate the maturity of THz-driven ultrafast electron sources for use in precision applications.

physics.optics↗

arXiv2019

Full 3D+1 modelling of the tilted-pulse-front setups for single-cycle terahertz generation

The tilted-pulse-front setup utilizing a diffraction grating is one of the most successful methods to generate single- to few-cycle terahertz pulses. However, the generated terahertz pulses have a large spatial inhomogeneity, due to the noncollinear phase matching condition and the asymmetry of the prism-shaped nonlinear crystal geometry, especially when pushing for high optical-to-terahertz conversion efficiency. A 3D+1 (x,y,z,t) numerical model is necessary in order to fully investigate the terahertz generation problem in the tilted-pulse-front scheme. We compare in detail the differences between 1D+1, 2D+1 and 3D+1 models. The simulations show that the size of the optical beam in the pulse-front-tilt plane sensitively affects the spatio-temporal properties of the terahertz electric field. The terahertz electric field is found to have a strong spatial dependence such that a few-cycle pulse is only generated near the apex of the prism. The part of the beam farther from the apex contains a large fraction of the energy but has a waveform that deviates from a few-cycle. This strong spatial dependence must be accounted for when using the terahertz pulses for strong-field physics and carrier-envelope-phase sensitive experiments such as terahertz acceleration, coherent control of antiferromagnetic spin waves and terahertz high-harmonic generation.

physics.optics↗

arXiv2017

High-energy mid-infrared sub-cycle pulse synthesis from a parametric amplifier

High-energy, carrier-envelope phase (CEP)-stable, sub-cycle, mid-infrared (mid-IR) pulses can provide unique opportunities of exploring phase-sensitive strong-field light-matter interactions in atoms, molecules, and solids. In the mid-IR wavelength, the ponderomotive energy of laser pulses is dramatically increased (versus the visible/near-infrared) and, therefore, the Keldysh parameter is much smaller than unity even at relatively modest laser intensities. This enables to study the sub-cycle electron dynamics in solids via high-harmonic generation (HHG) without damage. One can also control the electron emissions from nano-devices in the sub-cycle time scale. These efforts are opening a great opportunity towards petahertz electronics. Here, we present a high-energy, sub-cycle pulse synthesizer based on a mid-IR optical parametric amplifier (OPA), pumped by CEP-stable, 2.1 um femtosecond pulses, and its application to HHG in solids. The signal and idler combined spectrum spans from 2.5 to 9.0 um, which covers the whole midwave-infrared (MWIR) region. We coherently synthesize the passively CEP-stable few-cycle signal and idler pulses to generate 33 uJ, 0.88-cycle (12.4 fs), multi-GW pulses centered at ~4.2 um, which is further energy scalable. The in-line synthesis of the CEP-stable sub-cycle pulse is realized through the type-I collinear OPA with minimal temporal walk-off. The MWIR sub-cycle pulse is used for driving HHG in thin silicon samples, producing harmonics up to ~19th order with a continuous spectral coverage due to the isolated emission by the sub-cycle driver. Our demonstration offers an energy scalable and technically simple platform of laser sources generating CEP-stable sub-cycle pulses in the whole MWIR region for investigating isolated phase-sensitive strong-field interactions in solids and gases.

physics.optics↗