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F. Schmidt

Publications and source records attributed to F. Schmidt.

At least 37 records · Page 2Linked to original sources
arXiv2013

Numerical analysis of nanostructures for enhanced light extraction from OLEDs

Nanostructures, like periodic arrays of scatters or low-index gratings, are used to improve the light outcoupling from organic light-emitting diodes (OLED). In order to optimize geometrical and material properties of such structures, simulations of the outcoupling process are very helpful. The finite element method is best suited for an accurate discretization of the geometry and the singular-like field profile within the structured layer and the emitting layer. However, a finite element simulation of the overall OLED stack is often beyond available computer resources. The main focus of this paper is the simulation of a single dipole source embedded into a twofold infinitely periodic OLED structure. To overcome the numerical burden we apply the Floquet transform, so that the computational domain reduces to the unit cell. The relevant outcoupling data are then gained by inverse Flouqet transforming. This step requires a careful numerical treatment as reported in this paper.

physics.optics↗
arXiv2013

Fast simulation method for parameter reconstruction in optical metrology

A method for automatic computation of parameter derivatives of numerically computed light scattering signals is demonstrated. The finite-element based method is validated in a numerical convergence study, and it is applied to investigate the sensitivity of a scatterometric setup with respect to geometrical parameters of the scattering target. The method can significantly improve numerical performance of design optimization, parameter reconstruction, sensitivity analysis, and other applications.

physics.optics↗
arXiv2013

Surface reflectance of Mars observed by CRISM/MRO: 2. Estimation of surface photometric properties in Gusev Crater and Meridiani Planum

The present article proposes an approach to analyze the photometric properties of the surface materials from multi-angle observations acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on-board the Mars Reconnaissance Orbiter. We estimate photometric parameters using Hapke model in a Bayesian inversion framework. This work also represents a validation of the atmospheric correction provided by the Multi-angle Approach for Retrieval of Surface Reflectance from CRISM Observations (MARS-ReCO) proposed in the companion article.The latter algorithm retrieves photometric curves of surface materials in reflectance units after removing the aerosol contribution. This validation is done by comparing the estimated photometric parameters to those obtained from in situ measurements by Panoramic Camera instrument at the Mars Exploration Rover (MER)-Spirit and MER-Opportunity landing sites. Consistent photometric parameters with those from in situ measurements are found, demonstrating that MARS-ReCO gives access to accurate surface reflectance. Moreover the assumption of a non-Lambertian surface as included in MARS-ReCO is shown to be significantly more precise to estimate surface photometric properties from space in comparison to methods based on a Lambertian surface assumption. In the future, the presented method will allow us to map from orbit the surface bidirectional reflectance and the related photometric parameters in order to characterize the Martian surface.

astro-ph.EP↗
arXiv2012

Reconstruction of the wavefunctions of coupled nanoscopic emitters using a coherent optical technique

We show that using coherent, spatially resolved spectroscopy, complex hybrid wave functions can be disentangled into the individual wave functions of the individual emitters. This way, detailed information on the coupling of the individual emitters, not available in far-field spectroscopy can be obtained. The proposed quantum state tomography relies on the ability to selectively excite each emitter individually by spatially localized pulses. Simulations of coupled semiconductor Ga/InAs quantum dots, using light fields available in current nanoplasmonics, show that even undesired resonances can be removed from measured spectra. The method can also be applied to study the internal coupling of pigments in photosythesis and artificial light harvesting.

cond-mat.mes-hall↗
arXiv2012

3D finite element simulation of optical modes in VCSELs

We present a finite element method (FEM) solver for computation of optical resonance modes in VCSELs. We perform a convergence study and demonstrate that high accuracies for 3D setups can be attained on standard computers. We also demonstrate simulations of thermo-optical effects in VCSELs.

physics.optics↗
arXiv2011

Rigorous Simulations of 3D Patterns on Extreme Ultraviolet Lithography Masks

Simulations of light scattering off an extreme ultraviolet lithography mask with a 2D-periodic absorber pattern are presented. In a detailed convergence study it is shown that accurate results can be attained for relatively large 3D computational domains and in the presence of sidewall-angles and corner-roundings.

physics.optics↗
arXiv2010

Water ice in the dark dune spots of Richardson crater on Mars

In this study we assess the presence, nature and properties of ices - in particular water ice - that occur within these spots using HIRISE and CRISM observations, as well as the LMD Global Climate Model. Our studies focus on Richardson crater (72°S, 179°E) and cover southern spring and summer (LS 175° - 17 341°). Three units have been identified of these spots: dark core, gray ring and bright halo. Each unit show characteristic changes as the season progress. In winter, the whole area is covered by CO2 ice with H2O ice contamination. Dark spots form during late winter and early spring. During spring, the dark spots are located in a 10 cm thick depression compared to the surrounding bright ice-rich layer. They are spectrally characterized by weak CO2 ice signatures that probably result from spatial mixing of CO2 ice rich and ice free regions within pixels, and from mixing of surface signatures due to aerosols scattering. The bright halo shaped by winds shows stronger CO2 absorptions than the average ice covered terrain, which is consistent with a formation process involving CO2 re-condensation. According to spectral, morphological and modeling considerations, the gray ring is composed of a thin layer of a few tens of μm of water ice. Two sources/processes could participate to the enrichment of water ice in the gray ring unit: (i) water ice condensation at the surface in early fall (prior to the condensation of a CO2 rich winter layer) or during winter time (due to cold trapping of the CO2 layer); (ii) ejection of dust grains surrounded by water ice by the geyser activity responsible for the dark spot. In any case, water ice remains longer in the gray ring unit after the complete sublimation of the CO2. Finally, we also looked for liquid water in the near-IR CRISM spectra using linear unmixing modeling but found no conclusive evidence for it.

physics.geo-ph↗
arXiv2010

Finite Element Simulation of the Optical Modes of Semiconductor Lasers

In the present article we investigate optical near fields in semiconductor lasers. We perform finite element simulations for two different laser types, namely a super large optical waveguide (SLOW) laser, which is an edge emitter, and a vertical cavity surface emitting laser (VCSEL). We give the mathematical formulation of the different eigenvalue problems that arise for our examples and explain their numerical solution with the finite element method. Thereby, we also comment on the usage of transparent boundary conditions, which have to be applied to respect the exterior environment, e.g., the very large substrate and surrounding air. For the SLOW laser we compare the computed near fields to experimental data for different design parameters of the device. For the VCSEL example a comparison to simplified 1D mode calculations is carried out.

physics.optics↗
arXiv2010

Reduced basis method for source mask optimization

Image modeling and simulation are critical to extending the limits of leading edge lithography technologies used for IC making. Simultaneous source mask optimization (SMO) has become an important objective in the field of computational lithography. SMO is considered essential to extending immersion lithography beyond the 45nm node. However, SMO is computationally extremely challenging and time-consuming. The key challenges are due to run time vs. accuracy tradeoffs of the imaging models used for the computational lithography. We present a new technique to be incorporated in the SMO flow. This new approach is based on the reduced basis method (RBM) applied to the simulation of light transmission through the lithography masks. It provides a rigorous approximation to the exact lithographical problem, based on fully vectorial Maxwell's equations. Using the reduced basis method, the optimization process is divided into an offline and an online steps. In the offline step, a RBM model with variable geometrical parameters is built self-adaptively and using a Finite Element (FEM) based solver. In the online step, the RBM model can be solved very fast for arbitrary illumination and geometrical parameters, such as dimensions of OPC features, line widths, etc. This approach dramatically reduces computational costs of the optimization procedure while providing accuracy superior to the approaches involving simplified mask models. RBM furthermore provides rigorous error estimators, which assure the quality and reliability of the reduced basis solutions. We apply the reduced basis method to a 3D SMO example. We quantify performance, computational costs and accuracy of our method.

physics.optics↗
arXiv2010

Metrology of EUV Masks by EUV-Scatterometry and Finite Element Analysis

Extreme ultraviolet (EUV) lithography is seen as a main candidate for production of future generation computer technology. Due to the short wavelength of EUV light (around 13 nm) novel reflective masks have to be used in the production process. A prerequisite to meet the high quality requirements for these EUV masks is a simple and accurate method for absorber pattern profile characterization. In our previous work we demonstrated that the Finite Element Method (FEM) is very well suited for the simulation of EUV scatterometry and can be used to reconstruct EUV mask profiles from experimental scatterometric data. In this contribution we apply an indirect metrology method to periodic EUV line masks with different critical dimensions (140 nm and 540 nm) over a large range of duty cycles (1:2, ..., 1:20). We quantitatively compare the reconstructed absorber pattern parameters to values obtained from direct AFM and CD-SEM measurements. We analyze the reliability of the reconstruction for the given experimental data. For the CD of the absorber lines, the comparison shows agreement of the order of 1nm. Furthermore we discuss special numerical techniques like domain decomposition algorithms and high order finite elements and their importance for fast and accurate solution of the inverse problem.

physics.optics↗
arXiv2010

Reduced basis method for computational lithography

A bottleneck for computational lithography and optical metrology are long computational times for near field simulations. For design, optimization, and inverse scatterometry usually the same basic layout has to be simulated multiple times for different values of geometrical parameters. The reduced basis method allows to split up the solution process of a parameterized model into an expensive offline and a cheap online part. After constructing the reduced basis offline, the reduced model can be solved online very fast in the order of seconds or below. Error estimators assure the reliability of the reduced basis solution and are used for self adaptive construction of the reduced system. We explain the idea of reduced basis and use the finite element solver JCMsuite constructing the reduced basis system. We present a 3D optimization application from optical proximity correction (OPC).

physics.optics↗
arXiv2010

Finite element method for accurate 3D simulation of plasmonic waveguides

Optical properties of hybrid plasmonic waveguides and of low-Q cavities, formed by waveguides of finite length are investigated numerically. These structures are of interest as building-blocks of plasmon lasers. We use a time-harmonic finite-element package including a propagation-mode solver, a resonance-mode solver and a scattering solver for studying various properties of the system. Numerical convergence of all used methods is demonstrated.

physics.optics↗
arXiv2010

Numerical Investigation of Photonic Crystal Microcavities in Silicon-on-Insulator Waveguides

Optical resonances in 1D photonic crystal microcavities are investigated numerically using finite-element light scattering and eigenmode solvers. The results are validated by comparison to experimental and theoretical findings from the literature. The influence of nanometer-scale geometry variations on the resonator performance is studied. Limiting factors to ultra-high Q-factor performance are identified.

physics.optics↗
arXiv2009

Benchmark of Rigorous Methods for Electromagnetic Field Simulations

We have developed an interface which allows to perform rigorous electromagnetic field (EMF) simulations with the simulator JCMsuite and subsequent aerial imaging and resist simulations with the simulator Dr.LiTHO. With the combined tools we investigate the convergence of near-field and far-field results for different DUV masks. We also benchmark results obtained with the waveguide-method EMF solver included in Dr.LiTHO and with the finite-element-method EMF solver JCMsuite. We demonstrate results on convergence for dense and isolated hole arrays, for masks including diagonal structures, and for a large 3D mask pattern of lateral size 10 microns by 10 microns.

physics.optics↗
arXiv2009

Finite-Element Simulations of Light Propagation through Circular Subwavelength Apertures

Light transmission through circular subwavelength apertures in metallic films with surrounding nanostructures is investigated numerically. Numerical results are obtained with a frequency-domain finite-element method. Convergence of the obtained observables to very low levels of numerical error is demonstrated. Very good agreement to experimental results from the literature is reached, and the utility of the method is demonstrated in the investigation of the influence of geometrical parameters on enhanced transmission through the apertures.

physics.optics↗
arXiv2009

The 2pt+: an enhanced 2 point correlation function

We introduce a new method for testing departure from isotropy of points on a sphere based on an enhanced form of the two-point correlation function that we named 2pt+. This method uses information from the two extra variables that define the vector between two points on a sphere. We show that this is a powerful method to test departure from isotropy of a distribution of points on a sphere especially when the number of events is small. We apply the method to a few examples in astronomy and discuss the relevance for limited datasets, such as the case of ultra-high energy cosmic rays.

astro-ph.CO↗