arXiv subjects

L. E. Helseth

Publications and source records attributed to L. E. Helseth.

8 recordsLinked to original sources

arXiv2002

Magnetically induced signatures in a thin film superconductor

We study the interaction between a one dimensional magnetic nanostructure and a thin film superconductor. It is shown that different magnetic distributions produce characteristic magnetic field signatures. Moreover, the magnetic structure can induce a weak link in the superconducting film, or be positioned directly above a predefined nonsuperconducting weak link. We estimate the magnetic flux associated with such a structure, and discuss a general expression for the energy calculated within the London model.

cond-mat.supr-con↗

arXiv2002

Electromagnetic focusing through a tilted dielectric interface

Focusing through a tilted dielectric interface is studied, and an explicit expression for the electric field in the focal region is found. In the case of small tilt angles, one obtains a focal shift, and only a simple aberration term remains.

physics.optics↗

arXiv2002

Interaction between a magnetic domain wall and a superconductor

The interaction between a magnetic thin film and a superconductor is studied. In particular, the equilibrium width of a Bloch wall is estimated with and without the superconductor. It is shown that the Bloch wall experiences a small shrinkage on cooling through the critical temperature of the superconductor. Furthermore, the interaction between the Bloch wall and a single vortex is estimated, and a simple expression for the force is found.

cond-mat.supr-con↗

arXiv2002

Faraday rotation and sensitivity of (100) bismuth-substituted ferrite garnet films

We have investigated the Faraday rotation of in-plane magnetized bismuth - substituted ferrite garnet films grown by liquid phase epitaxy on (100) oriented gadolinium gallium garnet substrates. The Faraday spectra were measured for photon energies between 1.7 - 2.6 eV. To interprete the spectra, we use a model based on two electric dipole transitions, one tetrahedral and one octahedral. Furthermore, the Faraday rotation sensitivity was measured at 2.3 eV, and found to be in good agreement with the theoretical predicitions. In particular, we find that the sensitivity increases linearly with the bismuth content and nonlinearly with the gallium content.

cond-mat.mtrl-sci↗

arXiv2002

Optical detection of magnetic data using magnetooptic indicators with in-plane magnetization

We investigate detection of magnetic data using magnetooptical indicators with in-plane magnetization. A simple model for the magnetooptical detection system is presented. We find that the signal to noise ratio changes strongly with the bit size, the polarization noise and the distance between the magnetic carrier and the indicator. In particular, it is found that within our model a signal to noise ratio of 30 is possible for a bit size of 200 nm. We also estimate the resolution of the system, and find that a spot size of $\sim 200$ nm can be obtained using a suitably designed solid immersion lens. Finally, we discuss detection of several magnetic tracks simultaneously.

cond-mat.mtrl-sci↗

arXiv2002

Theoretical model for magnetooptic imaging

A theoretical model for magnetooptic imaging is presented. The model gives a detailed description of the magnetooptic indicator and the optical imaging system, where the intensity at the detector plane is described by a set of diffraction integrals. To demonstrate the applicability of the model, some issues concerning imaging of single vortices in superconductors are studied. It is found that the useful signal is strongly dependent on the penetration depth of the superconductor, and also the sensitivity and thickness of the indicator.

cond-mat.mtrl-sci↗

arXiv2002

Faraday rotation spectra of bismuth-substituted ferrite garnet films with in-plane magnetization

Single crystalline films of bismuth-substituted ferrite garnets have been synthesized by the liquid phase epitaxy method where GGG substrates are dipped into the flux. The growth parameters are controlled to obtain films with in-plane magnetization and virtually no domain activity, which makes them excellently suited for magnetooptic imaging. The Faraday rotation spectra were measured across the visible range of wavelengths. To interprete the spectra we present a simple model based on the existence of two optical transitions of diamagnetic character, one tetrahedral and one octahedral. We find excellent agreement between the model and our experimental results for photon energies between 1.77 and 2.53 eV, corresponding to wavelengths between 700 and 490 nm. It is shown that the Faraday rotation changes significantly with the amount of substituted gallium and bismuth. Furthermore, the experimental results suggest that the magnetooptic response changes linearly with the bismuth substitution.

cond-mat.mtrl-sci↗

arXiv2001

Roles of polarization, phase and amplitude in solid immersion lens systems

By altering the polarization, phase and amplitude at the exit pupil, the intensity distribution near the focal plane of a Solid Immersion Lens(SIL) system can be changed. We have studied how the resolution and focal depth changes for a few particular cases. It was seen that by impinging radial polarization on a SIL system, we may obtain a rotational symmetric z-component of the focused wavefront with spot size similar to that predicted by scalar theory. We also found that it was possible to 'play' with the the contributions from the homogeneous and inhomogeneous waves behind the SIL by changing the amplitude and phase distribution at the aperture.

physics.optics↗