Investigation of nonlinear optical responses and observing diffraction rings in acid dye (Patent Green)

The nonlinear optical responses and diffraction pattern in far-field of a dye type acid (Patent Green) are investigated with irradiation of 75mW CW He-Ne laser. The second-order nonlinear refractive index and absorption coefficient of acid dye in different concentrations are measured using z-scan technique. But diffraction pattern in far-field for some concentrations of the dye culminates in observing large phase shifts which cannot be accounted for. At low laser powers, the z-scan equations are valid because Δ□0 < π. However; the phase shifts becomes more than π with when experiments are conducted with high laser power in dye solutions of high concentration. But the phase shift reach to more than in the both high powers and high concentrations therefore it would be possible to observe the far-field diffraction pattern. Further, it is demonstrated that both nonlinear refraction and absorption increase with increasing concentration and power.