IGF



Bachelor thesis

Spectrometry based on the theory of compressive sensing

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Anna Kęsik

Rafał Kotyński

Wydział Fizyki, Uniwersytet Warszawski

2019

The aim of the study was an attempt to construct a spectrometer without dispersive or refractive elements such as diffraction grids or prisms, and without complex detectors such as rulers or CCD cameras. The idea of the system's operation is presented in the articles Y. August et al., Opt. Lett, vol. 38, 4996, 2013 and I. August et al., Sci. Rep. 23524, 2016. The system uses a single photodiode as an intensity detector and a liquid crystal retardation cell with dynamically modulated phase difference, uses compressive indirect measurement and requires the use theory of compressive sensing to reconstruct the measured spectrum. The potential of the study comes from the replacement of the photodiode with a CCD camera, it could be used to construct a spectral imaging system with a much simpler structure than commonly used. The compressed spectrometer system was built, pre-calibrated and the first results of spectral measurements were obtained for several spectral laser lines and several polychromatic sources. There were many difficulties limiting the use of the system, such as difficulty in calibration, the sensitivity of the measurement to the presence of spectral components in the beam beyond the measured range, the long time of data acquisition and spectrum reconstruction and the spatial heterogeneity of the liquid crystal cell and its temperature sensitivity. At the same time, the operating mechanism of the system have been confirmed and its potential for further development into a spectral imaging system.


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