Biomedical Engineering Reference
In-Depth Information
17
Adaptive Optical
Microscopy Using Direct
Wavefront Measurements
17.1
Introduction ...................................................................................... 315
17.2
AO Wide-Field Microscope.............................................................320
Fluorescent Imaging at Diferent Wavelengths
Oscar Azucena
University of California
at Santa Cruz
Xiaodong Tao
University of California
at Santa Cruz
17.3
AO Confocal Fluorescence Microscope ........................................328
17.4
Using Fluorescent Proteins as Guide Stars ...................................335
Joel A. Kubby
University of California
at Santa Cruz
17.5
Discussion and Conclusion .............................................................339
17.1 Introduction
he telescope and the microscope have allowed scientists to study the universe and the world we live in
(Van Helden 1977). Both microscopes and telescopes sufer from optical aberrations created by changes
in the index of refraction in the optical path. Dunn and Richards-Kortum (1996) have studied the
changes in the index of refraction inside biological tissues. heir results indicate that structures with
large changes in the index of refraction have large contrast ratios as long as they are near the surface
of the biological sample. hese changes in the index of refraction degrade the contrast ratio for objects
lying much deeper in the tissue. he efect is much worse for samples with a lot of ine structures, since
they introduce higher-order aberrations in the images. Schwertner et al. (2004) measured the specimen-
induced aberrations for a range of typical biological samples (Schwertner 2007). heir results indicate
that the Zernike-mode representation is a useful tool for describing these aberrations. heir results also
indicate that lower-order aberrations are more pronounced than higher-order ones and that spherical
aberrations dominate overall.
Adaptive optics (AO) is a method used in the telescope for improving astronomical images. Babcock
(1953) irst introduced the idea of improving astronomical seeing by compensating for the atmosphere-
induced aberrations. His proposal was to measure the deviations of the light rays from all parts of the
mirror and feed that information back so as to locally correct for the deviations. Although the idea was
scientiically sound, it had a few minor technical complications, and it was not put into action until
20 years later when the irst real-time AO system was used for national-defense applications (Hardy
315
