“…Various methods have been devised to compensate for flicker and drift of high-intensity CW light sources and for pulse-to-pulse variations characteristic of pulsed light sources such as xenon flash tubes and lasers. These methods include dualbeam, time-shared single detection, (43,44), optical feedback (45-47), and dual-beam-dual-detector ratiometric detection (48). Each of these methods, however, suffers some inadequacy.…”