Efficient control of ultrafast optical nonlinearity of reduced graphene oxide by infrared reduction

Abstract

Simultaneous occurrence of saturable absorption nonlinearity and two-photon absorption nonlinearity in the same medium is well sought for the devices like optical limiter and laser mode-locker. Pristine graphene sheet consisting entirely of sp2-hybridized carbon atoms has already been identified having large optical nonlinearity. However, graphene oxide (GO), a precursor of graphene having both sp2 and sp3-hybridized carbon atom, is increasingly attracting cross-discipline researchers for its controllable properties by reduction of oxygen containing groups. In this work, GO has been prepared by modified Hummers method, and it has been further reduced by infrared (IR) radiation. Characterization of reduced graphene oxide (RGO) by means of Raman spectroscopy, X-ray photoelectron spectroscopy, and UV-Visible absorption measurements confirms an efficient reduction with infrared radiation. Here, we report precise control of non-linear optical properties of RGO in femtosecond regime with increased degrees of IR reduction measured by open aperture z-scan technique. Depending on the intensity, both saturable absorption and two-photon absorption effects are found to contribute to the non-linearity of all the samples. Saturation dominates at low intensity (∼127 GW/cm2) while two-photon absorption becomes prominent at higher intensities (from 217 GW/cm2 to 302 GW/cm2). The values of two-photon absorption co-efficient (∼0.0022–0.0037 cm/GW for GO, and ∼0.0128–0.0143 cm/GW for RGO) and the saturation intensity (∼57 GW/cm2 for GO, and ∼194 GW/cm2 for RGO) increase with increasing reduction, indicating GO and RGO as novel tunable photonic devices. We have also explained the reason of tunable nonlinear optical properties by using amorphous carbon model.

Topological Insulators: An In‐Depth Review of Their Use in Modelocked Fiber Lasers

“…Note that the presence of Dirac cone in the band structure is mainly responsible for the broad band saturable adsorption property of graphene. [65] Therefore, from the above discussion we can conclude that Bi 2 Se 3 can be used for modelocking at different wavelengths (near-IR to mid-IR regime) as found in the literature, whereas, Bi 2 Te 3 is found to be useful as SA for modelocking mostly at ≈1.55 µm.…”

Electrical transport properties and ultrafast optical nonlinearity of rGO–metal chalcogenide ensembles

“…It was found that with a higher degree of reduction of GO to rGO, both the saturation intensity and TPA coefficient (b eff ) increase which is due to a higher TPA cross-section of the sp 2 domain over the sp 3 matrix. 29 It is shown in several reports that rGO-nanomaterial composites show enhanced NLO properties as compared to pure nanomaterials due to better photoinduced charge transfer from nanomaterials to rGO sheets. 27,30 In an experiment, laser pulses tend to heat up the samples resulting in thermally generated charge carriers.…”

Physical properties and device applications of graphene oxide

“…During increasing the concentration of sp 2 C-C bonds from 48.31% to 61.75% by reduction, the two-photon absorption coefficient increases from 1.44 to 4.60 cm/GW and the saturation intensity changes from 1.5 to 2 .5 GW/cm 2 . Similarly, Bhattachraya et al[386] pointed out that, for the RGO measured by open aperture Z-scan technique, saturation dominates at low intensity about 127 GW/cm 2 , while two-photon absorption becomes prominent at higher intensities from 217 to 302 GW/cm 2 . For the GO samples with different concentration of sp 2 C-C bonds, the values of two-photon absorption coefficient and the saturation intensity increase with increasing extent of reduction, as shown inTable 6, where the concentrations of sp 2 carbons are 49.27% for GO, 57.76% for RGO1, 60.66% for RGO2 and 90.54% for RGO3, respectively.…”

“…Reproduced 99 from Ref [383][385,386]. For example, Shi et al[385] studied nonlinear optical properties of both GO and RGO by single beam Z-scan measurement at 532 nm in the picosecond region.…”

“…Isat and βeff represent the saturation intensity and the twophoton absorption coefficient, respectively. Reproduced from Ref [386]…”