Santhi Ani Joseph

Size dependent optical properties of the CdSe-CdS core-shell quantum dots in the strong confinement regime

We have investigated the third-order optical nonlinearity in CdSe and CdSe-CdS core-shell quantum dots with particle sizes in the range 4.4–5.2 nm by the z-scan technique. Optical absorption and fluorescence properties show quantum confinement effect and the fluorescence peak is shifted when the diameter of the core-shell quantum dots becomes large. Their nonlinear absorption and nonlinear refraction were observed with nanosecond laser radiation of 532-nm wavelength. At an excitation irradiance of 392 MW/cm2, the CdSe-CdS core-shell quantum dots exhibit a reverse saturation and a negative nonlinear refractive index indicating a clear nonlinear behavior. The introduction of CdS shell around CdSe core gives large third-order nonlinearity and third-order optical susceptibility decreases with increasing particle core size in the case of core-shell quantum dots within the range of our investigations. The third-order susceptibility of these quantum dots vary from 3.39 × 10−11 to 5.77 × 10−11 esu. The optical li...

Band-gap tuning and nonlinear optical characterization of Ag:TiO2 nanocomposites

Silver/titanium dioxide nanoparticles with varied concentration of silver have been synthesized by a simple laser light induced chemical reaction, where bulk titanium dioxide powder is used as the starting material. The particle size, morphology, crystal structure, and optical properties were characterized by transmission electron microscopy, x-ray diffraction, UV-Vis absorption spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. The x-ray diffraction pattern revealed that the TiO2 nanoparticles obtained are in pure rutile phase. The important observation from transmission electron microscopic images is that the Ag particles are distributed over the surface of titanium dioxide nanoparticles. The band gap of the TiO2 nanoparticles was tuned between 1.75 and 2.75 eV by varying Ag concentration. The nonlinear optical absorption and optical limiting performance of Ag:TiO2 nanocomposites were investigated by open aperture z-scan using nanosecond Nd:YAG laser pulses operating a...

LINEAR AND NONLINEAR OPTICAL PROPERTIES OF GOLD NANOPARTICLES STABILIZED WITH POLYVINYL ALCOHOL

The nonlinear optical absorption of gold nanoparticles dispersed in polyvinyl alcohol (Au:PVA) is investigated using open aperture Z-scan technique. Au:PVA nanocomposite material is synthesized by chemical method. The characterization of the material is done by UV/Vis absorption spectroscopy, transmission electron microscopy and X-ray diffractometry (XRD). It is observed that the nature of the nonlinear absorption depends on the excitation wavelength. The optical limiting capability of the sample is also demonstrated at a wavelength of 532 nm.

Structural and Optical Properties of Zinc Oxide Micro Rods Synthesized By Low Temperature Hydrothermal Route

We have studied the structural and optical properties of ZnO micro rods. These rods are synthesized by low temperature hydrothermal method, which is under the treatment of 80 °c/22 hrs. The synthesized rods have an average length of 5 μm with hexagonal cross section. They are characterized by absorption spectrum, fluorescence spectrum, back scattering, SEM, HRTEM, and SAED. The photoluminescence from the spectrophotometer shows broad visible emission.

Laser-induced Bessel beams can realize fast all-optical switching in gold nanosol prepared by pulsed laser ablation

We demonstrate the possibility of realizing, all-optical switching in gold nanosol. Two overlapping laser beams are used for this purpose, due to which a low-power beam passing collinear to a high-power beam will undergo cross phase modulation and thereby distort the spatial profile. This is taken to advantage for performing logic operations. We have also measured the threshold pump power to obtain a NOT gate and the minimum response time of the device. Contrary to the general notion that the response time of thermal effects used in this application is of the order of milliseconds, we prove that short pump pulses can result in fast switching. Different combinations of beam splitters and combiners will lead to the formation of other logic functions too.