The optical length effect, diffraction pattern and thermal lensing of Disperse Orange 25

• The nonlinear optical properties of DO25 are investigated.
• The effect of optical length as well as concentration of DO25 was measured.
• At 632 nm, the laser radius variation due to thermal lensing effect investigated.
• At 532 nm, the diffraction rings appeared and increase with the incident power.

The nonlinear responses of an azo dye, Disperse Orange 25 (DO25), are investigated under two irradiation of continuous Lasers at 532 and 632 nm wavelengths and the third order refractive index is measured by use of Z-scan technique. At 632 nm wavelength (far from the absorption peak), the close z-scan plots show that this material has a very good nonlinear response with negative sign indicating self-defocusing. The effect of optical length and concentration of samples in nonlinear responses have been investigated experimentally. Also, the radius variation at far field observed due to thermal lens effect. Finally, at other wavelength, 532 nm (near from the absorption peak), the nonlinear optical responses increase sharply so the diffraction rings appear and the numbers of rings increase with the incident laser power.