Confocal Optical Imaging Systems and Their Applications in Microscopy and Range Sensing

Confocal optical imaging systems have been the subject of much recent studies. They have found their applications in biomedical imaging and integrated circuit metrology. Confocal systems differ from the standard optical imaging systems in their use of point illumination and point detection, gaining an improved transverse resolution and superior depth resolution. The depth discrimination capability allows confocal imaging systems to optically cross section translucent objects or to image three-dimensional structures. The improvement in transverse resolution permits them to image structures with more detail and better contrast. This thesis has focused on the design and implementation of the confocal optical imaging systems and their applications. A nonparaxial confocal optical imaging theory is developed based on the scalar Rayleigh-Sommerfeld diffraction theory and Sine Condition without the normally-used thin-lens approximation. Two confocal optical range sensors and a Real-time Confocal Scanning Optical Microscope (RSOM) are demonstrated. It is shown that our RSOM has tremendous advantages over other confocal microscopes both in scanning speed and in the ease of use and alignment. The dependence of the imaging characteristics on the pinhole size and the lens is fully discussed. Experimental measurements are compared with the theoretical calculations. Good agreement is obtained. Also demonstrated in this thesis are numerous applications of the RSOM in integrated circuit metrology and biomedical imaging. Deep trenches as narrow as 1 μm and deep as 6 mu m are observed with the RSOM. The RSOM is not only able to measure the trench depth but, is also able to inspect individual defects inside the trench. Linewidth measurement is also investigated. The RSOM is shown to have an excellent optical cross-sectioning capability. Sectioned images of bones, teeth, and the unprepared cornea of a rabbit eye have been observed. Well-defined sectioned images have been obtained. Fluorescence images have also been taken with the RSOM to demonstrate its image improvement over the standard fluorescence microscope.