Improved Axial Resolution Using Asymmetric Apodisation


Authors: R. Komala*1 and P. Sangeetha Lakshmi2

Pages: 17-24, 2020

Open Access!

Apodisation is the technique alters the imaging properties of an optical system such that the system impulse ceases the ringing effect by manipulating its entrance pupil. It helps to differentiate direct image of faint object which is close to very bright object. The results of an optical system can be improved by two methods namely modification of the optical system and the post detection processing. The former one involves optimization of the optical system itself and the latter involves operations on the systems output. The pupil function can be modified with suitable spatial filters to obtain Asymmetric apodisation. The unwanted ringing around the point spead function (PSF) can be filtered using this technique. The point spread function (PSF) of an optical system obtained with asymmetric apodization consists of unequal distribution of intensities on either side of the central lobe. The portion of PSF with side lobes of more intensities is termed as bad side and the portion with side lobes of less intensities is termed as good side. This asymmetrical PSF is obtained by introducing apodiser in the central region and introducing semi-circular edge rings. The asymmetry in the PSF has been found to change with the width of the edge rings and on the apodization parameter of the central region. This technique can be used to calculate Full width at half maximum (FWHM) of an asymmetrically apodised point spread function. It is observed that as semi-circular ring width increases half maximum area is affected. This technique can be used to improve the quality of image with improved axial resolution, which helps in the study of microorganisms under a microscope and to study weak spectral lines in presence of bright spectral lines.

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