arXiv subjects

Alexander Heidt

Publications and source records attributed to Alexander Heidt.

6 recordsLinked to original sources

arXiv2026

A tunable feedback-controlled magnetic trap for a magnet in free fall

Ferromagnets in free space are predicted to exhibit pure Larmor precession at near-zero magnetic fields and provide exceptional sensitivity for magnetometry and gyroscopy. Notably, pure Larmor precession has not been observed in a macroscopic ferromagnetic particle, despite its fundamental importance and potential for probing relativistic effects and dark-matter interactions. Realizing such dynamics requires true free fall to eliminate clamping losses and trap-induced systematics. A central challenge is designing a tunable trap that is weak enough to permit near-free evolution yet robust enough to withstand the disturbances of launch and release. Here, we propose and demonstrate a novel master proportional-integral-differential magnetic trap (MPIDMT) combining a PID-controlled coil system with a master control coil system. Implemented in the third-generation drop tower - Einstein-Elevator, during the microgravity phase the system stably levitates a ferromagnetic particle against shock accelerations up to 1.5 g and resolves its motion in both a low-field (0.4 g) configuration and in pure free fall. These results represent a key step toward free-fall ferromagnetic magnetometry, the long-sought direct observation of macroscopic Larmor precession, and future space-based experiments.

physics.atom-ph↗

arXiv2025

Dark Energy Search by Atom Interferometry in the Einstein-Elevator

The DESIRE project aims to test chameleon field theories as potential candidates for dark energy. The chameleon field is a light scalar field that is subject to screening mechanisms in dense environments making them hardly detectable. The project is designed to overcome this challenge. To this end, a specially designed source mass generates periodic gravitational and chameleon potentials. The design of the source mass allows for adjustment of the amplitude and periodicity of the gravitational potential while keeping the chameleon potential unchanged. The periodicity of the potentials makes them distinguishable from the environment and allows for resonant detection using multiloop atom interferometry under microgravity conditions.

physics.atom-ph↗

arXiv2021

Saturation-Aware Model Predictive Energy Management for Droop-Controlled Islanded Microgrids

In this paper, we propose a minimax model predictive control (MPC)-based energy management system that is robust with respect to uncertainties in renewable infeed and load. The MPC formulation includes a model of low-level droop control with saturation at the power and energy limits of the units. Robust MPC-based energy management systems tend to under-utilize the renewable energy sources to guarantee safe operation. In order to mitigate this effect, we further consider droop control of renewable energy sources. For a microgrid with droop-controlled units, we show that enhancing droop feedback with saturation enlarges the space of feasible control actions. However, the resulting controller requires to solve a mixed-integer problem with additional variables and equations representing saturation. We derive a computationally tractable formulation for this problem. Furthermore, we investigate the performance gained by using droop with saturation, renewable droop and combination of both in a case study.

math.OC↗

arXiv2020

Generalized spectral phase-only time-domain ptychographic phase reconstruction applied in nonlinear microscopy

Nonlinear microscopy has evolved over the last few decades to become a powerful tool for imaging and spectroscopic applications in biological sciences. In this study, I$^2$PIE, a novel spectral phase control technique, was implemented in order to compress broad-bandwidth supercontinuum light pulses generated in an all-normal-dispersion (ANDi) photonic crystal fiber (PCF). The technique, based on time-domain ptychography, is demonstrated here in a nonlinear microscopy application for the first time, to the best of our knowledge. The first real-world application of this technique for second-harmonic generation and two-photon excitation fluorescence microscopies in biological samples is presented. We further show that in our implementation, I$^2$PIE leads to improved contrast and signal-to-noise ratios in the generated images, compared to conventional compression techniques used in nonlinear microscopy.

physics.optics↗

arXiv2020

Implementation of temporal ptychography algorithm, I$^2$PIE, for improved single-beam coherent anti-Stokes Raman scattering measurements

We present an improvement on the signal-to-background of single-beam coherent anti-Stokes Raman scattering (SB-CARS) spectroscopy measurements for systems employing ultrafast supercontinuum sources based on all-normal dispersion photonic crystal fibers. Improvements to the signal-to-background arise in the use of a new pulse-reconstruction algorithm based on temporal ptychography, I$^2$PIE. A simple SB-CARS strategy is used to measure the spectrum of para-xylene, where the supercontinuum pulses used are compressed using multiphoton intrapulse interference phase scan (MIIPS) and, for the first time to the best of our knowledge, I$^2$PIE using the same single-beam setup. With the I$^2$PIE implementation, the signal-to-background is improved by nearly a factor of 4 in comparison with MIIPS. More notably, the integrated SB-CARS spectral intensity is increased by a factor of 6.5.

physics.optics↗

arXiv2018

Dispersion Measurement of Ultra-High Numerical Aperture Fibers covering Thulium, Holmium, and Erbium Emission Wavelengths

We present broadband group velocity dispersion (GVD) measurements of commercially available ultra-high numerical aperture fibers (UHNA1, UHNA3, UHNA4, UHNA7 and PM2000D from Coherent-Nufern). Although these fibers are attractive for dispersion management in ultrafast fiber laser systems in the 2 μm wavelength region, experimental dispersion data in literature is scarce and inconsistent. Here we demonstrate the measurements using the spectral interferometry technique covering the typically used erbium, thulium and holmium emission bands. The results are characterized in terms of the standard-deviation uncertainty and compared with previous literature reports. Fitting parameters are provided for each fiber allowing for the straightforward replication of the measured dispersion profiles. This work is intended to facilitate the design of ultrafast fiber laser sources and the investigations of nonlinear optical phenomena.

physics.ins-det↗