International Journal of Innovative Technology and Exploring Engineering (IJITEE) ISSN: 2278-3075, Volume-5 Issue-9, February 2016 7 Published By: Blue Eyes Intelligence Engineering & Sciences Publication Pvt. Ltd. Phase Effects at Second Harmonic Generation in Zinc Oxide, Grown on Glass Substrate Rena J. Kasumova, V.C. Mamedova, G.A. Safarova Abstract- Theoretical investigation of frequency conversion in ZnO films laid over glass substrates with account for phase effects has been developed. For this the constant-intensity approximation of fundamental radiation is applied. The numerical calculation of the efficacy obtained in constant- intensity approximation confirms the following that because of dispersion of the second order nonlinear optical coefficients the generated signal decreases for an increasing fundamental wavelength. Furthermore, the zinc oxide films generate stronger second harmonic signal because of the larger interaction length of the nonlinear medium. Method of analysis of second harmonic generation in zinc oxide, grown on glass substrate used in the present work, may be involved for research of other films. Keywords: nanocompo site film; glass substrate; second harmonic generation; constant-intensity approximation; frequency conversion. I. INTRODUCTION In order to be able to process all of optical signals we need to have developed switches for example all optical switches and this requires new nonlinear materials. Among those required candidate one must pay attention to good optical quality (e.g. small amount of dissipation) [1, 2]. Among these ZnO could be considered as an interesting semiconductor with a wide band gap of 3.3 eV at the room temperature, which could be combined with high excitonic gain and binding energy [3]. According to recent studies, ZnO thin films happen to have a strong nonlinear suscepitibilty of second-order which cause for them to be a candidate for generating effective second harmonics [4, 5]. Nanosize structure technology is being used in order to construct miniaturized versions of these devices. This implies deploying new method, which is using of thin dielectric and semiconductor films instead of bulk material itself as the technology of bulk, also, is not very economical because of their requirement of developed technology of crystal growth and time consuming processing. The morphology and structure of these compounds could be informative via exploration of semiconductors and dielectrics by harmonic generation method [6]. It was outlined in work [7] that the studied patterns were manufactured based on ZnO films over a glass substrate using the technology of sputtering ion beam. This work illustrates the theoretical model for the analysis of the experimental data and also is going to discuss preliminary deductions for the structure of the ZnO crystalline relying on measurements of nonlinear optical properties carried out by authors. Revised Version Manuscript Received on January 13, 2016. Rena J. Kasumova, Department of Physics, Baku State University, Zahid Khalil, Bakı, Azerbaijan. V.C. Mamedova, Department of Physics, Baku State University, Zahid Khalil, Bakı, Azerbaijan. G.A. Safarova, Department of Physics, Baku State University, Zahid Khalil, Bakı, Azerbaijan. A couple of works, e.g. [8-10] are dedicated to the theory of nonlinear interaction in the thin films of zinc oxide, particularly, at second harmonic generation (SHG). Authors of these works deploy the analysis of frequency conversion, particularly, the constant-field approximation (CFA) [11- 12]. For the case of CFA, the coherent length of nonlinear medium is the total function of mismatch of wave vectors. This approximation will only be acceptable at the initial phase of the interaction for we can ignore the effect of the excited harmonic waves of basic radiation. This will cause losing some information regarding qualitative features of nonlinear process. To analyze the process, we can make direct numerical solution of reduced equation. This will allow us to obtain exact analytical expressions and determining the appropriate parameters in order to get highest conversion efficiency using optimized analytical method. We can calculate the phase change and losses for interacting waves simultaneously which is the advantage of constant intensity approximation CIA [13-14] while considering the reverse reaction of the excited wave over pump wave. Furthermore, the coherent length in this approach depends on parameters such as basic radiation intensity and dissipation in the medium besides mismatch of interacting waves. We are going to analyze the CIA for nonlinear interaction for generating of second harmonic in ZnO samples laid over glass substrates while considering the losses and phase changes of all interacting waves. It is proved though because of the dispersion regarding second order nonlinear optical coefficients, the generated signal decrease as the fundamental wavelength increase. We are also going to analyze factors causing restriction of efficiency conversion. II. THEORY Here we are going to take a closer look at redoubling frequency process for laser radiation with the frequency of 1  for ZnO with noncentrosymmetric structure for the case of scalar phase matching of first kind. For nonlinear conversion, the known system of reduced equation is deployed to analyze the interaction of waves to describe second harmonic generation with the frequency of 2  while considering linear losses in a structure [11-12] * 1 1 1 1 2 1 2 2 2 2 2 1 exp( ), exp( ), dA A i AA iz dz dA A i A iz dz           (1) Here, 1,2 A are the complex amplitudes of the pump wave and its second harmonic at frequencies 1,2  ( 2 1 2    ),