Apparatus for the measurement of small absorption change kinetics at 820 nm in the nanosecond range after a ruby laser flash.

An apparatus for the measurement of kinetics of small absorption changes (DeltaA approximately 10(-3)-10(-4)) at 820 nm in a biological sample in the nanosecond range after a short high-intensity ruby laser flash (200 mJ, 8 ns) is described. The laser-induced fluorescence artefact is greatly reduced by the use of a solid-state laser diode as source of measuring light, in combination with a microscope lens and a diaphragm. The signal-to-noise ratio is enhanced by the use of an avalanche photodetector connected to a laboratory-made low-noise and interference-free amplifier. The signals are processed by a transient digitizer in combination with a signal averager. The response time of the apparatus is about 20 ns. With some modifications the apparatus can be used to measure absorption changes in a broad spectral range.