Abstract

Recently, metallophthalocyanine solutions have shown promise as optical-limiting elements for sensor protection applications. The mechanism, referred to as reverse saturable absorption, is primarily due to excited-state absorption (ESA). We report the separation of nonlinear absorption and refraction in phthalocyanine solutions on a picosecond time scale, using a combined nonlinear transmittance and beam distortion method, which we refer to as a Z-scan.¹ Measurements were made on solutions of chloroaluminum phthalocyanine (CAP) and on a silicon naphthalocyanine (Nc) derivative, [Si(OSi(hexyl)₃)₂Nc; referred to as SiNc], We find that both nonlinear absorption and refraction are dominated by creation of a real population of excited states, although the wavelength of observation lies between absorption bands. With using nanosecond pulses, excited-triplet-state absorption limits the transmission; however, with picosecond pulses, excited-singlet-state absorption becomes important, and self-focusing is observed.

© 1991 Optical Society of America