Contribution to a book

Due to improvements of the performance of FELs, the measurements of the beam’s slice energy spread is becoming increasingly important for optimization of the brightness. Of particular interest are measurements of the uncorrelated energy spread near the gun as this determines the lower limit of the energy spread for the rest of the machine. [...]

Frequency conversion in nonlinear crystals is a well-established method to provide narrowband, multicycle terahertz (THz) radiation for applications requiring high spectral purity like spectroscopy and electron acceleration [1], [2]. While significant progress has been made by using laser systems that produce pairs of narrow spectral lines separated by the THz frequency, optical-to- THz conversion efficiencies still remain below one percent [3], [4]. [...]

Low efficiencies for narrowband optical-to-terahertz down-conversion remain a primary limiting factor for many applications of intense, laser-driven terahertz (THz) sources, highly sought after in material science and THz acceleration. Although simulations predict improvements in efficiency by using tailored trains of laser pulses as a driver, few studies have targeted this configuration. [...]

A main limitation for many applications of laser-driven sources of narrowband terahertz (THz) radiation in spectroscopy and particle acceleration is the low optical-to-THz conversion efficiency. Due to power limitations, it is often necessary to use small sizes of the optical pump beam in the range of the THz wavelength to achieve sufficient intensity to effectively drive the nonlinear process. [...]

Efficiencies of nonlinear optical-to-terahertz (THz) conversion below one percent remain a limiting factor for applications of multicycle THz radiation like THz-driven acceleration and inspired the use of multi-line pump spectra. To overcome the difficulty of phase stabilization of multiple narrowband sources required by the multi-line approach, we exploit its temporal analog, i.e., regular pulse trains with THz repetition rate, in which the THz waves generated by rectifying the individual pulses add coherently. [...]

The misalignment mechanism for axion-like particles (ALPs) is a leading explanation for dark matter. In this work we investigate ALPs with non-periodic potentials, which allow for large misalignment of the field from the minimum and make it possible for ALPs to match the relic density of dark matter in a large part of the parameter space. [...]

During the fibrillation process amyloid proteins undergo structural changes at very different length and time scales. Small angle X-ray scattering (SAXS) is a method that is uniquely suitable for the structural analysis of this process [...]

Deviations in the trilinear self-coupling of the Higgs boson at 125 GeV from the Standard Model (SM) prediction are a sensitive test of physics Beyond the SM (BSM). The LHC experiments searching for the simultaneous production of two Higgs bosons start to become sensitive to such deviations. [...]