arXiv subjects

Carlas Smith

Publications and source records attributed to Carlas Smith.

4 recordsLinked to original sources

arXiv2024

Online input design for discrimination of linear models using concave minimization

Stochastic Closed-Loop Active Fault Diagnosis (CLAFD) aims to select the input sequentially in order to improve the discrimination of different models by minimizing the predicted error probability. As computation of these error probabilities encompasses the evaluation of multidimensional probability integrals, relaxation methods are of interest. This manuscript presents a new method that allows to make an improved trade-off between three factors -- namely maximized accuracy of diagnosis, minimized number of consecutive measurements to achieve that accuracy, and minimized computational effort per time step -- with respect to the state-of-the-art. It relies on minimizing an upper bound on the error probability, which is in the case of linear models with Gaussian noise proven to be concave in the most challenging discrimination conditions. A simulation study is conducted both for open-loop and feedback controlled candidate models. The results demonstrate the favorable trade-off using the new contributions in this manuscript.

eess.SY↗

arXiv2018

Blind single-frame deconvolution by tangential iterative projections (TIP)

Deconvolution serves as a computational means of removing the effect of optical aberrations from recorded images and is employed in many technical and scientific fields of study. In most imaging scenarios the nature of the blurring kernel or point-spread function (PSF) of the imaging system is unknown and both the object and PSF can be estimated using different forms of mathematical optimisation. The Tangential Iterative Projections (TIP) algorithm is a multi-frame deconvolution framework where multiple images can be combined to obtain a single estimate of the object. It is shown here that this framework may be also used for single-frame deconvolution with a few modifications to the algorithm. This step from multiple to one frame is non-trivial and greatly improves the applicability of the TIP framework to most imaging scenarios.

eess.IV↗

arXiv2018

Anisoplanatic adaptive optics in parallelized laser scanningmicroscopy

Inhomogeneities in the refractive index of a biological sample can introduce phase aberrationsin microscopy systems, severely impairing the quality of images. Adaptive optics can be employed to correct for phase aberrations and improve image quality. However, conventional adaptive optics can only correct a single phase aberration for the whole field of view (isoplanatic correction) while, due to the three dimensional nature of biological tissues, sample induced aberrations in microscopy often vary throughout the field of view (anisoplanatic aberration), limiting significantly the effectiveness of adaptive optics. This paper reports on a new approach for aberration correction in laser scanning confocal microscopy, in which a spatial light modulator is used to generate multiple excitation points in the sample to simultaneously scan different portions of the field of view with completely independent correction, achieving anisoplanatic compensation of sample induced aberrations. The method was tested in 150 μm thick whole Drosophila brains, showing a dramatic improvement in resolution and sharpness when compared to conventional isoplanatic adaptive optics.

physics.optics↗

arXiv2018

High precision wavefront control in point spread function engineering for single emitter localization

Point Spread Function (PSF) engineering is used in single emitter localization to measure the emitter position in 3D and possibly other parameters such as the emission color or dipole orientation as well. Advanced PSF models such as spline fits to experimental PSFs or the vectorial PSF model can be used in the corresponding localization algorithms in order to model the intricate spot shape and deformations correctly. The complexity of the optical architecture and fit model makes PSF engineering approaches particularly sensitive to optical aberrations. Here, we present a calibration and alignment protocol for fluorescence microscopes equipped with a spatial light modulator (SLM) with the goal of establishing a wavefront error well below the diffraction limit for optimum application of complex engineered PSFs. We achieve high-precision wavefront control, to a level below 20 m$λ$ wavefront aberration over a 30 minute time window after the calibration procedure, using a separate light path for calibrating the pixel-to-pixel variations of the SLM, and alignment of the SLM with respect to the optical axis and Fourier plane within 3 $μ$m ($x/y$) and 100 $μ$m ($z$) error. Aberrations are retrieved from a fit of the vectorial PSF model to a bead $z$-stack and compensated with a residual wavefront error comparable to the error of the SLM calibration step. This well-calibrated and corrected setup makes it possible to create complex `3D+$λ$' PSFs that fit very well to the vectorial PSF model. Proof-of-principle bead experiments show precisions below 10~nm in $x$, $y$, and $λ$, and below 20~nm in $z$ over an axial range of 1 $μ$m with 2000 signal photons and 12 background photons.

physics.optics↗