Laser excitation of the 1-2 transition in singly-ionized helium.

Laser spectroscopy of atomic hydrogen and hydrogen-like atoms is a powerful tool for tests of fundamental physics. The 1-2 transition of hydrogen in particular is a cornerstone for stringent Quantum Electrodynamics (QED) tests and for an accurate determination of the Rydberg constant. We report laser excitation of the 1-2 transition in singly-ionized helium (He), a hydrogen-like ion with much higher sensitivity to QED than hydrogen itself.

A simple graphics processing unit-accelerated propagation routine for laser pulses in the strong-field regime.

We present a simple and easy-to-implement Graphics Processing Unit (GPU)-accelerated routine to numerically simulate the propagation of ultrashort and intense laser pulses as they interact with a medium. The routine is based on the solution of Maxwell's wave equation in the frequency domain with an extended Crank-Nicolson algorithm implemented in the Nvidia CUDA C++ programming language. The main advantages of our method are its significant speed-up factor and its ease of implementation, requiring only basic knowledge of CUDA and C++.

Characterizing post-compression of mJ-level ultrafast pulses via loose focusing in a gas cell.

The ability to generate high-intensity ultrashort laser pulses is a key driver for advancing the strong-field physics and its applications. Post-compression methods aim to increase the peak intensity of amplified laser pulses via spectral broadening through self-phase modulation (SPM), followed by temporal pulse compression. However, other unavoidable nonlinear self-action effects, which typically occur parallel to SPM, can lead to phase distortions and beam quality degradation.

Sub-cycle dynamics in two-color high-harmonic generation from laser-produced plasmas.

We present high-order harmonic generation (HHG) in laser-produced aluminium and tin plasmas driven by a two-color field with orthogonal polarization, leading to the generation of both odd and even harmonics. We shape the effective drive field with sub-cycle resolution by controlling the phase between the fundamental wave and its second harmonic. The shape of the drive field influences the electron trajectories of the various harmonics generated in these plasmas.

Pauli blocking of stimulated emission in a degenerate Fermi gas.

The Pauli exclusion principle in quantum mechanics has a profound influence on the structure of matter and on interactions between fermions. Almost 30 years ago it was predicted that the Pauli exclusion principle could lead to a suppression of spontaneous emission, and only recently several experiments confirmed this phenomenon. Here we report that this so-called Pauli blockade not only affects incoherent processes but also, more generally, coherently driven systems.