21 April 2016 Infrared reduction, an efficient method to control the non-linear optical property of graphene oxide in femtosecond regime
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Graphene Oxide (GO) has been prepared by modified Hummers method and it has been reduced using an IR bulb (800-2000 nm). Both as grown GO and reduced graphene oxide (RGO) have been characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Raman spectra shows well documented Dband and G-band for both the samples while blue shift of G-band confirms chemical functionalization of graphene with different oxygen functional group. The XPS result shows that the as-prepared GO contains 52% of sp2 hybridized carbon due to the C=C bonds and 33% of carbon atoms due to the C-O bonds. As for RGO, increment of the atomic % of the sp2 hybridized carbon atom to 83% and rapid decrease in atomic % of C=O bonds confirm an efficient reduction with infrared radiation. UV-Visible absorption spectrum also confirms increment of conjugation with increased reduction. Non-linear optical properties of both GO and RGO are measured using single beam open aperture Z-Scan technique in femtosecond regime. Intensity dependent nonlinear phenomena are observed. Depending upon the intensity, both saturable absorption and two photon absorption contribute to the non-linearity of both the samples. Saturation dominates at low intensity (~ 127 GW/cm2) while two photon absorption become prominent at higher intensities (from 217 GW/cm2 to 302 GW/cm2). We have calculated the two-photon absorption co-efficient and saturation intensity for both the samples. The value of two photon absorption co-efficient (for GO~ 0.0022-0.0037 cm/GW and for RGO~ 0.0128-0.0143 cm/GW) and the saturation intensity (for GO~57 GW/cm2 and for RGO~ 194GW/cm2) is increased with reduction. Increase in two photon absorption coefficient with increasing intensity can also suggest that there may be multi-photon absorption is taking place.
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S. Bhattacharya, S. Bhattacharya, R. Maiti, R. Maiti, S. Saha, S. Saha, A. C. Das, A. C. Das, S. Mondal, S. Mondal, S. K. Ray, S. K. Ray, S. B. N. Bhaktha, S. B. N. Bhaktha, P. K. Datta, P. K. Datta, "Infrared reduction, an efficient method to control the non-linear optical property of graphene oxide in femtosecond regime", Proc. SPIE 9884, Nanophotonics VI, 98842L (21 April 2016); doi: 10.1117/12.2227328; https://doi.org/10.1117/12.2227328

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