Wideband dispersion-free THz waveguide platform

Abstract We present a versatile THz waveguide platform for frequencies between 0.1 THz and 1.5 THz, designed to exhibit vacuum-like dispersion and electric as well as magnetic field enhancement. While linear THz spectroscopy benefits from the extended interaction length in combination with moderate losses, nonlinear THz spectroscopy profits from the field enhancement and zero dispersion, with the associated reshaping-free propagation of broadband single- to few-cycle THz pulses. Moreover, the vacuum-like dispersion allows for velocity matching in mixed THz and visible to infrared pump-probe experiments. The platform is based on the motif of a metallic double ridged waveguide. We experimentally characterize essential waveguide properties, for instance, propagation and bending losses, but also demonstrate a junction and an interferometer, essentially because those elements are prerequisites for THz waveform synthesis, and hence, for coherently controlled linear and nonlinear THz interactions

New methods for theranostic radioisotope production with solid targets at the Bern medical cyclotron

The production of theranostic radionuclides using solid targets is challenging and requires an accurate knowledge of the production crosssections as well as the energy, positioning and focusing of the beam. A research program is ongoing at the 18 MeV Bern medical cyclotron, equipped with a Solid Target Station (STS) and a 6 m Beam Transfer Line (BTL) ending in a separate bunker with independent access. A novel target coin was designed and built to irradiate compressed powder pellets, together with a compact focalization system to optimize the irradiation procedure. Furthermore, methods were developed to measure the beam energy, the production cross-sections and the EoB-activity

Time-resolved THz Stark spectroscopy of molecules in solution

Abstract For decades, it was considered all but impossible to perform Stark spectroscopy on molecules in a liquid solution, because their concomitant orientation to the applied electric field results in overwhelming background signals. A way out was to immobilize the solute molecules by freezing the solvent. While mitigating solute orientation, freezing removes the possibility to study molecules in liquid environments at ambient conditions. Here we demonstrate time-resolved THz Stark spectroscopy, utilizing intense single-cycle terahertz pulses as electric field source. At THz frequencies, solute molecules have no time to orient their dipole moments. Hence, dynamic Stark spectroscopy on the time scales of molecular vibrations or rotations in both non-polar and polar solvents at arbitrary temperatures is now possible. We verify THz Stark spectroscopy for two judiciously selected molecular systems and compare the results to conventional Stark spectroscopy and first principle calculations