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Pålitligheten av fasrekonstruktion i koherent diffraktiv avbildning
KTH, School of Engineering Sciences (SCI).
KTH, School of Engineering Sciences (SCI).
2019 (Swedish)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesisAlternative title
Reliability of phase reconstruction in coherent diffraction imaging (English)
Abstract [sv]

Det här projektet undersöker pålitligheten av fasåterskapning i koherent diffraktiv avbildning, där elektrondensiteten av en partikel återskapas från magnituden av dess Fouriertransform. Vi använder oss av en simulerad experimentell uppställning och skapar högkontrastpartiklar med olika nivåer av inre detalj, tillsammans med tre olika signalstyrkor och två olika typer av brus i detektionsprocessen. Fasåterskapning gjordes med hjälp av Hybrid Input-Output- och Error-Reduction-algoritmerna för att skapa oberoende återskapningar som startar från slumpmässiga faser, och faserna jämfördes sedan med hjälp av den så kallade Phase Retrieval Transfer Function (PRTF) som ett mått på noggrannhet. Resultaten indikerade att både partikeldetalj och mängden signal var viktiga parametrar för rekonstruktionens noggrannhet. Närvaron av Gaussiskt brus tillsammans med Poissonbrus hade en större påverkan i högsignalfallet, och PRTF:en var inte ett bra mått på noggrannheten i lågsignalsfallet. Framtida förbättringar skulle kunna inkludera undersökning av olika typer av brus och en större bredd parametrar.

 

Abstract [en]

This project examines the reliability of the process of phase reconstruction in coherent diffraction imaging, where the electron density of a particle is reconstructed from the magnitude of it's Fourier transform. We use a simulated experimental setup and produce high contrast test particles with different levels of internal detail, together with three different amounts of signal and two different kinds of noise present in the detection process. Phase reconstruction was done using the Hybrid Input-Output and Error-Reduction algorithms to produce independent reconstructions starting from randomized phases, and the reconstructions were compared using the Phase Retrieval Transfer Function (PRTF) as a measure of accuracy. The results indicated that both particle detail and the amount of signal were important parameters for an accurate reconstruction. The presence of Gaussian noise together with Poisson noise had a larger impact in the high signal case, and the PRTF was not a good measure of reconstruction accuracy in the low signal situation. Future improvements to these simulations could examine different types of noise distributions and a wider range of parameters.

 

Place, publisher, year, edition, pages
2019.
Series
TRITA-SCI-GRU ; 2019:132
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-255841OAI: oai:DiVA.org:kth-255841DiVA, id: diva2:1342377
Supervisors
Examiners
Available from: 2019-08-13 Created: 2019-08-13 Last updated: 2019-08-13Bibliographically approved

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