arXiv subjects

Matthias C. Wapler

Publications and source records attributed to Matthias C. Wapler.

12 recordsLinked to original sources

arXiv2018

Diffraction-limited axial scanning in thick biological tissue employing an aberration correcting adaptive lens

Diffraction-limited focusing deep into biological tissue is challenging due to spherical aberrations that lead to a broadening of the focal spot particularly in axial direction. While the diffraction-limit can be restored employing aberration correction with a deformable mirror or spatial light modulator, a bulky optical setup results due to the required beam-folding. We propose a bi actor adaptive lens, that enables axial scanning and at the same time correction of specimen induced spherical aberrations while offering a compact setup. Using the bi-actor lens in a confocal microscope, we show diffraction limited axial scanning up to \SI{340}{\micro m} deep inside a phantom specimen. Applying this technique for in-vivo measurements of zebrafish embryos with reporter gene-driven fluorescence in the thyroid gland reveals substructures of thyroid follicles.

physics.optics↗

arXiv2016

Depth-controlled Bessel beams

We present a ring aperture with independently switchable segments for the three-dimensional control of quasi propagation invariant beams. We demonstrate that our liquid crystal design concept preserves coherence and generates the Bessel beam structure.

physics.optics↗

arXiv2016

Topological in-plane polarized piezo actuation for compact adaptive lenses with aspherical correction

In this contribution, we investigate the effects of using in-plane polarized piezo actuators with topological buckling displacement to drive glass-piezo composite membranes for adaptive lenses with aspherical control. We find that the effects on the focal power and aspherical tuning range are relatively small, whereas the tuning speed is improved significantly with a first resonance of 1 kHz for a 13 mm aperture lens.

physics.optics↗

arXiv2016

Single-Sided Contacting of Out-of-Plane Polarized Piezo Films for Fluid Membrane Lenses

We present an adaptive lens which tunes its focal length with a glass membrane that is deformed by an integrated piezo bending actuator. A particular challenge in the fabrication of this type of actuator is the need to contact the electrodes on both sides of the piezo element, i.e. also on the glass surface. Therefore, we show a novel contacting method where the top electrode on the piezo is segmented and the backside electrode is left at a floating potential. With this setup we achieve tuning capabilities of more than 13 dpt and response times in the range of less than 4 ms at a usable aperture of 4.5 mm.

physics.optics↗

arXiv2014

A compact, large-aperture tunable lens with adaptive spherical correction

In this paper, we present the proof of concept of a very fast adaptive glass membrane lens with a large aperture/diameter ratio, spherical aberration correction and integrated actuation. The membrane is directly deformed using two piezo actuators that can tune the focal length and the conical parameter. This operating principle allows for a usable aperture of the whole membrane diameter. Together with the efficient actuation mechanism, the aperture is around 2/3 of the total system diameter - at a thickness of less than 2mm. The response time is a few milliseconds at 12mm aperture, which is fast compared to similar systems.

physics.optics↗

arXiv2013

Focusing Mirror with Tunable Eccentricity

We present a new kind of varifocal mirror with independently adjustable curvatures in the major directions. For actuation we use two stacked piezo bending actuators with crossed in-plane polarization. This mirror can be used for example as an off-axis focusing device with tunable focal length and compensation for a variable angle of incidence or for coma correction. We demonstrate the prototype of such a mirror and characterize the mechanical deflection, as well as the focusing capabilities.

physics.optics↗

arXiv2012

Physical Response Functions of Strongly Coupled Massive Quantum Liquids

We study physical properties of strongly coupled massive quantum liquids from their spectral functions using the AdS/CFT correspondence. The generic model that we consider is dense, heavy fundamental matter coupled to SU(N_c) super Yang-Mills theory at finite temperature above the deconfinement phase transition but below the scale set by the baryon number density. In this setup, we study the current-current correlators of the baryon number density using new techniques that employ a scaling behavior in the dual geometry. Our results, the AC conductivity, the quasi-particle spectrum and the Drude-limit parameters like the relaxation time are simple temperature-independent expressions that depend only on the mass-squared to density ratio and display a crossover between a baryon- and meson-dominated regime. We concentrated on the (2+1)-dimensional defect case, but in principle our results can also be generalized straightforwardly to other cases.

hep-th↗

arXiv2011

Three Roads to Probe-Brane Superconductivity

We study a defect system of two parallel D5 probe branes in a large-N_c D3 background. Using the non-abelian DBI action, we study three different fields that can give rise to a superconducting phase transition: A vector (p-wave), a scalar corresponding to a non-trivial "separation"' of the branes in the (3+1) field theory directions and a scalar corresponding to a separation in the "internal" S^5 (both s-wave). Comparing these phases first in the α'^2 expansion, we find that the internal scalar has the largest critical temperature and is always thermodynamically preferred. Further, there is an interesting attractor behavior. Taking a simplified version of the full DBI action that preserves its regularity and geometry, we find that the divergences of the α'^2 expansion are resolved and some second order transitions turn into first order ones. In addition to some other changes of the phase diagram due to the structure of the DBI action, we observe that the ground state degeneracy of the unbroken theory is lifted. We also isolate the unphysical artifacts of our simplification.

hep-th↗

arXiv2010

Massive Quantum Liquids from Holographic Angel's Trumpets

We explore the small-temperature regime in the deconfined phase of massive fundamental matter at finite baryon number density coupled to the 3+1 dimensional N=4 SYM theory. In this setting, we can demonstrate a new type of non-trivial temperature-independent scaling solutions for the probe brane embeddings. Focusing mostly on matter supported in 2+1 dimensions, the thermodynamics indicate that there is a quantum liquid with interesting density-dependent low-temperature physics. We also comment about 3+1 and 1+1 dimensional systems, where we further find for example a new thermodynamic instability.

hep-th↗

arXiv2010

Thermodynamics of Holographic Defects

Using the AdS/CFT correspondence, we study the thermodynamic properties and the phase diagram of matter fields on (2+1)-dimensional defects coupled to a (3+1)-dimensional N=4 SYM "heat bath". Considering a background magnetic field, (net) quark density, defect "magnitude" $δN_c$ and the mass of the matter, we study the defect contribution to the thermodynamic potentials and their first and second derivatives to map the phases and study their physical properties. We find some features that are qualitatively similar to other systems e.g. in (3+1) dimensions and a number of features that are particular to the defect nature, such as its magnetic properties, unexpected properties at T->0 and finite density; and the finite $δN_c$ effects, e.g. a diverging susceptibility and vanishing density of states at small temperatures, a physically consistent negative heat capacity and new types of consistent phases.

hep-th↗

arXiv2009

Transport Properties of Holographic Defects

We study the charge transport properties of fields confined to a (2+1)-dimensional defect coupled to (3+1)-dimensional super-Yang-Mills at large-$\nc$ and strong coupling, using AdS/CFT techniques applied to linear response theory. The dual system is described by $\nf$ probe D5- or D7-branes in the gravitational background of $\nc$ black D3-branes. Surprisingly, the transport properties of both defect CFT's are essentially identical -- even though the D7-brane construction breaks all supersymmetries. We find that the system possesses a conduction threshold given by the wave-number of the perturbation and that the charge transport arises from a quasiparticle spectrum which is consistent with an intuitive picture where the defect acquires a finite width. We also examine finite-$λ$ modifications arising from higher derivative interactions in the probe brane action.

hep-th↗

arXiv2007

Charges from Attractors

We describe how to recover the quantum numbers of extremal black holes from their near horizon geometries. This is achieved by constructing the gravitational Noether-Wald charges which can be used for non-extremal black holes as well. These charges are shown to be equivalent to the U(1) charges of appropriately dimensionally reduced solutions. Explicit derivations are provided for 10 dimensional type IIB supergravity and 5 dimensional minimal gauged supergravity, with illustrative examples for various black hole solutions. We also discuss how to derive the thermodynamic quantities and their relations explicitly in the extremal limit, from the point of view of the near-horizon geometry. We relate our results to the entropy function formalism.

hep-th↗