S. Pramodini

Effect of annealing on the structural and nonlinear optical properties of ZnO thin films under cw regime

We report on the studies of the effects of annealing on the structural and third-order nonlinear optical properties of ZnO thin films deposited on quartz substrates by the RF magnetron sputtering technique. The films were annealed in the temperature range 400–1000 °C. The third-order nonlinear optical studies were carried out using the z-scan technique under continuous wave (cw) He–Ne laser irradiation at 633 nm wavelength. The effects of annealing on the structural properties were examined using x-ray diffraction and atomic force microscopy (AFM). The (0 0 2) preferred orientation increased with increase in annealing temperature up to 800 °C. The crystalline phases of SiO2 were observed at higher annealing temperatures. The appearance of an extraneous phase was confirmed by AFM images and optical transmittance spectra. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. The negative sign of the nonlinear refractive index n2 indicated that the films exhibit self-defocusing property due to thermal nonlinearity. The nonlinear refractive index n2, the nonlinear absorption coefficient βeff and the third-order optical susceptibility χ(3) were found to be of the highest orders. The estimated value of third-order optical susceptibility χ(3) was of the order of 10−3 esu. Multiple diffraction rings were observed when the samples were exposed to the laser beam. The appearance of rings was due to the refractive index change and thermal lensing. With increase in laser intensity, the variations of the self-diffraction ring patterns were studied experimentally. The films also exhibited strong optical limiting properties under cw laser excitation, and reverse saturable absorption was the dominant process leading to the observed nonlinear behaviour.

Structural, photoinduced optical effects and third-order nonlinear optical studies on Mn doped and Mn–Al codoped ZnO thin films under continuous wave laser irradiation

We report the photoinduced optical effects, third-order nonlinearity, and optical power limiting of Mn doped and Mn‐Al codoped ZnO thin films. The thin films were prepared by the spray pyrolysis technique. The structural properties of the deposited films were examined by x-ray diffraction studies. Z -scan measurements were conducted to evaluate the nonlinear optical parameters using a He‐Ne laser operating in continuous wave mode at 633 nm wavelength. The present study reveals that the introduction of Mn and Mn‐Al into ZnO leads to significant changes in the third-order nonlinear susceptibility. Photoinduced second-harmonic generation studies also reveal the dependence of the nonlinear optical properties on the Mn content. Switching over from saturable absorption to reverse saturable absorption was observed. The optical limiting studies show that the films possess a lower limiting threshold and clamping level, which is essential for use in eye and sensor protection applications. Hence, the Mn doped and Mn‐Al codoped ZnO thin films investigated here emerge as promising candidates for future optoelectronic and photonic device applications such as optical power limiters.

Studies on third-order optical nonlinearity and power limiting of conducting polymers using the z-scan technique for nonlinear optical applications

We present the synthesis and characterization of third-order optical nonlinearity and optical limiting of the conducting polymers poly (aniline-co-o-anisidine) and poly (aniline-co-pyrrole). Nonlinear optical studies were carried out by employing the z-scan technique using a He–Ne laser operating in continuous wave mode at 633 nm. The copolymers exhibited a reverse saturable absorption process and self-defocusing properties under the experimental conditions. The estimated values of βeff, n2 and χ(3) were found to be of the order of 10−2 cm W−1, 10-5 esu and 10−7 esu respectively. Self-diffraction rings were observed due to refractive index change when exposed to the laser beam. The copolymers possess a lower limiting threshold and clamping level, which is essential to a great extent for power limiting devices. Therefore, copolymers of aniline emerge as a potential candidate for nonlinear optical device applications.

Structural, linear, and nonlinear optical properties of radio frequency-sputtered nitrogen-doped ZnO thin films studied using z-scan technique

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 β eff and the third-order nonlinear optical susceptibility χ (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.