M. Bala Murali Krishna

Synthesis and structural, spectroscopic and nonlinear optical measurements of graphene oxide and its composites with metal and metal free porphyrins†

In this paper we present the structure and spectroscopic, photophysical and nonlinear optical studies of covalently functionalized novel graphene oxide–[Cu, Zn, Sn, H2 (metal free), VO] porphyrin composites. The composites were characterized by Field Enhanced Scanning Electron Microscopy (FE-SEM), micro-Raman, optical absorption, Fourier transform infrared (FT-IR), steady state and time resolved fluorescence spectroscopic techniques. The composites exhibit strong fluorescence quenching, suggesting strong electronic interactions between the porphyrin and graphene oxide molecules. Nonlinear optical absorption (NLA) studies of graphene oxide–porphyrin composites were investigated using the Z-scan technique at 532 and 800 nm with nanosecond (ns) and femtosecond (fs) laser pulses. Composites show strong two-photon absorption (TPA) as well as excited state absorption (ESA) leading to reverse saturable absorption (RSA) behaviour in the ns regime and saturable absorption (SA) behaviour was observed in fs regime. The metal free porphyrin–graphene oxide (GO) composite shows significant nonlinear absorption behaviour as well as highest fluorescence quenching behaviour compared to other GO–porphyrin composites. We further observed the enhanced figure of merit (FOM) values for composites in comparison with individual molecules.

Nonlinear optical properties of covalently linked graphene-metal porphyrin composite materials

The nonlinear optical (NLO) and optical limiting (OL) properties of covalently linked graphene-porphyrin composite materials were investigated using Z-scan technique in nanosecond regime. We observed enhanced NLO and OL properties of graphene-porphyrin composites in comparison to the individual graphene and porphyrins. The improved OL property of composites is attributed to energy transfer between porphyrin and graphene, which improved excited state absorption and nonlinear scattering. Nonlinear optical susceptibilities χ(3) of graphene and graphene-porphyrin composites were, in the order of 10−12 esu, measured using degenerate four wave mixing technique in nanosecond regime. High values of excited state absorption and two-photon absorption were observed for the composites.

Optical transmission control in graphene oxide and its organic composites with ultrashort laser pulses

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.

Nonlinear optical properties of graphene‐ (OH, Sn) porphyrin composites in picosecond regime

The nonlinear optical (NLO) properties of covalently linked Graphene‐(Sn, OH) porphyrin composite materials were investigated using Z‐scan technique at 532 nm with picosecond laser pulses. We have observed enhanced figure of merit values for composites in comparison with individual graphene, copper and zinc porphyrin. The enhanced figure of merit values for graphene‐porphyrin composite material should be attributed to two‐photon absorption and excited state absorption. We also observed different behavior, reverse saturable absorption to saturable absorption and back to reverse saturable absorption in composite molecules leading to better ultrafast nonlinear optical switching applications.

Application of 3D Polystyrene Photonic Crystals for Optical Limiting Studies

Optical limiting measurements are carried out with the 3D polystyrene (PS) photonic crystals (PhCs) fabricated by vertical deposition method using the reflection Z‐scan (RZ‐scan) technique. Interestingly we found that nonlinear reflectance decreases up to 80% which leads to good optical limiting (OL) behavior for PS PhCs compared with the thin films prepared by spin coating.

Nonlinear enhancement in 1-D photonic crystal with ZnO defect fabricated by rf sputtering

Large enhancement in nonlinear absorption (NLA) was observed in 1-D photonic crystal containing ZnO defect fabricated by rf sputtering. The enhancement in NLA is due to the strong confinement of the optical field around the defect layer.