Studies on thermally induced third-order optical nonlinearity and optical power limiting response of Azure B under CW He-Ne laser excitation

We present the characterizations of thermally induced third-order nonlinearity, optical power limiting and self-induced diffraction rings in Azure B dye. Nonlinear measurements were carried out by employing the single beam z-scan technique. He-Ne laser operating in continuous wave mode at 633 nm wavelength was used as the source of excitation. Azure B possesses self-defocusing type of nonlinearity. Self-diffraction rings pattern were observed due to thermal lensing and change in the refractive index. Nonlinear absorption process in Azure B was due to the reverse saturable absorption. The nonlinear refractive index n₂, the nonlinear absorption coefficient β_eff and the third-order optical susceptibility χ⁽³⁾ were found to be of the order 10^-5 esu, 10 ^-2 cm/W and 10^-7 esu respectively. Azure B also displays good optical power handling capability of laser beam at the experimental wavelength, indicating the possible photonics device application such as all-optical power limiting.