Abstract
Nonlinear optical transmission of graphene oxide–(Cu, Zn, Sn, H2) porphyrin composites was
investigated using the Z-scan technique at 532 nm with picosecond (ps) and 800 nm with
femtosecond laser pulses. Pure porphyrins show saturable absorption (SA) in reverse saturable
absorption (RSA) behaviour and graphene oxide shows complete RSA behaviour, observed in
an open aperture Z-scan curve. Interestingly, composites have shown a switch-over from
reverse RSA to SA and back to RSA behaviour, observed with variation of intensity towards
the focus, due to strong two-photon absorption as well as excited state absorption in the ps
regime. This switching behaviour was interpreted as due to long lifetimes and saturation of the
excited states. This may find application in optical switching.
