417 research outputs found
Impact Study of Numerical Discretization Accuracy on Parameter Reconstructions and Model Parameter Distributions
In optical nano metrology numerical models are used widely for parameter
reconstructions. Using the Bayesian target vector optimization method we fit a
finite element numerical model to a Grazing Incidence X-Ray fluorescence data
set in order to obtain the geometrical parameters of a nano structured line
grating. Gaussian process, stochastic machine learning surrogate models, were
trained during the reconstruction and afterwards sampled with a Markov chain
Monte Carlo sampler to determine the distribution of the reconstructed model
parameters. The numerical discretization parameters of the used finite element
model impact the numerical discretization error of the forward model. We
investigated the impact of the polynomial order of the finite element ansatz
functions on the reconstructed parameters as well as on the model parameter
distributions. We showed that such a convergence study allows to determine
numerical parameters which allows for efficient and accurate reconstruction
results.Comment: Submitted to Metrologia Focus Issue on MATHMET 2023 conferenc
Optimized diamond inverted nanocones for enhanced color center to fiber coupling
Nanostructures can be used for boosting the light outcoupling of color
centers in diamond; however, the fiber coupling performance of these
nanostructures is rarely investigated. Here, we use a finite element method for
computing the emission from color centers in inverted nanocones and the overlap
of this emission with the propagation mode in a single-mode fiber. Using
different figures of merit, the inverted nanocone parameters are optimized to
obtain maximal fiber coupling efficiency, free-space collection efficiency, or
rate enhancement. The optimized inverted nanocone designs show promising
results with 66% fiber coupling or 83% free-space coupling efficiency at the
tin-vacancy center zero-phonon line wavelength of 619 nm. Moreover, when
evaluated for broadband performance, the optimized designs show 55% and 76% for
fiber coupling and free-space efficiencies respectively, for collecting the
full tin-vacancy emission spectrum at room temperature. An analysis of
fabrication insensitivity indicates that these nanostructures are robust
against imperfections. For maximum emission rate into a fiber mode, a design
with a Purcell factor of 2.34 is identified. Finally, possible improvements
offered by a hybrid inverted nanocone, formed by patterning into two different
materials, are investigated, and increases the achievable fiber coupling
efficiency to 71%.Comment: The following article has been accepted by Applied Physics Letters.
After it is published, it will be found at https://doi.org/10.1063/5.005033
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