We report on our investigations of the third order optical properties of two novel prophyrin dimers and their optical
limiting behaviors. Our experiments were performed by using single beam z-scan technique and with Q-switched Nd:
YAG nanosecond laser pulses at 532nm and CW laser at 532nm respectively for two different optical limiting
mechanisms, strong excited state absorption (ESA) and thermal self-defocusing. In the experiments with pulsed laser, the
open aperture results indicated that the two dimers showed strong excited state absorption which occurs when the excited
state has an absorption cross-section higher than that of ground state. In the experiments with CW laser, optical limiting
behaviors have also been observed. In this case, the third order optical nonlinearitiy is caused by thermal self-defocusing
mechanism. Our results indicated that both novel prophyrin dimers showed potential use in optical limiters, optical
switches and optical modulators.
The nonlinear refraction index <i>n<sub>2</sub></i> and the reverse saturation absorption (RSA) coefficient β of a series of hydroxylphenyl porphyrin have been measured using single beam Z-scan technique with a 8 ns laser pulse at 532nm and the third-order nonlinear susceptibility χ<sup>(3)</sup> of the samples are calculated. It is seen that a series of hydroxylphenyl porphyrin have large value of the reverse saturation absorption and cubic nonlinear refraction. The effects of molecular structures on the third-order nonlinear optical properties were discussed. Experimental results show that the effects of different numbers and different positions of substituent to the nonlinear refraction of porphyrin are evident.