EXCITED-STATE ABSORPTION IN RED PERYLIMIDE DYE IN SOLUTION

We measured the gain spectrum of red perylimide dye (RPD) dissolved in cyclohexane. A frequency-doubled Nd:YAG laser at 1 Hz repetition rate was used for pumping. A probe pulsed laser beam was obtained using a series of laser-grade dyes. Gain is observed in the region 550-660 nm and loss in the region 660-730 nm. The loss is interpreted as absorption from the first singlet excited state S1 to a higher singlet excited state S(n). The cross section sigma1n is calculated as 1.3 x 10(-16) cm2/molecule in the region 550-600 nm and 5 X 10(-17) cm2/molecule in the region 650-710 nm. This process competes with the stimulated emission to a lower state, which establishes the mechanism for the dye-laser action.