NEW DUAL-CHANNEL FREQUENCY-DOMAIN FLUOROMETER FOR THE DETERMINATION OF PICOSECOND ROTATIONAL CORRELATION TIMES.

A new dual-channel multifrequency fluorometer is described which employs a mode-locked argon-ion laser as a polarized excitation source. The laser produces high-frequency sinusoidal intensity modulations in the MHz to GHz regime which are used to simultaneously probe the fluorescent molecules. The resulting orthogonally polarized components of the emission are collected by two opposite matched detection channels. With the new instrument, rotational correlation times as short as 15 ps can be routinely determined with data-acquisition times as short as 10 ms.