Absorption characteristic and limiting effect of Congo red doped PVA film

The absorption spectrum of Congo red doped PVA film is measured. With Z-scan method, the nonlinear optical properties of the sample are investigated, and experimental data on the nonlinear refractive index and the change of refractive index are obtained. As a result, the intensity-dependent index n2 of the film has been determined to be −2.1 × 10−9 m2/W. The nonlinear absorption of the film at three wavelengths is measured respectively. Under the condition that the sample is excitated by 441.6 nm or 535 nm, the characteristics of absorption at 633 nm as a function of the probe power are determined. By using nanosecond laser pulse at 532 nm, the limiting effect of the sample is studied and the results indicate the film possesses good characteristic of optical limiting.