Phase fluorometry using a continuously modulated laser diode

The authors report phase fluorometrlc measurements using directly amplitude-modulated 670- and 791-nm laser diodes as the excitation source. Fluorescence lifetimes ranging from 220 ps to 1.7 ns were measured using a commercial phase fluorometer. It was found that higher amounts of radio frequency power were required to achieve comparable degrees of modulation when the dc current on the diode was Increased and that rf power above a certain level created distortion In the light output. Results are shown for common cyanlne laser dyes emitting at wavelengths to 840 nm.