Simultaneous contribution of saturation in absorption and nonlinear photoacoustic effects in CuTPP under blue laser irradiation

Abstract The nonlinear optical responses of CuTPP are studied in toluene under the irradiation of a blue laser beam focused using a convergent lens. The z-scan setup is applied in order to determine nonlinear optical responses. Besides the nonlinear absorption response, which indicates reversed saturable absorption, intensity dependence photoacoustic waves are created in both hearable sound and ultrasonic waves. Hearable sound is recorded by a microphone and analyzed by Fourier transform analyzes in order to calculate the sonic frequencies. Because of the high absorption of dye molecules, a dilute solution is prepared to enhance transmittance from the cell to analyze profile of the passing beam. Diffraction rings pattern is observed with about 30 dense rings, in which the number of rings depends on the beam intensity that could be attributed to the higher frequency photoacoustic waves and the corresponding refractive grating induced by the waves. The nonlinear refraction of the solution is a simultaneous contribution of thermal lensing and photoacoustic effects, in addition to the saturation in absorption process which influences the nonlinear absorption behavior. This compound can be proposed as a good candidate in mode locking, Q-switching devises, and short pulse generators where we need a pattern from the activity of the saturable absorber at the cross section of the beam.