Document Detail


Separating twin images and locating the center of a microparticle in dense suspensions using correlations among reconstructed fields of two parallel holograms.
MedLine Citation:
PMID:  25322116     Owner:  NLM     Status:  In-Data-Review    
Abstract/OtherAbstract:
This paper deals with two issues affecting the application of digital holographic microscopy (DHM) for measuring the spatial distribution of particles in a dense suspension, namely discriminating between real and virtual images and accurate detection of the particle center. Previous methods to separate real and virtual fields have involved applications of multiple phase-shifted holograms, combining reconstructed fields of multiple axially displaced holograms, and analysis of intensity distributions of weakly scattering objects. Here, we introduce a simple approach based on simultaneously recording two in-line holograms, whose planes are separated by a short distance from each other. This distance is chosen to be longer than the elongated trace of the particle. During reconstruction, the real images overlap, whereas the virtual images are displaced by twice the distance between hologram planes. Data analysis is based on correlating the spatial intensity distributions of the two reconstructed fields to measure displacement between traces. This method has been implemented for both synthetic particles and a dense suspension of 2 μm particles. The correlation analysis readily discriminates between real and virtual images of a sample containing more than 1300 particles. Consequently, we can now implement DHM for three-dimensional tracking of particles when the hologram plane is located inside the sample volume. Spatial correlations within the same reconstructed field are also used to improve the detection of the axial location of the particle center, extending previously introduced procedures to suspensions of microscopic particles. For each cross section within a particle trace, we sum the correlations among intensity distributions in all planes located symmetrically on both sides of the section. This cumulative correlation has a sharp peak at the particle center. Using both synthetic and recorded particle fields, we show that the uncertainty in localizing the axial location of the center is reduced to about one particle's diameter.
Authors:
Hangjian Ling; Joseph Katz
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Applied optics     Volume:  53     ISSN:  1539-4522     ISO Abbreviation:  Appl Opt     Publication Date:  2014 Sep 
Date Detail:
Created Date:  2014-10-17     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0247660     Medline TA:  Appl Opt     Country:  United States    
Other Details:
Languages:  eng     Pagination:  G1-G11     Citation Subset:  IM    
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