4f Pump-probe Technique To Study The Dynamic Excited-state Nonlinearities Of Chloroaluminum Phthalocyanine (CAP) Solution

Nonlinear optical (NLO) materials have been extensively investigated for their potential value in optical switching and limiting applications. Simple and reliable measurement technique is necessary for searching the expected NLO materials. So the nonlinear measurement technique has become the key point to investigate the nonlinear optical materials. Instantaneous processes of the dynamic excited-state optical nonlinearities within materials provide important physical mechanisms for realizing super-fast optical limiting and switching applications. Time-resolved pump-probe scheme is one of the most effective methods to study the dynamic excited-state nonlinearities of materials.In this paper we experimentally studied the dynamic excited-state nonlinearities of chloroaluminum phthalocyanine (CAP)/ethanol solution excited by 22ps laser pulse at the wavelength of 532nm by using the newly developed time-resolved pump-probe system based on 4f NIT-PO. Dynamic absorption coefficient and nonlinear refractive index are deduced through analyzing seventy frames of nonlinear image with different time delay during the delay region -400ps to 2000ps from the standpoint of information. The experimental results indicate that the CAP/solution has an instantaneous reverse saturable absorption and positive extra refraction excited by the 22ps laser pulse. Then both the nonlinear absorption and refraction relax towards the equilibrium with comparatively slower steps, and the first excited singlet state dominates the excited-state nonlinearities in the process. Some photophysical parameters of the CAP are obtained by theoretically fitting the experimental curves using the excited-state nonlinearity theory and molecular five-energy-level model: the absorption cross sections of first excited singlet state σ1 =25×10?mand the molecular refractive index difference between the first excited singlet state and ground-stateΔη=2 .2×10?28m3. On the other side it is demonstrated the pump-probe system based on 4f NIT-PO plays a responsible role in measuring the dynamic excited-states nonlinearities of materials.