Biomedical Engineering Reference
In-Depth Information
Fig. 11.3.
Evanescent illumination of fluorescent complexes at the surface of the
core of a partially clad waveguide. Reprinted from Ligler and Taitt (2002) with
permission from Elsevier
Fig. 11.4.
Strategies for separation of excitation and emission light paths (Ligler
and Taitt, 2002). Figure reprinted with permission from Elsevier
originally suggested that dipoles close to the surface could emit approximately
2% of their radiated power (fluorescence) into modes coupled back up the fiber;
however, Polercky et al. (2000) have more recently analyzed films of dipoles
and concluded that a much higher proportion of the radiation can couple into
guided modes.
A variety of configurations have been utilized with optical fibers for excit-
ing fluorescence and collecting the emitted signal. In Fig. 11.4a, a traditional
dichroic mirror is used to separate excitation and emission on the basis of the
difference in wavelengths. The excitation light may pass through the mirror,
while the emission light is reflected onto a detector (left) or, in a scheme that
has generally proven more effective, the stronger excitation light is reflected
onto the end of the fiber, while the emitted light passes straight through. In
Fig. 11.4b, the excitation light passes through a hole in an off-axis parabolic
