Third-order Nonlinear Refractive Index Changes Research Articles

A comprehensive investigation of structural and optical properties of the spray coated Nd-doped ZnO

We report on the synthesis and characterization of Nd3+ doped Zinc oxide (ZnO) thin films fabricated using the chemical spray pyrolysis technique at 723 K. A comprehensive investigation using a combination of experimental techniques is undertaken to unveil the structural, morphological, compositional, electrical, linear, and nonlinear optical characteristics of the Nd-doped (a higher ionic radius dopant) ZnO thin films. The X-ray diffraction reveals a hexagonal wurtzite structure of the polycrystalline deposits with preferred orientation change from (101) to (002) plane at dopant concentrations above 5%. The inclusion of Nd dopants causes the morphology to change from fibrous to needle-like. The oxidation states of the dopant elements were identified by using XPS spectra. The Raman spectroscopy elucidates the deterioration of crystallinity with the increase in the dopant concentrations. The additional absorption band at higher dopant concentrations in the Fourier transform infrared spectra points to a new phase. The optical bandgap and charge carrier concentrations decrease and increase, respectively, with dopant concentrations up to 5 at%, followed by a reversal in the trend at still higher doping. The optical refractive index and extinction coefficient of the doped samples show an increase compared to pure ZnO. The defect-mediated energy transfer from the host ZnO to Nd dopants was identified from photoluminescence spectra. The sign of the third-order nonlinear refractive index changes from negative for pure ZnO to positive with Nd doping.

Magnetic field effects on the linear and nonlinear optical properties of coaxial cylindrical quantum well wires

In this work, the influence of an external magnetic field on the refractive index changes and optical absorption coefficients of a typical GaAs/AlxGa1−xAs coaxial cylindrical quantum well wire is studied. Energy eigenvalues and eigenvectors in the presence of a magnetic field are calculated using the fourth-order Runge-Kutta method and optical properties are obtained using the compact density matrix approach. It is found that the resonant peak values of the linear and the third-order nonlinear refractive index changes as well as the optical absorption coefficients of a cylindrical quantum wire decrease with increasing the magnetic field. However, these optical properties of a coaxial cylindrical quantum well wire are nonmonotonic functions of the magnetic field, due to the anticrossing of the subbands. The anticrossing effect leads to a large increase of the resonant peak values of these optical properties. Results also indicate that the resonant peak values of these optical properties decrease with increasing the barrier width.

Electronic structure and nonlinear optical properties of a two-dimensional hexagonal quantum dot

In this work electronic structure, the linear and the third-order nonlinear refractive index changes as well as optical absorption coefficients of a two-dimensional hexagonal quantum dot are investigated. Energy eigenvalues and eigenfunctions of the system are calculated by the matrix diagonalization technique, and optical properties are also obtained using the compact density matrix approach. As our results indicate, both the dot size and the confinement potential have a great influence on the intersubband energy intervals, the transition probability and consequently, the linear and the third-order nonlinear refractive index changes and optical absorption coefficients.

LINEAR AND NONLINEAR INTERSUBBAND REFRACTIVE INDEX CHANGES IN WURTZITEAlGaN/GaNDOUBLE QUANTUM WELLS: EFFECTS OF PIEZOELECTRICITY AND SPONTANEOUS POLARIZATION

Based on the density-matrix approach and iterative treatment, a detailed procedure for the calculation of the linear and nonlinear intersubband refractive index changes (RICs) in wurtzite GaN-based coupling quantum wells (CQWs) is given. The simple analytical formulas for electronic eigenstates and the linear and third-order nonlinear RICs in the systems are also deduced. Numerical result on a typical AlGaN / GaN CQW shows that the linear and nonlinear RICs sensitively depend on the structural parameters of the CQW system as well as the doped fraction of nitride semicondutor.