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## Elaboration of measuring system for characterization of polarizing filters in a coronagraph

### Przemysław Kaźmierczak

#### Abstract

The aim of the thesis was to develop a method for precise measurement of the angle of rotation of the transmission axis of linear polarizers installed in a filter wheel assembly. These measurements were to be used both to determine the accuracy of the montage of polarizing elements in the wheel assembly, and to determine for which step of the stepper motor controlling the rotation of the filter wheel the change of the state of polarization of the beam passing through the given wheel filter is corresponds with the requirements. The first stage of the work was to cognize the methods of measuring the rotation of the plane of polarization of a beam passing through an object. Subsequently it was decided to use the method based on the principle of differential polarimetry. In this method, the beam passing through the tested element is compared after a rotating analyzer with the reference beam, which was created earlier by splitting the original beam. Behind the analyzer, the beams are registered by photodetectors, and then subjected to analysis, which by using the Fourier transform and filtration algorithms determines the phase shift between the two beams, and then determines the angle of rotation of the measured object’s transmission axis. In this case the measured object is a linear polarizer. The method was tested by means of a laboratory experiment. The measurement system composed of simple optical elements allowed to perform measurements, the results of which confirmed the correctness of the chosen method. The next stage of the work was to design a filter wheel mounting assembly which would enable a precise and controlled rotation of the wheel with a micrometer screw. This system is to be used for measuring the accuracy of the montage of polarizing elements in the filter wheel assembly. In the next stage, a MATLAB script has been written which analyzes the signals according to the method used in the work. This script, after loading the signals registered by the photodetectors, reduces the noise in them and carries out an analysis from which the rotation angle of the axis of transmission of the tested element is received. The efficiency of the algorithm has been tested in numerous simulations, the results of which were then discussed. Finally, the chosen method proved to meet all the requirements made for the thesis. The measurement system worked as expected, and the algorithm processing registered signals returned results with accuracy is much higher than required. The measuring system consisting of high-quality optical elements, optomechanics and photodetectors based on the method described in the thesis should allow to obtain very precise measurements of the rotation of the polarizing filter transmission axis.
Diploma type
Engineer's / Bachelor of Science
Diploma type
Engineer's thesis
Author
Przemysław Kaźmierczak (FM) Przemysław Kaźmierczak,, Faculty of Mechatronics (FM)
Title in Polish
Opracowanie systemu do charakteryzacji filtrów polaryzacyjnych stosowanych w układzie koronografu
Supervisor
Adam Styk (FM/IMPh) Adam Styk,, The Institute of Micromechanics and Photonics (FM/IMPh)Faculty of Mechatronics (FM)
Certifying unit
Faculty of Mechatronics (FM)
Affiliation unit
The Institute of Micromechanics and Photonics (FM/IMPh)
Study subject / specialization
, Mechatronika
Language
(pl) Polish
Status
Finished
Defense Date
21-11-2019
Issue date (year)
2019
Reviewers
Julianna Winnik (FM/IMPh) Julianna Winnik,, The Institute of Micromechanics and Photonics (FM/IMPh)Faculty of Mechatronics (FM) Adam Styk (FM/IMPh) Adam Styk,, The Institute of Micromechanics and Photonics (FM/IMPh)Faculty of Mechatronics (FM)
Keywords in Polish
polarymetria różnicowa, elipsometria, polaryzacja
Keywords in English
differential polarimetry, ellipsometry, polarization
Abstract in Polish
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Local fields
Identyfikator pracy APD: 31825

Uniform Resource Identifier
https://repo.pw.edu.pl/info/bachelor/WUT2d1ffc82a70f477fb9505ef4a9ba8d1c/
URN
urn:pw-repo:WUT2d1ffc82a70f477fb9505ef4a9ba8d1c

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