Trinity College Dublin, Department of Physics

Prof. Eithne McCabe's Home Page

Confocal Microscopy: Three-dimensional high-resolution imaging


Biographical sketch: Professor  E. McCabe, M.A.(Oxon), D.Phil.(Oxon), B.E.(NUI), F.Inst.P., C.Phys.


Fellow, Trinity College Dublin.
Fellow, Institute of Physics.


Lecturer, Magdalen College Oxford, 1991-1992.
Research Fellow of the Royal Commission for the Exhibition of 1851, University of Oxford, 1991-1992.
Fellow of Magdalen College Oxford, 1987-1991.
Member of Governing Body, Magdalen College Oxford, 1987-1991.
Postdoctoral Member of Technical Staff, AT&T Bell Laboratories, New Jersey, USA. All of 1988.
Consultant, AT&T Bell Laboratories, Summer 1989.
Zonta Amelia Earhart International Fellowship Award, 1988.
Senior Scholar, Lincoln College Oxford, 1986-1987.
Royal Television Society Baird Travelling Scholarship, 1986.
The Hewlett Packard award for Innovation in Electrical Engineering, 1984.
Institute of Chemistry Gold Medal for First Place in Leaving Certificate Chemistry, 1980.

Administrative experience - outline:

International Union of Pure and Applied Physics team leader for Women in Physics initiative, 2001/2002
Member of organising committee/Chair for the SPIE (The International society for Optical Engineering)Photonics West conference, San Jose, USA, 1999-2003
Secretary and member of the Institute of Physics Education sub-group, 1996-2001
Institute of Physics Tyndall lecture series coordinator.
Enterprise Ireland research grant committees, 1998-
Member of Finance Committee, TCD, 2001-
Member of Working Party on Teaching and Learning, TCD, 2001-
Member of Staff Appointments Committee, TCD, 2000-
Member of Catering Management Committee, TCD, 2001-
Member of Graduate Studies Committee, TCD, 1993-1996

 (a)                                                                                            (b)

 (c)                                                                                             (d)

Confocal photoluminescence images of a II-VI laser structure showing the progressive stages of degradation and annealing in a ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructure: (a) t=0, (b) t=15 sec., (c) t=2 min., (d) t= 40 min.


Other group members: Dr. L.Yang, Dr.A.Dunbar, Mr.S.Walker, Mr.A.MacRaighne, Ms.J.Garry


 Optical microscopy has seen many rapid changes over the last twenty years. The field of confocal microscopy has revolutionised the way biologists, physicists and engineers alike use light to image a whole range of samples from biological cells to semiconductor devices. The three-dimensional, high-resolution, non-destructive features of confocal microscopy are captivating new microscope users and driving the development of radically new types of confocal microscopes. The confocal group at Trinity focuses in considerable detail on the theoretical as well as the experimental aspects of confocal imaging.

Confocal imaging in a confocal microscope is usualy achieved by placing a small pinhole in front of the photodetector in a scanned imaging system. This results in two key features of confocal imaging:

    (1) Increased lateral resolution (typically 0.5 micron using a red light source, and even better resolution using shorter wavelength sources)

    (2) An optical sectioning capability: Essentially only the part of the specimen in the focal plane of the objective lens is imaged. Light collected from outside the focal plane of the lens is rejected by the pinhole. In this way a slice of an object may be imaged. Scanning permits very many slices to be imaged. In this way high resolution, three-dimensional images may be built up of a variety of specimens in a non-destructive fashion.

      These images may be brightfield, or reflection, giving surface topography, for example or they may show sub-surface features. The images above show how confocal photoluminescence imaging may be used to image features in the active region of a II-VI laser structure. This research was carried out in collaboration with Sony in Japan and Dr. John Donegan in Trinity who is an expert in wide-bandgap materials. In this case the defects imaged change with time and conditions. These changes may be explained in terms of both device degradation and annealing.

      A direct-view microscope is a significant modification of a confocal microscope in that it uses multiple-aperture arrays in the source and detector planes. By scanning these apertures, real-time images may be built up. In practice this aperture array consists of a disk with many pinholes. By scanning this disk, quasi-confocal images may be obtained at speed.


      Direct-view microscope setup

      One of the current research interests of the confocal research group at Trinity is the issue of developing a theory which optimises this pinhole congiguration in terms of shape and aperture spacing in direct-view microscopy. A state-of-the-art confocal microscope in our laboratory acts as a test-bed for experimental work to test our theory.

       The Trinity confocal group is currently investigating the adaptation of current microscopes to improve imaging properties of three-dimensional confocal microscopes. There is also significant emphasis on the design of entirely new kinds of microscopes. The group is involved in the whole applications side of confocal microscopy, both from a physics and engineering perspective, and would welcome further industrial and academic interaction. There is already strong interaction with Optronics which is an Irish government sponsored initiative whose aim is to bring suitable optoelectronic research ideas to prototype stage and beyond.

      For further information contact:

      Prof. Eithne McCabe
      Department of Physics
      Trinity College Dublin
      Dublin 2

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