Refractive third-order nonlinearity in vanadium-oxide phthalocyanine micro-crystals

We report a study on the resonant third-order nonlinear optical response of vanadyl-phthalocyanine micro-crystals. The refractive and absorptive contr ibutions to the nonlinear response at several wavelengths across resonance were determined by employing the z-scan technique with a tunable picosecond pulsed laser source. The samples studied were cyclohexane suspensions of v anadium-oxide phthalocyanine micro-crystals 40 nm in diameter. These micro- crystals represent an interesting alternative for the production of solid s tate samples of good optical quality through relatively simple techniques. Experimental results show that for wavelengths above 610 nm, the sample pre sents saturation of absorption, while for shorter wavelengths, induced abso rption is found. Around 610nm however, the absorptive contribution to the n onlinearity vanishes while a finite refractive contribution remains. This w avelength region is therefore potentially useful for all-optical switching applications.