Amplitude and phase nonlinear response of bleachable dyes using picosecond excitation

Amplitude and phase responses of bleachable dyes are experimentally investigated using a picosecond pump and probe pulse technique combined with light polarization measurements. In the measurements, the amplitude response appears in the form of dichroism of bleaching, and the phase response appears in the form of induced birefringence. The method of measurement is adapted for dyes with fast relaxation of the excited state; these dyes are used for mode locking in ultrashort pulse lasers. Experimental results of phase response contribution and mutual relaxation time of amplitude and phase responses are presented for some polymethine dyes.