Type of Document Master's Thesis Author Kourakos, Alexander William URN etd-052199-162314 Title Extended Depth-of-focus in a Laser Scanning System Employing a Synthesized Difference-of-Gaussians Pupil Degree Master of Science Department Electrical and Computer Engineering Advisory Committee
Advisor Name Title Poon, Ting-Chung Committee Chair Brown, Gary S. Committee Member Indebetouw, Guy J. Committee Member Keywords
- extended depth of field
- optical scanning microscopy
- pupil synthesis
Date of Defense 1999-05-11 Availability unrestricted Abstract
Traditional laser scanning systems, such as those used for microscopy, typically image objects of finite thickness. If the depth-of-focus of such systems is low, as is the case when a simple clear pupil is used, the object must be very thin or the image will be distorted. Several methods have been developed to deal with this problem. A microscope with a thin annular pupil has a very high depth-of-focus and can image the entire thickness of a sample, but most of the laser light is blocked, and the image shows poor contrast and high noise. In confocal laser microscopy, the depth-of-focus problem is eliminated by using a small aperture to discard information from all but one thin plane of the sample. However, such a system requires scanning passes at many different depths to yield an image of the entire thickness of the sample, which is a time-consuming process and is highly sensitive to registration errors.
In this thesis, a novel type of scanning system is considered. The sample is simultaneously scanned with a combination of two Gaussian laser beams of different widths and slightly different temporal frequencies. Information from scanning with the two beams is recorded with a photodetector, separated electronically, and processed to form an image. This image is similar to one formed by a system using a difference-of-Gaussians pupil, except no light has been blocked or wasted. Also, the entire sample can be scanned in one pass. The depth-of-focus characteristics of this synthesized difference-of-Gaussians pupil are examined and compared with those of well-known functions such as the circular, annular, and conventional difference-of-Gaussians pupils.
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