Nonlinear absorption in an azo-containing ion liquid crystal polymer in the different excitation regimes

The nonlinear absorption of an azo-containing ion liquid crystal polymer, in dimethylformamide solution or solid thin film, has been investigated using Z-scan technique. Under the excitation of nanosecond or picosecond pulses at 532 nm, the film presents large saturable absorption (SA), while the solution shows reverse saturable absorption. The alteration of nonlinear absorption behavior is due to the change of excited state cross-section and the time of intersystem crossing in solution and film. Irradiated by a continuous wave laser, SA is observed in both solution and film due to the low excitation optical intensity and thermal effect.