Superior optical limiting, stabilization, and spatio-temporal reshaping of ultrashort laser pulses in an opto-stable intrinsic polymer film

A chemically modified poly(fluorene-alt-benzothiadiazole) (PFBT) polymer film is reported to exhibit high twophoton absorbing capability and chemical/physical stability upon the action of high-power laser pulses of ∼780nm wavelength and ∼160fs duration. A nonlinear transmission measurement is conducted by varying the input intensity from ∼20 to ∼600 GW=cm², the corresponding nonlinear transmission ofa ∼70μmthick filmis reduced from ∼0·8 to 0.18, indicating a superior optical limiting behavior. In the meantime, intensity fluctuation of laser pulses can be significantly reduced after passing through the same film sample. Based on the intensity-dependent nonlinear attenuation mechanism, a straightforward optical reshaping effect on spatio-temporal profiles of the laser pulses has also been demonstrated.