Ramazan Esen

The effect of annealing on structural and optical properties of ZnO thin films grown by pulsed filtered cathodic vacuum arc deposition

Thin ZnO films were deposited at room temperature on glass substrates by a pulsed filtered cathodic vacuum arc deposition system. The crystallographic structure and the size of the crystallites in the films were studied by means of x-ray diffraction. These measurements show that all the films are crystallized in the wurtzite form, present in a preferred orientation along the (002) direction, and the grain size is estimated to be 18.9–42 nm. The crystallite sizes were found to increase and the x-ray diffraction patterns were sharpened by annealing. Optical properties of the ZnO films were studied using a UV–visible spectrometer and calculations made using the envelope method. The absorption coefficient and optical band gap of the films were increased while the refractive index was decreased by annealing. The best annealing temperature for pulsed cathodic vacuum arc deposition grown ZnO thin films on glass substrates was found to be 600 °C from optical properties. This temperature is as high as can be measured for glass substrates samples because of the glass properties.

Graded index optical microresonators: analytical and numerical analyses

It is known that the spectra of optical modes supported by microresonators are shape and size dependent. We have introduced an additional parameter, i.e., spatially varying refractive index, to tailor the spectra of optical modes in a microdisk resonator while keeping size and shape intact. A new class of whispering gallery mode microresonators, referred to as graded index (GRIN) microresonators, is proposed. The GRIN profile belongs to a special inhomogeneous medium known as Maxwell’s fish eye. The modal analysis of the structure is investigated both analytically and numerically. Solution of the Helmholtz equation is attempted under the spatially varying refractive index scenario and numerical verification of the analytical findings is tested by the finite-difference time-domain method. It is found that the two approaches support each other. It is expected that the findings of the GRIN microresonator may open up new research and device opportunities in photonics.