arXiv subjects

Akos Hoffmann

Publications and source records attributed to Akos Hoffmann.

5 recordsLinked to original sources

arXiv2026

Two-phase driving of a linear radio-frequency ion trap

A linear radio-frequency Paul trap is traditionally driven with one diagonal pair of electrodes grounded and the other connected to a high-voltage radio-frequency source. This method simplifies impedance matching of the voltage source to the trap. However, for several architectures it leads to increasing the axial micromotion amplitude, for example, when the capacitance between radio-frequency and end-cap electrodes is not negligible. Here, we present a technique to generate two high-voltage radio-frequency signals \SI{180}{\degree} out of phase to drive a linear Paul trap with opposite voltages between neighbouring electrodes. Using this, we have successfully trapped and cooled a chain of Ytterbium ions in a linear radio-frequency Paul trap.

quant-ph↗

arXiv2014

A flux calibration device for the SuperNova Integral Field Spectrograph (SNIFS)

Observational cosmology employing optical surveys often require precise flux calibration. In this context we present SNIFS Calibration Apparatus (SCALA), a flux calibration system developed for the SuperNova Integral Field Spectrograph (SNIFS), operating at the University of Hawaii 2.2 m telescope. SCALA consists of a hexagonal array of 18 small parabolic mirrors distributed over the face of, and feeding parallel light to, the telescope entrance pupil. The mirrors are illuminated by integrating spheres and a wavelength-tunable (from UV to IR) light source, generating light beams with opening angles of 1 degree. These nearly parallel beams are flat and flux-calibrated at a subpercent level, enabling us to calibrate our "telescope + SNIFS system" at the required precision.

astro-ph.IM↗

arXiv2013

A large-area single photon sensor employing wavelength-shifting and light-guiding technology

Large-scale underground water-Cherenkov neutrino observatories rely on single photon sensors whose sensitive area for Cherenkov photons one wants to maximise. Low dark noise rates and dense module spacing will thereby allow to substantially decrease the energy threshold in future projects. We describe a feasibility study of a novel type of single photon sensor that employs organic wavelength-shifting material (WLS) to capture Cherenkov photons and guide them to a PMT readout. Different WLS materials have been tested in lab measurements as candidates for use in such a sensor and photon capture efficiencies as high as 50 % have been achieved. Based on these findings we estimate that the effective photosensitive area of a prototype built with existing technology can easily exceed that of modules currently used e. g. in IceCube. Additionally, the dark noise rate of such a module can be exceptionally low in the order of 10 Hz. This is of special importance when targeting low-energy neutrinos that yield only few photons that need to be distinguished from noise hits.

astro-ph.IM↗

arXiv2009

Depth Resolution of Piezoresponse Force Microscopy

Given that a ferroelectric domain is generally a three dimensional entity, the determination of its area as well as its depth is mandatory for full characterization. Piezoresponse force microscopy (PFM) is known for its ability to map the lateral dimensions of ferroelectric domains with high accuracy. However, no depth profile information has been readily available so far. Here, we have used ferroelectric domains of known depth profile to determine the dependence of the PFM response on the depth of the domain, and thus effectively the depth resolution of PFM detection.

cond-mat.mtrl-sci↗

arXiv2007

Impact of elasticity on the piezoresponse of adjacent ferroelectric domains investigated by scanning force microscopy

As a consequence of elasticity, mechanical deformations of crystals occur on a length scale comparable to their thickness. This is exemplified by applying a homogeneous electric field to a multi-domain ferroelectric crystal: as one domain is expanding the adjacent ones are contracting, leading to clamping at the domain boundaries. The piezomechanically driven surface corrugation of micron-sized domain patterns in thick crystals using large-area top electrodes is thus drastically suppressed, barely accessible by means of piezoresponse force microscopy.

cond-mat.mtrl-sci↗