Technische Universität Wien

Free-space optical communications on CubeSats require precise pointing mechanisms to maintain stable links. State-of-the-art CubeSat-sized laser communication terminals rely on satellite body pointing, which imposes constraints on system flexibility. This paper presents the proposed control strategy of a gimbaled-prism-based coarse pointing assembly for hemispherical pointing in CubeSat optical communications. The gimbal design employs a compact mechanical structure with direct-drive actuation for azimuth and elevation control. A hierarchical control strategy is implemented, combining a cascaded servo control loop with an s-curve profiler for ephemeris-based pointing and a second-order trajectory controller for fine pointing assembly offloading. Therefore, the dynamics of the low-level controller can be decoupled from the trajectory control design. The performed experimental validation includes hardware characterization, system response identification, and closed-loop performance analysis, demonstrating the capability to achieve accurate and stable pointing of the developed coarse pointing assembly. Results confirm that the proposed approach meets stringent dynamics and stability requirements while maintaining a pointing accuracy suitable for CubeSat optical communication applications.

In this work, we explore the scheme of attosecond quantum interferometry (AQI), the quantum optical version of classical attosecond interferometry, which allows to measure quantum optical properties on the attosecond time-scale. We develop how the scheme of AQI can be used for engineering the phase-space and photon statistics properties of the emitted harmonics, using the relative phase of a two-color driving field as a control, and further enables to manipulate the field correlations as well as their entanglement characteristics. In addition, this scheme allows us to learn properties of the phase-space distribution of the harmonic quantum state, by means of measuring an attosecond quantum tomography trace. This serves as a new type of protocol for in situ attosecond measurements of quantum optical observables. With this, we achieve to further connect all-optical attosecond measurement schemes with quantum optics, allowing for a rich manifold of observations.

Insulating oxides are among the most abundant solid materials in the universe 1–3 . Of the many ways in which they influence natural phenomena, perhaps the most consequential is their capacity to transfer electrical charge during contact 4–10 —which occurs even between samples of the same oxide—yet the symmetry-breaking parameter that causes this remains unidentified 11,12 . Here we show that adventitious carbonaceous molecules adsorbed from the environment are the symmetry-breaking factor in same-material oxide contact electrification (CE). We use acoustic levitation to measure charge exchange between a sphere and a plate composed of identical amorphous silicon dioxide (SiO 2 ). Although charging polarity is random for co-prepared samples, we control it with baking or plasma treatment. Observing the charge-exchange relaxation afterwards, we see dynamics over a timescale of hours and connect this directly to the presence of adventitious carbon with time-of-flight mass spectrometry, low-energy ion scattering and infrared spectroscopy. Going further, we confirm that adventitious carbon can even determine charge exchange among different oxides. Our results identify the symmetry-breaking parameter that causes insulating oxides to exchange charge in settings ranging from desert sands 4 to volcanic plumes 5,6 , while simultaneously highlighting an overlooked factor in CE more broadly.