Faculty Publications
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Item Third-order nonlinear optical properties of Mn doped ZnO thin films under cw laser illumination(Elsevier B.V., 2013) Nagaraja, K.K.; Pramodini, S.; Santhosh Kumar, A.; Nagaraja, H.S.; Poornesh, P.; Kekuda, D.We report the measurements of third-order nonlinear optical properties of undoped zinc oxide and manganese doped zinc oxide thin films with different doping concentrations investigated using z-scan technique. Thin films were prepared by radio frequency magnetron sputtering using a compound target on glass substrate at room temperature. The structural properties of the deposited films were analysed by X-ray diffraction studies. The atomic force microscope analysis of the deposited films reveals that the grain size and roughness of the films depend on the Mn concentration. The direct energy band gap of the deposited film increases with the increase in Mn concentration in the films. The nonlinear optical measurements were carried out using a cw He-Ne laser at 633 nm wavelength. The z-scan results reveal that the films exhibit self-defocusing nonlinearity. The third-order nonlinear optical susceptibility ?(3) is found to be of the order of 10-3 esu. The films investigated here exhibit good optical power limiting at the experimental wavelength. © 2012 Elsevier B.V. All rights reserved.Item Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye(Elsevier B.V., 2013) Pramodini, S.; Poornesh, P.; Nagaraja, K.K.We report the investigations of thermally induced third-order nonlinear optical and optical limiting characterizations for various concentrations of acid blue 40 dye in N,N-Dimethyl Formamide, studied by employing z-scan technique under cw He-Ne laser irradiation at 633 nm wavelength. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. For lower concentration, the samples display both saturable absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails. The estimated values of the effective coefficients of nonlinear absorption ?eff, nonlinear refraction n2 and third-order nonlinear susceptibility ?(3) were found to be of the order of 10-2 cm/W, 10-4 esu and 10-6 esu respectively. Multiple diffraction rings were observed when the samples were exposed to laser beam due to refractive index change and thermal lensing. The effect of concentration and the laser intensity on the self-diffraction ring patterns was studied experimentally. The acid blue 40 dye also exhibited strong optical limiting properties under cw excitation and reverse saturable absorption is found to be the dominant nonlinear optical process leading to the observed nonlinear behaviour. © 2013 Elsevier B.V. All rights reserved.Item Third harmonic generation process in Al doped ZnO thin films(2014) Abd-Lefdil, M.; Douayar, A.; Belayachi, A.; Reshak, A.H.; Fedorchuk, A.O.; Pramodini, S.; Poornesh, P.; Nagaraja, K.K.; Nagaraja, H.S.We have performed studies on the third-order nonlinear optical susceptibility of Al doped ZnO (AZO) thin films using z-scan and third harmonic generation techniques. From the present studies, it reveals that the introduction of Al in ZnO leads to substantial changes in the third-order nonlinear susceptibility. Additionally we have shown that using treatment by the 707 nm laser pulses of the Er:glass 20 ns laser also influence on the third harmonic generation. Such behavior is explained by the photoinduced charge re-occupation of the trapping levels on the borders substrate and ZnO. Further, the sign and magnitude of nonlinear absorption coefficient ?eff, nonlinear refractive index n2, real and imaginary parts of third-order nonlinear susceptibility were evaluated. Finally, the optical limiting studies for various concentrations of AZO thin films were determined. Reverse saturable absorption was the dominant process leading to the observed nonlinear behavior. © 2013 Elsevier B.V. All rights reserved.Item Structural, linear, and nonlinear optical properties of radio frequency-sputtered nitrogen-doped ZnO thin films studied using z-scan technique(Institute of Physics Publishing custserv@iop.org, 2014) Nagaraja, K.K.; Pramodini, S.; Santhosh Kumar, A.S.; Nagaraja, H.S.; Poornesh, P.The third-order nonlinear optical properties of undoped and nitrogen-doped ZnO thin films were evaluated using the z-scan technique. The films were sputter-deposited on glass substrates using radio frequency power. The He-Ne continuous wave laser operating at 633 nm was used as an irradiation source. A change in the growth mode in the nitrogen-doped films was observed. The grain size and roughness were found to be dependent on the nitrogen concentration, as shown by atomic force microscopy analysis. The optical band gap was determined and found to increase with nitrogen concentration in the films. Both nonlinear absorption and refraction nonlinearities were exhibited by the deposited films. The nonlinear refractive index n2, the nonlinear absorption coefficient ?eff and the third-order nonlinear optical susceptibility ?(3) were determined and found to be largest. Multiple diffraction ring patterns were observed when the samples were made to interact with the laser beam and were attributed to refractive index change and thermal lensing. Further, optical power-limiting experiments were performed to determine the optical-limiting threshold and clamping values for undoped and nitrogen-doped ZnO films. © 2014 Astro Ltd.Item Influence of annealing on the linear and nonlinear optical properties of Mn doped ZnO thin films examined by z-scan technique in CW regime(Elsevier B.V., 2016) Nagaraja, K.K.; Pramodini, S.; Poornesh, P.; Rao, A.; Nagaraja, H.S.We present the studies on the influence of annealing on the third-order nonlinear optical properties of RF magnetron sputtered manganese doped zinc oxide (MZO) thin films with different doping concentration. It is revealed that the incorporation of Mn into ZnO and annealing lead to prominent changes in the third order nonlinearity. Nonlinear optical measurements were carried out by employing the z-scan technique using a continuous wave (CW) He-Ne laser of 633 nm. The z-scan results reveal that the films exhibit self-defocusing thermal nonlinearity. The third-order nonlinear optical susceptibility ?(3) was found to be of the order of 10-3 esu and 10-2 esu for annealed MZO thin films at 200 °C and 400 °C respectively. The dependence of grain size on the observed nonlinearity was revealed by atomic force microscopy analysis. Optical limiting studies were carried out for a range of input power levels and an optical limiting of about ?8 mW was observed indicating the possible application for photonic devices. © 2016 Elsevier B.V. All rights reserved.Item Continuous wave laser probed thermal nonlinearity in TiO2 and TiO2-dye nano colloidal(Elsevier Ltd, 2021) Pramodini, S.; Aravinda, L.S.; Nagaraja, K.K.; Poornesh, P.Herein, we report on the nonlinear optical studies on the nano colloidal solutions of titanium dioxide (TiO2), TiO2-dye and acid blue dye in distilled water under continuous wave laser using the z-scan technique. The phase and structural properties of the sol–gel synthesized TiO2 nanoparticles at different temperatures were analyzed by x-ray powder diffraction (XRD) studies. The transmission electron microscopy (TEM) images confirmed that with an increase in calcination temperature, crystallite size increases. Further, the Fourier transform infrared (FTIR) spectra validate the synthesized TiO2 nano particle's structure. The results from the z-scan reveal self-defocusing and reverse saturable absorption (RSA) behaviors of nano colloidal. The real and imaginary parts of third-order nonlinear optical susceptibility ?(3) were determined and estimated as 10?6 esu. Also, the optical limiting behavior of the samples is studied; a clamping of around ~ 4 mW is observed for the TiO2-dye nano colloidal. © 2021 Elsevier Ltd