Biomedical Engineering Reference
In-Depth Information
4
Aberrations and the
Beneit of Their Correction
in Confocal Microscopy
4.1
Introduction: Why Measure Specimen-Induced Aberration?..... 51
4.2
Deinition of Aberrations ..................................................................52
4.3
Zernike Mode Analysis of the Aberrated Wavefront....................53
4.4
Sources of Aberrations.......................................................................55
4.5
Efect of Aberrations on the Imaging Quality of the
Confocal Microscope .........................................................................55
4.6
Experimental System for Aberration Measurement .....................57
4.7
Data Acquisition .................................................................................59
4.8
Phase Extraction .................................................................................60
4.9
Results for Aberration Measurements at Low
Numerical Aperture ........................................................................... 61
4.10
Setup for Large Numerical Aperture, Specimens
Investigated, and Data Acquisition..................................................66
4.11
Example Results for High Numerical Aperture ............................67
4.12
Simulation of the Zernike Modal Correction ................................68
4.13
Wavefront Quality Characterization...............................................69
4.14
Which Level of Correction Is Sensible?...........................................70
4.15
Efect of the Numerical Aperture on Aberrations.........................71
Michael Schwertner
confovis GmbH
4.16
Discussion and Conclusion ...............................................................72
4.1 Introduction: Why Measure Specimen-Induced
Aberration?
he ultimate goal is to design a microscope that fully corrects aberrations and thus can deliver optimum
performance and difraction-limited imaging in confocal microscopy. his requires knowledge about
the nature of aberrations encountered under conditions found in biomedical imaging.
Before we start the design of an adaptive optics system, we need to address the following
questions:
• What type and amount of the specimen-induced aberration do we have to expect from typical
biological specimen?
• How many Zernike modes do we need to correct to reduce aberrations to an acceptable level?
• Can we optimize the correction process by limiting the sensing and correction to a few Zernike
modes while neglecting modes that are either not caused by the specimen or not transmitted by
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