Determination of picosecond relaxation times of bleachable dyes by the method of cross polarizers

A background-free method is proposed for the determination of the time constants of fast relaxation of bleachable dyes. The method utilizes exciting and probe ultrashort light pulses. The absence of background is ensured by the use of crossed polarizers. The results are given of a determination (by the new method) of picosecond relaxation times of bleachable dyes of the kind used for mode locking of neodymium laser radiation. These results are in good agreement with the data obtained by the familiar absorption method.